Ti2AlNb合金超塑性能及四层立筋结构超塑成形/扩散连接工艺

对Ti-22Al-27Nb合金四层结构件SPF/DB组合工艺进行试验研究,对Ti-22Al-27Nb合金的超塑性能及扩散连接性能进行探究。拉伸实验表明,当变形温度为960℃、应变速率为1×10^?4 s^?1时,材料伸长率达到最大,为230%。对温度、保温时间和扩散压力对Ti-22Al-27Nb合金接头质量的影响进行研究,结果表明Ti-22Al-27Nb合金扩散连接的最佳工艺参数为(960℃,10 MPa,2 h)。根据高温拉伸试验结果,利用有限元模拟软件对中空四层结构件超塑成形过程进行模拟。通过SPF/DB组合工艺成形得到外观质量良好的Ti-22Al-27Nb合金中空四层结构件,成形构件壁厚分布均匀。     

Microstructure and mechanical properties of Ti-6Al-4V/Ti-22Al-25Nb joint formed by diffusion bonding

Ti-6Al-4V (wt.%) and Ti-22Al-25Nb (at.%) were joined by diffusion bonding at 950 °C and 15 MPa for 100 min, and the microstructure and mechanical properties of the resulting joints were investigated. The composition of the diffusion layer is B2/discontinuous α/α₂ layer/necklace-shaped β+α′ layer, where the content of any element at a given point mainly depends on the distance of the point from the interface and the phase type at the point. The tensile strength of the joint is 894 MPa, which is almost the same as that of the Ti-22Al-25Nb base alloy. The fracture surfaces on both sides of the joint are composed of two main regions. One region displays a relatively flat surface and fractures along the bonding interface. The other is composed of a moderate number of irregularly-shaped cavities on the Ti-6Al-4V side and many irregularly-shaped bulges on the Ti-22Al-25Nb side. Both regions result from fracture along the boundaries between β+α′ layers and α_p grains or from the transcrystalline fracture of α_p grains.     

Diffusion bonding of Ti-6Al-4V to ZQSn10-10 in vacuum

The experimental investigation of the direct diffusion bonding of Ti-6Al-4V to ZQSn10-10 was carried out in vacuum. The microstructure of bonded joint was studied by scanning electron microscopy （SEM）, energy dispersive spectroscopy （ EDS ） and the mechanical properties were detected by the tensile experiments. The microstructure and tensile strength of the joint mainly depend on the bonding temperature and bonding time. A satisfying diffusion bonded interface with a tensile strength of 73.9 MPa can be obtained under the condition of bonding temperature 850℃ for 30 rain. Three kinds of reaction products were observed in the bonded interface, namely β-Ti, CoaTi and CuSn3Ti5. And the brittle Cu3Ti and CuSn3 Ti5 are mainly responsible for lowering the strength of the bonded joint. The diffusion distances of Sn , Cu and Ti and square root of bonding time are approximately linear relationship. And diffusion velocity of Sn, Cu and Ti in the diffusion reaction layer are 0. 013 9,0. 069 7 and 0. 056 4 mm^2/s.     

Effect of Hydrogen on Diffusion Bonding Behavior and Mechanism of Ti-6Al-4V alloy

研究了置氢Ti-6AL-4V合金在800~860℃温度范围内气压扩散连接行为与机理。在840℃对置氢0.11%(质量分数,下同)的纯钛和Ti-6AL-4V合金进行了扩散连接。应用光学显微镜(OM)、扫描电子显微镜(SEM)和电子探针显微分析仪(EPMA)研究了氢对扩散连接接头焊合率及元素扩散行为的影响。结果表明:氢能够显著提高扩散连接接头的焊合率(置氢0.11%在840℃的焊合率大于98%);氢含量为0.11%的Ti-6Al-4V合金扩散连接后仍为等轴组织,而高氢含量(0.32%~0.48%H)Ti-6Al-4V合金扩散连接后组织转变为粗大的魏氏组织;氢对扩散连接行为的改善作用主要是由于氢的弱键效应及其对元素扩散系数的提高;相对于未置氢Ti-6Al-4V合金,0.11%的氢能够将Al和V元素的扩散系数提高一个数量级,并使扩散连接温度降低了40℃。     

Ti-6Al-4V合金超塑性变形中的组织演变及变形机制

920℃、应变速率为1×10.3和2×10.4 s.1时,对不同初始晶粒尺寸(2.6、6.5和16.2 μm)的Ti-6Al-4V合金进行超塑性拉伸变形.采用光学显微镜、透射电镜观察变形后的显微组织.结果表明,初始晶粒尺寸的不同对超塑性变形中的组织演变及变形机制有着显著的影响.拉伸变形中晶粒明显粗化,变形诱发晶粒长大是超塑性变形组织的重要特征之一;随着变形程度的增大,应变诱发的晶粒长大显著增大,并且远大于静态长大的增幅.对于细晶粒材料(2.6和6.5 μm),位错运动协调的界面滑动是其变形的主要机制.而对于晶粒较粗的材料(16.2 μm),超塑变形机制是晶界滑动与晶内位错运动的共同作用.随着晶粒尺寸的增大,以晶界滑动为主的变形方式逐渐转向以晶内位错运动为主.     

Fracture toughness of superplastic formed/diffusion bonded interfaces

The present paper is concerned with the interfacial fracture problem of bi-material interfaces of superplastic forming/diffusion bonding (SPF/DB) components. It has been known that the interfacial fracture toughness is a strong function of the mode mixture of crack tip, which is the most important characteristic of interfacial problems. Micromechanical models have been proposed to understand this trend of interfacial toughness curves, based on which a modified criterion for fracture under mixed-mode loading is advanced in this paper to predict phenomenological functional forms of toughness curves. On the ground of linear elastic fracture mechanics (LEFM), mode I and mode II interfacial fracture toughnesses of SPF/DB components formed under different processing conditions have been measured in this paper using the double cantilever beam (DCB) and end-notched flexure (ENF) specimens, respectively. It is found that, just as is the general trend of interfacial fracture toughness curves, the experimental results of mode II toughness values are much greater than those of mode I toughness values, and the fluctuation of mode II toughness values under different processing conditions is much greater than that of mode I toughness values. On the basis of the experimental results, the four basic parameters in the modified criterion are obtained and the interfacial toughness curve of Ti-50A/Ti-6Al-4V SPF/DB components is determined using the modified criterion for fracture under mixed-mode loading. Comparison between the results shows that the agreement between experiment and theory is excellent.     

HIP diffusion bonding of P/M titanium alloy Ti-6Al-4V and stainless steel 1Cr18Ni9Ti

The HIP diffusion bonding of P/M titanium alloy Ti-6A1-4V and stainless steel 1Cr18Ni9Ti using pure Ni as intermediate layer was studied. Bonding joint with complex bonding interface was obtained by HIPing pre-alloyed Ti-6Al-4V powders and stainless steel 1Crl 8Ni9Ti in a vacuum canning. The joint strengths were examined and the characteristics of bonding joint were observed. The result shows that the maximized strength of HIP diffusion bonding between P/M titanium alloy Ti-6Al-4V and stainless steel 1Cr18Ni9Ti can be up to 388 MPa and the microstructure of bonding joint is acceptable.     

Ti-6Al-4V合金双半球结构脉冲电流辅助超塑成形

针对Ti-6Al-4V合金板材超塑成形能耗高、效率低的问题,提出了一种脉冲电流辅助超塑成形工艺。该工艺将成形坯料直接串联到脉冲电流回路,利用脉冲电流迅速将坯料加热至超塑成形温度。通过脉冲电流加热实验,分析了平均脉冲电流密度对坯料温度及升温速率的影响。结果表明,采用该加热方式可将坯料加热时间从数十分钟缩短至几十秒,能量消耗降至传统工艺的20%左右,极大地提高了加热效率、降低了能耗,实现了节能环保的绿色超塑成形技术。利用该工艺成形了Ti-6Al-4V合金双半球结构,并分析了在脉冲电流辅助工艺条件下细晶态Ti-6Al-4V合金的超塑变形机制。     

Examination of superplastic forming combined with diffusion bonding for titanium: Perspective from experience

Superplastic forming (SPF) combined with diffusion bonding (DB) has been used successfully for the fabrication of titanium aerospace hardware. Many of these applications have been for military aircraft, whereby a complex built-up structure has been replaced with monolithic parts. Several methods for applying the two- and four-sheet titanium SPF/DB processes have been devised, including the welding of sheets prior to forming and the use of silk-screened stop-off (yttria) to prevent bonding where it is undesirable. Very little progress has been made in the past few years toward understanding and modeling the SPF/DB process using constitutive equations and data by laboratory testing. Concerns that engineers face in designing for fatigue life, acceptable design loads, and damage tolerance are currently being studied, but the database is very limited. This is a summary of past work found in the literature and forms the foundation for additional research. This paper was presented at the International Symposium on Superplasticity and Superplastic Forming sponsored by the Manufacturing Critical Sector at the ASM International AeroMat 2004 Conference and Exposition, June 8–9, 2004, in Seattle, WA. The symposium was organized by Daniel G. Sanders, The Boeing Company.     

激光快速成形TA15残余应力影响因素的研究

采用小孔法对激光快速成形TA15钛合金样件进行残余应力影响因素的研究。结果表明:激光功率、扫描速度、送粉速度、扫描方式等工艺参数对残余应力均有显著影响。激光功率越大,残余应力越大;随着扫描速度的增大,残余应力则不断减小;随着送粉速度的增大,残余应力有增加的趋势;3种扫描方式中的交错扫描是残余应力最小的成形扫描方式。最后,对成形样件不同位置的残余应力进行了测定分析,得出成形件中间位置是残余应力峰值点的结论。     

Cytotoxicity of Ti–6Al–4V–5Cu Alloy to MC3T3-E1 Cells

The aim of this work was to study the cytotoxicity of Ti–6 Al–4 V–5 Cu(TC4–Cu) alloy for dental applications and evaluate the cell viability of diff erent fabricated TC4–Cu alloys in contact with MC3 T3-E1 cells in vitro. Ti–6 Al–4 V(TC4) alloy was used as a negative control to evaluate the cytotoxicity level of TC4–Cu alloy so as to provide basic support for the dental clinical application. Control group TC4 and experimental group TC4–Cu with diff erent fabrications were incubated in the cell culture medium. The absorbance value of mouse osteoblast MC3 T3-E1 cells was detected by CCK-8 assay after 1, 3 and 7 days, respectively. The relative proliferation rate of cells was calculated, and then the toxicity level was valued for each group. Cell morphology on the surface was also studied by observing the cytoskeleton through F-actin filament staining. The experimental results showed that the absorbance values for the experimental and the negative control groups were not same at diff erent time points. Compared with diff erent fabricated TC4–Cu alloys, the annealing-TC4–Cu alloy showed much better biocompatibility. The mouse osteoblast MC3 T3-E1 cells cultured with annealing-TC4–Cu, rolling-TC4–Cu and solution + aging-TC4–Cu have no toxic eff ects, and these alloys could promote the proliferation of mouse osteoblasts.     

Effect of heat treatment processing on microstructure and tensile properties of Ti-6Al-4V-10Nb alloy

Effects of heat treatment processing on the microstructure and mechanical properties of Ti-6Al-4V-10Nb alloy were investigated. The microstructures were investigated by SEM, TEM and XRD, and the mechanical properties were evaluated by tensile tests at room and elevated temperatures. The results indicate that the lath-like and globular primary α phase, secondary α phase and β phase are obtained after forging and heat treatment processing. The size of secondary α phase is much smaller than that of primary α phase. After heat treatment, the volume fraction of primary α phase is decreased, and that of secondary α phase is increased. With the increase of solution temperature, the volume fraction of primary α phase is gradually decreased, and that of secondary α phase is obviously increased. The yield strength and tensile strength of Ti-6Al-4V-10Nb alloy are significantly enhanced with the solution temperature increasing.     

铸态Ti-6Al-4V-0.1B合金的热变形行为及加工图

在Gleeble-1500热模拟试验机上进行高温压缩试验,研究了变形温度为1000～1100℃,初始应变速率为0.01～1 s-1的铸态Ti-6Al-4V-0.1B合金的变形行为。基于动态材料模型建立了加工图,并观察了变形组织。结果表明:该合金为热敏感和应力敏感型合金,热变形的最佳变形参数为1050～1100℃,应变速率在0.1～1 s-1之间。铸态大变形区组织为沿着变形方向拉长的原始β晶粒,晶粒组织内部出现针状马氏体,TiB相在变形的过程中出现折断,并沿着加工流线分布。     

Study of diffusion bonding of Ti-6Al-4V and ZQSn10-10 with metal interlayer

The diffusion bonding was carried out to join Ti alloy (Ti-6Al-4V) and tin-bronze (ZQSn10-10) with Ni and Ni Cu interlayer. The microstructures of the diffusion bonded joints were analyzed by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The results show that when the interlayer is Ni or Ni Cu transition metals both could effectively prevent the diffusion between Ti and Cu and avoid the formation of the Cu-Ti intermetallic compounds (Cu3Ti, CuTi etc.). But the Ni-Ti intermetallic compounds (NiTi, Ni3Ti) are formed on the Ti-6Al-4V/Ni interface. When the interlayer is Ni, the optimum bonding parameters are 830℃/10 MPa/30min. And when the interlayer is Ni Cu, the optimum bonding parameters are 850℃/10MPa/20min. With the optimum bonding parameters, the tensile strength of the joints with Ni and Ni Cu interlayer both are 155.8MPa, which is 65 percent of the strength of ZQSn10-10 base metal.     

Diffusion bonding of Ti-6Al-4V by pulse current heating and hot-pressing

Pulse current heating （PCH） was used to join Ti-6Al-4V alloy at two cases of with die and without die. Hot-pressing （HP） method was used to provide a comparison between the two methods. Microstructures near the contacting surfaces were observed in optical microscope. Temperature distribution was analyzed. After joining, the tensile properties of the samples were evaluated. Experimental results show that grains and phases grow transversely on contacting surfaces, which makes two parts into a whole with a certain of tensile strength. PCH joining is a different temperature joining method. The highest temperature is located at the interface. The comparison of tensile strengths of samples joined by the two methods indicates that joining temperature and holding time needed by PCH are lower and less than those needed for HP.     

双时效对Ti-4Al-5Mo-6Cr-5V-1Nb合金显微组织和力学性能的影响

研究了固溶、固溶后单时效以及固溶后双时效处理对Ti-4Al-5Mo-6Cr-5V-1Nb合金组织和力学性能的影响。结果表明,820℃下固溶0.5 h后,合金中的α相完全溶解;单/双时效合金的硬度均随时效时间增加先升高后降低;合金经300℃/8 h+500℃/8 h双时效处理后可达到4580 MPa的峰值硬度(HV),1462 MPa抗拉强度以及3.4%延伸率,其强度比原始合金高6%,也高于单时效合金。界面能计算结果表明ω相使α相形核的阻力降低50%,促进了α相的析出并细化α板条,从而提升合金的硬度,强度及塑性。