Ti60合金的热变形行为及工艺参数优化

在变形温度600～950℃,应变速率0.001～10s_^-1条件下,采用Thermecmaster-Z型热加工模拟试验机对Ti60合金进行等温恒应变速率压缩实验。通过分析流动应力行为,计算应变速率敏感指数m和应变硬化指数n,并综合考虑加工图和变形微观组织来研究该合金的热变形行为,得到优化的工艺参数范围。研究结果表明,Ti60合金的流动应力-应变曲线在不同热力参数条件下分别呈现流动稳态型和流动软化型。应变速率敏感指数m随着变形温度升高和应变速率降低而增大。应变硬化指数n随着变形温度升高而减小;随着应变速率的增加在低应变速率(0.001～0.1s_^-1)区间增大,在高应变速率(1～10s_^-1)区间减小;随着应变的增加在高温段(800～950℃)的低应变速率(0.001～0.1s_^-1)区间较缓慢地减小,在高温段(800～950℃)的高应变速率(1～10s_^-1)区间以及低温段(600～750℃)的所有应变速率(0.001～10s_^-1)区间较明显地减小。Ti60合金存在两个功率耗散效率峰值区域,其对应的热力参数窗口分别为温度725～875℃,应变速率≤0.003s_^-1和温度875～938℃,应变速率≤0.04s_^-1。从流动应力行为、应变速率敏感指数m、应变硬化指数n以及加工图综合考虑,Ti60合金的最佳热加工工艺参数为：温度800～875℃,应变速率0.001～0.003s_^-1,或温度875～938℃,应变速率0.001～0.04s_^-1。     

GH2907合金热变形行为及热加工图

通过热模拟压缩实验研究了GH2907合金在变形温度为950~1100℃、应变速率为0.01~10s_^-1、变形量为60%条件下的热变形行为,流变应力随着变形温度的升高或应变速率的降低而显著降低;根据Arrhenius方程和Zener-Hollomon参数,计算了热变形激活能Q,建立了GH2907合金的热变形本构方程;根据动态材料模型,确定了GH2907合金在不同应变下的功率耗散图,功率耗散效率η较高的区域位于温度为1050~1100℃,应变速率为0.01~0.03s_^-1范围,在该变形区域内组织发生了明显的动态再结晶现象;基于Preased失稳判据,绘制了GH2907合金在不同应变下的热加工图,流变失稳区位于高温高应变速率区域,即温度为970~1100℃,应变速率为0.6~10s_^-1范围,在该变形区域内动态再结晶晶粒沿着绝热剪切带和局部流动分布。根据GH2907合金热加工图及微观组织分析得到适宜的加工区域是温度为1050~1100℃,应变速率为0.01~0.03s_^-1范围。     

新型钛合金Ti-555热变形行为及热加工图研究

本文通过高温热压缩试验研究Ti-555钛合金热变形过程中变形温度、应变速率对流变应力的影响,采用Arrhenius双曲正弦函数模型推导出Ti-555本构方程,并依据动态材料模型建立了ε=0.6时的热加工图。结果表明,Ti-555钛合金流变应力对应变速率和变形温度较为敏感,热变形时随变形温度升高或应变速率降低,流变应力下降。根据热加工图确定了两个热加工安全区参数为(1)变形温度为850～950 ℃、应变速率为0.6～10 s_^-1;(2)变形温度为950～1150 ℃、应变速率为0.36～0.9 s_^-1。     

低成本Ti-Al-V-Fe-O钛合金热变形行为及热加工图

通过真空非自耗熔炼炉制备了低成本Ti-6Al-2.5V-1.5Fe-0.15O合金,利用Gleeble-1500D热模拟机,研究了其热加工参数为：变形温度875℃-1100℃、应变速率0.001s_-1-1s_-1,变形量为70%时的热变形行为,建立了Ti-6Al-2.5V-1.5Fe-0.15O合金考虑应变量的Arrhenius本构方程,基于动态材料模型建立热加工图。研究结果表明：变形温度升高,应变速率降低,流变应力降低。通过本构方程计算可得两相区平均热激活能为398.824KJ/mol,远大于纯钛自激活能,表明热变形软化机制与动态再结晶有关。单相区热激活能为210.93KJ/mol,略大于纯钛自激活能,以动态回复为主。通过热加工图确定两个失稳区,中等变形温度(950℃-1070℃)高应变速率(0.31-0.1s_-1)易发生绝热剪切,结合热加工图确定适合的加工区间：应变速率为0.001-0.01s_-1,变形温度为875℃-925℃。     

W80-Cu20复合材料热变形行为及加工图研究

采用Gleeble-1500热模拟机研究了W80-Cu20(wt.％)复合材料在变形温度为810~970 ℃和应变速率为0.01~10 s_^-1条件下真应变达0.69的热变形行为,基于改进动态材料模型(MDMM)和Malas’s准则建立功率耗散图和热加工图,结合微观组织确定出合理热加工参数,并对材料的损伤方式进行分析。结果表明：W80-Cu20复合材料的应力-应变曲线表现出典型的动态再结晶型特征,峰值应力随变形温度的降低和应变速率的增加而增加;确定出W80-Cu20复合材料的合理热加工区域为：840~885℃、0.2~1.42 s_^-1和885~917℃、0.83~2.05 s_^-1;W80-Cu20复合材料的损伤方式主要有Cu相撕裂、W-Cu界面分离、W-W界面分离以及W颗粒破碎。     

一种新型Ni-Cr-Co基合金的热变形行为及其组织演变研究

采用Gleeble-3800热压缩实验机研究了新型Ni-Cr-Co基合金在1050~1250 ℃、0.001~1 s_^-1条件下的热变形行为,并利用EBSD探讨了变形温度和应变速率对合金组织演变和动态再结晶形核机制的影响。结果表明,流变应力随变形温度的升高而降低,而随应变速率的增大而增加。基于流变应力曲线,建立合金的Arrhenius本构方程和热加工图,得到热变形激活能为520.03 kJ/mol,最佳热加工区间为1175~1250 ℃、0.006~1 s_^-1,该区域最大功率耗散效率为45％。动态再结晶分数随变形温度的升高和应变速率的降低而增加,且动态再结晶过程形成均匀细小的等轴晶粒以及∑3孪晶界。动态再结晶形核主要以晶界“弓出”为特征的不连续动态再结晶机制主导。低温高应变速率下,持续亚晶转动诱导的连续动态再结晶作为辅助形核机制发挥作用。     

超高W含量NiW中/重合金热加工行为研究

采用Gleeble-1500D研究了高密度Ni-42W-10Co-1Mo(wt.%)中/重合金(MHA)在1150~1300°C和应变速率0.001~1s_?1^{下流变行为和}微观组织演化规律。研究结果表明,该合金初始组织由面心立方基体和初生σ相构成。流变应力对变形温度和应变速率敏感,在1150℃变形,应力-应变曲线呈现出典型的动态回复软化特征,而在1200-1350℃变形呈现出典型动态再结晶软化特征。基于应力-应变曲线建立Arrhenius本构方程,计算得到Ni-42W-10Co-1Mo合金热变形激活能为446.2 kJ/mol。基于动态材料模型构建该合金热加工图,发现在1300℃高应变速率下存在失稳区。通过微观组织观察,揭示其动态再结晶机制主要为不连续动态再结晶,σ相促进动态再结晶优先在其周围形核。最终优化获得了Ni-42W-10Co-1Mo合金最佳的热加工窗口：1250–1300°C,应变速率0.1–0.01s_?1^。     

基于加工图的新型钛合金斜轧穿孔温度预测

采用GLeeble-3500热模拟机对新型海洋用钛合金Ti80进行压缩试验,研究了该合金流动应力在不同变形参数下的变化,并建立了高温本构方程和热加工图。由加工图中优化出的高功率耗散安全区,初步判断斜轧穿孔法制备Ti80合金无缝管坯时的棒料初始温度；并由有限元模拟及物理实验予以验证。结果表明：在同一应变速率下,Ti80合金流动应力对温度的敏感程度不同,在两相区变形,流变应力会随温度的降低而急剧增大；在单相区变形,流动应力则相差不大。建立的应变补偿型Arrhenius双曲正弦函数,经验证能够准确预测流动应力的变化。所绘热加工图明确指出了Ti80合金热塑性成型时两个优化的工艺窗口：一是在两相区低应变速率,即925-975℃/0.01-0.1s_-1附近；二是在单相区中等应变率,即1050-1100℃/0.1-1s_-1附近。进一步对棒料初始温度在950、1050和1100℃条件下的斜轧穿孔过程进行三维热力耦合有限元模拟,发现950℃穿孔时顶头轴向力会激增为单相区穿孔时的5-6倍,从而导致扎卡；而单相区穿孔均能顺利进行。为降低能耗,最终确定棒料初始温度1050℃为最优穿孔温度,并且在狄舍尔斜轧穿孔机上一火次成功试制出Ti80合金无缝管坯。     

锻态GH4742合金的热变形行为及组织性能演变

利用单道次等温压缩实验获得了锻态GH4742合金在变形温度为 1020~1150 ℃、应变速率为0.001~1 s_^-1、真应变为0.65时的真应力-应变曲线,构建了GH4742合金的热变形本构方程和热加工图,并采用SEM、EBSD等研究了热变形过程中微观亚结构以及γ′相的演变规律,建立了变形工艺条件-组织形态差异-性能变化之间的关联性。结果表明：合金的组织性能演化机制与Z参数密切相关,1080 ℃低温变形时,应变速率由0.001 s_^-1增加至1 s_^-1后,lnZ值由75.6增加至82.6,热效应增强,小角度晶界比例降低,动态再结晶比例增加,组织发生细化,基体硬度增加;1110 ℃高温变形时,随着应变速率增加,lnZ值由74增加至78.5,位错滑移和晶界迁移减缓,小角度晶界比例增加,动态再结晶比例降低,加工硬化程度增加,基体硬度增加。GH4742合金不发生动态再结晶晶粒粗化的临界lnZ值为73。结合热加工图和变形组织分析得出锻态GH4742合金良好的加工区域为变形温度1110～1150 ℃、应变速率0.01～0.1s_^-1。     

反应堆耐压壳体用Ti-5Al-3V-3Zr-0.7Cr合金热变形行为研究

利用Gleeble-3800型热模拟试验机对经过三次真空自耗熔炼的Ti-5Al-3V-3Zr-0.7Cr(wt%)合金进行热模拟等温压缩试验,研究了在750~900℃及0.001~1s_-1应变速率下的高温流变行为及再结晶行为。结果表明,在合金的高温变形过程中,流变曲线呈现出明显的先硬化后软化的流变行为特征,应变速率的降低或温度的升高都会使合金的流动应力降低;造成该合金流变软化的主要原因是动态再结晶。动态再结晶的临界应变与峰值应变之间成线性关系,随着温度和真应变增加,再结晶体积分数呈“S”型增加;应变速率减小,再结晶体积分数也呈抛物线增长。合金的最佳高温塑形变形参数为：750℃/0.001-0.01s_-1和850-900℃/ 0.01-0.1s_-1。     

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.