钛合金低温超塑性的研究进展

介绍了降低钛合金超塑成形（SPF）温度的三种主要方法，即通过添加氢、细化晶粒、在β相中加入具有高扩散系数的元素均可有效地降低SPF温度，从而利于提高超塑成形的效率及节省能源和降低模具的损耗。同时还介绍了细晶超塑性的变形机理和氢对超塑性的作用机理。最后指出大塑性变形技术和氢处理技术是制备细晶组织钛合金的简单而可行的工艺方法。     

超塑性在钛合金压力加工和焊接方面的应用

简要介绍了超塑性在压力加工方面以及相变超塑性在焊接方面的应用。重点介绍了超塑性成形和超塑性成形/扩散焊接技术在钛合金上的应用、超塑成形模具材料选择的原则、以及提高SPF部件性能的措施。     

超塑性钛合金的研究进展

简要介绍了国内外对α、α β、β钛合金以及金属基复合材料的超塑性研究，并介绍了合金的晶粒尺寸、微量元素氢对钛合金超塑性的影响。结果表明，细化晶粒后，合金的超塑性能得到很大提高，表现在超塑形变温度降低100℃以上，应变速率提高1～2个数量级。晶界扩散控制晶界滑动是低温超塑行为的主要机理。氢含量低时，合金的伸长率与原始合金板材的接近，氢的添加可使合金超塑性温度降低。另外还给出一些超塑性钛合金的应用情况。最后指出未来研究方向重点为先进材料超塑性的研究、低温高速超塑性的研究以及非理想超塑材料的超塑性变形规律的研究。     

置氢对Ti-55高温钛合金超塑变形行为的影响

钛合金的超塑成形技术在工业领域已经得到广泛的应用,但其成形温度高,成形速率低的问题大大限制了该技术的发展。向钛合金中添加适量的氢,可有效改善合金的热加工性能。以Ti-55高温钛合金为对象,通过金相观察、高温拉伸试验等方法,研究了置氢对合金微观组织和超塑变形行为影响,得出了氢含量、变形温度和初始应变速率对其伸长率和峰值应力的影响规律。研究发现,置氢0.1%之后,合金在825℃变形时伸长率提高了95.5%,峰值应力降低了37.8%;置氢0.1%使得Ti-55的最佳超塑成形温度降低了约125℃;置氢后合金对于变形温度和应变速率的变化更加敏感,且最佳超塑性的温度和应变速率范围变窄。     

TC6钛合金的超塑变形机制研究

提出了一种全新的超塑性研究方法：基于m值的高效超塑变形机制。采用该方法对TC6钛合金进行高温拉伸实验,研究其超塑性能,并与最大m值法超塑性进行比较分析。实验结果表明,细晶组织的该合金具有优良的超塑性,最佳变形温度在900℃,最大m值超塑变形可以获得20倍的最大延伸率;基于m值的高效超塑变形可以显著提高超塑成形效率,在获得延伸率为16.96倍的优良超塑性前提下,成形效率可提高13倍。     

第二届钛合金结构成形技术交流会暨第七届超塑性学术研讨会纪要

第二届钛合金结构成形技术交流会暨第七届超塑性学术研讨会于2006年6月26日～30日在桂林圆满结束。此次会议由北京航空制造工程研究所主办，中国航空一集团科技发展部、中国锻压学会超塑性专业分会、中国航空学会工艺专业分会协办，法国奥伯杜瓦公司独家赞助，是继2002年上海会议以来，又一次关于钛合金结构成形技术方面的全国性技术、学术交流会。本次会议共有来自航空、航天、兵器和船舶等国防工业部门以及高校等50多个单位的130多名代表出席会议。与会代表主要围绕钛合金新结构设计与应用技术、SPF和SPF／DB技术及其模拟仿真、钛合金的热成形技术、管件成形技术、旋压成形技术、钛合金薄壁结构焊接技术、钛合金化铣和阳极氧化技术等专题进行了交流，     

钛合金超塑板制备研究进展

超塑成形/扩散连接(SPF/DB)技术为钛合金在航空航天领域的应用打开了一条通道,该技术的发展也对所需的钛合金超塑板提出了更高的要求。介绍了国内外在TC4钛合金超塑板、新型钛合金低温超塑板和新型短时高温钛合金超塑板方面的研究进展。指出,我国经过三十多年的持续技术攻关和应用经验积累,钛合金超塑板的生产技术水平基本与国际先进水平同步,尤其是自主研发的特种轧制技术,能够有效控制钛合金超塑性板材的晶粒度和各向异性,保证后续SPF/DB工艺的需要。最后对我国钛材研发企业提出了几点建议,指出了未来钛合金超塑板研究的工作重点。     

TA15钛合金超塑及扩散连接性能

TA15钛合金是一种近α型钛合金,具有较好的综合力学性能,最高使用温度可以达到500℃,在飞机和发动机结构中有着广阔的应用前景。通过研究TA15钛合金的超塑性和扩散连接特性,揭示了温度、压力、时间等工艺参数对TA15钛合金超塑成形伸长率和变形后的力学性能、扩散连接接头界面焊合率和微观组织的影响规律,获得了TA15钛合金最佳超塑成形/扩散连接(SPF/DB)工艺参数及其典型结构SPF/DB制备工艺路线。通过制备典型结构件及对其组织和性能分析,验证了采用SPF/DB工艺制备TA15典型结构件的工艺可行性。     

镁合金超塑性的变形机理﹑研究现状及发展趋势

综述不同成形条件下的镁合金激活能及本构方程,对粗晶和细晶镁合金的超塑性变形机理予以详细的介绍。并对常见的几种镁合金超塑性加工方式进行探讨,并概述超塑性镁合金的发展趋势,认为未来超塑性镁合金将取得快速发展。获得高应变速率与低温超塑性镁合金并实现镁合金低成本化、安全化、环保化是目前研究的热点。     

第2届钛合金结构成形技术交流会暨第7届超塑性学术研讨会在广西桂林召开

第二届钛合金结构成形技术交流会暨第七届超塑性学术研讨会于2006年5月26日至30日在桂林圆满结束。此次会议由北京航空制造工程研究所主办，中国航空一集团科技发展部、中国锻压学会超塑性专业分会、中国航空学会工艺专业分会协办，法国奥伯杜瓦公司独家赞助，是继2002年上海会议以来，又一次关于钛合金结构成形技术方面的全国性技术、学术交流会。本次会议共有来自航空、航天、兵器和船舶等国防工业部门以及高校等50多个单位的130多名代表出席了会议。与会代表主要围绕钛合金新结构设计与应用技术、SPF和SPF／DB技术及其模拟仿真、钛合金的热成形技术、管件成形技术、旋压成形技术、钛合金薄壁结构焊接技术、钛合金化铣和阳极氧化技术等专题进行了交流，并邀请了一些高校和研究院所的知名专家学者就相关主题做了学术与技术报告，充分展示了近年来我国在钛合金结构成形方面的科研、生产中的新进展，显示出钛合金结构成形技术在武器装备领域的良好应用前景。     

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.     

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.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

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.