This study systematically investigated the microstructural evolution of binary Ni-Cu alloys(Cu55Ni45,Cu60Ni40,and Ni65Cu35)under deep undercooling conditions.The controlled rapid solidification experiments combined wi...This study systematically investigated the microstructural evolution of binary Ni-Cu alloys(Cu55Ni45,Cu60Ni40,and Ni65Cu35)under deep undercooling conditions.The controlled rapid solidification experiments combined with optical microscopy and electron backscatter diffraction(EBSD)analysis demonstrate that increasing undercooling(ΔT)can induce a consistent sequence of microstructural transitions:coarse dendrites,fine equiaxed grains(first refinement),oriented fine dendrites,and fine equiaxed grains(second refinement).Two distinct grain refinement events are identified,with critical undercooling thresholds(ΔT)dependent on composition:increasing Cu content increases the critical undercoolingΔT*required for the second refinement(Cu55Ni45:227 K;Cu60Ni40:217 K;Ni65Cu35:200 K).The BCT(Bridgman Crystal Growth)model quantitatively elucidates this behavior,revealing a shift from solute-diffusion-dominated growth at low undercooling to thermally dominated diffusion at high undercooling(ΔT).Crucially,refined grains at high undercooling exhibit smaller sizes(10μm)and higher uniformity than those at low undercooling(20μm).These findings provide fundamental insights into non-equilibrium solidification mechanisms and establish a foundation for designing high-performance Ni-Cu alloys via deep undercooling processing.展开更多
The 304 austenitic stainless steel was processed by high-pressure torsion(HPT)at room temperature with 10,20,and 30 rotations under a pressure of 3 GPa and a rotation speed of 1 r/min.The phase transformation and micr...The 304 austenitic stainless steel was processed by high-pressure torsion(HPT)at room temperature with 10,20,and 30 rotations under a pressure of 3 GPa and a rotation speed of 1 r/min.The phase transformation and microstructural evolution of 304 stainless steel after HPT were investigated by X-ray diffraction(XRD)analysis,electron backscatter diffraction(EBSD)analysis,transmission electron microscopy(TEM),nanoindentation test and differential scanning calorimetry(DSC)analysis.The experimental results show that HPT causes elongated nanocrystalline grains of 25 nm width along the torsion direction.After 10 turns of HPT,the deformation-induced martensitic transformation is completed and the hardness increases from 3 GPa to 8.5 GPa at the edge of the disc.However,a local reverse phase transformation from martensite to austenite is observed in the peripheral regions of the sample after 30 turns of HPT,leading to a higher volume fraction of austenite,and the hardness of the sample also decreases accordingly.展开更多
To clarify the densification behavior,deformation response and strengthening mechanisms of selective laser melted(SLM)Mg-RE alloys,this study systematically investigates a representative WE43 alloy via advanced materi...To clarify the densification behavior,deformation response and strengthening mechanisms of selective laser melted(SLM)Mg-RE alloys,this study systematically investigates a representative WE43 alloy via advanced material characterization techniques.A suitable laser output mode fell into the transition mode,allowing for the fabrication of nearly full-density samples(porosity=0.85±0.021%)with favorable mechanical properties(yield strength=351 MPa,ultimate tensile strength=417 MPa,the elongation at break=6.5%and microhardness=137.9±6.15 HV_(0.1))using optimal processing parameters(P=80 W,v=250 mm/s and d=50μm).Viscoplastic self-consistent analysis and transmission electron microscopy observations reveal that the plastic deformation response of the SLM Mg-RE alloys is primarily driven by basal and prismatic slips.Starting from a random texture before deformation(maximum multiple of ultimate density,Max.MUD=3.95),plastic stretching led the grains to align with the Z-axis,finally resulting in a{0001}<1010>texture orientation after fracture(Max.MUD=8.755).Main phases of the SLM state are mainly composed ofα-Mg,Mg_(24)Y_(5) andβ'-Mg_(41)Nd_(5),with an average grain size of only 4.27μm(about a quarter of that in the extruded state),resulting in a favorable strength-toughness ratio.Except for the nano-β'phase and semi-coherent Mg_(24)Y_(5) phase(mismatch=16.12%)around the grain boundaries,a small amount of nano-ZrO_(2) and Y_(2)O_(3) particles also play a role in dispersion strengthening.The high mechanical properties of the SLM state are chiefly attributed to precipitation hardening(44.41%),solid solution strengthening(34.06%)and grain boundary strengthening(21.53%),with precipitation hardening being predominantly driven by dislocation strengthening(67.77%).High-performance SLM Mg-RE alloy components were manufactured and showcased at TCT Asia 2024,receiving favorable attention.This work underscores the significant application potential of SLM Mg-RE alloys and establishes a strong foundation for advancing their use in the biomedical fields.展开更多
Isothermal compression tests were used to establish constitutive models of the hot deformation of GH4742 superalloy. The microstructural evolution of double cone samples with large strain gradients during hot deformat...Isothermal compression tests were used to establish constitutive models of the hot deformation of GH4742 superalloy. The microstructural evolution of double cone samples with large strain gradients during hot deformation and subsequent solvus treatment was studied. The results showed that the grain size during dynamic recrystallization (DRX) did not exceed 6 μm, and the volume fraction during DRX did not exceed 45% at all reduction rates when it deformed below the γ′ solvus temperature (1080 ℃). When deformed near the γ′ solvus temperature (1110 ℃), the volume fraction and grain size increase significantly during DRX due to the dissolution and coarsening of some γ′ precipitates. When deformed above the γ′ solvus temperature (1140 ℃), even at a high reduction rate of 20 mm/s, the volume fraction during DRX reached 75%, and the grain size during DRX increased to 25 μm. At a reduction rate of 0.5 mm/s, the grain size during DRX reached 65 μm. When the sample is deformed below the γ′ solvus temperature (1080 ℃), stored strain energy accumulates in the sample, which is beneficial for the development of post dynamic recrystallization during subsequent subsolvus heat treatment, resulting in a noticeable increase in the recrystallization volume fraction. The recrystallization volume fraction of predeformed samples deformed at 1110 and 1140 ℃, followed by subsolvus heat treatment, was almost unchanged. The microstructure of the predeformed sample following supersolvus heat treatment consists of coarse equiaxed grains.展开更多
Microstructural evolution features have been systematically investigated for the weld metal of EH36 shipbuilding steel under an in situ confocal scanning laser microscope.The influence of cooling rate on microstructur...Microstructural evolution features have been systematically investigated for the weld metal of EH36 shipbuilding steel under an in situ confocal scanning laser microscope.The influence of cooling rate on microstructural changes during the transformation from austenite to ferrite has been clarified.It is found that ferrite side plates form preceding to acicular ferrites,although the starting temperature of respective component decreases as the cooling rate is raised.In particular,the growth rate of acicular ferrite is measured to increase significantly,rising from 30.4μm/s at a cooling rate of 3 K/s to 109.0μm/s at 15 K/s,driven primarily by an ever-increasing degree of undercooling.These findings highlight the critical role of cooling rate in dictating the sequence and growth rate of microstructural transformations,which is crucial for optimizing welding processes to obtain desired microstructures while avoiding the formation of deleterious components.展开更多
The directional annealing technique is widely used to prepare columnar grains or single crystals.To investigate the effect of hot zone temperature and temperature gradient on the growth of columnar crystals,Ti43Al all...The directional annealing technique is widely used to prepare columnar grains or single crystals.To investigate the effect of hot zone temperature and temperature gradient on the growth of columnar crystals,Ti43Al alloys were heat treated by the directional annealing technique and their mechanical properties were tested.The results show that columnar grains with a maximum size of 22.29 mm can be obtained at a hot zone temperature of 1,350℃ and a temperature gradient of 8 K·mm^(-1).During the directional annealing process,Ti43Al alloys are heated toαsingle-phase domain to start the phase transformation.Columnar grains with a microstructure of fully lamellar colonies are obtained at different hot zone temperatures and temperature gradients.The distribution of the orientation difference for theα2 phase was found to be more random,suggesting that the growth of the columnar crystals may be stochastic in nature.Tensile testing results show that the strength and elongation of directional annealed Ti43Al alloy at 1,400℃-8 K·mm^(-1) are 411.23 MPa and 2.29%,and the remaining directional annealed alloys show almost plasticity.展开更多
In order to develop a marine engineering material with excellent mechanical properties and corrosion resistance,a novel non-equiatomic Co_(1.5)CrFeNi_(1.5)Ti_(0.6)high-entropy alloy(HEA)was fabricated through mechanic...In order to develop a marine engineering material with excellent mechanical properties and corrosion resistance,a novel non-equiatomic Co_(1.5)CrFeNi_(1.5)Ti_(0.6)high-entropy alloy(HEA)was fabricated through mechanical alloying and spark plasma sintering.The results revealed that the sintering temperature significantly affected the microstructure and phase composition of the HEA owing to the diffusion rate,homogenization,and sluggish diffusion effect of metal atoms.At sintering temperatures below 1050℃,HEA mainly consisted of face-centered cubic(FCC),Ni_(3)Ti(ε),Ni_(2.67)Ti_(1.33)(R),and Fe-Cr(σ)phases.The microstructure of alloy comprised coarse dendritic crystals,whose content and size gradually decreased with increasing sintering temperature.However,the HEA sintered above 1100℃contained only fine equiaxed crystals.HEA sintered at 1100℃featured only the FCC solid solution,while theε-phase precipitated at temperatures above 1150℃.At a sintering temperature of 1050℃,the alloy microstructure consisted of short rod-like dendrites and fine equiaxed crystals.This alloy achieved the highest yield strength of 1198.71 MPa owing to the effects of precipitation strengthening and grain boundary strengthening.Meanwhile,HEA sintered above 1050℃exhibited significantly improved corrosion resistance.Considering the microstructure,mechanical,and corrosion properties,1050℃was identified as the optimal sintering temperature for Co_(1.5)CrFeNi_(1.5)Ti_(0.6)HEA.展开更多
In the harsh service environment of high temperature and intense neutron irradiation in water-cooled nuclear reactors,the austenitic stainless steel weld overlay cladding on the inner surface of the reactor pressure v...In the harsh service environment of high temperature and intense neutron irradiation in water-cooled nuclear reactors,the austenitic stainless steel weld overlay cladding on the inner surface of the reactor pressure vessel suffers from thermal aging and irradiation damage simultaneously,which can induce microstructural evolution and hardening of the material.Since it is quite difficult to achieve this simul-taneous process out of the pile,two kinds of combined experiments,i.e.,post-irradiation thermal aging and post-aging irradiation were performed on 308 L stainless steel weld metals in this work.The interactive effect of thermal aging and proton irradiation on microstructural evolution and hardening ofδ-ferrite in 308 L weld metal was investigated by combining atom probe tomography,transmission elec-tron microscopy and nanoindentation tests.The results revealed that thermal aging could eliminate the dislocation loops induced by irradiation and affect the phase transition process by accelerating spinodal decomposition and G-phase precipitation,thus enhancing hardening of irradiatedδ-ferrite.For the effect of irradiation on the microstructure and hardening of thermally agedδ-ferrite,however,intensive collision cascades can intensify G-phase precipitation and dislocation loop formation but decrease spinodal decomposition,leading to a limited effect on hardening of thermally agedδ-ferrite.Furthermore,the interaction of thermal aging and irradiation can promote G-phase precipitation.Meanwhile,the interaction can causeδ-ferrite hardening,which is mainly influenced by spinodal decomposition,followed by G-phase and dislocation loops,where spinodal decomposition and G-phase cause hardening by inducing strain fields.展开更多
Ultralight Mg-Li alloys offer promising applications across various fields.Mg-Li alloys enriched with Al and Zn hold theoretical potential for achieving excellent mechanical strength and corrosion resistance.However,t...Ultralight Mg-Li alloys offer promising applications across various fields.Mg-Li alloys enriched with Al and Zn hold theoretical potential for achieving excellent mechanical strength and corrosion resistance.However,the structural and performance characteristics of such Mg-Li alloys,particularly after thermo-mechanical processing,remain inadequately explored and understood.This study investigated the mi-crostructural evolution of a Mg-9Li-5Al-4Zn alloy after friction stir processing and its consequent effects on the mechanical and corrosion performance.The grain size of the alloy was effectively refined and sta-bilized during friction stir processing at various heat inputs.The yield strength of the alloy increased by 86.4%after friction stir processing under the highest heat input condition,which was attributed to fine grain strengthening,solid solution strengthening and dispersion strengthening.Concurrently,the alloy ex-perienced a slight decrease in elongation after the friction stir processing.The alloy subjected to friction stir processing with the highest heat input exhibited a minimal corrosion current density of 6.10×10^(−6) A/cm^(2),which was only 25%of the base metal.The enhanced anti-corrosion properties can be attributed to the dispersion and distribution of precipitated particles induced by friction stir processing,which hin-dered the micro-galvanic corrosion and promoted the generation of a compact surface film,leading to minimal and uniform corrosion.This investigation can be significant for understanding the metallurgical mechanisms and performance evolution of Mg-Li alloys during thermomechanical processes.展开更多
The microstructural evolution and composition distribution of an Al-Zn-Cu-Mg-Sc-Zr alloy during homogenization were investigated by optical microscopy（OM）,scanning electron microscopy（SEM）,energy dispersive spectr...The microstructural evolution and composition distribution of an Al-Zn-Cu-Mg-Sc-Zr alloy during homogenization were investigated by optical microscopy（OM）,scanning electron microscopy（SEM）,energy dispersive spectrometry（EDS）,X-ray diffraction（XRD） and differential scanning calorimetry（DSC）.The results show that severe dendritic segregation exists in Al-Zn-Cu-Mg-Sc-Zr alloy ingot.There are a lot of eutectic phases at grain boundary and the distribution of the main elements varies periodically along interdendritic region.The main eutectic phases at grain boundary are Al7Cu2Fe phase and T（Al2Mg3Zn3）.The residual phases are dissolved into the matrix gradually during homogenization with increasing temperature and prolonging holding time,which can be described by a constitutive equation in exponential function.The overburnt temperature of the alloy is 473.9 ℃.The optimum parameters of homogenization are 470 ℃ and 24 h,which is consistent with the result of homogenization kinetic analysis.展开更多
The microstructural evolution of a Mg, Ag and Zn micro-alloyed Al?3.8Cu?1.28Li (mass fraction, %) alloy ingot during two-step homogenization was examined in detail by optical microscopy (OM), differential scanning cal...The microstructural evolution of a Mg, Ag and Zn micro-alloyed Al?3.8Cu?1.28Li (mass fraction, %) alloy ingot during two-step homogenization was examined in detail by optical microscopy (OM), differential scanning calorimetry (DSC), electron probe micro-analysis (EPMA) and X-ray diffraction (XRD) methods. The results show that severe dendritic segregation exists in the as-cast ingot. There are many secondary phases, includingTB(Al7Cu4Li),θ(Al2Cu),R(Al5CuLi3) andS(Al2CuMg) phases, and a small amount of (Mg+Ag+Zn)-containing and AlCuFeMn phases. The fractions of intermetallic phases decrease sharply after 2 h of second-step homogenization. By prolonging the second-step homogenization time, theTB,θ,R,S and (Mg+Ag+Zn)-containing phases completely dissolve into the matrix. The dendritic segregation is eliminated, and the homogenization kinetics can be described by a constitutive equation in exponential function. However, it seems that the AlCuFeMn phase is separated into Al7Cu2Fe and AlCuMn phases, and the size of Al7Cu2Fe phase exhibits nearly no change when the second-step homogenization time is longer than 2 h.展开更多
The microstructural evolution of AZ61 magnesium alloy predeformed by equal channel angular extrusion（ECAE） during semisolid isothermal treatment（SSIT） was investigated by means of optical metalloscopy and image an...The microstructural evolution of AZ61 magnesium alloy predeformed by equal channel angular extrusion（ECAE） during semisolid isothermal treatment（SSIT） was investigated by means of optical metalloscopy and image analysis equipment.The process involved application of ECAE to as-cast alloy at 310 ℃ to induce strain prior to heating in the semisolid region for different time lengths.The results show that extrusion pass,isothermal temperature and processing route have an influence on microstructural evolution of predeformed AZ61 magnesium alloy during SSIT.With the increase of extrusion pass,the solid particle size is reduced gradually.When isothermal temperature increases from 530 ℃ to 560 ℃,the average particle size increases from 22 μm to 35 μm.When isothermal temperature is 575 ℃,the average particle size decreases.The particle size of microstructure of AZ61 magnesium alloy predeformed by ECAE at BC during SSIT is the finest.展开更多
As-received nickel-titanium （NiTi） shape memory alloy with a nominal composition of Ni50.9Ti49.1 （mole fraction,%） was subjected to solution treatment at 1123 K for 2 h and subsequent aging for 2 h at 573 K, 723 K...As-received nickel-titanium （NiTi） shape memory alloy with a nominal composition of Ni50.9Ti49.1 （mole fraction,%） was subjected to solution treatment at 1123 K for 2 h and subsequent aging for 2 h at 573 K, 723 K and 873 K, respectively. The influence of solution treatment and aging on microstructural evolution and mechanical behavior of NiTi alloy was systematically investigated by transmission electron microscopy （TEM）, high resolution transmission electron microscopy （HRTEM）, scanning electron microscopy （SEM） and compression test. Solution treatment contributes to eliminating the Ti2Ni phase in the as-received NiTi sample, in which the TiC phase is unable to be removed. Solution treatment leads to ordered domain of atomic arrangement in NiTi alloy. In all the aged NiTi samples, the Ni4Ti3 precipitates, the R phase and the B2 austenite coexist in the NiTi matrix at room temperature, while the martensitic twins can be observed in the NiTi samples aged at 873 K. In the NiTi samples aged at 573 and 723 K, the fine and dense Ni4Ti3 precipitates distribute uniformly in the NiTi matrix, and thus they are coherent with the B2 matrix. However, in the NiTi sample aged at 873 K, the Ni4Ti3 precipitates exhibit the very inhomogeneous size, and they are coherent, semi-coherent and incoherent with the B2 matrix. In the case of aging at 723 K, the NiTi sample exhibits the maximum yield strength, where the fine and homogeneous Ni4Ti3 precipitates act as the effective obstacles against the dislocation motion, which results in the maximum critical resolved shear stress for dislocation slip.展开更多
The microstructural evolution of Al-Zn-Mg-Zr alloy with trace amount of Sc during homogenization treatment was studied by means of metallographic analysis, scanning electron microscopy （SEM）, energy dispersive X-ray...The microstructural evolution of Al-Zn-Mg-Zr alloy with trace amount of Sc during homogenization treatment was studied by means of metallographic analysis, scanning electron microscopy （SEM）, energy dispersive X-ray （EDX） and differential scanning calorimetry （DSC）. The results show that serious dendritic segregation exists in studied alloy ingot. There are many eutectic phases with low melting-point at grain boundary and the distribution of main elements along interdendritic region varies periodically. Elements Zn, Mg and Cu distribute unevenly from grain boundary to the inside of alloy. With increasing the homogenization temperature or prolonging the holding time, the residual phases are dissolved into matrix α（Al） gradually during homogenization treatment, all elements become more homogenized. The overburnt temperature of studied alloy is 476.7 °C. When homogenization temperature increases to 480 °C, some spherical phases and redissolved triangular constituents at grain boundaries can be easily observed. Combined with microstructural evolution and differential scanning calorimeter, the optimum homogenization parameter is at 470 °C for 24 h.展开更多
Microstructural evolution of AZ91 magnesium alloy was investigated during homogenizing annealing treatment, hot extrusion and ageing treatment, respectively. The results exhibited that both the divorced eutectic β-Mg...Microstructural evolution of AZ91 magnesium alloy was investigated during homogenizing annealing treatment, hot extrusion and ageing treatment, respectively. The results exhibited that both the divorced eutectic β-Mg17Al12 and the precipitated β-Mg17Al12 phases appeared in the as-cast alloy. The β-Mg17Al12 phase dissolved into α-Mg matrix mostly and the structure kept fine after the optimized homogenization treatment at 380 °C for 15 h. Dynamic recrystallization and consequent grain refinement occurred during extrusion. The banded β-Mg17Al12 precipitates paralleled to the extrusion direction were observed after ageing treatment. The banded precipitation should be attributed to the solidification segregation which was elongated during the subsequent extrusion. Furthermore, the effects of temperature, holding time of homogenization and ageing treatment, and extrusion processing parameters on the microstructural evolution of AZ91 alloy were also discussed in details according to the experimental results.展开更多
The hot deformation behavior of Al-Zn-Mg-0.25Sc-Zr alloy and its microstructural evolution were investigated by isothermal axisymmetric hot compression tests at temperatures from 340 to 500°C and strain rates ran...The hot deformation behavior of Al-Zn-Mg-0.25Sc-Zr alloy and its microstructural evolution were investigated by isothermal axisymmetric hot compression tests at temperatures from 340 to 500°C and strain rates ranging from 0.001 to 10 s -1 .The steady flow stress increased with increasing the strain rate or decreasing the deformation temperature,which can be described by a hyperbolic-sine constitutive equation with the deformation activation energy of 150.25 kJ/mol.The tendency of dynamic recrystallization enhanced at high deforming temperatures and low strain rates,which corresponded to low Z values.With decreasing Z value,the main softening mechanism of the alloy transformed from dynamic recovery to dynamic recrystallization, correspondingly,the subgrain size increased and the dislocation density decreased.展开更多
The microstructural evolution of Al-0.66Mg-0.85Si alloy was investigated by optical microscopy （OM）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and differential scanning calorimet...The microstructural evolution of Al-0.66Mg-0.85Si alloy was investigated by optical microscopy （OM）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and differential scanning calorimetry （DSC）. The as-cast microstructure is typical dendritical structure, consisting of α（Al）, Al（FeMn）Si, Mg2Si, AlCuMgSi and Si phases. The electron diffraction analyses indicate that the Al（FeMn）Si phase is Al15（FeMn）3Si2 and the AlCuMgSi phase is Q（Al1.9CuMg4.1Si3.3）. There are two kinds of Mg2Si phases in the as-cast microstructure. One is formed in the casting process, and the other is formed in the cooling process after casting process is finished. The phases have different crystal structures. After homogenization treatment at 545 ℃ for 20 h, Mg2Si, Si and Q intermetallic compounds are dissolved into matrix completely, and the remaining phases are α（Al） and Al15（FeMn）3Si2. The size of Al15（FeMn）3Si2 phase is decreased, and the phase is spheroidized and distributes along grain boundary discontinuously. The Zn-containing phases are not found during solidification and homogenization process.展开更多
The effects of rapid solidification on the microstructure and melting behavior of the Sn-8Zn-3Bi alloy were studied. The evolution of the microstructuraI characteristics of the solder/Cu joint after an isothermal agin...The effects of rapid solidification on the microstructure and melting behavior of the Sn-8Zn-3Bi alloy were studied. The evolution of the microstructuraI characteristics of the solder/Cu joint after an isothermal aging at 150 ℃ was also analyzed to evaluate the interconnect reliability. Results showed that the Bi in Sn-8Zn-3Bi solder alloy completely dissolved in the Sn matrix with a dendritic structure after rapid solidification. Compared with as-solidified Sn-8Zn-3Bi solder alloy, the melting temperature of the rapid solidified alloy rose to close to that of the Sn-Zn eutectic alloy due to the extreme dissolution of Bi in Sn matrix. Meanwhile, the adverse effect on melting behavior due to Bi addition was decreased significantly. The interfacial intermetallic compound （IMC） layer of the solder/Cu joint was more compact and uniform. Rapid solidification process obviously depressed the formation and growth of the interfacial IMC during the high-temperature aging and improved the high-temperature stability of the Sn-8Zn-3Bi solder/Cu joint.展开更多
A newly designed TiAl alloy containing W,Nb,and B was produced through magnetic-flotation-melting method.Mass production of this TiAl-based alloy,15 kg ingot size,which is quite different from the 0.05 kg small ingot ...A newly designed TiAl alloy containing W,Nb,and B was produced through magnetic-flotation-melting method.Mass production of this TiAl-based alloy,15 kg ingot size,which is quite different from the 0.05 kg small ingot produced by arc-melting,has a large effect on the metallurgical properties,such as the grain size and the phase structures of the alloy.Heat treatments were carefully designed in order to reduce the amount of the high-temperature remaining β phase in the alloy,and to obtain optimal microstructures for mechanical behavior studies.A room-temperature ductility of 1.9% was obtained in the cast TiAl-based alloy after the appropriate heat treatment.The mechanical behavior of the large ingot through mass production of the TiAl-based alloy was largely improved by the alloy design and subsequent heat treatments.展开更多
The effect of ball milling on the microstructural evolution was investigated during partial remelting of 6061 aluminum alloy prepared by cold-pressing of atomized alloy powders.The results indicate that the microstruc...The effect of ball milling on the microstructural evolution was investigated during partial remelting of 6061 aluminum alloy prepared by cold-pressing of atomized alloy powders.The results indicate that the microstructural evolution of 6061 aluminum alloy can be divided into three stages,the dissolution of eutectic phases and the coarsening and growth behavior of the resulting grains,structural separation and spheroidization of primary particles,and the final coarsening behavior of the particles.Compared with the alloy without ball milling,ball milling accelerates the first stage of microstructural evolution due to the energy stored in the powders,but the latter two stages are slowed down because of the formation of large-sized powders.Moreover,the finer the as-cold-pressed microstructure is,the smaller and more spherical the primary particles in the final semisolid microstructure are.Furthermore,properly elevating the heating temperature is beneficial for obtaining small and spheroidal particles.展开更多
基金Funded by the Central Government-Guided Local Development Fund Project(No.YDZJSX2025D042)the Key R&D Program of Shanxi Province(No.202202150401018)+1 种基金the Basic Research Program of Shanxi Province(No.20210302124220)the State Key Laboratory of CAD/CG of Zhejiang University(No.A2325)。
文摘This study systematically investigated the microstructural evolution of binary Ni-Cu alloys(Cu55Ni45,Cu60Ni40,and Ni65Cu35)under deep undercooling conditions.The controlled rapid solidification experiments combined with optical microscopy and electron backscatter diffraction(EBSD)analysis demonstrate that increasing undercooling(ΔT)can induce a consistent sequence of microstructural transitions:coarse dendrites,fine equiaxed grains(first refinement),oriented fine dendrites,and fine equiaxed grains(second refinement).Two distinct grain refinement events are identified,with critical undercooling thresholds(ΔT)dependent on composition:increasing Cu content increases the critical undercoolingΔT*required for the second refinement(Cu55Ni45:227 K;Cu60Ni40:217 K;Ni65Cu35:200 K).The BCT(Bridgman Crystal Growth)model quantitatively elucidates this behavior,revealing a shift from solute-diffusion-dominated growth at low undercooling to thermally dominated diffusion at high undercooling(ΔT).Crucially,refined grains at high undercooling exhibit smaller sizes(10μm)and higher uniformity than those at low undercooling(20μm).These findings provide fundamental insights into non-equilibrium solidification mechanisms and establish a foundation for designing high-performance Ni-Cu alloys via deep undercooling processing.
基金Funded by the National Natural Science Foundation of China(No.51905215)the Postgraduate Research&Practice Innovation Program of Jiangsu Province(No.SJCX231233)。
文摘The 304 austenitic stainless steel was processed by high-pressure torsion(HPT)at room temperature with 10,20,and 30 rotations under a pressure of 3 GPa and a rotation speed of 1 r/min.The phase transformation and microstructural evolution of 304 stainless steel after HPT were investigated by X-ray diffraction(XRD)analysis,electron backscatter diffraction(EBSD)analysis,transmission electron microscopy(TEM),nanoindentation test and differential scanning calorimetry(DSC)analysis.The experimental results show that HPT causes elongated nanocrystalline grains of 25 nm width along the torsion direction.After 10 turns of HPT,the deformation-induced martensitic transformation is completed and the hardness increases from 3 GPa to 8.5 GPa at the edge of the disc.However,a local reverse phase transformation from martensite to austenite is observed in the peripheral regions of the sample after 30 turns of HPT,leading to a higher volume fraction of austenite,and the hardness of the sample also decreases accordingly.
基金supported by the National Key Research and Development Program of China(No.2022YFC2406000)the Guangdong Basic and Applied Basic Research Foundation(2024A1515011024)+5 种基金the Guangzhou Science and Technology Project(2024A04J4943)the Guangdong Academy of Sciences Development Special Fund Project(2022GDASZH-2022010107)the Guangdong province Science and Technology Plan Projects(2023B1212120008,2023B1212060045)the GDAS Projects of International cooperation platform of Science and Technology(2022GDASZH-2022010203-003)Special Support Foundation of Guangdong Province(2023TQ07Z559)Shenzhen Basic Research Project(JCYJ20210324120001003 and JCYJ20220531091802006)。
文摘To clarify the densification behavior,deformation response and strengthening mechanisms of selective laser melted(SLM)Mg-RE alloys,this study systematically investigates a representative WE43 alloy via advanced material characterization techniques.A suitable laser output mode fell into the transition mode,allowing for the fabrication of nearly full-density samples(porosity=0.85±0.021%)with favorable mechanical properties(yield strength=351 MPa,ultimate tensile strength=417 MPa,the elongation at break=6.5%and microhardness=137.9±6.15 HV_(0.1))using optimal processing parameters(P=80 W,v=250 mm/s and d=50μm).Viscoplastic self-consistent analysis and transmission electron microscopy observations reveal that the plastic deformation response of the SLM Mg-RE alloys is primarily driven by basal and prismatic slips.Starting from a random texture before deformation(maximum multiple of ultimate density,Max.MUD=3.95),plastic stretching led the grains to align with the Z-axis,finally resulting in a{0001}<1010>texture orientation after fracture(Max.MUD=8.755).Main phases of the SLM state are mainly composed ofα-Mg,Mg_(24)Y_(5) andβ'-Mg_(41)Nd_(5),with an average grain size of only 4.27μm(about a quarter of that in the extruded state),resulting in a favorable strength-toughness ratio.Except for the nano-β'phase and semi-coherent Mg_(24)Y_(5) phase(mismatch=16.12%)around the grain boundaries,a small amount of nano-ZrO_(2) and Y_(2)O_(3) particles also play a role in dispersion strengthening.The high mechanical properties of the SLM state are chiefly attributed to precipitation hardening(44.41%),solid solution strengthening(34.06%)and grain boundary strengthening(21.53%),with precipitation hardening being predominantly driven by dislocation strengthening(67.77%).High-performance SLM Mg-RE alloy components were manufactured and showcased at TCT Asia 2024,receiving favorable attention.This work underscores the significant application potential of SLM Mg-RE alloys and establishes a strong foundation for advancing their use in the biomedical fields.
基金supported by the National Science and Technology Major Project of China(2017-VI-0018-0090).
文摘Isothermal compression tests were used to establish constitutive models of the hot deformation of GH4742 superalloy. The microstructural evolution of double cone samples with large strain gradients during hot deformation and subsequent solvus treatment was studied. The results showed that the grain size during dynamic recrystallization (DRX) did not exceed 6 μm, and the volume fraction during DRX did not exceed 45% at all reduction rates when it deformed below the γ′ solvus temperature (1080 ℃). When deformed near the γ′ solvus temperature (1110 ℃), the volume fraction and grain size increase significantly during DRX due to the dissolution and coarsening of some γ′ precipitates. When deformed above the γ′ solvus temperature (1140 ℃), even at a high reduction rate of 20 mm/s, the volume fraction during DRX reached 75%, and the grain size during DRX increased to 25 μm. At a reduction rate of 0.5 mm/s, the grain size during DRX reached 65 μm. When the sample is deformed below the γ′ solvus temperature (1080 ℃), stored strain energy accumulates in the sample, which is beneficial for the development of post dynamic recrystallization during subsequent subsolvus heat treatment, resulting in a noticeable increase in the recrystallization volume fraction. The recrystallization volume fraction of predeformed samples deformed at 1110 and 1140 ℃, followed by subsolvus heat treatment, was almost unchanged. The microstructure of the predeformed sample following supersolvus heat treatment consists of coarse equiaxed grains.
基金support from the National Natural Science Foundation of China(Grant Nos.U20A20277 and 52350610226)National Key Research and Development Plan of China(Grant No.2022YFE0123300).
文摘Microstructural evolution features have been systematically investigated for the weld metal of EH36 shipbuilding steel under an in situ confocal scanning laser microscope.The influence of cooling rate on microstructural changes during the transformation from austenite to ferrite has been clarified.It is found that ferrite side plates form preceding to acicular ferrites,although the starting temperature of respective component decreases as the cooling rate is raised.In particular,the growth rate of acicular ferrite is measured to increase significantly,rising from 30.4μm/s at a cooling rate of 3 K/s to 109.0μm/s at 15 K/s,driven primarily by an ever-increasing degree of undercooling.These findings highlight the critical role of cooling rate in dictating the sequence and growth rate of microstructural transformations,which is crucial for optimizing welding processes to obtain desired microstructures while avoiding the formation of deleterious components.
基金supported by the National Natural Science Foundation of China(Grant Nos.52074229,52371035)the Key R&D Plan of Sichuan Province(Grant No.SC2022A1C01J)the State Key Lab of Advanced Metals and Materials(Grant No.2020-ZD05).
文摘The directional annealing technique is widely used to prepare columnar grains or single crystals.To investigate the effect of hot zone temperature and temperature gradient on the growth of columnar crystals,Ti43Al alloys were heat treated by the directional annealing technique and their mechanical properties were tested.The results show that columnar grains with a maximum size of 22.29 mm can be obtained at a hot zone temperature of 1,350℃ and a temperature gradient of 8 K·mm^(-1).During the directional annealing process,Ti43Al alloys are heated toαsingle-phase domain to start the phase transformation.Columnar grains with a microstructure of fully lamellar colonies are obtained at different hot zone temperatures and temperature gradients.The distribution of the orientation difference for theα2 phase was found to be more random,suggesting that the growth of the columnar crystals may be stochastic in nature.Tensile testing results show that the strength and elongation of directional annealed Ti43Al alloy at 1,400℃-8 K·mm^(-1) are 411.23 MPa and 2.29%,and the remaining directional annealed alloys show almost plasticity.
基金supported by Special Fund for the Development of 1500-Meter Subsea Christmas Trees and Control Systems.
文摘In order to develop a marine engineering material with excellent mechanical properties and corrosion resistance,a novel non-equiatomic Co_(1.5)CrFeNi_(1.5)Ti_(0.6)high-entropy alloy(HEA)was fabricated through mechanical alloying and spark plasma sintering.The results revealed that the sintering temperature significantly affected the microstructure and phase composition of the HEA owing to the diffusion rate,homogenization,and sluggish diffusion effect of metal atoms.At sintering temperatures below 1050℃,HEA mainly consisted of face-centered cubic(FCC),Ni_(3)Ti(ε),Ni_(2.67)Ti_(1.33)(R),and Fe-Cr(σ)phases.The microstructure of alloy comprised coarse dendritic crystals,whose content and size gradually decreased with increasing sintering temperature.However,the HEA sintered above 1100℃contained only fine equiaxed crystals.HEA sintered at 1100℃featured only the FCC solid solution,while theε-phase precipitated at temperatures above 1150℃.At a sintering temperature of 1050℃,the alloy microstructure consisted of short rod-like dendrites and fine equiaxed crystals.This alloy achieved the highest yield strength of 1198.71 MPa owing to the effects of precipitation strengthening and grain boundary strengthening.Meanwhile,HEA sintered above 1050℃exhibited significantly improved corrosion resistance.Considering the microstructure,mechanical,and corrosion properties,1050℃was identified as the optimal sintering temperature for Co_(1.5)CrFeNi_(1.5)Ti_(0.6)HEA.
基金supported by the National Natural Science Foundation of China(No.52071018).
文摘In the harsh service environment of high temperature and intense neutron irradiation in water-cooled nuclear reactors,the austenitic stainless steel weld overlay cladding on the inner surface of the reactor pressure vessel suffers from thermal aging and irradiation damage simultaneously,which can induce microstructural evolution and hardening of the material.Since it is quite difficult to achieve this simul-taneous process out of the pile,two kinds of combined experiments,i.e.,post-irradiation thermal aging and post-aging irradiation were performed on 308 L stainless steel weld metals in this work.The interactive effect of thermal aging and proton irradiation on microstructural evolution and hardening ofδ-ferrite in 308 L weld metal was investigated by combining atom probe tomography,transmission elec-tron microscopy and nanoindentation tests.The results revealed that thermal aging could eliminate the dislocation loops induced by irradiation and affect the phase transition process by accelerating spinodal decomposition and G-phase precipitation,thus enhancing hardening of irradiatedδ-ferrite.For the effect of irradiation on the microstructure and hardening of thermally agedδ-ferrite,however,intensive collision cascades can intensify G-phase precipitation and dislocation loop formation but decrease spinodal decomposition,leading to a limited effect on hardening of thermally agedδ-ferrite.Furthermore,the interaction of thermal aging and irradiation can promote G-phase precipitation.Meanwhile,the interaction can causeδ-ferrite hardening,which is mainly influenced by spinodal decomposition,followed by G-phase and dislocation loops,where spinodal decomposition and G-phase cause hardening by inducing strain fields.
基金supported by the National Natural Science Foundation of China(grant Nos.U23A20541 and 52305385).
文摘Ultralight Mg-Li alloys offer promising applications across various fields.Mg-Li alloys enriched with Al and Zn hold theoretical potential for achieving excellent mechanical strength and corrosion resistance.However,the structural and performance characteristics of such Mg-Li alloys,particularly after thermo-mechanical processing,remain inadequately explored and understood.This study investigated the mi-crostructural evolution of a Mg-9Li-5Al-4Zn alloy after friction stir processing and its consequent effects on the mechanical and corrosion performance.The grain size of the alloy was effectively refined and sta-bilized during friction stir processing at various heat inputs.The yield strength of the alloy increased by 86.4%after friction stir processing under the highest heat input condition,which was attributed to fine grain strengthening,solid solution strengthening and dispersion strengthening.Concurrently,the alloy ex-perienced a slight decrease in elongation after the friction stir processing.The alloy subjected to friction stir processing with the highest heat input exhibited a minimal corrosion current density of 6.10×10^(−6) A/cm^(2),which was only 25%of the base metal.The enhanced anti-corrosion properties can be attributed to the dispersion and distribution of precipitated particles induced by friction stir processing,which hin-dered the micro-galvanic corrosion and promoted the generation of a compact surface film,leading to minimal and uniform corrosion.This investigation can be significant for understanding the metallurgical mechanisms and performance evolution of Mg-Li alloys during thermomechanical processes.
基金Project (2006AA03Z523) supported by the National High-tech Research and Development Program of China
文摘The microstructural evolution and composition distribution of an Al-Zn-Cu-Mg-Sc-Zr alloy during homogenization were investigated by optical microscopy（OM）,scanning electron microscopy（SEM）,energy dispersive spectrometry（EDS）,X-ray diffraction（XRD） and differential scanning calorimetry（DSC）.The results show that severe dendritic segregation exists in Al-Zn-Cu-Mg-Sc-Zr alloy ingot.There are a lot of eutectic phases at grain boundary and the distribution of the main elements varies periodically along interdendritic region.The main eutectic phases at grain boundary are Al7Cu2Fe phase and T（Al2Mg3Zn3）.The residual phases are dissolved into the matrix gradually during homogenization with increasing temperature and prolonging holding time,which can be described by a constitutive equation in exponential function.The overburnt temperature of the alloy is 473.9 ℃.The optimum parameters of homogenization are 470 ℃ and 24 h,which is consistent with the result of homogenization kinetic analysis.
基金Project(2013JSJJ0001)supported by Teachers’Research Found,ChinaProject(2013AA032401)supported by the National High Technology Research and Development Program of ChinaProject supported by the Nonferrous Metal Oriented Advanced Structural Materials and Manufacturing Cooperative Innovation Center,China
文摘The microstructural evolution of a Mg, Ag and Zn micro-alloyed Al?3.8Cu?1.28Li (mass fraction, %) alloy ingot during two-step homogenization was examined in detail by optical microscopy (OM), differential scanning calorimetry (DSC), electron probe micro-analysis (EPMA) and X-ray diffraction (XRD) methods. The results show that severe dendritic segregation exists in the as-cast ingot. There are many secondary phases, includingTB(Al7Cu4Li),θ(Al2Cu),R(Al5CuLi3) andS(Al2CuMg) phases, and a small amount of (Mg+Ag+Zn)-containing and AlCuFeMn phases. The fractions of intermetallic phases decrease sharply after 2 h of second-step homogenization. By prolonging the second-step homogenization time, theTB,θ,R,S and (Mg+Ag+Zn)-containing phases completely dissolve into the matrix. The dendritic segregation is eliminated, and the homogenization kinetics can be described by a constitutive equation in exponential function. However, it seems that the AlCuFeMn phase is separated into Al7Cu2Fe and AlCuMn phases, and the size of Al7Cu2Fe phase exhibits nearly no change when the second-step homogenization time is longer than 2 h.
基金Project(51075099) supported by the National Natural Science Foundation of ChinaProject(E201038) supported by Natural Science Foundation of the Heilongjiang Province,China+3 种基金Project(20090460884) supported by the China Postdoctoral Science Foundation Project(SKLSP201121) supported by the Fund of the State Key Laboratory of Solidification Processing in NWPU,ChinaProject (2011RFQXG010) supported by the Harbin City Young Scientists Foundation,ChinaProject(LBH-T1102) supported by the Specially Postdoctoral Science Foundation of Heilongjiang Province,China
文摘The microstructural evolution of AZ61 magnesium alloy predeformed by equal channel angular extrusion（ECAE） during semisolid isothermal treatment（SSIT） was investigated by means of optical metalloscopy and image analysis equipment.The process involved application of ECAE to as-cast alloy at 310 ℃ to induce strain prior to heating in the semisolid region for different time lengths.The results show that extrusion pass,isothermal temperature and processing route have an influence on microstructural evolution of predeformed AZ61 magnesium alloy during SSIT.With the increase of extrusion pass,the solid particle size is reduced gradually.When isothermal temperature increases from 530 ℃ to 560 ℃,the average particle size increases from 22 μm to 35 μm.When isothermal temperature is 575 ℃,the average particle size decreases.The particle size of microstructure of AZ61 magnesium alloy predeformed by ECAE at BC during SSIT is the finest.
基金Project (51071056) supported by the National Natural Science Foundation of ChinaProjects (HEUCF121712,HEUCF201317002) supported by the Fundamental Research Funds for the Central Universities of China
文摘As-received nickel-titanium （NiTi） shape memory alloy with a nominal composition of Ni50.9Ti49.1 （mole fraction,%） was subjected to solution treatment at 1123 K for 2 h and subsequent aging for 2 h at 573 K, 723 K and 873 K, respectively. The influence of solution treatment and aging on microstructural evolution and mechanical behavior of NiTi alloy was systematically investigated by transmission electron microscopy （TEM）, high resolution transmission electron microscopy （HRTEM）, scanning electron microscopy （SEM） and compression test. Solution treatment contributes to eliminating the Ti2Ni phase in the as-received NiTi sample, in which the TiC phase is unable to be removed. Solution treatment leads to ordered domain of atomic arrangement in NiTi alloy. In all the aged NiTi samples, the Ni4Ti3 precipitates, the R phase and the B2 austenite coexist in the NiTi matrix at room temperature, while the martensitic twins can be observed in the NiTi samples aged at 873 K. In the NiTi samples aged at 573 and 723 K, the fine and dense Ni4Ti3 precipitates distribute uniformly in the NiTi matrix, and thus they are coherent with the B2 matrix. However, in the NiTi sample aged at 873 K, the Ni4Ti3 precipitates exhibit the very inhomogeneous size, and they are coherent, semi-coherent and incoherent with the B2 matrix. In the case of aging at 723 K, the NiTi sample exhibits the maximum yield strength, where the fine and homogeneous Ni4Ti3 precipitates act as the effective obstacles against the dislocation motion, which results in the maximum critical resolved shear stress for dislocation slip.
基金Project (2012CB619503) supported by the National Basic Research Program of China
文摘The microstructural evolution of Al-Zn-Mg-Zr alloy with trace amount of Sc during homogenization treatment was studied by means of metallographic analysis, scanning electron microscopy （SEM）, energy dispersive X-ray （EDX） and differential scanning calorimetry （DSC）. The results show that serious dendritic segregation exists in studied alloy ingot. There are many eutectic phases with low melting-point at grain boundary and the distribution of main elements along interdendritic region varies periodically. Elements Zn, Mg and Cu distribute unevenly from grain boundary to the inside of alloy. With increasing the homogenization temperature or prolonging the holding time, the residual phases are dissolved into matrix α（Al） gradually during homogenization treatment, all elements become more homogenized. The overburnt temperature of studied alloy is 476.7 °C. When homogenization temperature increases to 480 °C, some spherical phases and redissolved triangular constituents at grain boundaries can be easily observed. Combined with microstructural evolution and differential scanning calorimeter, the optimum homogenization parameter is at 470 °C for 24 h.
基金Project (2011A090200104) supported by Guangdong Science and Technology Special Projects, China
文摘Microstructural evolution of AZ91 magnesium alloy was investigated during homogenizing annealing treatment, hot extrusion and ageing treatment, respectively. The results exhibited that both the divorced eutectic β-Mg17Al12 and the precipitated β-Mg17Al12 phases appeared in the as-cast alloy. The β-Mg17Al12 phase dissolved into α-Mg matrix mostly and the structure kept fine after the optimized homogenization treatment at 380 °C for 15 h. Dynamic recrystallization and consequent grain refinement occurred during extrusion. The banded β-Mg17Al12 precipitates paralleled to the extrusion direction were observed after ageing treatment. The banded precipitation should be attributed to the solidification segregation which was elongated during the subsequent extrusion. Furthermore, the effects of temperature, holding time of homogenization and ageing treatment, and extrusion processing parameters on the microstructural evolution of AZ91 alloy were also discussed in details according to the experimental results.
基金Project(2012CB619503)supported by the High-tech Research and Development Program of China
文摘The hot deformation behavior of Al-Zn-Mg-0.25Sc-Zr alloy and its microstructural evolution were investigated by isothermal axisymmetric hot compression tests at temperatures from 340 to 500°C and strain rates ranging from 0.001 to 10 s -1 .The steady flow stress increased with increasing the strain rate or decreasing the deformation temperature,which can be described by a hyperbolic-sine constitutive equation with the deformation activation energy of 150.25 kJ/mol.The tendency of dynamic recrystallization enhanced at high deforming temperatures and low strain rates,which corresponded to low Z values.With decreasing Z value,the main softening mechanism of the alloy transformed from dynamic recovery to dynamic recrystallization, correspondingly,the subgrain size increased and the dislocation density decreased.
基金Project (2012CB723903) supported by the National Basic Research Program of China
文摘The microstructural evolution of Al-0.66Mg-0.85Si alloy was investigated by optical microscopy （OM）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and differential scanning calorimetry （DSC）. The as-cast microstructure is typical dendritical structure, consisting of α（Al）, Al（FeMn）Si, Mg2Si, AlCuMgSi and Si phases. The electron diffraction analyses indicate that the Al（FeMn）Si phase is Al15（FeMn）3Si2 and the AlCuMgSi phase is Q（Al1.9CuMg4.1Si3.3）. There are two kinds of Mg2Si phases in the as-cast microstructure. One is formed in the casting process, and the other is formed in the cooling process after casting process is finished. The phases have different crystal structures. After homogenization treatment at 545 ℃ for 20 h, Mg2Si, Si and Q intermetallic compounds are dissolved into matrix completely, and the remaining phases are α（Al） and Al15（FeMn）3Si2. The size of Al15（FeMn）3Si2 phase is decreased, and the phase is spheroidized and distributes along grain boundary discontinuously. The Zn-containing phases are not found during solidification and homogenization process.
基金Project(50675234)supported by the National Natural Science Foundation of China
文摘The effects of rapid solidification on the microstructure and melting behavior of the Sn-8Zn-3Bi alloy were studied. The evolution of the microstructuraI characteristics of the solder/Cu joint after an isothermal aging at 150 ℃ was also analyzed to evaluate the interconnect reliability. Results showed that the Bi in Sn-8Zn-3Bi solder alloy completely dissolved in the Sn matrix with a dendritic structure after rapid solidification. Compared with as-solidified Sn-8Zn-3Bi solder alloy, the melting temperature of the rapid solidified alloy rose to close to that of the Sn-Zn eutectic alloy due to the extreme dissolution of Bi in Sn matrix. Meanwhile, the adverse effect on melting behavior due to Bi addition was decreased significantly. The interfacial intermetallic compound （IMC） layer of the solder/Cu joint was more compact and uniform. Rapid solidification process obviously depressed the formation and growth of the interfacial IMC during the high-temperature aging and improved the high-temperature stability of the Sn-8Zn-3Bi solder/Cu joint.
基金Project(11X-SP173V) supported by the U.S. Fossil Energy Materials ProgramProject supported by the U.S. National Science Foundation Combined Research-Curriculum Development(CRCD) ProgramProject(DE-AC05-00OR-22725 UT-Battelle,LLC) supported by Division of Materials Science and Engineering,Office of Basic Energy Science,U.S.Department of Energy
文摘A newly designed TiAl alloy containing W,Nb,and B was produced through magnetic-flotation-melting method.Mass production of this TiAl-based alloy,15 kg ingot size,which is quite different from the 0.05 kg small ingot produced by arc-melting,has a large effect on the metallurgical properties,such as the grain size and the phase structures of the alloy.Heat treatments were carefully designed in order to reduce the amount of the high-temperature remaining β phase in the alloy,and to obtain optimal microstructures for mechanical behavior studies.A room-temperature ductility of 1.9% was obtained in the cast TiAl-based alloy after the appropriate heat treatment.The mechanical behavior of the large ingot through mass production of the TiAl-based alloy was largely improved by the alloy design and subsequent heat treatments.
基金Project(G2010CB635106)supported by the National Basic Research Program of ChinaProject(NCET-10-0023)supported by the Program for New Century Excellent Talents in University of China+1 种基金Project supported by the Program for Hongliu Outstanding Talents of Lanzhou University of Technology,ChinaProject(2014-07)supported by the Basic Scientific Research Expenses of Gansu University,China
文摘The effect of ball milling on the microstructural evolution was investigated during partial remelting of 6061 aluminum alloy prepared by cold-pressing of atomized alloy powders.The results indicate that the microstructural evolution of 6061 aluminum alloy can be divided into three stages,the dissolution of eutectic phases and the coarsening and growth behavior of the resulting grains,structural separation and spheroidization of primary particles,and the final coarsening behavior of the particles.Compared with the alloy without ball milling,ball milling accelerates the first stage of microstructural evolution due to the energy stored in the powders,but the latter two stages are slowed down because of the formation of large-sized powders.Moreover,the finer the as-cold-pressed microstructure is,the smaller and more spherical the primary particles in the final semisolid microstructure are.Furthermore,properly elevating the heating temperature is beneficial for obtaining small and spheroidal particles.
