Ti-47Al-2Nb-2Cr-0.4（W, Mo） （mole fraction, %） alloy ingot fabricated using vacuum consumable melting was containerless near-isothermally forged, and the high temperature forgeability, microstructure and tensile pr...Ti-47Al-2Nb-2Cr-0.4（W, Mo） （mole fraction, %） alloy ingot fabricated using vacuum consumable melting was containerless near-isothermally forged, and the high temperature forgeability, microstructure and tensile properties were investigated. The results show that the TiAl ingot exhibits good heat workability during containerless near-isothermally forging process, and there are not evident cracks on the surface of as-forged TiAl pancake with a total deformation degree of 60%. The microstructure of the TiAl ingot appears to be typical nearly-lamellar（NL）, comprising a great amount of lamellar colonies （α2＋γ） and a few equiaxed γ grains. After near-isothermally forging, the as-forged pancake shows primarily fine equiaxed γ grains with an average grain size of 20 μm and some broken lamellar pieces, and some bent lamellas still exist in the hard-deformation zone. Tensile tests at room temperature show that ultimate tensile strength increases from 433 MPa to 573 MPa after forging due to grain refinement effect.展开更多
The dynamic recrystallization behavior of microalloyed forged steel was investigated with a compression test in the temperature range of 1 223-1 473 K and a strain rate of 0. 01-5 s^-1. Activation energy was calculate...The dynamic recrystallization behavior of microalloyed forged steel was investigated with a compression test in the temperature range of 1 223-1 473 K and a strain rate of 0. 01-5 s^-1. Activation energy was calculated to be 305.9 kJ/mol by regression analysis. Modeling equations were developed to represent the dynamic recrystallization volume fraction and grain size. Parameters of the modeling equations were determined as a function of the Zener-Hollomon parameter. The developed modeling equation will be combined with finite element modeling to predict microstructural change during the hot forging processing.展开更多
Transmission electron microscopy(TEM),scanning electron microscopy(SEM),hardness tests and tensile tests were performed to investigate the effect of aging on microstructure and mechanical properties of forged Al-4.4Cu...Transmission electron microscopy(TEM),scanning electron microscopy(SEM),hardness tests and tensile tests were performed to investigate the effect of aging on microstructure and mechanical properties of forged Al-4.4Cu-0.7Mg-0.6Si alloy.The results show that the alloy exhibits splendid mechanical properties with an ultimate tensile strength of504MPa and an elongation of10.1%after aging at170°C for16h.With tensile testing temperature increasing to150°C,the strength of the alloy declines slightly to483MPa.Then,the strength drops quickly when temperature reaches over200°C.The high strength of the alloy in peak-aged condition is caused by a considerable amount ofθ'and AlMgSiCu(Q)precipitates.The relatively stable mechanical properties tested below150°C are mainly ascribed to the stability ofθ'precipitates.The growth ofθ'and Q precipitates and the generation ofθphase lead to a rapid drop of the strength when temperature is over150°C.展开更多
With a focus on the backup roll, a rolling-contact-fatigue experiment was performed on samples of 5% Cr forged steel. The P-S-N fatigue curves were determined and the fatigue strength was calculated. The emergence of ...With a focus on the backup roll, a rolling-contact-fatigue experiment was performed on samples of 5% Cr forged steel. The P-S-N fatigue curves were determined and the fatigue strength was calculated. The emergence of cracks on the test-sample surfaces was observed at different fatigue cycles. A micro-hardness tester was used to measure the hardness of the subsurface fatigue layer. The microstructures were analyzed at various magnifications with an optical microscope, scanning electron microscope, and transmission electron microscope. Based on these tests, the rolling-contact-fatigue mechanism of the large forged steel backup roll was also considered. The results showed that the contact-fatigue strength of the tested backup roll steel was 1 249 MPa;the surface fatigue crack lengthened continuously as the number of cycles increased and followed an S-shaped curve; the subsurface fatigue hardness reached its highest value at about 90 （HV） increment from the matrix hardness of 540 （HV） in the backup roll; the subsurface martensite/bainite microstructure was crushed and the dislocation density was greatly increased. Under alternating contact stresses,the surface/subsurface material was damaged and exhibited many microdefects. At the least, the surface fatigue layer on backup rolls should be fully removed before the microcracks enter a period of rapid propagation.展开更多
structure with a significant reduction in casting porosity, while the texture changed to sharp basaMeasured mechanical properties of the forged alloy showed that strength did not change, howductility improved by 75%. ...structure with a significant reduction in casting porosity, while the texture changed to sharp basaMeasured mechanical properties of the forged alloy showed that strength did not change, howductility improved by 75%. The analysis of the fracture surface of the forged alloy under tension rea ductile fracture with dimple morphology, while the as-cast alloy displayed a brittle fracture with pores. This demonstrated that the reduction of casting defects and dendritic morphology, as well evolution of recrystallized grains, enhanced ductility, while partial dynamic recrystallization throuforging process resulted in only marginal modification of strength in the forged condition.. 2017 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials SciTechno展开更多
Semi-solid forging of iron-based alloys during solidification has unique characteristics distinct from those of the classical hot forging.With the aim of acquiring precise knowledge concerning the microstructural evol...Semi-solid forging of iron-based alloys during solidification has unique characteristics distinct from those of the classical hot forging.With the aim of acquiring precise knowledge concerning the microstructural evolution of bearing steel Cr4 Mo4 V in this process,a series of semi-solid forging experiments were carried out in which samples were wrapped in a designed pure iron sheath.The effects of forging temperature and forging reduction on the grain morphology and liquid flow behavior were investigated,respectively.By forging solidifying metal(FSM),bulky primary dendrites were broken and spheroidal grains with an average shape factor of 0.87 were obtained at 1360?C.With the decreasing forging temperature to 1340?C,the microstructural homogeneity can be improved.On the other hand,it shows that a higher forging reduction(50%)is essential for the spheroidization of grains and elimination of liquid segregation.Those microstructural characteristics are related to different motion mechanisms of solid and liquid phases at different forging temperatures.Additionally,the effect of semi-solid forging on the eutectic carbides was also investigated,and the results demonstrate that the higher diffusion capacity and less liquid segregation jointly lower the large eutectic carbides and consequently cause its uniform distribution during FSM.展开更多
The microstructural evolution and tensile properties of a forged Ti−42Al−5Mn alloy subjected to different heat treatments were studied.The results showed that,when the forged alloy was aged at 800℃ for 24 h,the inter...The microstructural evolution and tensile properties of a forged Ti−42Al−5Mn alloy subjected to different heat treatments were studied.The results showed that,when the forged alloy was aged at 800℃ for 24 h,the interlamellar spacing(λ)andγgrain size at colony boundaries are generally coarsened.Whereas,when the alloy was first annealed at 1300℃ and then aged at 800℃ for 24 h,this coarsening of related microstructures appears less pronounced.The suggested annealing temperatures for the forged Ti−42Al−5Mn alloy are in the range of 1250−1300℃.It was found that,on the condition of the same annealing system,both the strength and ductility were improved as the aging temperature changed from 1000 to 800℃.The secondary precipitatedβo(β_(o,sec))at colony boundaries could be responsible for improving the strength,and theγphase at colony boundaries with the grain size about 6μm might be one of the main reasons for the better ductility.展开更多
A Cu-1.5 wt.%Ti/Diamond(55 vol.%)composite was fabricated by hot forging from powder mixture of copper,titanium and diamond powders at 1050?C.A nano-thick TiC interfacial layer was formed between the diamond particle ...A Cu-1.5 wt.%Ti/Diamond(55 vol.%)composite was fabricated by hot forging from powder mixture of copper,titanium and diamond powders at 1050?C.A nano-thick TiC interfacial layer was formed between the diamond particle and copper matrix during forging,and it has an orientation relationship of(111)TiC//(002)Cu&[110]TiC//[110]Cuwith the copper matrix.HRTEM analysis suggests that TiC is semicoherently bond with copper matrix,which helps reduce phonon scattering at the TiC/Cu interface and facilitates the heat transfer,further leading to the hot-forged copper/diamond composite(referred as to Cu-Ti/Dia-0)has a thermal conductivity of 410 W/m K,and this is about 74%of theoretical thermal conductivity of hot-forged copper/composite(552 W/m K).However,the formation of thin amorphous carbon layer in diamond particle(next to the interfacial TiC layer)and deformed structure in the copper matrix have adverse effect on the thermal conductivity of Cu-Ti/Dia-0 composite.800℃-annealing eliminates the discrepancy in TiC interface morphology between the diamond-{100}and-{111}facets of Cu-Ti/Dia-0 composite,but causes TiC particles coarsening and agglomerating for the Cu-Ti/Dia-2 composite and interfacial layer cracking and spallation for the Cu-Ti/Dia-1 composite.In addition,a large amount of graphite was formed by titanium-induced diamond graphitization in the Cu-Ti/Dia-2 composite.All these factors deteriorate the heat transfer behavior for the annealed Cu-Ti/Dia composites.Appropriate heat treatment needs to be continually investigated to improve the thermal conductivity of hot-forged CuTi/Dia composite by eliminating deformed structure in the copper matrix with limit/without impacts on the formed TiC interfacial layer.展开更多
Multidirectional forging(MDF)was successfully applied to fabricate large-size Mg-Gd-Y-Zn-Zr-Ag alloy in this work and effects of T4,T5 and T6 treatments on the microstructure and mechanical properties of the as-forged...Multidirectional forging(MDF)was successfully applied to fabricate large-size Mg-Gd-Y-Zn-Zr-Ag alloy in this work and effects of T4,T5 and T6 treatments on the microstructure and mechanical properties of the as-forged alloy were analyzed.Results show that dynamic recrystallization(DRX)occurs and second phase particles precipitate along the grain boundary during the MDF process.After annealing treatment(T4),the volume fraction and size of dynamic precipitates slightly increase at a lower temperature(430℃)compared with those of MDFed sample,while they are dissolved into theα-Mg matrix at a higher temperature(450℃).At the meantime,short plate-shaped long-period stacking ordered(LPSO)phases are observed in the DRX grains of the MDFed sample and then dissolved into theα-Mg matrix during annealing at both temperatures.Typical basal texture is identified in the MDFed sample,but the basal pole tilts away from final forging direction and rare-earth texture component with<1121>orientation parallel to penultimate forging direction becomes visible after annealing.The T6 sample annealing at 430℃for 4 h and ageing at 200℃for 34 h exhibits the superior strength and ductility in this study.The ultimate tensile strength,tensile yield strength and elongation to failure,which is 455 MPa,308 MPa and 7.7%,respectively,are overall improved compared with the directly-aged(T5)sample.This paper provides a superior heat treatment schedule to manufacture high-performance large-scale Mg-Gd-Y-Zn-Zr-Ag components for industrial production.展开更多
Effect of multi-directional forging(MDF)on wear properties of Mg-Zn alloys(with 2,4,and 6wt%Zn)is investigated.Dry sliding wear test was performed using pin on disk machine on MDF processed and homogenized samples.Wea...Effect of multi-directional forging(MDF)on wear properties of Mg-Zn alloys(with 2,4,and 6wt%Zn)is investigated.Dry sliding wear test was performed using pin on disk machine on MDF processed and homogenized samples.Wear behavior of samples was analyzed at loads of ION and 20 N,with sliding distances of 2000m and 4000m,at a sliding velocity of 3m/s.Microstructures of worn samples were observed under scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),and x-ray diffraction(XRD)and the results were analyzed.Mechanical properties were evaluated using microhardness test.After 5 passes of MDF,the average grain size was found to be 30±4p m,22±3 pm,and 18±3 pm,in Mg-2%Zn,Mg-4%Zn,and Mg-6%Zn alloys,respectively,with significant improvement in hardness in all cases.Wear resistance was improved after MDF processing,as well as,with increment in Zn content in Mg alloy.However,it decreased when the load and the sliding distance increased.Worn surface exhibited ploughing,delamination,plastic deformation,and wear debris along sliding direction,and abrasive wear was found to be the main mechanism.展开更多
Elemental titanium(Ti)and nickel(Ni)powders were consolidated by spark plasma sintering(SPS)to fabricate Ti-51%Ni(mole fraction)shape-memory alloys(SMAs).The objective of this study is to enhance the superelasticity o...Elemental titanium(Ti)and nickel(Ni)powders were consolidated by spark plasma sintering(SPS)to fabricate Ti-51%Ni(mole fraction)shape-memory alloys(SMAs).The objective of this study is to enhance the superelasticity of SPS produced Ti-Ni alloy using free forging as a secondary process.Products from two processes(with and without free forging)were compared in terms of microstructure,transformation temperature and superelasticity.The results showed that,free forging effectively improved the tensile and shape-memory properties.Ductility increased from 6.8%to 9.2%after forging.The maximum strain during superelasticity increased from 5%to 7.5%and the strain recovery rate increased from 72%to 92%.The microstructure of produced Ti-51%Ni SMA consists of the cubic austenite(B2)matrix,monoclinic martensite(B19′),secondary phases(Ti3Ni4,Ti2Ni and TiNi3)and oxides(Ti4Ni2O and Ti3O5).There was a shift towards higher temperatures in the martensitic transformation of free forged specimen(aged at 500°C)due to the decrease in Ni content of B2 matrix.This is related to the presence of Ti3Ni4 precipitates,which were observed using transmission electron microscope(TEM).In conclusion,free forging could improve superelasticity and mechanical properties of Ti-51%Ni SMA.展开更多
NiTi-Al-based alloys are promising high-tem- perature structural materials for aerospace and astronautics applications. A new NiTi-Al-based alloy Ni--43Ti-4AI- 2Nb-2Hf （at%） was processed via isothermal forging. The...NiTi-Al-based alloys are promising high-tem- perature structural materials for aerospace and astronautics applications. A new NiTi-Al-based alloy Ni--43Ti-4AI- 2Nb-2Hf （at%） was processed via isothermal forging. The microstructure and mechanical properties at room temperature and high temperature were investigated through scanning electron microscope （SEM）, X-ray diffraction （XRD）, and tensile tests. Results show that the micro- structure of as-forged Ni-43Ti--4AI-2Nb-2Hf alloy con- sists of NiTi matrix, Ti2Ni phase, and Hf-rich phase. The simultaneous addition of Nb and Hf, which have strong affinities for Ti sites, promotes the precipitation of Hf-rich phases along the grain boundaries. The tensile strengths of Ni-43Ti-4A1-2Nb-2Hf alloy are dramatically increased compared with the ternary Ni-46Ti-4A1 alloy. At room temperature and 650℃, the yield stress of Ni--43Ti-4Al- 2Nb-2Hf alloy reaches 1,070 and 610 MPa, respectively, which are 30 % and 150 % higher than those of Ni--46Ti- 4Al alloy. The improved tensile property results from the solid solution strengthening by Nb and Hf, as well as the dispersion hardening of the Ti2Ni and Hf-rich phases.展开更多
In this study,typical microstructural characteristics of a metastableβTi alloy(Ti–5Al–5Mo–5V–3Cr–1Fe)forged in a dual-phase region(strain of 54%at 820℃)were investigated in detail by the combined use of X-ray d...In this study,typical microstructural characteristics of a metastableβTi alloy(Ti–5Al–5Mo–5V–3Cr–1Fe)forged in a dual-phase region(strain of 54%at 820℃)were investigated in detail by the combined use of X-ray diff raction,energy dispersive spectroscopy,electron channeling contrast imaging and electron backscatter diff raction techniques.Results show that the microstructure of the forged alloy is composed of bulkαgrains,αplates andβmatrix.The bulkαgrains correspond to retained primaryαphase(αp,average grain size^2.4μm),while theαplates are secondaryαphase(αs,width^70 nm)precipitated from theβmatrix during air cooling.During forging,theβmatrix experiences dynamic recovery with many subgrains and signifi cant orientation gradients formed.Analyses of the orientation relationship between theαandβphases show that the Burgers orientation relationship is not maintained between someα_p andβphases,which should be related to thermal deformation-induced changes of their orientations.In contrast,all of theαs plates are found to maintain well the Burgers orientation relationship with theβphase.展开更多
Cold closed-die forging is a suitable process to produce spur-bevel gears due to its advantages, such as saving materials and time, reducing costs, increasing die life and improving the quality of the product. The hom...Cold closed-die forging is a suitable process to produce spur-bevel gears due to its advantages, such as saving materials and time, reducing costs, increasing die life and improving the quality of the product. The homogeneity of microstructure of cold closed-die forged gears can highly affect their service performance. The homogeneity of microstructure and Vickers hardness in cold closed-die forged gear of 20 Cr Mn Ti alloy is comprehensively studied by using optical microscopy and Vickers hardness tester. The results show that the distribution homogeneity of the aspect ratio of grain and Vickers hardness is the same. In the circumferential direction of the gear tooth, the distribution of the aspect ratio of grain and Vickers hardness is inhomogeneous and they gradually decrease from the surface to the center of the tooth. In the radial direction, the distribution of the aspect ratio of grain and Vickers hardness is inhomogeneous on the surface of the gear tooth; while it is relatively homogeneous in the center of the gear tooth. In the axial direction of the gear tooth, the distribution of the aspect ratio of grain and Vickers hardness is relatively homogeneous from the small-end to the large-end of the gear tooth.展开更多
This paper investigated the high cycle fatigue behavior of a forged Mg-7Gd-5Y-1Nd-0.5Zr alloy with different stress concentration factor(Kt),under different stress ratio(R),and along different loading direction.The sm...This paper investigated the high cycle fatigue behavior of a forged Mg-7Gd-5Y-1Nd-0.5Zr alloy with different stress concentration factor(Kt),under different stress ratio(R),and along different loading direction.The smooth specimen(Kt=1),under R=0.1 and along longitude direction,shows a high fatigue strength of 162 MPa at 107 cycles.The fatigue behavior of the forged Mg-7Gd-5Y-1Nd-0.5Zr alloy exhibits a high sensitive to the notch.Moreover,change of stress ratio from 0.1 to−1 may also result in a bad fatigue property.The flux inclusions were elongated along longitude direction and/or transverse direction during the forging process of the Mg-7Gd-5Y-1Nd-0.5Zr alloy.The interface between the flux inclusion and the matrix may debond and serve as the crack initiation site during the fatigue loading process,leading to the deterioration of the fatigue property along thickness direction and a high anisotropic fatigue behavior between longitude direction and thickness direction.展开更多
In this study, AA2519 alloy was initially processed by multi axial forging (MAF) at room and cryogenic temperatures. Subsequently, the microstructure and the mechanical behavior of the processed samples under quasi-st...In this study, AA2519 alloy was initially processed by multi axial forging (MAF) at room and cryogenic temperatures. Subsequently, the microstructure and the mechanical behavior of the processed samples under quasi-static loading were investigated to determine the influence of cryogenic forging on alloys’ subgrains dimensions, grain boundaries interactions, strength, ductility and toughness. In addition, the failure mechanisms at the tensile rupture surfaces were characterized using scanning electron micro-scope (SEM). The results show significant improvements in the strength, ductility and toughness of the alloy as a result of the cryogenic MAF process. The formation of nanoscale crystallite microstructure, heavily deformed grains with high density of grain boundaries and second phase breakage to finer particles were characterized as the main reasons for the increase in the mechanical properties of the cryogenic forged samples. The cryogenic processing of the alloy resulted in the formation of an ultrafine grained material with tensile strength and toughness that are ~41% and ~80% higher respectively after 2 cycles MAF when compared with the materials processed at ambient temperature. The fractography analysis on the tested materials shows a substantial ductility improvement in the cryoforged (CF) samples when compared to the room temperature forged (RTF) samples which is in alignment with their stress-strain profiles. However, extended forging at higher cycles than 2 cycles led only to increase in strength at the expense of ductility for both the CF and RTF samples.展开更多
Nowadays there is a continuous demand,particularly from the automotive industry,for cheaper,lighter and more reliable components.It is not surprising then that steel research has been focused during the last decades i...Nowadays there is a continuous demand,particularly from the automotive industry,for cheaper,lighter and more reliable components.It is not surprising then that steel research has been focused during the last decades in new qualities and processes.This paper is dealing with the use of vanadium microalloyed steels on one of those new processes,warm forging.For its low precipitation temperature and its recognised ability to strengthen steel microstructures via austenite grain growth control,precipitation hardening and interference of the static recrystallization process,vanadium in microalloyed steels seem to be an appropriate candidate for warm forging.展开更多
Al7075 sheets are widely used in aerospace industry and their higher strength-plasticity collaborative improvement requirement is urgent.In this study,the microstructure inheriting the evolution and me-chanical proper...Al7075 sheets are widely used in aerospace industry and their higher strength-plasticity collaborative improvement requirement is urgent.In this study,the microstructure inheriting the evolution and me-chanical properties of Al7075 sheets during multidirectional rotary forging(MRF)and T6 heat treatment are analyzed.The results show that the average grain size exhibits near-parabolic evolution with increas-ing MRF deformation amount.MRF20%+T6(20%MRF deformation amount+T6)condition possesses the largest grain size of 72.6μm,and its abnormal grain growth mechanism is that the medium deformation energy and high deformation heterogeneity in MRF20%deformed grains could cause asynchronous re-crystallization behavior during T6 heat treatment,and the grains with comparatively higher deformation energy get recrystallized firstly and devour adjacent grains along preferred011or223misorientation axis.MRF70%+T6 condition possesses the finest grain size of 14.2μm,and its fine grain inheriting mech-anism is that the uniformly high deformation energy in MRF70%deformed grains causes uniformly rapid recrystallization,and rapidly recrystallized grains effectively suppress grain boundary motion from adja-cent grains.With increasing MRF deformation amount,tensile strength and elongation values both exhibit near-antiparabolic evolution.MRF70%+T6 condition possesses the largest tensile strength(563 MPa)and elongation(17.73%),which increases by 8.27%and 80.55%compared to as-annealed+T6(MRF0%+T6)condition(tensile strength is 520 MPa and elongation is 9.82%),respectively.The strength-plasticity col-laborative improvement is mainly because the combination of effectively inherited fine grains,refined inclusion particles,and uniformly distributed fineη’particles after T6 heat treatment could promote smooth dislocation movement and coordinated slip behavior in most matrix grains,which contributes to the delay of stress localization and strength-plasticity collaborative improvement.展开更多
Al5A06 sheets by large cold plastic deformation usually have high strength but low plasticity,i.e.weak strength-plasticity matching,which may lead to their poor fatigue property.In this study,annealing treat-ments are...Al5A06 sheets by large cold plastic deformation usually have high strength but low plasticity,i.e.weak strength-plasticity matching,which may lead to their poor fatigue property.In this study,annealing treat-ments are applied on cold rotary forged Al5A06 sheets to regulate strength-plasticity matching and im-prove fatigue properties.The microstructures,tensile mechanical properties and fatigue properties un-der different annealing parameters were analyzed.The abnormal grain growth mechanism of cold rotary forged Al5A06 sheets during 300℃ annealing treatment was investigated,and the fatigue failure mech-anism of Al5A06 sheets with different annealing temperatures was also investigated.The abnormal grain growth during 300℃ annealing treatment is mainly due to the asynchronous recrystallization behavior with low recrystallization driving force,which leads to the early recrystallized regions directly absorb-ing adjacent grains along134crystal direction.The cold rotary forged Al5A06 sheets after 250℃-2 h annealing treatment exhibit the best fatigue property,which is mainly because the optimum strength-plasticity matching brings about coordinate plastic deformation throughout most grains,and the effective dislocation movement between adjacent grains can delay the appearance of strain localization and ac-commodate continuous fatigue cyclic loading.展开更多
Nonmetallic inclusions mixed into large forged metal objects destroy the continuity in the metal and affect the quality of the forged product.Research on how inclusions affect the plastic deformation of a matrix shows...Nonmetallic inclusions mixed into large forged metal objects destroy the continuity in the metal and affect the quality of the forged product.Research on how inclusions affect the plastic deformation of a matrix shows the significance of the formation mechanism of inclusion defects.For upset forging,the nonlinear finite element model was shown to be appropriate for the ingot hot-forging process by comparing the results with experiments involving plastic and hard inclusions inserted into the forged piece.The high-temperature stress-strain curves of MnS plastic inclusions were obtained experimentally.The results show how,during upsetting,the morphology of MnS plastic inclusions varies from spherical to ellipsoidal,until finally becoming flat in shape.The larger the inclusion is,the larger the degree of deformation of the inclusion is,and large inclusions enhance the risk of the final product failing to pass inspection for inclusion flaws.Strain significantly concentrates in the matrix near a hard inclusion.When the hard inclusion reaches a certain size,conical fractures form on both sides of the inclusion.To pass inclusion-flaw inspection and close hole defects to the extent possible,the flat-anvil upsetting is recommended.Finally,the inclusiondeformation state obtained by finite element simulation is verified experimentally.展开更多
基金Project (2011CB605505) supported by the National Basic Research Program of ChinaProject (2008AA03A233) supported by the National High-Tech Research and Development Program of China
文摘Ti-47Al-2Nb-2Cr-0.4（W, Mo） （mole fraction, %） alloy ingot fabricated using vacuum consumable melting was containerless near-isothermally forged, and the high temperature forgeability, microstructure and tensile properties were investigated. The results show that the TiAl ingot exhibits good heat workability during containerless near-isothermally forging process, and there are not evident cracks on the surface of as-forged TiAl pancake with a total deformation degree of 60%. The microstructure of the TiAl ingot appears to be typical nearly-lamellar（NL）, comprising a great amount of lamellar colonies （α2＋γ） and a few equiaxed γ grains. After near-isothermally forging, the as-forged pancake shows primarily fine equiaxed γ grains with an average grain size of 20 μm and some broken lamellar pieces, and some bent lamellas still exist in the hard-deformation zone. Tensile tests at room temperature show that ultimate tensile strength increases from 433 MPa to 573 MPa after forging due to grain refinement effect.
基金National Natural Science Foundation of China (50275094)
文摘The dynamic recrystallization behavior of microalloyed forged steel was investigated with a compression test in the temperature range of 1 223-1 473 K and a strain rate of 0. 01-5 s^-1. Activation energy was calculated to be 305.9 kJ/mol by regression analysis. Modeling equations were developed to represent the dynamic recrystallization volume fraction and grain size. Parameters of the modeling equations were determined as a function of the Zener-Hollomon parameter. The developed modeling equation will be combined with finite element modeling to predict microstructural change during the hot forging processing.
基金Project(51301209)supported by the National Natural Science Foundation of China
文摘Transmission electron microscopy(TEM),scanning electron microscopy(SEM),hardness tests and tensile tests were performed to investigate the effect of aging on microstructure and mechanical properties of forged Al-4.4Cu-0.7Mg-0.6Si alloy.The results show that the alloy exhibits splendid mechanical properties with an ultimate tensile strength of504MPa and an elongation of10.1%after aging at170°C for16h.With tensile testing temperature increasing to150°C,the strength of the alloy declines slightly to483MPa.Then,the strength drops quickly when temperature reaches over200°C.The high strength of the alloy in peak-aged condition is caused by a considerable amount ofθ'and AlMgSiCu(Q)precipitates.The relatively stable mechanical properties tested below150°C are mainly ascribed to the stability ofθ'precipitates.The growth ofθ'and Q precipitates and the generation ofθphase lead to a rapid drop of the strength when temperature is over150°C.
文摘With a focus on the backup roll, a rolling-contact-fatigue experiment was performed on samples of 5% Cr forged steel. The P-S-N fatigue curves were determined and the fatigue strength was calculated. The emergence of cracks on the test-sample surfaces was observed at different fatigue cycles. A micro-hardness tester was used to measure the hardness of the subsurface fatigue layer. The microstructures were analyzed at various magnifications with an optical microscope, scanning electron microscope, and transmission electron microscope. Based on these tests, the rolling-contact-fatigue mechanism of the large forged steel backup roll was also considered. The results showed that the contact-fatigue strength of the tested backup roll steel was 1 249 MPa;the surface fatigue crack lengthened continuously as the number of cycles increased and followed an S-shaped curve; the subsurface fatigue hardness reached its highest value at about 90 （HV） increment from the matrix hardness of 540 （HV） in the backup roll; the subsurface martensite/bainite microstructure was crushed and the dislocation density was greatly increased. Under alternating contact stresses,the surface/subsurface material was damaged and exhibited many microdefects. At the least, the surface fatigue layer on backup rolls should be fully removed before the microcracks enter a period of rapid propagation.
基金financially supported by the Natural Sciences and Engineering Research Council of Canada, the Automotive Partnership Canada (APC) program under APCPJ 459269-13 grant with contributions from Multimatic Technical Centre, Ford Motor Company, and Centerline Windsor
文摘structure with a significant reduction in casting porosity, while the texture changed to sharp basaMeasured mechanical properties of the forged alloy showed that strength did not change, howductility improved by 75%. The analysis of the fracture surface of the forged alloy under tension rea ductile fracture with dimple morphology, while the as-cast alloy displayed a brittle fracture with pores. This demonstrated that the reduction of casting defects and dendritic morphology, as well evolution of recrystallized grains, enhanced ductility, while partial dynamic recrystallization throuforging process resulted in only marginal modification of strength in the forged condition.. 2017 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials SciTechno
基金supported financially by the National Key Research and Development Program(No.2018YFA0702900)the National Natural Science Foundation of China(Nos.U1508215,51774265 and 51701225)+3 种基金the National Science and Technology Major Project of China(No.2019ZX06004010)the Key Program of the Chinese Academy of Sciences(No.ZDRW-CN-2017-1)the Program of CAS Interdisciplinary Innovation TeamGleeble engineer Jiajun He for her technical support in superhot experiments.
文摘Semi-solid forging of iron-based alloys during solidification has unique characteristics distinct from those of the classical hot forging.With the aim of acquiring precise knowledge concerning the microstructural evolution of bearing steel Cr4 Mo4 V in this process,a series of semi-solid forging experiments were carried out in which samples were wrapped in a designed pure iron sheath.The effects of forging temperature and forging reduction on the grain morphology and liquid flow behavior were investigated,respectively.By forging solidifying metal(FSM),bulky primary dendrites were broken and spheroidal grains with an average shape factor of 0.87 were obtained at 1360?C.With the decreasing forging temperature to 1340?C,the microstructural homogeneity can be improved.On the other hand,it shows that a higher forging reduction(50%)is essential for the spheroidization of grains and elimination of liquid segregation.Those microstructural characteristics are related to different motion mechanisms of solid and liquid phases at different forging temperatures.Additionally,the effect of semi-solid forging on the eutectic carbides was also investigated,and the results demonstrate that the higher diffusion capacity and less liquid segregation jointly lower the large eutectic carbides and consequently cause its uniform distribution during FSM.
基金the Jihua Laboratory Scientific Research Project,China (No.X210291TL210)the National Natural Science Foundation of China (No.51971215)the Natural Science Foundation of Liaoning Province of China (No.2019-MS-330)。
文摘The microstructural evolution and tensile properties of a forged Ti−42Al−5Mn alloy subjected to different heat treatments were studied.The results showed that,when the forged alloy was aged at 800℃ for 24 h,the interlamellar spacing(λ)andγgrain size at colony boundaries are generally coarsened.Whereas,when the alloy was first annealed at 1300℃ and then aged at 800℃ for 24 h,this coarsening of related microstructures appears less pronounced.The suggested annealing temperatures for the forged Ti−42Al−5Mn alloy are in the range of 1250−1300℃.It was found that,on the condition of the same annealing system,both the strength and ductility were improved as the aging temperature changed from 1000 to 800℃.The secondary precipitatedβo(β_(o,sec))at colony boundaries could be responsible for improving the strength,and theγphase at colony boundaries with the grain size about 6μm might be one of the main reasons for the better ductility.
基金supported by the Air Force Office of Scientific Research under award number FA2386-17-14025。
文摘A Cu-1.5 wt.%Ti/Diamond(55 vol.%)composite was fabricated by hot forging from powder mixture of copper,titanium and diamond powders at 1050?C.A nano-thick TiC interfacial layer was formed between the diamond particle and copper matrix during forging,and it has an orientation relationship of(111)TiC//(002)Cu&[110]TiC//[110]Cuwith the copper matrix.HRTEM analysis suggests that TiC is semicoherently bond with copper matrix,which helps reduce phonon scattering at the TiC/Cu interface and facilitates the heat transfer,further leading to the hot-forged copper/diamond composite(referred as to Cu-Ti/Dia-0)has a thermal conductivity of 410 W/m K,and this is about 74%of theoretical thermal conductivity of hot-forged copper/composite(552 W/m K).However,the formation of thin amorphous carbon layer in diamond particle(next to the interfacial TiC layer)and deformed structure in the copper matrix have adverse effect on the thermal conductivity of Cu-Ti/Dia-0 composite.800℃-annealing eliminates the discrepancy in TiC interface morphology between the diamond-{100}and-{111}facets of Cu-Ti/Dia-0 composite,but causes TiC particles coarsening and agglomerating for the Cu-Ti/Dia-2 composite and interfacial layer cracking and spallation for the Cu-Ti/Dia-1 composite.In addition,a large amount of graphite was formed by titanium-induced diamond graphitization in the Cu-Ti/Dia-2 composite.All these factors deteriorate the heat transfer behavior for the annealed Cu-Ti/Dia composites.Appropriate heat treatment needs to be continually investigated to improve the thermal conductivity of hot-forged CuTi/Dia composite by eliminating deformed structure in the copper matrix with limit/without impacts on the formed TiC interfacial layer.
基金supported by National Natural Science Foundation of China(Grant No.51874367 and 51574291)。
文摘Multidirectional forging(MDF)was successfully applied to fabricate large-size Mg-Gd-Y-Zn-Zr-Ag alloy in this work and effects of T4,T5 and T6 treatments on the microstructure and mechanical properties of the as-forged alloy were analyzed.Results show that dynamic recrystallization(DRX)occurs and second phase particles precipitate along the grain boundary during the MDF process.After annealing treatment(T4),the volume fraction and size of dynamic precipitates slightly increase at a lower temperature(430℃)compared with those of MDFed sample,while they are dissolved into theα-Mg matrix at a higher temperature(450℃).At the meantime,short plate-shaped long-period stacking ordered(LPSO)phases are observed in the DRX grains of the MDFed sample and then dissolved into theα-Mg matrix during annealing at both temperatures.Typical basal texture is identified in the MDFed sample,but the basal pole tilts away from final forging direction and rare-earth texture component with<1121>orientation parallel to penultimate forging direction becomes visible after annealing.The T6 sample annealing at 430℃for 4 h and ageing at 200℃for 34 h exhibits the superior strength and ductility in this study.The ultimate tensile strength,tensile yield strength and elongation to failure,which is 455 MPa,308 MPa and 7.7%,respectively,are overall improved compared with the directly-aged(T5)sample.This paper provides a superior heat treatment schedule to manufacture high-performance large-scale Mg-Gd-Y-Zn-Zr-Ag components for industrial production.
文摘Effect of multi-directional forging(MDF)on wear properties of Mg-Zn alloys(with 2,4,and 6wt%Zn)is investigated.Dry sliding wear test was performed using pin on disk machine on MDF processed and homogenized samples.Wear behavior of samples was analyzed at loads of ION and 20 N,with sliding distances of 2000m and 4000m,at a sliding velocity of 3m/s.Microstructures of worn samples were observed under scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),and x-ray diffraction(XRD)and the results were analyzed.Mechanical properties were evaluated using microhardness test.After 5 passes of MDF,the average grain size was found to be 30±4p m,22±3 pm,and 18±3 pm,in Mg-2%Zn,Mg-4%Zn,and Mg-6%Zn alloys,respectively,with significant improvement in hardness in all cases.Wear resistance was improved after MDF processing,as well as,with increment in Zn content in Mg alloy.However,it decreased when the load and the sliding distance increased.Worn surface exhibited ploughing,delamination,plastic deformation,and wear debris along sliding direction,and abrasive wear was found to be the main mechanism.
基金the Ministry of Higher Education of Malaysia for the Malaysian International Scholarship and research funding under FRGS vote No. R.J13000.7824.4F810
文摘Elemental titanium(Ti)and nickel(Ni)powders were consolidated by spark plasma sintering(SPS)to fabricate Ti-51%Ni(mole fraction)shape-memory alloys(SMAs).The objective of this study is to enhance the superelasticity of SPS produced Ti-Ni alloy using free forging as a secondary process.Products from two processes(with and without free forging)were compared in terms of microstructure,transformation temperature and superelasticity.The results showed that,free forging effectively improved the tensile and shape-memory properties.Ductility increased from 6.8%to 9.2%after forging.The maximum strain during superelasticity increased from 5%to 7.5%and the strain recovery rate increased from 72%to 92%.The microstructure of produced Ti-51%Ni SMA consists of the cubic austenite(B2)matrix,monoclinic martensite(B19′),secondary phases(Ti3Ni4,Ti2Ni and TiNi3)and oxides(Ti4Ni2O and Ti3O5).There was a shift towards higher temperatures in the martensitic transformation of free forged specimen(aged at 500°C)due to the decrease in Ni content of B2 matrix.This is related to the presence of Ti3Ni4 precipitates,which were observed using transmission electron microscope(TEM).In conclusion,free forging could improve superelasticity and mechanical properties of Ti-51%Ni SMA.
基金supported by the National Natural Science Foundation of China (No. 51201016)
文摘NiTi-Al-based alloys are promising high-tem- perature structural materials for aerospace and astronautics applications. A new NiTi-Al-based alloy Ni--43Ti-4AI- 2Nb-2Hf （at%） was processed via isothermal forging. The microstructure and mechanical properties at room temperature and high temperature were investigated through scanning electron microscope （SEM）, X-ray diffraction （XRD）, and tensile tests. Results show that the micro- structure of as-forged Ni-43Ti--4AI-2Nb-2Hf alloy con- sists of NiTi matrix, Ti2Ni phase, and Hf-rich phase. The simultaneous addition of Nb and Hf, which have strong affinities for Ti sites, promotes the precipitation of Hf-rich phases along the grain boundaries. The tensile strengths of Ni-43Ti-4A1-2Nb-2Hf alloy are dramatically increased compared with the ternary Ni-46Ti-4A1 alloy. At room temperature and 650℃, the yield stress of Ni--43Ti-4Al- 2Nb-2Hf alloy reaches 1,070 and 610 MPa, respectively, which are 30 % and 150 % higher than those of Ni--46Ti- 4Al alloy. The improved tensile property results from the solid solution strengthening by Nb and Hf, as well as the dispersion hardening of the Ti2Ni and Hf-rich phases.
基金financially supported by the Technology Innovation and Application Demonstration Project of Chongqing(Grant No.cstc2018jszx-cyzdX0080)the Fundamental and Cutting-Edge Research Plan of Chongqing(Grant No.cstc2018jcyjAX0299)。
文摘In this study,typical microstructural characteristics of a metastableβTi alloy(Ti–5Al–5Mo–5V–3Cr–1Fe)forged in a dual-phase region(strain of 54%at 820℃)were investigated in detail by the combined use of X-ray diff raction,energy dispersive spectroscopy,electron channeling contrast imaging and electron backscatter diff raction techniques.Results show that the microstructure of the forged alloy is composed of bulkαgrains,αplates andβmatrix.The bulkαgrains correspond to retained primaryαphase(αp,average grain size^2.4μm),while theαplates are secondaryαphase(αs,width^70 nm)precipitated from theβmatrix during air cooling.During forging,theβmatrix experiences dynamic recovery with many subgrains and signifi cant orientation gradients formed.Analyses of the orientation relationship between theαandβphases show that the Burgers orientation relationship is not maintained between someα_p andβphases,which should be related to thermal deformation-induced changes of their orientations.In contrast,all of theαs plates are found to maintain well the Burgers orientation relationship with theβphase.
基金Project(51105287)supported by the National Natural Science Foundation of ChinaProject(2013M531750)supported by China Postdoctoral Science Foundation
文摘Cold closed-die forging is a suitable process to produce spur-bevel gears due to its advantages, such as saving materials and time, reducing costs, increasing die life and improving the quality of the product. The homogeneity of microstructure of cold closed-die forged gears can highly affect their service performance. The homogeneity of microstructure and Vickers hardness in cold closed-die forged gear of 20 Cr Mn Ti alloy is comprehensively studied by using optical microscopy and Vickers hardness tester. The results show that the distribution homogeneity of the aspect ratio of grain and Vickers hardness is the same. In the circumferential direction of the gear tooth, the distribution of the aspect ratio of grain and Vickers hardness is inhomogeneous and they gradually decrease from the surface to the center of the tooth. In the radial direction, the distribution of the aspect ratio of grain and Vickers hardness is inhomogeneous on the surface of the gear tooth; while it is relatively homogeneous in the center of the gear tooth. In the axial direction of the gear tooth, the distribution of the aspect ratio of grain and Vickers hardness is relatively homogeneous from the small-end to the large-end of the gear tooth.
基金This work was funded by the National Basic Research Program of China(973 Program)through project No.2013CB632202National Natural Science Foundation of China(NSFC)through projects No.51105350 and No.51301173,respectively.
文摘This paper investigated the high cycle fatigue behavior of a forged Mg-7Gd-5Y-1Nd-0.5Zr alloy with different stress concentration factor(Kt),under different stress ratio(R),and along different loading direction.The smooth specimen(Kt=1),under R=0.1 and along longitude direction,shows a high fatigue strength of 162 MPa at 107 cycles.The fatigue behavior of the forged Mg-7Gd-5Y-1Nd-0.5Zr alloy exhibits a high sensitive to the notch.Moreover,change of stress ratio from 0.1 to−1 may also result in a bad fatigue property.The flux inclusions were elongated along longitude direction and/or transverse direction during the forging process of the Mg-7Gd-5Y-1Nd-0.5Zr alloy.The interface between the flux inclusion and the matrix may debond and serve as the crack initiation site during the fatigue loading process,leading to the deterioration of the fatigue property along thickness direction and a high anisotropic fatigue behavior between longitude direction and thickness direction.
文摘In this study, AA2519 alloy was initially processed by multi axial forging (MAF) at room and cryogenic temperatures. Subsequently, the microstructure and the mechanical behavior of the processed samples under quasi-static loading were investigated to determine the influence of cryogenic forging on alloys’ subgrains dimensions, grain boundaries interactions, strength, ductility and toughness. In addition, the failure mechanisms at the tensile rupture surfaces were characterized using scanning electron micro-scope (SEM). The results show significant improvements in the strength, ductility and toughness of the alloy as a result of the cryogenic MAF process. The formation of nanoscale crystallite microstructure, heavily deformed grains with high density of grain boundaries and second phase breakage to finer particles were characterized as the main reasons for the increase in the mechanical properties of the cryogenic forged samples. The cryogenic processing of the alloy resulted in the formation of an ultrafine grained material with tensile strength and toughness that are ~41% and ~80% higher respectively after 2 cycles MAF when compared with the materials processed at ambient temperature. The fractography analysis on the tested materials shows a substantial ductility improvement in the cryoforged (CF) samples when compared to the room temperature forged (RTF) samples which is in alignment with their stress-strain profiles. However, extended forging at higher cycles than 2 cycles led only to increase in strength at the expense of ductility for both the CF and RTF samples.
基金VANITECthe Spanish Ministerio de Ciencia e Innovacion for their financial support
文摘Nowadays there is a continuous demand,particularly from the automotive industry,for cheaper,lighter and more reliable components.It is not surprising then that steel research has been focused during the last decades in new qualities and processes.This paper is dealing with the use of vanadium microalloyed steels on one of those new processes,warm forging.For its low precipitation temperature and its recognised ability to strengthen steel microstructures via austenite grain growth control,precipitation hardening and interference of the static recrystallization process,vanadium in microalloyed steels seem to be an appropriate candidate for warm forging.
基金supported by the National Natural Science Foundation of China(No.U21A20131)the Technical Development Project of COMAC Shanghai Aircraft Manufacturing Co.,Ltd.(No.COMAC-SFGS-2023-631)the 111 Project(No.B17034),andthe In-novative Research Team Development Program of Ministry of Edu-cation of China(No.IRT17R83).
文摘Al7075 sheets are widely used in aerospace industry and their higher strength-plasticity collaborative improvement requirement is urgent.In this study,the microstructure inheriting the evolution and me-chanical properties of Al7075 sheets during multidirectional rotary forging(MRF)and T6 heat treatment are analyzed.The results show that the average grain size exhibits near-parabolic evolution with increas-ing MRF deformation amount.MRF20%+T6(20%MRF deformation amount+T6)condition possesses the largest grain size of 72.6μm,and its abnormal grain growth mechanism is that the medium deformation energy and high deformation heterogeneity in MRF20%deformed grains could cause asynchronous re-crystallization behavior during T6 heat treatment,and the grains with comparatively higher deformation energy get recrystallized firstly and devour adjacent grains along preferred011or223misorientation axis.MRF70%+T6 condition possesses the finest grain size of 14.2μm,and its fine grain inheriting mech-anism is that the uniformly high deformation energy in MRF70%deformed grains causes uniformly rapid recrystallization,and rapidly recrystallized grains effectively suppress grain boundary motion from adja-cent grains.With increasing MRF deformation amount,tensile strength and elongation values both exhibit near-antiparabolic evolution.MRF70%+T6 condition possesses the largest tensile strength(563 MPa)and elongation(17.73%),which increases by 8.27%and 80.55%compared to as-annealed+T6(MRF0%+T6)condition(tensile strength is 520 MPa and elongation is 9.82%),respectively.The strength-plasticity col-laborative improvement is mainly because the combination of effectively inherited fine grains,refined inclusion particles,and uniformly distributed fineη’particles after T6 heat treatment could promote smooth dislocation movement and coordinated slip behavior in most matrix grains,which contributes to the delay of stress localization and strength-plasticity collaborative improvement.
基金financially supported by the National Natural Science Foundation of China(no.U21A20131)the Innovative Research Team Development Program of Ministry of Education of China(no.IRT17R83)for the support given to this research.
文摘Al5A06 sheets by large cold plastic deformation usually have high strength but low plasticity,i.e.weak strength-plasticity matching,which may lead to their poor fatigue property.In this study,annealing treat-ments are applied on cold rotary forged Al5A06 sheets to regulate strength-plasticity matching and im-prove fatigue properties.The microstructures,tensile mechanical properties and fatigue properties un-der different annealing parameters were analyzed.The abnormal grain growth mechanism of cold rotary forged Al5A06 sheets during 300℃ annealing treatment was investigated,and the fatigue failure mech-anism of Al5A06 sheets with different annealing temperatures was also investigated.The abnormal grain growth during 300℃ annealing treatment is mainly due to the asynchronous recrystallization behavior with low recrystallization driving force,which leads to the early recrystallized regions directly absorb-ing adjacent grains along134crystal direction.The cold rotary forged Al5A06 sheets after 250℃-2 h annealing treatment exhibit the best fatigue property,which is mainly because the optimum strength-plasticity matching brings about coordinate plastic deformation throughout most grains,and the effective dislocation movement between adjacent grains can delay the appearance of strain localization and ac-commodate continuous fatigue cyclic loading.
基金Item Sponsored by National Natural Science Foundation of China(51575475)College Innovation Team Leader Training Program of Hebei Province of China(LJRC012)
文摘Nonmetallic inclusions mixed into large forged metal objects destroy the continuity in the metal and affect the quality of the forged product.Research on how inclusions affect the plastic deformation of a matrix shows the significance of the formation mechanism of inclusion defects.For upset forging,the nonlinear finite element model was shown to be appropriate for the ingot hot-forging process by comparing the results with experiments involving plastic and hard inclusions inserted into the forged piece.The high-temperature stress-strain curves of MnS plastic inclusions were obtained experimentally.The results show how,during upsetting,the morphology of MnS plastic inclusions varies from spherical to ellipsoidal,until finally becoming flat in shape.The larger the inclusion is,the larger the degree of deformation of the inclusion is,and large inclusions enhance the risk of the final product failing to pass inspection for inclusion flaws.Strain significantly concentrates in the matrix near a hard inclusion.When the hard inclusion reaches a certain size,conical fractures form on both sides of the inclusion.To pass inclusion-flaw inspection and close hole defects to the extent possible,the flat-anvil upsetting is recommended.Finally,the inclusiondeformation state obtained by finite element simulation is verified experimentally.
