生物医用Ti-29Nb-13Ta-5Zr合金的超塑性行为

采用拉伸速率突变法,研究Ti-29Nb-13Ta-5Zr(Ti-29-13)合金冷轧后在700~800 ℃和5′10-4~1′10-2 s-1应变速率范围内的高温变形行为和变形机制,并与典型β钛合金Ti-15V-3Cr-3Sn-3Al(Ti-15-3)进行比较。结果显示两种合金中均出现了非连续屈服现象,Ti-29-13合金的亚晶行为不同于Ti-15-3合金。Ti-29-13合金的延伸率低于Ti-15-3合金,应力指数n几乎恒定为3.3,变形激活能为152~161 kJ/mol;Ti-15-3合金在730 ℃以上的n值为2.3~2.5,变形激活能为173~176 kJ/mol。     

置氢处理对铸态TiZrAlV合金高温变形行为及显微组织的影响

为了探究置氢处理对45Ti-47Zr-5Al-3V合金高温变形行为及显微组织的影响,利用动态热模拟试验机,对置氢与未置氢的铸态合金在不同变形条件下进行热压缩,并构建了本构方程及热加工图。结果表明,加入适量的氢可以显著降低TiZrAlV合金的流变应力和变形激活能,计算得到未置氢合金热压缩变形激活能为339.7 kJ/mol,而置氢后的激活能为286.5 kJ/mol,适宜的加工参数为650~900℃,0.01~1 s^-1。OM和EBSD微观组织观察表明,置氢能细化铸态组织,增加β相含量,促进动态再结晶,从而显著降低了合金的流变抗力,扩大了热加工窗口,提高了热加工性能。     

Ti-6Al-2Zr-1Mo-1V合金高温变形流动应力预测模型

通过高温压缩模拟实验,分析了Ti-6Al-2Zr-1Mo-1V合金在变形温度为850～1100℃,应变速率为0.01～10 s-1条件下的高温变形力学行为规律,并利用线性回归方法计算了不同温度范围内的应力指数n和变形激活能Q,获得了该合金高温变形力学行为计算模型.结果表明,Ti-6Al-2Zr-1Mo-1V合金对变形温度和应变速率非常敏感.在恒温时流动应力随应变速率的增大而增大,在恒应变速率时随变形温度的升高而降低.在850～950℃时,n、Q分别为7.0874和610.463 kJ/mol;而在950～1100℃时,n=4.7324,Q=238.030 kJ/mol,该预测模型的计算值与实测值之间的相对误差分别为6.341%和6.957%.     

Ti-6Al-2Zr-1Mo-1V合金的双曲正弦本构关系

用THERMECMASTOR-Z型热模拟试验机对Ti-6Al-2Zr-1Mo-1V合金进行了变形温度为750～1 100℃,应变速率为10-1～10 s-1,变形程度为50%的热压缩试验.研究了变形工艺参数对流动应力的影响,计算了不同温度范围的应力指数n和变形激活能Q,并建立了该合金的双曲正弦本构方程.结果表明,在750～950℃时,该合金的真应力-应变曲线呈流动软化型,1 000～1 100℃时呈稳态流动型;在750～1 000℃时变形激活能为828.9 kJ/mol,1 000～1 100℃时为197.1kJ/mol,预示在不同的温度区间具有不同的变形机制.     

GH4720Li合金热变形行为和相变

对GH4720Li合金在1080~1180℃、应变速率为0.01~10 s~(-1)条件下的单道次压缩变形行为进行了研究。利用压缩实验的应力-应变关系曲线,计算了变形条件下的热变形激活能,建立了相应的本构方程和热加工图。结果表明:动态再结晶是GH4720Li合金的主要软化机制;合金在1120~1180℃、应变速率在0.1~1 s~(-1)、真应变0.7时实现完全动态再结晶,最佳变形温度为1120~1140℃;γ′相的析出行为引起峰值应力和热变形激活能显著变化;热变形激活能在1160℃,达到最小值602 k J/mol;应变速率达到1 s~(-1)以上,合金出现失稳现象。     

BFe10-1-1合金的热压缩变形行为与本构关系研究

采用Gleeble-3500热模拟实验机,研究了BFe10-1-1合金在变形温度800～1000℃、应变速率0.01～15 s~(-1)条件下的等温热压缩流变应力行为。结果表明,该合金的流变应力随着应变速率的增大而增大,随着变形温度的升高而降低。求解得到了该合金的材料常数如下:结构因子A为1.405×10~(12)、变形激活能Q为305.2 kJ/mol、应力指数n为7.728、应力水平参数α为0.0139 MPa~(-1)。应变速率和变形温度对合金流变应力的影响可用包含Arrhenius等式的Z参数表示。     

Ti-22Al-24Nb合金热成形工艺参数优化研究

采用Gleeble-3500热模拟试验机研究Ti-22Al-24Nb合金在温度900～1110℃和应变速率0.01～10 s~(-1)条件下的热变形行为。分析了该合金的高温流变应力曲线特性和不同相区的热变形激活能及变形机制,并根据基于Prasad和Murty失稳判据下的加工图及相应的组织特征优化了该合金的热成形工艺参数。结果表明,Ti-22Al-24Nb合金的流变应力对热成形工艺参数敏感;其在(α_2+B2)两相区的主要变形机制为晶界滑移,对应的变形激活能为603.56 kJ/mol,而B2单相区的变形激活能为406.25kJ/mol,其变形主要以动态回复和动态再结晶的变形机制为主。根据这两种加工图的比较和组织观察可知,Ti-22Al-24Nb合金选择基于Prasad失稳判据下的加工图更为合理;其对应的主要失稳区为900～990℃、0.2～10 s~(-1)和1035～1095℃、1～10 s~(-1),且失稳区所预测的组织中主要存在绝热剪切带和局部流变失稳现象;而动态再结晶及胞状亚结构的组织易出现在η峰区,表明该合金较优的热力参数区间是990～1035℃、0.01～0.03 s~(-1),1040～1090℃、0.02～1 s~(-1)和1090～1110℃、0.01～0.18 s~(-1)。     

Ti-23Al-17Nb合金板材超塑性研究

对Ti-23Al-17Nb合金在温度为940~1000℃,恒应变速率为1.7×10-3~5.5×10-5s-1下的单向超塑拉伸变形行为进行了研究.结果表明,随着变形温度的升高,延伸率先增加后减小,在960℃,5.5×10-5s-1条件下获得最大延伸率为1447.5%.低应变速率条件下,Nb含量的增加使合金的加工硬化阶段增加.超塑变形有利于消除原始织构组织,对比原始组织,超塑拉伸过程中长条a2相发生了球化,并且其尺寸和含量随着温度升高逐渐减少,a2和B2相比例为50∶50时可达到最佳变形.利用Zener-Hollomn参数和Arrhenius方程建立了TAC-1B合金的峰值应力本构方程,其变形激活能Q=390.76 kJ/mol,为科学设计和有效控制Ti-23Al-17Nb合金的超塑成形工艺提供了理论依据.     

Ti-1300合金在热处理过程中的晶粒长大行为研究

采用金相法研究了Ti-1300合金在不同温度和保温时间下的晶粒长大行为。结果表明,加热温度在780~900℃时,晶粒随加热温度的升高,呈指数函数形式长大。当加热温度一定时,晶粒随保温时间增加呈对数函数形式增长。同时计算得到了Ti-1300合金的晶粒长大激活能Q为187.829kJ/mol,高于纯钛的β相自扩散激活能(Q=166kJ/mol)。     

热处理对Mg-8Gd-0.5Zr合金热压缩行为的影响

采用铸造法制备了Mg-8Gd-0.5Zr合金,对合金分别进行固溶处理(T4)及固溶+时效处理(T6),在应变速率0.002~0.1 s~(-1)、变形温度350~500℃、最大变形量50%条件下,对不同热处理后的合金进行热压缩变形实验,分析合金在不同变形条件下的真应力-真应变曲线、激活能及组织变化,研究热处理对热压缩行为的影响。结果表明:合金时效过程中析出β'-Mg_5Gd相,使热变形过程中峰值应力升高,激活能增加,T6态合金变形激活能(221.605 k J/mol)高于T4态合金(202.986 kJ/mol);在同样热压缩实验条件下,T6态合金热压缩过程中再结晶开始时间延迟,再结晶晶粒更细小,500℃热压缩后再结晶平均晶粒尺寸为15μm。     

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.