The rapid development of magnetic materials provides the possibility for the application of permanent magnet stirring(PMS).Numerical and experimental investigations were employed with respect to the solidification pro...The rapid development of magnetic materials provides the possibility for the application of permanent magnet stirring(PMS).Numerical and experimental investigations were employed with respect to the solidification process of the Al—2Sc alloy controlled by a novel PMS using NdFeB permanent magnets under various rotation speeds(0,50,100 and 150 r/min).The simulated results reveal that the maximum electromagnetic force increases proportionally from 4.14 to 12.39 kN/m^(3)and the maximum tangential velocity increases from 0.13 to 0.36 m/s when the rotation speed of PMS enhances from 50 to 150 r/min in the ingot melt.Besides,the experimental results demonstrate that PMS can achieve a uniform distribution of blocky Al_(3)Sc precipitated phase in the longitudinal direction under the impact of a forced fluid flow.Moreover,increasing rotation speed of PMS is beneficial to refining aluminum grain size significantly and decreasing the texture intensity in the alloy.In addition,the Brinell hardness of Al-2Sc alloy is increased by 33%to 27.8 HB and the tensile strength is enhanced by 34%-128.2 MPa,due to the improved distribution of the strengthening Al_(3)SC phase and the grain refinement of Al matrix under the impact of PMS.This work provides an effective application of NdFeB permanent magnets in the metal cast field.展开更多
Understanding the temperature dependent deformation behavior of Mg alloys is crucial for their expanding use in the aerospace sector.This study investigates the deformation mechanisms of hot-rolled AZ61 Mg alloy under...Understanding the temperature dependent deformation behavior of Mg alloys is crucial for their expanding use in the aerospace sector.This study investigates the deformation mechanisms of hot-rolled AZ61 Mg alloy under uniaxial tension along rolling direction(RD)and transverse direction(TD)at-50,25,50,and 150℃.Results reveal a transition from high strength with limited elongation at-50℃ to significant softening and maximum ductility at 150℃.TD samples consistently showed 2%-6%higher strength than RD;however,this yield anisotropy diminished at 150℃ due to the shift from twinning to thermally activated slip and recovery.Fractography indicated a change from semi-brittle to fully ductile fracture with increasing temperature.Electron backscattered diffraction(EBSD)analysis confirmed twinning-driven grain refinement at low temperatures,while deformation at high temperatures involved grain elongation along shear zones,enabling greater strain accommodation before material failure.展开更多
The formation of fine,non-dendritic equiaxed grains throughout a casting without the addition of refiners(i.e.independent of alloy chemistry),is made possible by using ultrasonic,magnetic or pulsed magnetic and electr...The formation of fine,non-dendritic equiaxed grains throughout a casting without the addition of refiners(i.e.independent of alloy chemistry),is made possible by using ultrasonic,magnetic or pulsed magnetic and electric current pulse techniques.The dominant mechanisms proposed for the grain refinement produced during the application of an external field are cavitation phenomena assisted nucleation or fragmentation of dendrites(ultrasonic field),wall crystals arising from the cold surface of the mould(electric current pulse,magnetic and pulsed magnetic fields).In all these cases fluid flow provides an additional contribution(e.g.reduced temperature gradients,growth rate and remelting of dendrites)to maintaining an equiaxed grain structure.The origin of equiaxed grains under an external field also depends on the casting conditions(volume and shape of casting)and the type of alloy other than the mechanisms specific to a particular technique.The current work aims to provide a detailed understanding of the various factors and mechanisms that influence the grain refinement achieved during the solidification of pure metals(magnesium and zinc)subjected to Ultra Sonic Treatment(UST).The role of the temperature range of UST application,time duration and an unpreheated sonotrode are examined with respect to the origin,evolution of equiaxed grain structure,morphology and the columnar to equiaxed transition.The origin of grains was analysed from three fundamental aspects that contribute to refinement(i)heterogeneous nucleation(ii)fragmentation of existing dendrites and(iii)grains produced from the colder surfaces(arising from mould walls or vibrating surfaces as wall crystals).A comparison of UST refinement with mechanical,low-frequency vibration,electric current pulse and magnetic field solidification of pure metals has also been provided to highlight the importance of the cold surfaces(sonotrode and mould wall)in influencing grain refinement.展开更多
In this work,the mechanical properties and strengthening mechanisms induced by microstructural evolution in a rheo-extruded 5087 alloy processed via accumulative continuous extrusion forming(ACEF)were investigated.Ele...In this work,the mechanical properties and strengthening mechanisms induced by microstructural evolution in a rheo-extruded 5087 alloy processed via accumulative continuous extrusion forming(ACEF)were investigated.Electron back-scattered diffraction(EBSD)and transmission electron microscopy(TEM)were utilized to characterize the microstructure of the alloy subjected to ACEF with various passes.The grain refinement caused by continuous dynamic recrystallization(CDRX)was discussed.The results demonstrated that after 3 passes of ACEF,there was a significant grain refinement effect on the alloy,and the average grain size decreased from 45.6μm to 2.5μm;the ultimate tensile strength(UTS)and yield strength(YS)of the alloy increased to 362.8 MPa and 234.6 MPa,respectively.Dislocation cells/walls generated during deformation promoted the formation of low angle grain boundaries(LAGBs).The accumulative strain accelerated the transformation of LAGBs to high angle grain boundaries(HAGBs).Dislocation pile-up enhanced the driving force of CDRX,and nano-sized Al_6(Mn,Fe)phases at the grain boundaries inhibited the growth of grains due to the pinning effect.Based on the quantitative estimation,dislocation strengthening and grain boundary strengthening dominated the enhancement in YS of the ACEFed alloy.展开更多
The uniform refinement mechanisms and methods of deformed mixed and coarse grains inside a solution-treatment Ni-based superalloy during two-stage annealing treatment have been investigated.The two-stage heat treatmen...The uniform refinement mechanisms and methods of deformed mixed and coarse grains inside a solution-treatment Ni-based superalloy during two-stage annealing treatment have been investigated.The two-stage heat treatment experiments include an aging annealing treatment(AT)and a subsequent recrystallization annealing treatment(RT).The object of AT is to precipitate someδphases and consume part of storage energy to inhibit the grain growth during RT,while the RT is to refine mixed and coarse grains by recrystallization.It can be found that the recrystallization grains will quickly grow up to a large size when the AT time is too low or the RT temperature is too high,while the deformed coarse grains cannot be eliminated when the AT time is too long or the RT temperature is too low.In addition,the mixed microstructure composed of some abnormal coarse recrystallization grains(ACRGs)and a large number of fine grains can be observed in the annealed specimen when the AT time is 3 h and RT temperature is 980℃.The phenomenon attributes to the uneven distribution ofδphase resulted from the heterogeneous deformation energy when the AT time is too short.In the regions with a large number ofδphases,the recrystallization nucleation rate is promoted and the growth of grains is limited,which results in fine grains.However,in the regions with fewδphases,the recrystallization grains around grain boundaries can easily grow up,and the new recrystallization nucleus is difficult to form inside grain,which leads to ACRGs.Thus,in order to obtain uniform and fine annealed microstructure,it is a prerequisite to precipitate even-distributedδphase by choosing a suitable AT time,such as 12 h.Moreover,a relative high RT temperature is also needed to promote the recrystallization nucleation aroundδphase.The optimal annealing parameters range for uniformly refining mixed crystal can be summarized as:900℃×12 h+990℃×(40-60 min)and 900℃×12 h+1000℃×(10-15 min).展开更多
The microstructure–mechanical property relationship of a Cu-bearing low-carbon high-strength low-alloy steel,subjected to a novel multistage heat treatment including quenching(Q),lamellarization(L)and tempering(T),is...The microstructure–mechanical property relationship of a Cu-bearing low-carbon high-strength low-alloy steel,subjected to a novel multistage heat treatment including quenching(Q),lamellarization(L)and tempering(T),is presented.Yield strength of 989.5 MPa and average toughness at-80℃of 41 J were obtained in this steel after quenching and tempering(QT)heat treatments.Specimen QLT gained a little lower yield strength(982.5 MPa),but greatly enhanced average toughness at-80℃(137 J).To further clarify the strengthening and toughening mechanisms in specimen QLT,parameters of microstructural characteristic and crack propagation process were compared and analyzed for specimens Q,QL,QT and QLT.The microstructure of tempered martensite/bainite(M/B)in specimen QT changed to refined tempered M/B matrix mixed with minor IF(inter-critical ferrite)in specimen QLT.Cu-rich precipitates existed in tempered M/B for both specimens QT and QLT,as well as in IF.Compared with QT,adding a lamellarization step before tempering made the effective grains of specimen QLT refined and also led to coarser Cu-rich precipitates in tempered M/B matrix.The weaker strengthening effect of coarser Cu-rich precipitates should be a key reason for the slightly lower yield strength in specimen QLT than in specimen QT.No austenite was found in all specimens Q,QL,QT and QLT.Specimen QLT showed purely ductile fracture mode at-80℃due to the refined effective grains.The greatly improved toughness is mainly attributed to the enhanced energy of crack propagation.The combination of refined microstructure,softened matrix and deformation of minor'soft'IF during crack propagation led to the most superior toughness of specimen QLT among all specimens.展开更多
The objective of the current study was to investigate the use of ultrasonic melt treatment technology in the production of grain-refined billets of the AC7 A alloy, which was intended for subsequent use as a feedstock...The objective of the current study was to investigate the use of ultrasonic melt treatment technology in the production of grain-refined billets of the AC7 A alloy, which was intended for subsequent use as a feedstock in forming operations. The experiments included the application of ultrasonic vibrations to the molten alloys via direct and indirect techniques. Several process parameters such as pouring temperatures(several temperatures between 740 and 660℃), and treatment time(from 12 min down to 2 min) were investigated. The experiment included continuous ultrasonic treatment from the liquid to the semisolid states. The results showed that both treatment techniques were viable for producing billets with the desirable microstructural characteristics. The optimum treatment conditions were the short treatment time(2 to 3 min), from about 660℃ down to 615℃ for the indirect treatment technique, and from 660℃ to 635℃ for the direct treatment technique. The resulting microstructures, at three positions along the height of the ingot, were characterized by fine, non-dendritic α(Al) grains in the order of a hundred microns, as compared to few thousands of microns for the conventional cast ingots. The intermetallic particles were also refined in size and modified in morphology by the ultrasonic treatment. The operating mechanisms by which the ultrasonic vibrations altered the ingot microstructures were discussed and analyzed.展开更多
A phase field model is developed to simulate the grain evolution of 17-4PH steel during cyclic heat treatment （CHT）. Our simulations successfully reproduce the grain morphologies of every CHT. In the process of ever...A phase field model is developed to simulate the grain evolution of 17-4PH steel during cyclic heat treatment （CHT）. Our simulations successfully reproduce the grain morphologies of every CHT. In the process of every CHT, phase transformation recrystallization happens. The recrystallized grains appear mainly on the original grain boundaries. The average grain size of 13.2 μm obtained by 1040 ℃×1 h solution treatment for this experimental steel can be refined to 2.2 μm after five CHT＇s. Furthermore, the effects of phenomenological parameters in our model are discussed.展开更多
The effect of titanium content on the refinement of austenite grain size in as-cast peritectic carbon steel was investigated by fast directional solidification experiments with simulating the solidification and growth...The effect of titanium content on the refinement of austenite grain size in as-cast peritectic carbon steel was investigated by fast directional solidification experiments with simulating the solidification and growth of surface and subsurface austenite in continuously cast slabs.Transmission electron microscope(TEM)and scanning electron microscope(SEM)were used to analyze the size and distribution of Ti(C,N)precipitates during solidification.Based on these results,the pinning pressure of Ti(C,N)precipitates on the growth of coarse columnar grains(CCGs)was studied.The results show that the austenite microstructure of as-cast peritectic carbon steel is mainly composed of the regions of CCGs and fine columnar grains(FCGs).Increasing the content of titanium reduces the region and the short axis of the CCGs.When the content of titanium is 0.09wt%,there is no CCG region.Dispersed microscale particles will firstly form in the liquid,which will decrease the transition temperature from FCGs to CCGs.The chain-like nanoscale Ti(C,N)will precipitate with the decrease of the transition temperature.Furthermore,calculations shows that the refinement of the CCGs is caused by the pinning effect of Ti(C,N)precipitates.展开更多
Refinement of grains and intermetallic phases in the as-solidified alloy structure offers uniform struc-tural properties,eliminates or minimizes common solidification defects,including segregation and hot cracking,and...Refinement of grains and intermetallic phases in the as-solidified alloy structure offers uniform struc-tural properties,eliminates or minimizes common solidification defects,including segregation and hot cracking,and improves thermomechanical processing of wrought alloys.Melt processing by an external field is an efficient process for achieving refinement of the solidification structure of Al and Mg alloys without altering the alloy composition.A wide range of melt processing methods and solidification stud-ies(conventional,directional,and in-situ approaches)have been reported in the literature that explore the mechanism of refinement.Identifying the dominant grain refinement mechanism has been a focus of most investigations because significant variations exist according to the casting conditions and the type of applied external treatments.The origin of fine grains occurs through either one or a combination of heterogenous nucleation,fragmentation of dendrites and grains formed and then separated from the surface of the melt and mould wall under vibration or agitation.The first part of this review describes the prominent external field techniques and the mechanisms proposed for the origin of fine grains.The second part critically compares the current understanding of these grain refinement mechanisms to de-termine differences and commonalities to identify the factors that promote the formation of equiaxed zones occupying a large volume fraction of the casting.展开更多
The trade-off between strength and ductility has been an enormous difficulty in the field of materials for an extended time due to their inverse correlation. In this work, friction stir processing(FSP) was for the fir...The trade-off between strength and ductility has been an enormous difficulty in the field of materials for an extended time due to their inverse correlation. In this work, friction stir processing(FSP) was for the first time performed to high-strength and high-melting-point Ni-Co based superalloy(GH4068),and enhanced strength and ductility were achieved in FSP samples. At room temperature, the FSP sample demonstrated significantly higher yield strength and ultimate tensile strength(1290 and 1670 MPa)than that of the base material(BM, 758 and 904 MPa) and advanced wrought GH4068 alloy(982 and 1291 MPa), concurrent with high tensile ductility(~24%). Compared with the BM, 70% higher yield strength of the FSP sample results from the remarkable contribution of grain-boundary and nanotwin strengthening, which has been confirmed by the multimechanistic model studied in this work. More importantly, with increasing temperature, an excellent strength-ductility synergy was obtained at 400 ℃,i.e., the yield strength of the FSP sample was increased by more than 50% compared with the BM(from789 to 1219 MPa);more interestingly, the elongation was also significantly increased from 17.9% in the BM to 28.5% in the FSP sample. Meanwhile, the Portevin-Le Chatelier effect was observed in the engineering stress-strain curve. The occurrence of this effect may be attributed to the interaction between solutes and defects like twins and mobile dislocations. Moreover, the grain refinement mechanism of FSP samples was proved to be discontinuous dynamic recrystallization.展开更多
A high-performance Ti-Ni-B alloy with good tensile properties and reduced mechanical anisotropy was developed by promoting the columnar to equiaxed transition(CET)of prior-βgrains and modifyingα-laths to equiaxed gr...A high-performance Ti-Ni-B alloy with good tensile properties and reduced mechanical anisotropy was developed by promoting the columnar to equiaxed transition(CET)of prior-βgrains and modifyingα-laths to equiaxed grains.Both Ni and B contributed to the refinement of columnar prior-βgrains during the L→βphase transformation by generating constitutional undercooling.Compared with Ni,B had a su-perior capability of generating constitutional undercooling,which not only replaced a significant amount of Ni with a minor addition to reduce the formation of brittle eutectoid,but also reacted with Ti to form TiB to promote heterogeneous nucleation ofα-Ti grains during theβ→αphase transformation.Together with the restricted growth ofα-laths induced by the refinement of prior-βgrains,a fully equiaxedα-Ti structure was obtained.The competition between the negative effect of brittle eutectoid and the positive role ofα-lath to equiaxed grain transition on the ductility of as-printed Ti-Ni-B alloys was fundamen-tally governed by the morphology of eutectoid and technically dependent on the Ni-B content.When the addition was 1.2Ni-0.06B(wt.%)or less,the positive effect ofα-lath on equiaxed grain transition can effectively mitigate the issue of reduced ductility caused by brittle eutectoid.In contrast,at 1.8Ni-0.09B or greater,the negative effect of eutectoid dominated.New insights into microstructural design obtained through the aforementioned approach were presented and discussed.展开更多
In this study, a serpentine channel pouring process was used to prepare the semi-solid A1-20%Si alloy slurry and refine primary Si grains in the alloy. The effects of the pouring temperature, number of curves in the s...In this study, a serpentine channel pouring process was used to prepare the semi-solid A1-20%Si alloy slurry and refine primary Si grains in the alloy. The effects of the pouring temperature, number of curves in the serpentine channel, and material of the serpentine channel on the size of primary Si grains in the semi-solid A1-20%Si alloy slurry were investigated. The results showed that the pouting temperature, number of the curves, and material of the channel strongly affected the size and distribution of the primary Si grains. The pouring tempera- ture exerted the strongest effect, followed by the number of the curves and then the material of the channel. Under experimental conditions of a four-curve copper channel and a pouring temperature of 701℃, primary Si grains in the semi-solid A1-20%Si alloy slurry were refined to the greatest extent, and the lath-like grains were changed into granular grains. Moreover, the equivalent grain diameter and the average shape coefficient of primary Si grains in the satisfactory semi-solid A1-20%Si alloy slurry were 24.4 μm and 0.89, respectively. Finally, the re- finement mechanism and distribution rule of primary Si grains in the slurry prepared through the serpentine channel pouring process were analyzed and discussed.展开更多
Nucleation sites of α-Al grains after addition of an Al-Ti-B master alloy into pure aluminium have been investigated using EPMA. The results show that either TiAl3 or boride particales can nucleate α-Al grains. But ...Nucleation sites of α-Al grains after addition of an Al-Ti-B master alloy into pure aluminium have been investigated using EPMA. The results show that either TiAl3 or boride particales can nucleate α-Al grains. But the number of TiAl3 nucleants is reduced with the holding time prolonged and the boride-nuclei are increasing gradually. Based on these results, a new refining method, adding molten Al-Ti-B into commercially pure aluminium, which has a quicker and better refining efficiency is presented.展开更多
The spatial arrangement,distribution and morphology of Fe-bearing intermetallics in AA6082 alloys depends on the manufacturing process of the alloy and thus influences the macroscopic properties.Here,the microstructur...The spatial arrangement,distribution and morphology of Fe-bearing intermetallics in AA6082 alloys depends on the manufacturing process of the alloy and thus influences the macroscopic properties.Here,the microstructure of a near industrial scale casting AA6082 Al alloy fabricated by:(a)direct chill casting,(b)Al-5 Ti-1 B grain refiner addition and(c)intensive melt shearing has been investigated by threedimensional visualization using SEM-based serial ultra microtomy tomography.The formation sequence of phases in AA6082 alloys is generally categorized into four stages:formation ofα-Al grains,Fe-bearing intermetallics,Mg_(2)Si phase,and eutectic rosettes.Results of three-dimensional visualization of the microstructure indicated that TiBparticles not only could nucleate Fe-bearingβ-intermetallics,but also could provide substrate for the formation of Fe-bearingα-intermetallics and Mg_(2)Si.A further deep analysis reveals that the essential condition for the formation of secondary phases such as Fe-bearing intermetallics and Mg_(2)Si phase is the build-up of a supersaturated solute front at theα-Al solid-liquid interface irrespective of the specific nucleation site.In addition,the results indicate that grain refinement processing causes the severe interconnectivity of Fe-bearingα-intermetallics.However,the intensive melt shearing is a better manufacturing process because the intermetallics are more evenly distributed and refined than with the addition of the grain refiner,thereby improving the properties of the alloy.展开更多
Hot torsion testing was performed on a low carbon Nb-Ti microalloyed steel to study the effects of hot tor- sion parameters, strain and strain rate, on ultrafine ferrite grains production through dynamic strain-induce...Hot torsion testing was performed on a low carbon Nb-Ti microalloyed steel to study the effects of hot tor- sion parameters, strain and strain rate, on ultrafine ferrite grains production through dynamic strain-induced trans- formation, at a deformation temperature just above At3. The initiation and evolution of ultrafine ferrite grains were studied. The results show that the amount of strain and strain rate has conversely effect on the volume fraction and grain size of ultrafine ferrite grains. With increasing strain, the interior of austenite grains become activated as nucle- ation sites for fine ferrite grains. As a result, ferrite grains continuously nucleate not only at the former austenite grain boundaries but also inside the austenite grains which leads to a rapid increase in volume fraction of ultrafine grains. Increasing of strain rate reduces the tendency of ferrite grains coarsening so that ultrafine ferrite grains are achieved, while the volume fraction of ultrafine grains decreases at the same strain level.展开更多
The formation reason and elimination method of non-uniform microstructure defects in Ti al- loy TC11 bar have been studied.The coagulating and coarsening into block of the part of grain boundary α and secondary α se...The formation reason and elimination method of non-uniform microstructure defects in Ti al- loy TC11 bar have been studied.The coagulating and coarsening into block of the part of grain boundary α and secondary α seem to be caused by the ingot cogging and initial forging temperature in the β region as well as no more enough deformation and uneven distribution. The grain α,elongated α and blocky α may be finally eliminated by adopting the technique of (α+β)thermomechanical processing+β processing,W.Q.+recrystallization annealing,A.C., thus the size of uniform and fine equiaxed α structure is believed to be reduced to 1.9258μm.展开更多
The pursuit of Ag-based alloys with both high strength and toughness has posed a longstanding chal-lenge.In this study,we investigated the cluster strengthening and grain refinement toughening mecha-nisms in fully oxi...The pursuit of Ag-based alloys with both high strength and toughness has posed a longstanding chal-lenge.In this study,we investigated the cluster strengthening and grain refinement toughening mecha-nisms in fully oxidized AgMgNi alloys,which were internally oxidized at 800℃ for 8 h under an oxy-gen atmosphere.We found that Mg-O clusters contributed to the hardening(138 HV)and strengthening(376.9 MPa)of the AgMg alloy through solid solution strengthening effects,albeit at the expense of duc-tility.To address this limitation,we introduced Ni nanoparticles into the AgMg alloy,resulting in signifi-cant grain refinement within its microstructure.Specifically,the grain size decreased from 67.2μm in the oxidized AgMg alloy to below 6.0μm in the oxidized AgMgNi alloy containing 0.3 wt%Ni.Consequently,the toughness increased significantly,rising from toughness value of 2177.9 MJ m^(-3) in the oxidized AgMg alloy to 6186.1 MJ m^(-3) in the oxidized AgMgNi alloy,representing a remarkable 2.8-fold enhancement.Furthermore,the internally oxidized AgMgNi alloy attained a strength of up to 387.6 MPa,comparable to that of the internally oxidized AgMg alloy,thereby demonstrating the successful realization of concurrent strengthening and toughening.These results collectively offer a novel approach for the design of high-performance alloys through the synergistic combination of cluster strengthening and grain refinement toughening.展开更多
This study investigates the adsorption mechanism,the film formation process,and the inhibition performance of benzotriazole(BTAH)on carbon steels with different grain sizes(i.e.,24.5,4.3,and 0.6μm)in 3.5 wt.%NaCl sol...This study investigates the adsorption mechanism,the film formation process,and the inhibition performance of benzotriazole(BTAH)on carbon steels with different grain sizes(i.e.,24.5,4.3,and 0.6μm)in 3.5 wt.%NaCl solution.The results demonstrate that grain refinement significantly impacts the adsorption and inhibition performance of BTAH on carbon steels.Ultra-refinement of steel grains to 0.6μm improves the maximum inhibition efficiency of BTAH to 90.0%within 168 h of immersion,which was much higher than that of the steels with 24.5μm(73.6%)and 4.3μm grain sizes(81.7%).Notably,grain sizes of 4.3 and 0.6μm facilitate a combination of physisorption and chemisorption of BTAH after 120 h of immersion,as evidenced by the X-ray photoelectron spectroscopy(XPS)results and Langmuir adsorption isotherms,while BTAH adsorbed on carbon steels with a grain size of 24.5μm through physisorption during the 168 h of immersion.Ultra-refinement of grains has beneficial impacts on promoting the formation of a stable and dense corrosion inhibitor film,leading to improved corrosion resistance and the mitigation of non-uniform corrosion.These advantageous effects can be attributed to the higher adsorption energy at grain boundaries(approximately-3.12 eV)compared to grain interiors(ranging from-0.79 to 2.47 eV),promoting both the physisorption and chemisorption of organic corrosion inhibitors.The investigation comprehensively illustrates,for the first time,the effects of grain size on the adsorption mechanism,film formation process,and inhibition performance of organic corrosion inhibitors on carbon steels.This study demonstrates a promising approach to enhancing corrosion inhibition performance through microstructural design.展开更多
Due to the low content of alloying elements and the lack of effective nucleation sites,the fusion zone(FZ)of tungsten inert gas(TIG)welded AZ31 alloy typically exhibits undesirable coarse columnar grains,which can res...Due to the low content of alloying elements and the lack of effective nucleation sites,the fusion zone(FZ)of tungsten inert gas(TIG)welded AZ31 alloy typically exhibits undesirable coarse columnar grains,which can result in solidification defects and reduced mechanical properties.In this work,a novel welding wire containing MgO particles has been developed to promote columnar-to-equiaxed transition(CET)in the FZ of TIG-welded AZ31 alloy.The results show the achievement of a fully equiaxed grain structure in the FZ,with a significant 71.9%reduction in grain size to 41 μm from the original coarse columnar dendrites.Furthermore,the combination of using MgO-containing welding wire and pulse current can further refine the grain size to 25.6 μm.Microstructural analyses reveal the homogeneous distribution of MgO particles in the FZ.The application of pulse current results in an increase in the number density of MgO(1-2 μm)from 5.16 × 10^(4) m^(-3) to 6.18 × 10^(4) m^(-3).The good crystallographic matching relationship between MgO and α-Mg matrix,characterized by the orientation relationship of[11(2)0]α-Mg//[0(1)1]MgO and(0002)_(α-Mg)//(111)_(MgO),indicates that the MgO particles can act as effective nucleation sites for α-Mg to reduce nucleation undercooling.According to the Hunt criteria,the critical temperature gradient for CET is greatly enhanced due to the significantly increased number density of MgO nucleation sites.In addition,the correlation with the thermal simulation results reveals a transition in the solidification conditions within the welding pool from the columnar grain zone to the equiaxed grain zone in the CET map,leading to the realization of CET.The exceptional grain refinement has contributed to a simultaneous improvement in the strength and plasticity of welded joints.This study presents a novel strategy for controlling equiaxed microstructure and optimizing mechanical properties in fusion welding or wire and arc additive manufacturing of Mg alloy components.展开更多
基金Project supported by the Natural Science Foundation of Hunan Province(2024JJ4056)the Key Project of Guangxi Zhuang Autonomous Region(AB22080089)the Government of Chongzuo,Guangxi Zhuang Autonomous Region(FA20210716)。
文摘The rapid development of magnetic materials provides the possibility for the application of permanent magnet stirring(PMS).Numerical and experimental investigations were employed with respect to the solidification process of the Al—2Sc alloy controlled by a novel PMS using NdFeB permanent magnets under various rotation speeds(0,50,100 and 150 r/min).The simulated results reveal that the maximum electromagnetic force increases proportionally from 4.14 to 12.39 kN/m^(3)and the maximum tangential velocity increases from 0.13 to 0.36 m/s when the rotation speed of PMS enhances from 50 to 150 r/min in the ingot melt.Besides,the experimental results demonstrate that PMS can achieve a uniform distribution of blocky Al_(3)Sc precipitated phase in the longitudinal direction under the impact of a forced fluid flow.Moreover,increasing rotation speed of PMS is beneficial to refining aluminum grain size significantly and decreasing the texture intensity in the alloy.In addition,the Brinell hardness of Al-2Sc alloy is increased by 33%to 27.8 HB and the tensile strength is enhanced by 34%-128.2 MPa,due to the improved distribution of the strengthening Al_(3)SC phase and the grain refinement of Al matrix under the impact of PMS.This work provides an effective application of NdFeB permanent magnets in the metal cast field.
基金supported by the Korea Institute of Energy Technology Evaluation and Planning(KETEP)the Ministry of Trade,Industry&Energy(MOTIE)of the Republic of Korea Program(No.RS-2025-02603127,Innovation Research Center for Zero-carbon Fuel Gas Turbine Design,Manufacture,and Safety)。
文摘Understanding the temperature dependent deformation behavior of Mg alloys is crucial for their expanding use in the aerospace sector.This study investigates the deformation mechanisms of hot-rolled AZ61 Mg alloy under uniaxial tension along rolling direction(RD)and transverse direction(TD)at-50,25,50,and 150℃.Results reveal a transition from high strength with limited elongation at-50℃ to significant softening and maximum ductility at 150℃.TD samples consistently showed 2%-6%higher strength than RD;however,this yield anisotropy diminished at 150℃ due to the shift from twinning to thermally activated slip and recovery.Fractography indicated a change from semi-brittle to fully ductile fracture with increasing temperature.Electron backscattered diffraction(EBSD)analysis confirmed twinning-driven grain refinement at low temperatures,while deformation at high temperatures involved grain elongation along shear zones,enabling greater strain accommodation before material failure.
基金funding support provided by the Australian Research Council Research Hub for Advanced Manufacturing of Medical Devices IH150100024the ARC Discovery grant DP140100702ARC linkage project LP150100950。
文摘The formation of fine,non-dendritic equiaxed grains throughout a casting without the addition of refiners(i.e.independent of alloy chemistry),is made possible by using ultrasonic,magnetic or pulsed magnetic and electric current pulse techniques.The dominant mechanisms proposed for the grain refinement produced during the application of an external field are cavitation phenomena assisted nucleation or fragmentation of dendrites(ultrasonic field),wall crystals arising from the cold surface of the mould(electric current pulse,magnetic and pulsed magnetic fields).In all these cases fluid flow provides an additional contribution(e.g.reduced temperature gradients,growth rate and remelting of dendrites)to maintaining an equiaxed grain structure.The origin of equiaxed grains under an external field also depends on the casting conditions(volume and shape of casting)and the type of alloy other than the mechanisms specific to a particular technique.The current work aims to provide a detailed understanding of the various factors and mechanisms that influence the grain refinement achieved during the solidification of pure metals(magnesium and zinc)subjected to Ultra Sonic Treatment(UST).The role of the temperature range of UST application,time duration and an unpreheated sonotrode are examined with respect to the origin,evolution of equiaxed grain structure,morphology and the columnar to equiaxed transition.The origin of grains was analysed from three fundamental aspects that contribute to refinement(i)heterogeneous nucleation(ii)fragmentation of existing dendrites and(iii)grains produced from the colder surfaces(arising from mould walls or vibrating surfaces as wall crystals).A comparison of UST refinement with mechanical,low-frequency vibration,electric current pulse and magnetic field solidification of pure metals has also been provided to highlight the importance of the cold surfaces(sonotrode and mould wall)in influencing grain refinement.
基金supported by the National Key Research and Development Program of China[No.2018YFB2001800]the National Natural Science Foundation of China(No.51871184)+1 种基金the Dalian High-level Talents Innovation Support Program(No.2021RD06)the Dongguan Graduate Workstation Project(No.20201900300032)。
文摘In this work,the mechanical properties and strengthening mechanisms induced by microstructural evolution in a rheo-extruded 5087 alloy processed via accumulative continuous extrusion forming(ACEF)were investigated.Electron back-scattered diffraction(EBSD)and transmission electron microscopy(TEM)were utilized to characterize the microstructure of the alloy subjected to ACEF with various passes.The grain refinement caused by continuous dynamic recrystallization(CDRX)was discussed.The results demonstrated that after 3 passes of ACEF,there was a significant grain refinement effect on the alloy,and the average grain size decreased from 45.6μm to 2.5μm;the ultimate tensile strength(UTS)and yield strength(YS)of the alloy increased to 362.8 MPa and 234.6 MPa,respectively.Dislocation cells/walls generated during deformation promoted the formation of low angle grain boundaries(LAGBs).The accumulative strain accelerated the transformation of LAGBs to high angle grain boundaries(HAGBs).Dislocation pile-up enhanced the driving force of CDRX,and nano-sized Al_6(Mn,Fe)phases at the grain boundaries inhibited the growth of grains due to the pinning effect.Based on the quantitative estimation,dislocation strengthening and grain boundary strengthening dominated the enhancement in YS of the ACEFed alloy.
基金the National Natural Science Foundation of China(No.51975593)the Hunan Provincial Natural Science Foundation of China(No.2020JJ4113)the Science and Technology Innovation Planning Project of Hunan Province(No.2019XK2301)。
文摘The uniform refinement mechanisms and methods of deformed mixed and coarse grains inside a solution-treatment Ni-based superalloy during two-stage annealing treatment have been investigated.The two-stage heat treatment experiments include an aging annealing treatment(AT)and a subsequent recrystallization annealing treatment(RT).The object of AT is to precipitate someδphases and consume part of storage energy to inhibit the grain growth during RT,while the RT is to refine mixed and coarse grains by recrystallization.It can be found that the recrystallization grains will quickly grow up to a large size when the AT time is too low or the RT temperature is too high,while the deformed coarse grains cannot be eliminated when the AT time is too long or the RT temperature is too low.In addition,the mixed microstructure composed of some abnormal coarse recrystallization grains(ACRGs)and a large number of fine grains can be observed in the annealed specimen when the AT time is 3 h and RT temperature is 980℃.The phenomenon attributes to the uneven distribution ofδphase resulted from the heterogeneous deformation energy when the AT time is too short.In the regions with a large number ofδphases,the recrystallization nucleation rate is promoted and the growth of grains is limited,which results in fine grains.However,in the regions with fewδphases,the recrystallization grains around grain boundaries can easily grow up,and the new recrystallization nucleus is difficult to form inside grain,which leads to ACRGs.Thus,in order to obtain uniform and fine annealed microstructure,it is a prerequisite to precipitate even-distributedδphase by choosing a suitable AT time,such as 12 h.Moreover,a relative high RT temperature is also needed to promote the recrystallization nucleation aroundδphase.The optimal annealing parameters range for uniformly refining mixed crystal can be summarized as:900℃×12 h+990℃×(40-60 min)and 900℃×12 h+1000℃×(10-15 min).
基金National Key Research and Development Program of China(No.2017YFB0304501).
文摘The microstructure–mechanical property relationship of a Cu-bearing low-carbon high-strength low-alloy steel,subjected to a novel multistage heat treatment including quenching(Q),lamellarization(L)and tempering(T),is presented.Yield strength of 989.5 MPa and average toughness at-80℃of 41 J were obtained in this steel after quenching and tempering(QT)heat treatments.Specimen QLT gained a little lower yield strength(982.5 MPa),but greatly enhanced average toughness at-80℃(137 J).To further clarify the strengthening and toughening mechanisms in specimen QLT,parameters of microstructural characteristic and crack propagation process were compared and analyzed for specimens Q,QL,QT and QLT.The microstructure of tempered martensite/bainite(M/B)in specimen QT changed to refined tempered M/B matrix mixed with minor IF(inter-critical ferrite)in specimen QLT.Cu-rich precipitates existed in tempered M/B for both specimens QT and QLT,as well as in IF.Compared with QT,adding a lamellarization step before tempering made the effective grains of specimen QLT refined and also led to coarser Cu-rich precipitates in tempered M/B matrix.The weaker strengthening effect of coarser Cu-rich precipitates should be a key reason for the slightly lower yield strength in specimen QLT than in specimen QT.No austenite was found in all specimens Q,QL,QT and QLT.Specimen QLT showed purely ductile fracture mode at-80℃due to the refined effective grains.The greatly improved toughness is mainly attributed to the enhanced energy of crack propagation.The combination of refined microstructure,softened matrix and deformation of minor'soft'IF during crack propagation led to the most superior toughness of specimen QLT among all specimens.
文摘The objective of the current study was to investigate the use of ultrasonic melt treatment technology in the production of grain-refined billets of the AC7 A alloy, which was intended for subsequent use as a feedstock in forming operations. The experiments included the application of ultrasonic vibrations to the molten alloys via direct and indirect techniques. Several process parameters such as pouring temperatures(several temperatures between 740 and 660℃), and treatment time(from 12 min down to 2 min) were investigated. The experiment included continuous ultrasonic treatment from the liquid to the semisolid states. The results showed that both treatment techniques were viable for producing billets with the desirable microstructural characteristics. The optimum treatment conditions were the short treatment time(2 to 3 min), from about 660℃ down to 615℃ for the indirect treatment technique, and from 660℃ to 635℃ for the direct treatment technique. The resulting microstructures, at three positions along the height of the ingot, were characterized by fine, non-dendritic α(Al) grains in the order of a hundred microns, as compared to few thousands of microns for the conventional cast ingots. The intermetallic particles were also refined in size and modified in morphology by the ultrasonic treatment. The operating mechanisms by which the ultrasonic vibrations altered the ingot microstructures were discussed and analyzed.
基金supported by National Natural Science Foundation of China(No.51071061)NSAF(No.11176011)
文摘A phase field model is developed to simulate the grain evolution of 17-4PH steel during cyclic heat treatment （CHT）. Our simulations successfully reproduce the grain morphologies of every CHT. In the process of every CHT, phase transformation recrystallization happens. The recrystallized grains appear mainly on the original grain boundaries. The average grain size of 13.2 μm obtained by 1040 ℃×1 h solution treatment for this experimental steel can be refined to 2.2 μm after five CHT＇s. Furthermore, the effects of phenomenological parameters in our model are discussed.
基金financially supported by the National Natural Science Foundation of China (Nos.51774075 and52174307)Liao Ning Revitalization Talents Program,China(No.XLYC1802032)
文摘The effect of titanium content on the refinement of austenite grain size in as-cast peritectic carbon steel was investigated by fast directional solidification experiments with simulating the solidification and growth of surface and subsurface austenite in continuously cast slabs.Transmission electron microscope(TEM)and scanning electron microscope(SEM)were used to analyze the size and distribution of Ti(C,N)precipitates during solidification.Based on these results,the pinning pressure of Ti(C,N)precipitates on the growth of coarse columnar grains(CCGs)was studied.The results show that the austenite microstructure of as-cast peritectic carbon steel is mainly composed of the regions of CCGs and fine columnar grains(FCGs).Increasing the content of titanium reduces the region and the short axis of the CCGs.When the content of titanium is 0.09wt%,there is no CCG region.Dispersed microscale particles will firstly form in the liquid,which will decrease the transition temperature from FCGs to CCGs.The chain-like nanoscale Ti(C,N)will precipitate with the decrease of the transition temperature.Furthermore,calculations shows that the refinement of the CCGs is caused by the pinning effect of Ti(C,N)precipitates.
基金support provided by the Australian Research Council Research Hub for Advanced Manufacturing of Medical Devices (No.IH150100024)the ARC Discovery (No.DP140100702)and the ARC linkage project (No.LP150100950).
文摘Refinement of grains and intermetallic phases in the as-solidified alloy structure offers uniform struc-tural properties,eliminates or minimizes common solidification defects,including segregation and hot cracking,and improves thermomechanical processing of wrought alloys.Melt processing by an external field is an efficient process for achieving refinement of the solidification structure of Al and Mg alloys without altering the alloy composition.A wide range of melt processing methods and solidification stud-ies(conventional,directional,and in-situ approaches)have been reported in the literature that explore the mechanism of refinement.Identifying the dominant grain refinement mechanism has been a focus of most investigations because significant variations exist according to the casting conditions and the type of applied external treatments.The origin of fine grains occurs through either one or a combination of heterogenous nucleation,fragmentation of dendrites and grains formed and then separated from the surface of the melt and mould wall under vibration or agitation.The first part of this review describes the prominent external field techniques and the mechanisms proposed for the origin of fine grains.The second part critically compares the current understanding of these grain refinement mechanisms to de-termine differences and commonalities to identify the factors that promote the formation of equiaxed zones occupying a large volume fraction of the casting.
基金financially supported by the National Key R&D Program of China (Nos.2017YFA0700703 and 2019YFA0705300)the National Natural Science Foundation of China (Grant Nos.11872354 and 11627803)+1 种基金the National Science and Technology Major Project (Grant Nos.J2019-V-0006-0100)the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant Nos.XDB22040502)。
文摘The trade-off between strength and ductility has been an enormous difficulty in the field of materials for an extended time due to their inverse correlation. In this work, friction stir processing(FSP) was for the first time performed to high-strength and high-melting-point Ni-Co based superalloy(GH4068),and enhanced strength and ductility were achieved in FSP samples. At room temperature, the FSP sample demonstrated significantly higher yield strength and ultimate tensile strength(1290 and 1670 MPa)than that of the base material(BM, 758 and 904 MPa) and advanced wrought GH4068 alloy(982 and 1291 MPa), concurrent with high tensile ductility(~24%). Compared with the BM, 70% higher yield strength of the FSP sample results from the remarkable contribution of grain-boundary and nanotwin strengthening, which has been confirmed by the multimechanistic model studied in this work. More importantly, with increasing temperature, an excellent strength-ductility synergy was obtained at 400 ℃,i.e., the yield strength of the FSP sample was increased by more than 50% compared with the BM(from789 to 1219 MPa);more interestingly, the elongation was also significantly increased from 17.9% in the BM to 28.5% in the FSP sample. Meanwhile, the Portevin-Le Chatelier effect was observed in the engineering stress-strain curve. The occurrence of this effect may be attributed to the interaction between solutes and defects like twins and mobile dislocations. Moreover, the grain refinement mechanism of FSP samples was proved to be discontinuous dynamic recrystallization.
基金This work was supported by the National Natural Science Foun-dation of China(Nos.52074254,51874271,and 52174349)the Key Projects of International Cooperation(No.122111KYSB20200034)+3 种基金the Project of Key Laboratory of Science and Technology on Par-ticle Materials(No.CXJJ-22S043)the CAS Project for Young Scientists in Basic Research(No.YSBR-025)This work was finan-cially supported by the Selection of Best Candidates to Undertake Key Research Projects(No.211110230200)This research work was also financially supported by the OU Master Plan Implementation Project promoted under Osaka University.
文摘A high-performance Ti-Ni-B alloy with good tensile properties and reduced mechanical anisotropy was developed by promoting the columnar to equiaxed transition(CET)of prior-βgrains and modifyingα-laths to equiaxed grains.Both Ni and B contributed to the refinement of columnar prior-βgrains during the L→βphase transformation by generating constitutional undercooling.Compared with Ni,B had a su-perior capability of generating constitutional undercooling,which not only replaced a significant amount of Ni with a minor addition to reduce the formation of brittle eutectoid,but also reacted with Ti to form TiB to promote heterogeneous nucleation ofα-Ti grains during theβ→αphase transformation.Together with the restricted growth ofα-laths induced by the refinement of prior-βgrains,a fully equiaxedα-Ti structure was obtained.The competition between the negative effect of brittle eutectoid and the positive role ofα-lath to equiaxed grain transition on the ductility of as-printed Ti-Ni-B alloys was fundamen-tally governed by the morphology of eutectoid and technically dependent on the Ni-B content.When the addition was 1.2Ni-0.06B(wt.%)or less,the positive effect ofα-lath on equiaxed grain transition can effectively mitigate the issue of reduced ductility caused by brittle eutectoid.In contrast,at 1.8Ni-0.09B or greater,the negative effect of eutectoid dominated.New insights into microstructural design obtained through the aforementioned approach were presented and discussed.
基金financially supported by the National Basic Research Program of China (No. 2011CB606300)the National Natural Science Foundation of China (No. 5077400)
文摘In this study, a serpentine channel pouring process was used to prepare the semi-solid A1-20%Si alloy slurry and refine primary Si grains in the alloy. The effects of the pouring temperature, number of curves in the serpentine channel, and material of the serpentine channel on the size of primary Si grains in the semi-solid A1-20%Si alloy slurry were investigated. The results showed that the pouting temperature, number of the curves, and material of the channel strongly affected the size and distribution of the primary Si grains. The pouring tempera- ture exerted the strongest effect, followed by the number of the curves and then the material of the channel. Under experimental conditions of a four-curve copper channel and a pouring temperature of 701℃, primary Si grains in the semi-solid A1-20%Si alloy slurry were refined to the greatest extent, and the lath-like grains were changed into granular grains. Moreover, the equivalent grain diameter and the average shape coefficient of primary Si grains in the satisfactory semi-solid A1-20%Si alloy slurry were 24.4 μm and 0.89, respectively. Finally, the re- finement mechanism and distribution rule of primary Si grains in the slurry prepared through the serpentine channel pouring process were analyzed and discussed.
文摘Nucleation sites of α-Al grains after addition of an Al-Ti-B master alloy into pure aluminium have been investigated using EPMA. The results show that either TiAl3 or boride particales can nucleate α-Al grains. But the number of TiAl3 nucleants is reduced with the holding time prolonged and the boride-nuclei are increasing gradually. Based on these results, a new refining method, adding molten Al-Ti-B into commercially pure aluminium, which has a quicker and better refining efficiency is presented.
基金financially supported by the EPSRC(No.EP/N007638/1)the 2021 Jiangsu Shuangchuang(Mass Innovation and Entrepreneurship)Talent Program(No.JSSCBS20210702)。
文摘The spatial arrangement,distribution and morphology of Fe-bearing intermetallics in AA6082 alloys depends on the manufacturing process of the alloy and thus influences the macroscopic properties.Here,the microstructure of a near industrial scale casting AA6082 Al alloy fabricated by:(a)direct chill casting,(b)Al-5 Ti-1 B grain refiner addition and(c)intensive melt shearing has been investigated by threedimensional visualization using SEM-based serial ultra microtomy tomography.The formation sequence of phases in AA6082 alloys is generally categorized into four stages:formation ofα-Al grains,Fe-bearing intermetallics,Mg_(2)Si phase,and eutectic rosettes.Results of three-dimensional visualization of the microstructure indicated that TiBparticles not only could nucleate Fe-bearingβ-intermetallics,but also could provide substrate for the formation of Fe-bearingα-intermetallics and Mg_(2)Si.A further deep analysis reveals that the essential condition for the formation of secondary phases such as Fe-bearing intermetallics and Mg_(2)Si phase is the build-up of a supersaturated solute front at theα-Al solid-liquid interface irrespective of the specific nucleation site.In addition,the results indicate that grain refinement processing causes the severe interconnectivity of Fe-bearingα-intermetallics.However,the intensive melt shearing is a better manufacturing process because the intermetallics are more evenly distributed and refined than with the addition of the grain refiner,thereby improving the properties of the alloy.
文摘Hot torsion testing was performed on a low carbon Nb-Ti microalloyed steel to study the effects of hot tor- sion parameters, strain and strain rate, on ultrafine ferrite grains production through dynamic strain-induced trans- formation, at a deformation temperature just above At3. The initiation and evolution of ultrafine ferrite grains were studied. The results show that the amount of strain and strain rate has conversely effect on the volume fraction and grain size of ultrafine ferrite grains. With increasing strain, the interior of austenite grains become activated as nucle- ation sites for fine ferrite grains. As a result, ferrite grains continuously nucleate not only at the former austenite grain boundaries but also inside the austenite grains which leads to a rapid increase in volume fraction of ultrafine grains. Increasing of strain rate reduces the tendency of ferrite grains coarsening so that ultrafine ferrite grains are achieved, while the volume fraction of ultrafine grains decreases at the same strain level.
文摘The formation reason and elimination method of non-uniform microstructure defects in Ti al- loy TC11 bar have been studied.The coagulating and coarsening into block of the part of grain boundary α and secondary α seem to be caused by the ingot cogging and initial forging temperature in the β region as well as no more enough deformation and uneven distribution. The grain α,elongated α and blocky α may be finally eliminated by adopting the technique of (α+β)thermomechanical processing+β processing,W.Q.+recrystallization annealing,A.C., thus the size of uniform and fine equiaxed α structure is believed to be reduced to 1.9258μm.
基金supported by the National Natural Science Foundation of China(Nos.51977027 and 51967008)the Scientific and Technological Project of Yunnan Precious Metals Lab-oratory(Nos.YPML-2023050250 and YPML-2022050206).
文摘The pursuit of Ag-based alloys with both high strength and toughness has posed a longstanding chal-lenge.In this study,we investigated the cluster strengthening and grain refinement toughening mecha-nisms in fully oxidized AgMgNi alloys,which were internally oxidized at 800℃ for 8 h under an oxy-gen atmosphere.We found that Mg-O clusters contributed to the hardening(138 HV)and strengthening(376.9 MPa)of the AgMg alloy through solid solution strengthening effects,albeit at the expense of duc-tility.To address this limitation,we introduced Ni nanoparticles into the AgMg alloy,resulting in signifi-cant grain refinement within its microstructure.Specifically,the grain size decreased from 67.2μm in the oxidized AgMg alloy to below 6.0μm in the oxidized AgMgNi alloy containing 0.3 wt%Ni.Consequently,the toughness increased significantly,rising from toughness value of 2177.9 MJ m^(-3) in the oxidized AgMg alloy to 6186.1 MJ m^(-3) in the oxidized AgMgNi alloy,representing a remarkable 2.8-fold enhancement.Furthermore,the internally oxidized AgMgNi alloy attained a strength of up to 387.6 MPa,comparable to that of the internally oxidized AgMg alloy,thereby demonstrating the successful realization of concurrent strengthening and toughening.These results collectively offer a novel approach for the design of high-performance alloys through the synergistic combination of cluster strengthening and grain refinement toughening.
基金support of the National Natural Science Foundation of China(Nos.52171063,52274362,and 52371049)the Key R&D projects of Henan Province(No.221111230800)+1 种基金the Doctoral Fund of Henan University of Technology(No.2023BS047)the Natural science Project of Zhengzhou Science and Technology Bureau(No.22ZZRDZX04)。
文摘This study investigates the adsorption mechanism,the film formation process,and the inhibition performance of benzotriazole(BTAH)on carbon steels with different grain sizes(i.e.,24.5,4.3,and 0.6μm)in 3.5 wt.%NaCl solution.The results demonstrate that grain refinement significantly impacts the adsorption and inhibition performance of BTAH on carbon steels.Ultra-refinement of steel grains to 0.6μm improves the maximum inhibition efficiency of BTAH to 90.0%within 168 h of immersion,which was much higher than that of the steels with 24.5μm(73.6%)and 4.3μm grain sizes(81.7%).Notably,grain sizes of 4.3 and 0.6μm facilitate a combination of physisorption and chemisorption of BTAH after 120 h of immersion,as evidenced by the X-ray photoelectron spectroscopy(XPS)results and Langmuir adsorption isotherms,while BTAH adsorbed on carbon steels with a grain size of 24.5μm through physisorption during the 168 h of immersion.Ultra-refinement of grains has beneficial impacts on promoting the formation of a stable and dense corrosion inhibitor film,leading to improved corrosion resistance and the mitigation of non-uniform corrosion.These advantageous effects can be attributed to the higher adsorption energy at grain boundaries(approximately-3.12 eV)compared to grain interiors(ranging from-0.79 to 2.47 eV),promoting both the physisorption and chemisorption of organic corrosion inhibitors.The investigation comprehensively illustrates,for the first time,the effects of grain size on the adsorption mechanism,film formation process,and inhibition performance of organic corrosion inhibitors on carbon steels.This study demonstrates a promising approach to enhancing corrosion inhibition performance through microstructural design.
基金supported by the National Natural Science Foundation of China(No.51871155).
文摘Due to the low content of alloying elements and the lack of effective nucleation sites,the fusion zone(FZ)of tungsten inert gas(TIG)welded AZ31 alloy typically exhibits undesirable coarse columnar grains,which can result in solidification defects and reduced mechanical properties.In this work,a novel welding wire containing MgO particles has been developed to promote columnar-to-equiaxed transition(CET)in the FZ of TIG-welded AZ31 alloy.The results show the achievement of a fully equiaxed grain structure in the FZ,with a significant 71.9%reduction in grain size to 41 μm from the original coarse columnar dendrites.Furthermore,the combination of using MgO-containing welding wire and pulse current can further refine the grain size to 25.6 μm.Microstructural analyses reveal the homogeneous distribution of MgO particles in the FZ.The application of pulse current results in an increase in the number density of MgO(1-2 μm)from 5.16 × 10^(4) m^(-3) to 6.18 × 10^(4) m^(-3).The good crystallographic matching relationship between MgO and α-Mg matrix,characterized by the orientation relationship of[11(2)0]α-Mg//[0(1)1]MgO and(0002)_(α-Mg)//(111)_(MgO),indicates that the MgO particles can act as effective nucleation sites for α-Mg to reduce nucleation undercooling.According to the Hunt criteria,the critical temperature gradient for CET is greatly enhanced due to the significantly increased number density of MgO nucleation sites.In addition,the correlation with the thermal simulation results reveals a transition in the solidification conditions within the welding pool from the columnar grain zone to the equiaxed grain zone in the CET map,leading to the realization of CET.The exceptional grain refinement has contributed to a simultaneous improvement in the strength and plasticity of welded joints.This study presents a novel strategy for controlling equiaxed microstructure and optimizing mechanical properties in fusion welding or wire and arc additive manufacturing of Mg alloy components.
