Cu-Cr-Zr-Ag合金高温热变形及组织演变

对Cu-Cr-Zr-Ag合金在Gleeble-1500D热模拟试验机上进行热压缩实验,对合金在应变速率为0.001~10 s-1、变形温度为650~950℃的高温变形过程中的流变应力行为、热变形过程中的组织演变和动态再结晶机制进行了研究。结果表明,流变应力随变形温度升高而减小,随应变速率提高而增大。Cu-Cr-Zr-Ag合金在热变形过程中的动态再结晶机制受变形温度和应变速率控制。当温度达到950℃,应变速率为0.001 s-1时,Cu-Cr-Zr-Ag合金发生完全的动态再结晶。该合金高温热压缩变形时的热变形激活能Q为343.23 k J/mol,同时利用逐步回归法建立了该合金的流变应力方程。     

Cu-Cr-Zr合金的高温热压缩变形行为

采用Gleeble-1500D热模拟试验机,对Cu-Cr-Zr合金在应变速率为0.001~10 s-1、变形温度为650~850℃的高温变形过程中的变形行为(流变应力和显微组织)进行研究。根据动态材料模型计算并分析该合金的热加工图,并结合变形显微组织观察确定该合金在实验条件下的高温变形机制及加工工艺。结果表明:流变应力随变形温度的升高而减小,随应变速率的提高而增大。从流变应力、应变速率和温度的相关性,得出该合金高温热压缩变形时的热变形激活能(Q)为392.5 kJ/mol,同时利用逐步回归的方法建立该合金的流变应力方程。利用热加工图确定热变形的流变失稳区,并且获得了实验参数范围内热变形过程的最佳工艺参数:温度范围为750~850℃,应变速率范围为0.001~0.1 s-1,并利用热加工图分析了该合金不同区域的高温变性特征以及组织变化。     

Cu-Cr-Zr合金热变形行为及动态再结晶

在Gleeble-1500D热模拟试验机上对Cu-Cr-Zr合金在应变速率为0.001~10 s-1、变形温度为650~850℃的高温变形过程中的流变应力行为进行了研究。利用光学显微镜分析了合金在热变形过程中的组织演变及动态再结晶机制。结果表明:流变应力随变形温度的升高而减小,随应变速率的提高而增大。升高变形温度以及降低应变速率,均有利于Cu-Cr-Zr合金的动态再结晶发生。从流变应力、应变速率和温度的相关性,得出了该合金高温热压缩变形时的热变形激活能Q为392.5 kJ/mol,同时利用逐步回归的方法建立了该合金的流变应力方程。     

Cu-Cr-Zr-Nd合金高温热变形及组织演变

在Gleeble-1500D热模拟试验机上对Cu-Cr-Zr-Nd合金进行热压缩实验,对合金在应变速率分别为0.001、0.01、0.1、1、10 s-1,变形温度分别为650、750、850、900、950℃的高温变形过程中的流变应力行为、热变形过程中的组织演变和动态再结晶机制进行研究。结果表明:流变应力随变形温度的升高而减小,随应变速率的提高而增大。Cu-Cr-Zr-Nd合金在热变形过程中的动态再结晶机制受变形温度和应变速率的影响。当温度为900℃、应变速率为10 s-1时,Cu-Cr-Zr-Nd合金发生完全的动态再结晶。从流变应力、应变速率和温度的相关性,得出该合金高温热压缩变形时的热变形激活能Q为404.84 k J/mol,同时利用逐步回归的方法建立该合金的流变应力方程。     

TC4-DT钛合金的热变形行为研究及加工图

采用Gleeble-1500D热模拟试验机进行热压缩实验,研究了TC4-DT钛合金在温度850～980℃、应变速率为0.001～10 s-1、变形量为50%条件下的热变形行为。根据应力–应变曲线分析了该合金的流变应力变化特点,建立了该合金的Arrhenius型本构方程及加工图。结果表明:流变应力随变形温度降低及应变速率增大而升高;变形温度与应变速率对TC4-DT合金应力影响显著;本实验测得的平均激活能为587.2 kJ/mol;该合金合适的加工条件为<0.6 s-1,温度大于850℃。     

70Cr3Mo钢热变形行为及加工图

采用Gleeble-1500热模拟实验机研究了70Cr3Mo钢在不同变形条件下的高温压缩热变形行为,变形温度850~1150℃,应变速率0.01~10 s-1。依据实验数据,分析了应力、应变间的关系,建立了流变应力本构方程和加工图。由应力、应变曲线可以得出:变形温度一定时,应力峰值随着应变速率的增加而增加;应变速率一定时,应力峰值随变形温度的增加而降低。计算分析了真应变为0.5的加工图,结果表明,70Cr3Mo钢在热压缩过程中存在两个失稳区:(1)变形温度为850~940℃、应变速率为0.01~1.6 s-1;(2)变形温度为975~1150℃、应变速率为1~10 s-1。并获得了最佳的工艺参数:变形温度为1000~1150℃、应变速率为0.01~0.36 s-1。     

5A90铝锂合金Nd:YAG激光焊缝组织的晶粒形态与晶粒取向

采用Gleeble-1500D热模拟试验机进行热压缩实验,研究了TC4-DT钛合金在温度850～980℃、应变速率为0.001～10 s-1、变形量为50％条件下的热变形行为.根据应力-应变曲线分析了该合金的流变应力变化特点,建立了该合金的Arrhenius型本构方程及加工图.结果表明:流变应力随变形温度降低及应变速率增大而升高;变形温度与应变速率对TC4-DT合金应力影响显著;本实验测得的平均激活能为587.2 kJ/mol;该合金合适的加工条件为ε＜0.6 s-1,温度大于850℃.     

TC18钛合金高温变形行为与加工图

采用Gleeble1500热模拟机进行了热压缩试验,研究了TC18钛合金在温度700～950℃,应变速率0.001～10s-1条件下的高温压缩变形行为,并根据应力-应变曲线建立了合金的加工图.研究结果表明:合金在两相区温度变形,应力-应变曲线呈现流变软化特征;而在单相温度区和高应变速率下,合金表现出间断的屈服现象.合金适宜的加工条件为T=700～850℃,(ε)=0.01～0.001s-1与T=850～900℃,(ε)=1～10s-1.合金热加工失稳区为T=700～750℃,应变速率为0.1～10s-1区域.     

Cu-Cr-Zr-Ag合金高温热变形行为与变形机制

在Gleeble-1500D热模拟试验机上对Cu-Cr-Zr-Ag合金进行高温等温压缩试验,当热压缩应变速率为0.001~10 s-1、热变形温度为650~950℃时,同时对合金高温热压缩的热加工图以及变形机制进行研究。结果表明:流变应力随变形温度的升高而减小,随应变速率的提高而增大;热变形过程中的稳态流变应力可用双曲正弦本构关系式来描述,其激活能为Q=343.23 k J/mol,同时利用逐步回归的方法建立了该合金的流变应力方程。根据动态材料模型计算并分析了合金的热加工图,并且获得了试验参数范围内热变形过程的最佳工艺参数:温度为750~800℃、应变速率范围为0.01~0.1 s-1,并利用热加工图分析了该合金不同区域的高温变性特征以及组织变化。     

Cu-0.23Be-0.84Co合金热变形行为

为实现Cu-Be-Co合金连续挤压的数值模拟和制定合理的热成形工艺参数,采用Gleeble-1500D热模拟机对Cu-Be-Co合金在变形温度为450℃~850℃和应变速率为0.1s-1~10s-1条件下的热变形行为进行研究;分析热压缩对合金组织的影响;根据Arrhenius方程对实验数据进行分析,建立Cu-Be-Co合金热变形本构方程。结果表明,Cu-Be-Co合金热变形的流变应力随应变速率的降低和变形温度的升高而减小,并且Cu-Be-Co合金在高温变形条件下发生动态再结晶。     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.     

Theoretical Analysis for the Motion and Temperature of Melt Droplets in Spray Degassing Process

The motion of melt droplets in spray degassing process was analyzed theoretically. The height of the treatment tank in spray degassing process could be determined by the results of theoretical calculation of motion of melt droplets. To know whether the melt droplets would solidify during spraying process, the balance temperature of melt droplets was also theoretically analyzed. Then proof experiments for theoretical results about temperature of melt droplets were carried. In comparison, the experimental results were nearly similar to the calculation results.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.