According to surface morphology,microhardness,X-ray diffraction,and static contact angle experiments,the changes in the surface integrity and corrosion resistance of 6061-T6 aluminum alloy after ultrasonic shot peenin...According to surface morphology,microhardness,X-ray diffraction,and static contact angle experiments,the changes in the surface integrity and corrosion resistance of 6061-T6 aluminum alloy after ultrasonic shot peening(USP)were investigated.Results show that the grain size of the material surface is reduced by 43%,the residual compressive stress has an increasing trend,the roughness and hardness are increased by approximately 211.1%and 35%,respectively.And the static contact angle is increased at first,followed by a slight decrease.Weighing,scanning electron microscope,and energy dispersive spectrometer were used to study the samples after a cyclic corrosion test.Results show that USP reduces the corrosion rate by 41.2%.A model of surface corrosion mechanism of USP is developed,and the mechanism of USP to improve the corrosion resistance of materials is discussed.The introduction of compressive residual stresses,grain refinement,increased grain boundaries,increased hardness,and increased static contact angle are the main factors related to the improvement of corrosion resistance in most materials,while increased roughness tends to weaken surface corrosion resistance.展开更多
Machine Hammer Peening(MHP)is an emergent treatment that induces high compressive Residual Stresses(RS)which can enhance the in-service performance of components.This paper studies the use of small diameter MHP tools ...Machine Hammer Peening(MHP)is an emergent treatment that induces high compressive Residual Stresses(RS)which can enhance the in-service performance of components.This paper studies the use of small diameter MHP tools to improve the Surface Integrity(SI)of the nickel-based alloy Inconel 718 used in critical aero-engine components.Complementarily,the relaxation of RS is analyzed by in-situ annealing tests at in-service temperature combined with X-ray diffraction measurement.For this purpose,age hardened Inconel 718 discs were turned as reference condition,and then a pneumatic MHP tool was used under different conditions:two tool diameters(4 mm and 12 mm),feed rates(2.5 m/min and 5.0 m/min)and stepover distances(0.07 mm and 0.35 mm).Subsequently,surface topography characterization,RS measurements,nanoindentation tests,and microstructural observations were conducted.The in-situ annealing tests were done in the X-ray diffractometer at 550°C for exposure periods from 0 to 20 h.The results demonstrate that 4 mm diameter tools generate smooth surfaces and induce significant compressive RS within a0.5 mm thick layer.Residual stresses are relaxed,but they remain compressive even after a long thermal exposure.The microstructure of the surface layer(<10–15μm)was affected by the preceding turning operation,but importantly,MHP did not induce additional damage.展开更多
To address problems in surface integrity and machining allowance distribution during combined electric arc-mechanical milling,this paper takes TC4 as the research object,examines the influence of electric arc milling(...To address problems in surface integrity and machining allowance distribution during combined electric arc-mechanical milling,this paper takes TC4 as the research object,examines the influence of electric arc milling(EAM)depth on recast layer thickness and surface roughness,alongside an analysis of the recast layer’s organization characteristics and sur-face morphology.A comparative evaluation of cutting forces,surface roughness,and surface hardening is conducted between combined milling and conventional mechanical milling.Key findings reveal that electric arc machining produces a recast layer with a hardness of 313.21 HV.As the EAM depth increases,the localized recast layer thickness and peak-to-valley(PV)differ-ences also rise.To ensure effective surface defect removal,the machining allowance for subsequent mechanical milling must exceed the combined thickness of the recast layer and the PV difference.Under identical parameters,combined milling yields higher surface roughness(0.584μm)and greater surface hardening(10.4%)compared to mechanical milling alone,alongside an 18.716 N increase in cutting force.Response surface methodology(RSM)analysis identifies feed per tooth as the most significant factor affecting surface roughness,followed by spindle speed,with milling depth having the least influence.展开更多
Machined surface integrity of workpieces in harsh environments has a remarkable influence on their performance.However,the complexity of the new type of machining hinders a comprehensive understanding of machined surf...Machined surface integrity of workpieces in harsh environments has a remarkable influence on their performance.However,the complexity of the new type of machining hinders a comprehensive understanding of machined surface integrity and its formation mechanism,thereby limiting the study of component performance.With increasing demands for high-quality machined workpieces in aerospace industry applications,researchers from academia and industry are increasingly focusing on post-machining surface characterization.The profile grinding test was conducted on a novel single-crystal superalloy to simulate the formation of blade tenons,and the obtained tenons were characterized for surface integrity elements under various operating conditions.Results revealed that ultrasonic vibration-assisted grinding(UVAG)led to multiple superpositions of abrasive grain trajectories,causing reduced surface roughness(an average reduction of approximately29.6%)compared with conventional grinding.After examining the subsurface layer of UVAG using transmission electron microscopy,the results revealed that the single-crystal tenon grinding subsurface layer exhibited a gradient evolution from the near-surface to the substrate.This evolution was characterized by an equiaxed nanocrystalline layer measuring 0.34μm,followed by a submicrocrystalline grain-forming zone spanning 0.6μm and finally,a constituent phase-twisted dis-torted deformation zone over 0.62μm.Under normal grinding conditions,the tenon exhibited low surface hardening(not exceeding 15%),and residual compressive stresses were observed on its surface.In cases where grinding burns occurred,a white layer appeared on the tenon's surface,which demonstrated varying thicknesses along the teeth from top to root due to thermal-force-structural coupling effects.Additionally,these burns introduced residual tensile stresses on the tenon's surface,potentially substantially affecting its fatigue life.This paper enhances our understanding of UVAG processes and establishes a foundation for their application in manufacturing singlecrystal turbine blades for next-generation aero-turbine engines.展开更多
The technique of creep feed grinding is most suitable for geometrical shaping, and therefore has been expected to improve effectively material removal rate and surface quality of components with complex profile. This ...The technique of creep feed grinding is most suitable for geometrical shaping, and therefore has been expected to improve effectively material removal rate and surface quality of components with complex profile. This article studies experimentally the effects of process parameters （i.e. wheel speed, workpiece speed and depth of cut） on the grindability and surface integrity of cast nickel-based superalloys, i.e. K424, during creep feed grinding with brazed cubic boron nitride （CBN） abrasive wheels. Some important factors, such as grinding force and temperature, specific grinding energy, size stability, surface topography, microhardhess and microstructure alteration of the sub-surface, residual stresses, are investigated in detail. The results show that during creep feed grinding with brazed CBN wheels, low grinding temperature at about 100 ℃ is obtained though the specific grinding energy of nickel-based superalloys is high up to 200-300 J/mm^3. A combination of wheel speed 22.5 m/s, workpiece speed 0.1 m/min, depth of cut 0.2 mm accomplishes the straight grooves with the expected dimensional accuracy. Moreover, the compressive residual stresses are formed in the bum-free and crack-free ground surface.展开更多
Titanium alloy tenon is creep feed ground with monolayer brazed cubic boron nitride （CBN） shaped wheels. The dimension accuracy of the tenon is assessed and the results indicate that it completely meets the requirem...Titanium alloy tenon is creep feed ground with monolayer brazed cubic boron nitride （CBN） shaped wheels. The dimension accuracy of the tenon is assessed and the results indicate that it completely meets the requirement of blade tenon of aero-engine. Residual stresses, surface roughness, microstructure and microhardness are measured on ground surfaces of the specimen, which are all compared with that ground with vitrified CBN wheels. Under all the circumstances, compressive residual stress is obtained and the depth of the machining affected zone is found to be less than 40 μm. No phase transformation is observed at depths of up to 100 lain below the surface, though plastic deformation is visible in the process of grain refinement. The residual stress and microhardness of specimens ground with brazed CBN wheels are observed to be lower than those ground with vitrified ones. The arithmetic mean roughness （Ra） values obtained are all below 0.8μm.展开更多
Surface integrity of a new damage-tolerant titanium alloy （TC21）, including surface roughness, microhardness and metallurgical structure is investigated when normal and high speed milling are used at different tool ...Surface integrity of a new damage-tolerant titanium alloy （TC21）, including surface roughness, microhardness and metallurgical structure is investigated when normal and high speed milling are used at different tool wear status. Results show that good surface integrity of TC21 can be obtained in high speed milling. In addition, even in acutely worn stages, there is no so-called serious hardening layer （or white layer） according to the studies on microhardness and metallurgical structure.展开更多
To evaluate the new designed cutting tools for high-efficiency milling of the hardened die steel SKD11,surface integrities of millers with different geometric structures are analyzed, considering the surface roughness...To evaluate the new designed cutting tools for high-efficiency milling of the hardened die steel SKD11,surface integrities of millers with different geometric structures are analyzed, considering the surface roughness, micrograph of chips, surface microhardness, residual stress and metallurgical texture of the surface layer. The in fluences of geometric characteristics of different cutting tools and their wear characteristics on the surface integrity are studied. Results show that the milling tool with rake angle; 5 of the hardened diesteel. The generation of saw-tooth chips is depressed when a reasonable positive rake angle is selected. And the compressive residual stress is induced on the machined surface in milling the hardened die steel. The occurrence of surface softening is postponed by increasing the clearance angle and reducing the tool flank wear.展开更多
Titanium alloys are widely used in aeronautics that demand a good combination of high strength, good corrosion resistance and low mass. The mechanical properties lead to challenges in machining operations such as high...Titanium alloys are widely used in aeronautics that demand a good combination of high strength, good corrosion resistance and low mass. The mechanical properties lead to challenges in machining operations such as high process temperature as well as rapidly increasing tool wear. The conventional tool materials are not able to maintain their hardness and other mechanical prop- erties at higher cutting temperatures encountered in high speed machining. In this work, the new material tools, which are poly- crystalline diamond （PCD） and polycrystalline cubic boron nitride （PCBN） tools, are used in high-speed milling of Ti-6.5AI-2Zr-IMo-IV （TA15） alloy. The performance and wear mechanism of the tools are investigated. Compared to PCBN tool, PCD tool has a much longer tool life, especially at higher cutting speeds. Analyses based on the SEM and EDX suggest that attrition, adhesion and diffusion are the main wear mechanisms of PCD and PCBN tools in high-speed milling of TA 15. Oxida- tion wear is also observed at PCBN tool/workpiece interface. Roughness, defects, micro-hardness and microstructure of the ma- chined surface are investigated. The recorded surface roughness values with PCD/PCBN tools are bellow 0.3 μm at initial and steady cutting stage. Micro-hardness analysis shows that the machined surface hardening depth with PCD and PCBN tools is small. There is no evidence of sub-surface defects with PCD and PCBN tools. It is concluded that for TA15 alloy, high-speed milling can be carried out with PCD/PCBN tools.展开更多
Ni3Al-based superalloy IC10 is widely used in high temperature components of aeroengines because of its superior mechanical properties.In this paper,the creep feed grinding properties of IC10 were investigated experim...Ni3Al-based superalloy IC10 is widely used in high temperature components of aeroengines because of its superior mechanical properties.In this paper,the creep feed grinding properties of IC10 were investigated experimentally.The effects of grinding parameters on the grinding forces and temperature were examined.Moreover,the influences of surface roughness and hardening on the high-cycle fatigue life of IC10 specimens were studied.To control the creep feed grinding parameters and enhance the fatigue life of IC10 components,the experimental results were summarized to offer a useful reference point.It is concluded that,the grinding depth is the most important factor which influencing the grinding forces and temperature;the surface roughness is the main and unfavorable factor on the fatigue life of IC10,while the surface hardening has a positive influence on the fatigue life;to obtain a better surface quality and improve the fatigue life of IC 10,the recommended grinding parameter domain involves wheel speed 2[15,20]m/s,feed rate∈[150,200]mm/min,and grinding depth∈[0.4,0.5]mm.展开更多
In-situ ceramics particle reinforced aluminum matrix composites are favored in the aerospace industry due to excellent properties.However,the hard ceramic particles as the reinforcement phase bring challenges to machi...In-situ ceramics particle reinforced aluminum matrix composites are favored in the aerospace industry due to excellent properties.However,the hard ceramic particles as the reinforcement phase bring challenges to machining.To study the effect of in-situ TiB_(2)particles on machinability and surface integrity of TiB_(2)/2024 composite and TiB_(2)/7075 composite,milling experiments were performed,and compared with conventional 2024 and 7075 aluminum alloys.In-situ TiB_(2)particles clustered at the grain boundaries and dispersed inside the matrix alloy grains hinder the dislocation movement of the matrix alloy.Therefore,the milling force and temperature of the composites are higher than those of the aluminum alloys due to the increase of the strength and the decrease of the plasticity.In the milling of composites,abrasive wear is the main wear form of carbide tools,due to the scratching of hard nano-TiB_(2)particles.The composites containing in-situ TiB_(2)particles have machining defects such as smearing,micro-scratches,micro-pits and tail on the machined surface.However,in-situ TiB_(2)particles impede the plastic deformation of the composites,which greatly reduces cutting edge marks on the machined surface.Therefore,under the same milling parameters,the surface roughness of TiB_(2)/2024 composite and TiB_(2)/7075 composite is much less than that of2024 and 7075 aluminum alloy respectively.Under the milling conditions of this experiment,the machined subsurface has no metamorphic layer,and the microhardness of the machined surface is almost the same as that of the material.Besides,compared with 2024 and 7075 aluminum alloy,machined surfaces of TiB_(2)/2024 composite and TiB_(2)/7075 composite both show tensile residual stress or low magnitude of compressive residual stress.展开更多
Presently,the service performance of new-generation high-tech equipment is directly affected by the manufacturing quality of complex thin-walled components.A high-efficiency and quality manufacturing of these complex ...Presently,the service performance of new-generation high-tech equipment is directly affected by the manufacturing quality of complex thin-walled components.A high-efficiency and quality manufacturing of these complex thin-walled components creates a bottleneck that needs to be solved urgently in machinery manufacturing.To address this problem,the collaborative manufacturing of structure shape and surface integrity has emerged as a new process that can shorten processing cycles,improve machining qualities,and reduce costs.This paper summarises the research status on the material removal mechanism,precision control of structure shape,machined surface integrity control and intelligent process control technology of complex thin-walled components.Numerous solutions and technical approaches are then put forward to solve the critical problems in the high-performance manufacturing of complex thin-wall components.The development status,challenge and tendency of collaborative manufacturing technologies in the high-efficiency and quality manufacturing of complex thin-wall components is also discussed.展开更多
Preferred surface integrity around the hole wall is one of the key parameters to ensure the optimized performance of hole components for nickel-based superalloy.The novel hole cold expansion technique introduced in th...Preferred surface integrity around the hole wall is one of the key parameters to ensure the optimized performance of hole components for nickel-based superalloy.The novel hole cold expansion technique introduced in this work involves the laser texturing process(LTP)followed by the Hertz contact rotary expansion process(HCREP),where the cylindrical sleeve is the critical component connecting the abovementioned two processes.The purpose of LTP is to obtain the most optimized strengthened cylindrical sleeve surface,preparing for the following HCREP.Hereafter,the HCREP acts on the nickel-based hole components by the rotary extruding movements of the strengthened sleeve and conical mandrel tools.As compared to the as-received GH4169 material,the surface integrity characterization for the strengthened hole shows that a plastic deformation layer with finer grains,higher micro-hardness,deeper compressive residual stress(CRS)distribution and lower surface roughness is formed at the hole wall.In addition,transmission electron microscope(TEM)observations reveal the microstructure evolution mechanism in the strengthened hole.Grain refinement near the hole wall is regarded as the fundamental reason for improving the surface integrity,where the aggregated dislocations and recombined dislocation walls can be clearly observed.展开更多
Imposing compressive residual stress field around a fastening hole serves as a universal method to enhance the hole fatigue strength in the aircraft assembly filed.Ultrasonic Peening Drilling(UPD)is a recently propose...Imposing compressive residual stress field around a fastening hole serves as a universal method to enhance the hole fatigue strength in the aircraft assembly filed.Ultrasonic Peening Drilling(UPD)is a recently proposed hybrid hole making process,which can achieve an integration of strengthening and precision-machining with a one-shot-drilling operation.Due to the ironing effect of tool flank surface,UPD introduces large compressive residual stress filed in hole subsurface.In order to reveal the strengthening mechanism of UPD,the influence of ultrasonic vibration and tool dynamic relief angle on ironing coverage rate and its corresponding effect on surface integrity in UPD were analyzed.The experiments were conducted to verify the influence of ironing effect on surface integrity and fatigue behavior of Ti-6Al-4V hole in UPD.The results indicate that the specimen features smaller surface roughness,higher micro-hardness,plastic deformation degree and circumferential compress residual stress under higher ironing coverage rate.The fatigue life increases with the raise of ironing coverage rate,and the fatigue source site in UPD shifts from surface to subsurface comparing with that without vibration assistance.The results demonstrates that a better strengthening effect can be obtained by reasonably controlling the ironing coverage rate in UPD.展开更多
Fatigue performance is a serious concern for mechanical components subject to cyclical stresses,particularly where safety is paramount.The fatigue performance of components relies closely on their surface integrity be...Fatigue performance is a serious concern for mechanical components subject to cyclical stresses,particularly where safety is paramount.The fatigue performance of components relies closely on their surface integrity because the fatigue cracks generally initiate from free surfaces.This paper reviewed the published data,which addressed the effects of machined surface integrity on the fatigue performance of metal workpieces.Limitations in existing studies and the future directions in anti-fatigue manufacturing field were proposed.The remarkable surface topography(e.g.,low roughness and few local defects and inclusions)and large compressive residual stress are beneficial to fatigue performance.However,the indicators that describe the effects of surface topography and residual stress accurately need further study and exploration.The effect of residual stress relaxation under cycle loadings needs to be precisely modeled precisely.The effect of work hardening on fatigue performance had two aspects.Work hardening could increase the material yield strength,thereby delaying crack nucleation.However,increased brittleness could accel-erate crack propagation.Thus,finding the effective control mechanism and method of work hardening is urgently needed to enhance the fatigue performance of machined components.The machining-induced metallurgical structure changes,such as white layer,grain refinement,dislocation,and martensitic transformation affect the fatigue performance of a workpiece significantly.However,the unified and exact conclusion needs to be investigated deeply.Finally,different surface integrity factors had complicated reciprocal effects on fatigue performance.As such,studying the comprehensive influence of surface integrity further and establishing the reliable prediction model of workpiece fatigue performance are meaningful for improving reliability of components and reducing test cost.展开更多
The Ti6Al4V parts produced by the existing selective laser melting(SLM)are mainly confronted with poor surface finish and inevitable interior defects,which substantially deteriorates the mechanical properties and perf...The Ti6Al4V parts produced by the existing selective laser melting(SLM)are mainly confronted with poor surface finish and inevitable interior defects,which substantially deteriorates the mechanical properties and performances of the parts.In this regard,ultrasonically-assisted machining(UAM)technique is commonly introduced to improve the machining quality due to its merits in increasing tool life and reducing cutting force.However,most of the previous studies focus on the performance of UAM with ultrasonic vibrations applied in the tangential and feed directions,whereas few of them on the impact of ultrasonic vibration along the vertical direction.In this study,the effects of feed rate on surface integrity in ultrasonically-assisted vertical milling(UAVM)of the Ti6Al4V alloy manufactured by SLM were systemically investigated compared with the conventional machining(CM)method.The results revealed that the milling forces in UAVM showed a lower amplitude than that in CM due to the intermittent cutting style.The surface roughness values of the parts produced by UAVM were generally greater than that by CM owing to the extra sinusoidal vibration textures induced by the milling cutter.Moreover,the extra vertical ultrasonic vibration in UAVM was beneficial to suppressing machining chatter.As feed rate increased,surface microhardness and thickness of the plastic deformation zone in CM raised due to more intensive plastic deformation,while these two material properties in UAVM were reduced owing to the mitigated impact effect by the high-frequency vibration of the milling cutter.Therefore,the improved surface microhardness and reduced thickness of the subsurface deformation layer in UAVM were ascribed to the vertical high-frequency impact of the milling cutter in UAVM.In general,the results of this study provided an in-depth understanding in UAVM of Ti6Al4V parts manufactured by SLM.展开更多
Electron beam melting(EBM),as an excellent Additive Manufacturing(AM)technology,enables the printing of Ti-6Al-4V alloy for a wide range of applications such as aerospace and biomechanical industries.It improves funct...Electron beam melting(EBM),as an excellent Additive Manufacturing(AM)technology,enables the printing of Ti-6Al-4V alloy for a wide range of applications such as aerospace and biomechanical industries.It improves functionality and integrity of components and negates complexities in assembly processes.However,due to the poor surface and sub-surface integrity represented by the rough surface finish and low dimensional accuracy,achieving a favorable surface condition is quite challenging.Therefore,post processing becomes essential for these electron beam melted(EBM-ed)Ti-6Al-4V alloys.Being the most common technique to improve such parts,milling of Ti-6Al-4V alloy is very challenging and resulting tool wear issues,due to its unique material properties.Thus,this paper presents a comprehensive study on the surface integrity of EBM-ed Ti-6Al-4V parts processed by precision grinding and electropolishing,aiming to qualitatively and quantitatively clarify the interrelation between process parameters and processed surface quality.The surface and subsurface characteristics such as profile accuracy,surface roughness,microstructure,defective layer and residual stress before and after post processing were compared and evaluated.The results show that by precision grinding,the profile accuracy was improved from over 300μm PV to 7μm PV,while surface roughness(R_(a))was reduced from 30μm to about 2μm.The layer with partially melt particles was removed,but introduced a deformed subsurface layer with more residual stress.Then by applying electropolishing,the residual stress was released and the deformed layer was removed.In addition,Ra was further reduced to 0.65μm.The research can serve as a reference for the integration of post machining processes with AM.展开更多
Gamma titanium-aluminum(γ-TiAl)intermetallic compounds are increasingly used in manufacturing key hot-end components(e.g.,blade tenon)in aero engines due to their high specific strength and lightweight properties.Cre...Gamma titanium-aluminum(γ-TiAl)intermetallic compounds are increasingly used in manufacturing key hot-end components(e.g.,blade tenon)in aero engines due to their high specific strength and lightweight properties.Creep feed profile grinding(CFPG)as a crucial precision process that is applied to produce the final profile of the blade tenon.However,sudden surface burns and microcracks of machined c-TiAl blade tenon often occur because of its low plasticity and high strength during grinding processes,leading to poor surface integrity.In this work,CFPG experiments based on the profile characteristics ofγ-TiAl blade tenon were performed and an associated undeformed chip thickness model considering grain–workpiece contact condition was established to explore the evolution of the surface integrity.Subsequently,the surface integrity was analyzed at different positions of the blade tenon in terms of surface roughness and morphology,metallographic structure,microhardness,and residual stress.Results show that the profile characteristics of blade tenon have a significant influence on machined surface integrity because of the thermomechanical effect at various detecting positions.The residual stress was established based on the undeformed chip thickness model considering the profile structure,with a prediction error of 10%–15%.The thermomechanical effect is more obvious at the bottom area,where the surface roughness,work hardening degree,and subsurface plastic deformation range are the largest,while the values at the bevel area are the smallest.Based on the undeformed chip thickness model,a residual stress finite element simulation was conducted by employing thermomechanical coupled effects.In addition,the error between the simulation and the experiment was between 10%–15%.Strain and strain rate equations were established through the relationship between material displacement and depth.The average strain and strain rate of the ground surface when ap is 1.0 mm are 18.8%and 33.2%larger than when ap is 0.5 mm,respectively.This study deepens the understanding of surface integrity under the influence of CFPGγ-TiAl and provides a practical reference and theoretical basis for realizing high-quality profile grinding of other complex parts.展开更多
Current Ti-based orthopedic implants often suffer from fatigue damage,therefore shortening their service lifespan.To solve this issue,in this study,mechanically polished Ti-6Al-7Nb(P-Ti6Al7Nb)was subjected to surface ...Current Ti-based orthopedic implants often suffer from fatigue damage,therefore shortening their service lifespan.To solve this issue,in this study,mechanically polished Ti-6Al-7Nb(P-Ti6Al7Nb)was subjected to surface mechanical attrition treatment(SMAT).Effects of various SMAT process parameters,including ball diameter and treatment duration,on the surface integrity of P-Ti6Al7Nb were investigated,specifically in terms of surface quality,surface nanocrystalline layer,and residual stress.Subsequently,the microstructure,in-depth residual stress and microhardness distributions,surface roughness,and fatigue behavior in simulated body fluids of optimally SMATed Ti-6Al-7Nb(S-Ti6Al7Nb)were examined and compared to those of P-Ti6Al7Nb.Results showed that based on the experimental conditions established in the present research,the optimal parameters were determined to be a 3 mm ball diameter and a 15 min treatment duration,which resulted in excellent surface integrity;S-Ti6Al7Nb showed a 300μm-thick gradient nanostructured layer comprising the thickest nanocrystalline layer of about 20μm,a 1000μm-deep residual compressive stress field with the maximum surface residual compressive stress,and a microconcave topography but free of any defects or cracks.The microstructural evolution mechanism was also elucidated,revealing that the combination of multidirectional primary and secondary twins’intersections and twin-dislocation interactions contributed to grain refinement.Compared to P-Ti6Al7Nb,S-Ti6Al7Nb exhibited a 40%improvement in fatigue strength,owing to synergistic effects of the gradient nanostructured layer,surface work hardening,high amplitude of residual compressive stress,and improved surface integrity.These factors effectively prevented the initiation of fatigue crack at the surface and shifted it to the sublayer,and inhibited the subsequent crack propagation.展开更多
GH4169 is the main material for aero-cngine blades and integrated blisks. Because GH4169 has a poor milling performance, the profile precision and surtace integrity of blades and integrated blisks are difficult to be ...GH4169 is the main material for aero-cngine blades and integrated blisks. Because GH4169 has a poor milling performance, the profile precision and surtace integrity of blades and integrated blisks are difficult to be met by utilizing the conventional milling process, which directly influence the global performance and reliability of aero-engines. Through grinding experiments on parameters and surface integrity optimization, the helical cantilever grinding process utilizing a 300# CBN RB wheel is presented and applied in finish machining of GH4169 blades. The profile errors of the blade surface are within ±0.01 mm, the roughness is less than 0.4μm, the residual compressive stresses and the hardening rate are appropriate, there are no phenomena of burr and smearing with the grinding chips, and the leading/trailing edge can be smoothly connected with the suction/pressure surface. All the experimental results indicate that this grinding process is greatly suitable for the profile finish machining of GH4169 blades.展开更多
基金Introduction of Talent Research Start-up Fund of Anhui University of Science and Technology(2022yjrc35)Colleges and Universities Excellent Young Talents Domestic Visit Research Project of Anhui Province(gxgnfx2022006)。
文摘According to surface morphology,microhardness,X-ray diffraction,and static contact angle experiments,the changes in the surface integrity and corrosion resistance of 6061-T6 aluminum alloy after ultrasonic shot peening(USP)were investigated.Results show that the grain size of the material surface is reduced by 43%,the residual compressive stress has an increasing trend,the roughness and hardness are increased by approximately 211.1%and 35%,respectively.And the static contact angle is increased at first,followed by a slight decrease.Weighing,scanning electron microscope,and energy dispersive spectrometer were used to study the samples after a cyclic corrosion test.Results show that USP reduces the corrosion rate by 41.2%.A model of surface corrosion mechanism of USP is developed,and the mechanism of USP to improve the corrosion resistance of materials is discussed.The introduction of compressive residual stresses,grain refinement,increased grain boundaries,increased hardness,and increased static contact angle are the main factors related to the improvement of corrosion resistance in most materials,while increased roughness tends to weaken surface corrosion resistance.
基金the financial support given by EPSRC to the Grant LOFAMO(No.EP/X023281/1)the Basque Government for the financial support given from Elkartek Program to the Project FRONTIERS 2022—Superficies Multifuncionales en la Frontera del Conocimiento(No.KK2022/00109)。
文摘Machine Hammer Peening(MHP)is an emergent treatment that induces high compressive Residual Stresses(RS)which can enhance the in-service performance of components.This paper studies the use of small diameter MHP tools to improve the Surface Integrity(SI)of the nickel-based alloy Inconel 718 used in critical aero-engine components.Complementarily,the relaxation of RS is analyzed by in-situ annealing tests at in-service temperature combined with X-ray diffraction measurement.For this purpose,age hardened Inconel 718 discs were turned as reference condition,and then a pneumatic MHP tool was used under different conditions:two tool diameters(4 mm and 12 mm),feed rates(2.5 m/min and 5.0 m/min)and stepover distances(0.07 mm and 0.35 mm).Subsequently,surface topography characterization,RS measurements,nanoindentation tests,and microstructural observations were conducted.The in-situ annealing tests were done in the X-ray diffractometer at 550°C for exposure periods from 0 to 20 h.The results demonstrate that 4 mm diameter tools generate smooth surfaces and induce significant compressive RS within a0.5 mm thick layer.Residual stresses are relaxed,but they remain compressive even after a long thermal exposure.The microstructure of the surface layer(<10–15μm)was affected by the preceding turning operation,but importantly,MHP did not induce additional damage.
基金supported by the National Natural Science Foundation of China“Study on the evolution law of discharge channel and deformation suppression method for low-pressure micro-arc milling machining of aerospace thin-walled parts”(52265061)The Tianshan Innovation Team“Robotics and intelligent equipment technology science and technology innovation team”(2022D14002).
文摘To address problems in surface integrity and machining allowance distribution during combined electric arc-mechanical milling,this paper takes TC4 as the research object,examines the influence of electric arc milling(EAM)depth on recast layer thickness and surface roughness,alongside an analysis of the recast layer’s organization characteristics and sur-face morphology.A comparative evaluation of cutting forces,surface roughness,and surface hardening is conducted between combined milling and conventional mechanical milling.Key findings reveal that electric arc machining produces a recast layer with a hardness of 313.21 HV.As the EAM depth increases,the localized recast layer thickness and peak-to-valley(PV)differ-ences also rise.To ensure effective surface defect removal,the machining allowance for subsequent mechanical milling must exceed the combined thickness of the recast layer and the PV difference.Under identical parameters,combined milling yields higher surface roughness(0.584μm)and greater surface hardening(10.4%)compared to mechanical milling alone,alongside an 18.716 N increase in cutting force.Response surface methodology(RSM)analysis identifies feed per tooth as the most significant factor affecting surface roughness,followed by spindle speed,with milling depth having the least influence.
基金supported by the National Natural Science Foundation of China(Nos.92160301,92060203,52175415,52205475,and 52322510)the Science Center for Gas Turbine Project(No.P2023-B-IV-003-001)+1 种基金the Huaqiao University Engineering Research Center of Brittle Materials Machining(No.2023IME-001)the Natural Science Foundation of Jiangsu Province(No.BK20210295).
文摘Machined surface integrity of workpieces in harsh environments has a remarkable influence on their performance.However,the complexity of the new type of machining hinders a comprehensive understanding of machined surface integrity and its formation mechanism,thereby limiting the study of component performance.With increasing demands for high-quality machined workpieces in aerospace industry applications,researchers from academia and industry are increasingly focusing on post-machining surface characterization.The profile grinding test was conducted on a novel single-crystal superalloy to simulate the formation of blade tenons,and the obtained tenons were characterized for surface integrity elements under various operating conditions.Results revealed that ultrasonic vibration-assisted grinding(UVAG)led to multiple superpositions of abrasive grain trajectories,causing reduced surface roughness(an average reduction of approximately29.6%)compared with conventional grinding.After examining the subsurface layer of UVAG using transmission electron microscopy,the results revealed that the single-crystal tenon grinding subsurface layer exhibited a gradient evolution from the near-surface to the substrate.This evolution was characterized by an equiaxed nanocrystalline layer measuring 0.34μm,followed by a submicrocrystalline grain-forming zone spanning 0.6μm and finally,a constituent phase-twisted dis-torted deformation zone over 0.62μm.Under normal grinding conditions,the tenon exhibited low surface hardening(not exceeding 15%),and residual compressive stresses were observed on its surface.In cases where grinding burns occurred,a white layer appeared on the tenon's surface,which demonstrated varying thicknesses along the teeth from top to root due to thermal-force-structural coupling effects.Additionally,these burns introduced residual tensile stresses on the tenon's surface,potentially substantially affecting its fatigue life.This paper enhances our understanding of UVAG processes and establishes a foundation for their application in manufacturing singlecrystal turbine blades for next-generation aero-turbine engines.
基金National Basic Research Program of China (2009CB724403)Program for Changjiang Scholars and Innovative Research Team in University (IRT0837)Program for New Century Excellent Talents in University from Ministry of Education of China (NCET-07-0435)
文摘The technique of creep feed grinding is most suitable for geometrical shaping, and therefore has been expected to improve effectively material removal rate and surface quality of components with complex profile. This article studies experimentally the effects of process parameters （i.e. wheel speed, workpiece speed and depth of cut） on the grindability and surface integrity of cast nickel-based superalloys, i.e. K424, during creep feed grinding with brazed cubic boron nitride （CBN） abrasive wheels. Some important factors, such as grinding force and temperature, specific grinding energy, size stability, surface topography, microhardhess and microstructure alteration of the sub-surface, residual stresses, are investigated in detail. The results show that during creep feed grinding with brazed CBN wheels, low grinding temperature at about 100 ℃ is obtained though the specific grinding energy of nickel-based superalloys is high up to 200-300 J/mm^3. A combination of wheel speed 22.5 m/s, workpiece speed 0.1 m/min, depth of cut 0.2 mm accomplishes the straight grooves with the expected dimensional accuracy. Moreover, the compressive residual stresses are formed in the bum-free and crack-free ground surface.
基金National Fundamental Research Program of China (2009CB724403)Program for New Century Excellent Talents in University from Ministry of Education of China (NCET-07-0435)
文摘Titanium alloy tenon is creep feed ground with monolayer brazed cubic boron nitride （CBN） shaped wheels. The dimension accuracy of the tenon is assessed and the results indicate that it completely meets the requirement of blade tenon of aero-engine. Residual stresses, surface roughness, microstructure and microhardness are measured on ground surfaces of the specimen, which are all compared with that ground with vitrified CBN wheels. Under all the circumstances, compressive residual stress is obtained and the depth of the machining affected zone is found to be less than 40 μm. No phase transformation is observed at depths of up to 100 lain below the surface, though plastic deformation is visible in the process of grain refinement. The residual stress and microhardness of specimens ground with brazed CBN wheels are observed to be lower than those ground with vitrified ones. The arithmetic mean roughness （Ra） values obtained are all below 0.8μm.
基金Supported by the National Natural Science Foundation of China(50975141)the National Scienceand Technology Major Project(2010ZX04012-042)the Aeronautical Science Foundation(2010352005)~~
文摘Surface integrity of a new damage-tolerant titanium alloy （TC21）, including surface roughness, microhardness and metallurgical structure is investigated when normal and high speed milling are used at different tool wear status. Results show that good surface integrity of TC21 can be obtained in high speed milling. In addition, even in acutely worn stages, there is no so-called serious hardening layer （or white layer） according to the studies on microhardness and metallurgical structure.
文摘To evaluate the new designed cutting tools for high-efficiency milling of the hardened die steel SKD11,surface integrities of millers with different geometric structures are analyzed, considering the surface roughness, micrograph of chips, surface microhardness, residual stress and metallurgical texture of the surface layer. The in fluences of geometric characteristics of different cutting tools and their wear characteristics on the surface integrity are studied. Results show that the milling tool with rake angle; 5 of the hardened diesteel. The generation of saw-tooth chips is depressed when a reasonable positive rake angle is selected. And the compressive residual stress is induced on the machined surface in milling the hardened die steel. The occurrence of surface softening is postponed by increasing the clearance angle and reducing the tool flank wear.
基金National High-tech Research and Development Program of China (2009AA04Z116)Program for Changjiang Scholars and Innovative Research Team in University ( IRT0837)
文摘Titanium alloys are widely used in aeronautics that demand a good combination of high strength, good corrosion resistance and low mass. The mechanical properties lead to challenges in machining operations such as high process temperature as well as rapidly increasing tool wear. The conventional tool materials are not able to maintain their hardness and other mechanical prop- erties at higher cutting temperatures encountered in high speed machining. In this work, the new material tools, which are poly- crystalline diamond （PCD） and polycrystalline cubic boron nitride （PCBN） tools, are used in high-speed milling of Ti-6.5AI-2Zr-IMo-IV （TA15） alloy. The performance and wear mechanism of the tools are investigated. Compared to PCBN tool, PCD tool has a much longer tool life, especially at higher cutting speeds. Analyses based on the SEM and EDX suggest that attrition, adhesion and diffusion are the main wear mechanisms of PCD and PCBN tools in high-speed milling of TA 15. Oxida- tion wear is also observed at PCBN tool/workpiece interface. Roughness, defects, micro-hardness and microstructure of the ma- chined surface are investigated. The recorded surface roughness values with PCD/PCBN tools are bellow 0.3 μm at initial and steady cutting stage. Micro-hardness analysis shows that the machined surface hardening depth with PCD and PCBN tools is small. There is no evidence of sub-surface defects with PCD and PCBN tools. It is concluded that for TA15 alloy, high-speed milling can be carried out with PCD/PCBN tools.
基金supported by NSAF(No.U1830122)the National Natural Science Foundation of China(No.51775443)。
文摘Ni3Al-based superalloy IC10 is widely used in high temperature components of aeroengines because of its superior mechanical properties.In this paper,the creep feed grinding properties of IC10 were investigated experimentally.The effects of grinding parameters on the grinding forces and temperature were examined.Moreover,the influences of surface roughness and hardening on the high-cycle fatigue life of IC10 specimens were studied.To control the creep feed grinding parameters and enhance the fatigue life of IC10 components,the experimental results were summarized to offer a useful reference point.It is concluded that,the grinding depth is the most important factor which influencing the grinding forces and temperature;the surface roughness is the main and unfavorable factor on the fatigue life of IC10,while the surface hardening has a positive influence on the fatigue life;to obtain a better surface quality and improve the fatigue life of IC 10,the recommended grinding parameter domain involves wheel speed 2[15,20]m/s,feed rate∈[150,200]mm/min,and grinding depth∈[0.4,0.5]mm.
基金the National Natural Science Foundation of China(No.51875356)。
文摘In-situ ceramics particle reinforced aluminum matrix composites are favored in the aerospace industry due to excellent properties.However,the hard ceramic particles as the reinforcement phase bring challenges to machining.To study the effect of in-situ TiB_(2)particles on machinability and surface integrity of TiB_(2)/2024 composite and TiB_(2)/7075 composite,milling experiments were performed,and compared with conventional 2024 and 7075 aluminum alloys.In-situ TiB_(2)particles clustered at the grain boundaries and dispersed inside the matrix alloy grains hinder the dislocation movement of the matrix alloy.Therefore,the milling force and temperature of the composites are higher than those of the aluminum alloys due to the increase of the strength and the decrease of the plasticity.In the milling of composites,abrasive wear is the main wear form of carbide tools,due to the scratching of hard nano-TiB_(2)particles.The composites containing in-situ TiB_(2)particles have machining defects such as smearing,micro-scratches,micro-pits and tail on the machined surface.However,in-situ TiB_(2)particles impede the plastic deformation of the composites,which greatly reduces cutting edge marks on the machined surface.Therefore,under the same milling parameters,the surface roughness of TiB_(2)/2024 composite and TiB_(2)/7075 composite is much less than that of2024 and 7075 aluminum alloy respectively.Under the milling conditions of this experiment,the machined subsurface has no metamorphic layer,and the microhardness of the machined surface is almost the same as that of the material.Besides,compared with 2024 and 7075 aluminum alloy,machined surfaces of TiB_(2)/2024 composite and TiB_(2)/7075 composite both show tensile residual stress or low magnitude of compressive residual stress.
基金supported by the National Natural Science Foundation of China(Nos.51921003,92160301,52175415 and 52205475)the Science Center for Gas Turbine Project(No.P2022-A-IV-002-001)Natural Science Foundation of Jiangsu Province(No.BK20210295).
文摘Presently,the service performance of new-generation high-tech equipment is directly affected by the manufacturing quality of complex thin-walled components.A high-efficiency and quality manufacturing of these complex thin-walled components creates a bottleneck that needs to be solved urgently in machinery manufacturing.To address this problem,the collaborative manufacturing of structure shape and surface integrity has emerged as a new process that can shorten processing cycles,improve machining qualities,and reduce costs.This paper summarises the research status on the material removal mechanism,precision control of structure shape,machined surface integrity control and intelligent process control technology of complex thin-walled components.Numerous solutions and technical approaches are then put forward to solve the critical problems in the high-performance manufacturing of complex thin-wall components.The development status,challenge and tendency of collaborative manufacturing technologies in the high-efficiency and quality manufacturing of complex thin-wall components is also discussed.
基金sponsored by the National Key Research and Development Program of China(2018YFC1902404)the National Natural Science Foundation of China(51725503,51705155)Innovation Program of Shanghai Municipal Education Commission(2019-01-07-00-02-E00068)。
文摘Preferred surface integrity around the hole wall is one of the key parameters to ensure the optimized performance of hole components for nickel-based superalloy.The novel hole cold expansion technique introduced in this work involves the laser texturing process(LTP)followed by the Hertz contact rotary expansion process(HCREP),where the cylindrical sleeve is the critical component connecting the abovementioned two processes.The purpose of LTP is to obtain the most optimized strengthened cylindrical sleeve surface,preparing for the following HCREP.Hereafter,the HCREP acts on the nickel-based hole components by the rotary extruding movements of the strengthened sleeve and conical mandrel tools.As compared to the as-received GH4169 material,the surface integrity characterization for the strengthened hole shows that a plastic deformation layer with finer grains,higher micro-hardness,deeper compressive residual stress(CRS)distribution and lower surface roughness is formed at the hole wall.In addition,transmission electron microscope(TEM)observations reveal the microstructure evolution mechanism in the strengthened hole.Grain refinement near the hole wall is regarded as the fundamental reason for improving the surface integrity,where the aggregated dislocations and recombined dislocation walls can be clearly observed.
基金supported by the National Natural Science Foundation of China(Nos.51905024,51975035 and 91960203).
文摘Imposing compressive residual stress field around a fastening hole serves as a universal method to enhance the hole fatigue strength in the aircraft assembly filed.Ultrasonic Peening Drilling(UPD)is a recently proposed hybrid hole making process,which can achieve an integration of strengthening and precision-machining with a one-shot-drilling operation.Due to the ironing effect of tool flank surface,UPD introduces large compressive residual stress filed in hole subsurface.In order to reveal the strengthening mechanism of UPD,the influence of ultrasonic vibration and tool dynamic relief angle on ironing coverage rate and its corresponding effect on surface integrity in UPD were analyzed.The experiments were conducted to verify the influence of ironing effect on surface integrity and fatigue behavior of Ti-6Al-4V hole in UPD.The results indicate that the specimen features smaller surface roughness,higher micro-hardness,plastic deformation degree and circumferential compress residual stress under higher ironing coverage rate.The fatigue life increases with the raise of ironing coverage rate,and the fatigue source site in UPD shifts from surface to subsurface comparing with that without vibration assistance.The results demonstrates that a better strengthening effect can be obtained by reasonably controlling the ironing coverage rate in UPD.
基金Supported by National Natural Science Foundation of China(Grant No.52005281)Major Program of Shandong Province Natural Science Foundation of China(Grant No.ZR2018ZA0401)Applied Basic Research Projects for Qingdao Innovation Plan(Grant No.18-2-2-67-jch).
文摘Fatigue performance is a serious concern for mechanical components subject to cyclical stresses,particularly where safety is paramount.The fatigue performance of components relies closely on their surface integrity because the fatigue cracks generally initiate from free surfaces.This paper reviewed the published data,which addressed the effects of machined surface integrity on the fatigue performance of metal workpieces.Limitations in existing studies and the future directions in anti-fatigue manufacturing field were proposed.The remarkable surface topography(e.g.,low roughness and few local defects and inclusions)and large compressive residual stress are beneficial to fatigue performance.However,the indicators that describe the effects of surface topography and residual stress accurately need further study and exploration.The effect of residual stress relaxation under cycle loadings needs to be precisely modeled precisely.The effect of work hardening on fatigue performance had two aspects.Work hardening could increase the material yield strength,thereby delaying crack nucleation.However,increased brittleness could accel-erate crack propagation.Thus,finding the effective control mechanism and method of work hardening is urgently needed to enhance the fatigue performance of machined components.The machining-induced metallurgical structure changes,such as white layer,grain refinement,dislocation,and martensitic transformation affect the fatigue performance of a workpiece significantly.However,the unified and exact conclusion needs to be investigated deeply.Finally,different surface integrity factors had complicated reciprocal effects on fatigue performance.As such,studying the comprehensive influence of surface integrity further and establishing the reliable prediction model of workpiece fatigue performance are meaningful for improving reliability of components and reducing test cost.
基金Supported by Shenzhen Municipal Science and Technology Innovation Commission of China(Grant Nos.Y01336107,GJHZ20180411143506667,JCYJ20170817111811303).
文摘The Ti6Al4V parts produced by the existing selective laser melting(SLM)are mainly confronted with poor surface finish and inevitable interior defects,which substantially deteriorates the mechanical properties and performances of the parts.In this regard,ultrasonically-assisted machining(UAM)technique is commonly introduced to improve the machining quality due to its merits in increasing tool life and reducing cutting force.However,most of the previous studies focus on the performance of UAM with ultrasonic vibrations applied in the tangential and feed directions,whereas few of them on the impact of ultrasonic vibration along the vertical direction.In this study,the effects of feed rate on surface integrity in ultrasonically-assisted vertical milling(UAVM)of the Ti6Al4V alloy manufactured by SLM were systemically investigated compared with the conventional machining(CM)method.The results revealed that the milling forces in UAVM showed a lower amplitude than that in CM due to the intermittent cutting style.The surface roughness values of the parts produced by UAVM were generally greater than that by CM owing to the extra sinusoidal vibration textures induced by the milling cutter.Moreover,the extra vertical ultrasonic vibration in UAVM was beneficial to suppressing machining chatter.As feed rate increased,surface microhardness and thickness of the plastic deformation zone in CM raised due to more intensive plastic deformation,while these two material properties in UAVM were reduced owing to the mitigated impact effect by the high-frequency vibration of the milling cutter.Therefore,the improved surface microhardness and reduced thickness of the subsurface deformation layer in UAVM were ascribed to the vertical high-frequency impact of the milling cutter in UAVM.In general,the results of this study provided an in-depth understanding in UAVM of Ti6Al4V parts manufactured by SLM.
基金financial support from LiaoNing Revitalization Talents Program(No.XLYC1807230)A*STAR Industrial Additive Manufacturing Program:Work Package 3(Electron Beam Melting,No.1325504103)Liaoning Natural Science Foundation Guidance Plan(No.20180550171)。
文摘Electron beam melting(EBM),as an excellent Additive Manufacturing(AM)technology,enables the printing of Ti-6Al-4V alloy for a wide range of applications such as aerospace and biomechanical industries.It improves functionality and integrity of components and negates complexities in assembly processes.However,due to the poor surface and sub-surface integrity represented by the rough surface finish and low dimensional accuracy,achieving a favorable surface condition is quite challenging.Therefore,post processing becomes essential for these electron beam melted(EBM-ed)Ti-6Al-4V alloys.Being the most common technique to improve such parts,milling of Ti-6Al-4V alloy is very challenging and resulting tool wear issues,due to its unique material properties.Thus,this paper presents a comprehensive study on the surface integrity of EBM-ed Ti-6Al-4V parts processed by precision grinding and electropolishing,aiming to qualitatively and quantitatively clarify the interrelation between process parameters and processed surface quality.The surface and subsurface characteristics such as profile accuracy,surface roughness,microstructure,defective layer and residual stress before and after post processing were compared and evaluated.The results show that by precision grinding,the profile accuracy was improved from over 300μm PV to 7μm PV,while surface roughness(R_(a))was reduced from 30μm to about 2μm.The layer with partially melt particles was removed,but introduced a deformed subsurface layer with more residual stress.Then by applying electropolishing,the residual stress was released and the deformed layer was removed.In addition,Ra was further reduced to 0.65μm.The research can serve as a reference for the integration of post machining processes with AM.
基金financially supported by the National Natural Science Foundation of China(Nos.92160301,92060203,52175415 and 52205475)the Science Center for Gas Turbine Project(Nos.P2022-AB-IV-002-001 and P2023-B-IV-003-001)+5 种基金the Natural Science Foundation of Jiangsu Province(No.BK20210295)the Superior Postdoctoral Project of Jiangsu Province(No.2022ZB215)the National Key Laboratory of Science and Technology on Helicopter Transmission(Nanjing University of Aeronautics and Astronautics)(No.HTL-A-22G12)the Postgraduate Research&Practice Innovation Program of Jiangsu Province(KYCX23-0355)the China Postdoctoral Science Foundation(No.2023T160315)the Interdisciplinary Innovation Fund for Doctoral Students of Nanjing University of Aeronautics and Astronautics(KXKCXJJ202305).
文摘Gamma titanium-aluminum(γ-TiAl)intermetallic compounds are increasingly used in manufacturing key hot-end components(e.g.,blade tenon)in aero engines due to their high specific strength and lightweight properties.Creep feed profile grinding(CFPG)as a crucial precision process that is applied to produce the final profile of the blade tenon.However,sudden surface burns and microcracks of machined c-TiAl blade tenon often occur because of its low plasticity and high strength during grinding processes,leading to poor surface integrity.In this work,CFPG experiments based on the profile characteristics ofγ-TiAl blade tenon were performed and an associated undeformed chip thickness model considering grain–workpiece contact condition was established to explore the evolution of the surface integrity.Subsequently,the surface integrity was analyzed at different positions of the blade tenon in terms of surface roughness and morphology,metallographic structure,microhardness,and residual stress.Results show that the profile characteristics of blade tenon have a significant influence on machined surface integrity because of the thermomechanical effect at various detecting positions.The residual stress was established based on the undeformed chip thickness model considering the profile structure,with a prediction error of 10%–15%.The thermomechanical effect is more obvious at the bottom area,where the surface roughness,work hardening degree,and subsurface plastic deformation range are the largest,while the values at the bevel area are the smallest.Based on the undeformed chip thickness model,a residual stress finite element simulation was conducted by employing thermomechanical coupled effects.In addition,the error between the simulation and the experiment was between 10%–15%.Strain and strain rate equations were established through the relationship between material displacement and depth.The average strain and strain rate of the ground surface when ap is 1.0 mm are 18.8%and 33.2%larger than when ap is 0.5 mm,respectively.This study deepens the understanding of surface integrity under the influence of CFPGγ-TiAl and provides a practical reference and theoretical basis for realizing high-quality profile grinding of other complex parts.
基金supported by the National Natural Science Foundation of China(Grant Nos.51631007 and 51971171).
文摘Current Ti-based orthopedic implants often suffer from fatigue damage,therefore shortening their service lifespan.To solve this issue,in this study,mechanically polished Ti-6Al-7Nb(P-Ti6Al7Nb)was subjected to surface mechanical attrition treatment(SMAT).Effects of various SMAT process parameters,including ball diameter and treatment duration,on the surface integrity of P-Ti6Al7Nb were investigated,specifically in terms of surface quality,surface nanocrystalline layer,and residual stress.Subsequently,the microstructure,in-depth residual stress and microhardness distributions,surface roughness,and fatigue behavior in simulated body fluids of optimally SMATed Ti-6Al-7Nb(S-Ti6Al7Nb)were examined and compared to those of P-Ti6Al7Nb.Results showed that based on the experimental conditions established in the present research,the optimal parameters were determined to be a 3 mm ball diameter and a 15 min treatment duration,which resulted in excellent surface integrity;S-Ti6Al7Nb showed a 300μm-thick gradient nanostructured layer comprising the thickest nanocrystalline layer of about 20μm,a 1000μm-deep residual compressive stress field with the maximum surface residual compressive stress,and a microconcave topography but free of any defects or cracks.The microstructural evolution mechanism was also elucidated,revealing that the combination of multidirectional primary and secondary twins’intersections and twin-dislocation interactions contributed to grain refinement.Compared to P-Ti6Al7Nb,S-Ti6Al7Nb exhibited a 40%improvement in fatigue strength,owing to synergistic effects of the gradient nanostructured layer,surface work hardening,high amplitude of residual compressive stress,and improved surface integrity.These factors effectively prevented the initiation of fatigue crack at the surface and shifted it to the sublayer,and inhibited the subsequent crack propagation.
基金co-supported by the National Natural Science Foundation of China (No. 51105024)the National Science and Technology Major Project of China (No. 2013ZX04001051)
文摘GH4169 is the main material for aero-cngine blades and integrated blisks. Because GH4169 has a poor milling performance, the profile precision and surtace integrity of blades and integrated blisks are difficult to be met by utilizing the conventional milling process, which directly influence the global performance and reliability of aero-engines. Through grinding experiments on parameters and surface integrity optimization, the helical cantilever grinding process utilizing a 300# CBN RB wheel is presented and applied in finish machining of GH4169 blades. The profile errors of the blade surface are within ±0.01 mm, the roughness is less than 0.4μm, the residual compressive stresses and the hardening rate are appropriate, there are no phenomena of burr and smearing with the grinding chips, and the leading/trailing edge can be smoothly connected with the suction/pressure surface. All the experimental results indicate that this grinding process is greatly suitable for the profile finish machining of GH4169 blades.
