基于Drucker-Prager/Cap模型的W–Cu20粉末轧制数值模拟

将Drucker-Prager/Cap塑性模型引入到高硬度W–Cu20粉末轧制有限元分析中,利用巴西圆盘试验、单轴压缩试验以及模压试验得到Drucker-Prager/Cap塑性模型参数,借助商业有限元软件ABAQUS以及Fortran自编的VUSDFLD子程序,建立粉末轧制的有限元模型,并与实际试验进行了比对。结果表明:模拟结果中的板料相对密度和板料厚度与实际实验结果吻合较好,最大误差为4.47%,说明Drucker-Prager/Cap塑性模型对粉末轧制工艺研究有参考意义。     

Ti-6Al-4V在步进轧制中的显微组织变化

对步进轧制在940℃α β区轧制Ti 6Al 4V合金棒材的锥形体取变形量不同的部位,利用光学显微镜、透射电镜观察其组织形貌及位错组态,分析了其变形机制,探讨了材料显微组织随变形量变化的规律及其形变硬化、回复、再结晶的演变过程.实验表明利用步进轧机加工,所得Ti 6Al 4V合金棒材芯部和边部的组织较均匀.     

粉末粒度对热压Ti-6Al-4V合金微观组织和力学性能的影响

以4种不同粒径的球形Ti-6Al-4V粉末为原料,采用真空热压法进行成形固结。利用X射线衍射仪(XRD)、金相显微镜、扫描电镜、万能材料试验机分别分析粉末Ti-6Al-4V合金的物相组成、微观组织、断口形貌以及力学性能,研究粉末粒度及其组成对烧结体微观组织和力学性能的影响。研究结果表明:热压烧结Ti-6Al-4V样品致密度均可达到98%以上。不同粒度粉末烧结后的合金均为网篮排列层片状组织。合金塑性主要受原始粉末粒度影响,随原始粉末粒度增大,烧结样品的晶粒尺寸增大,从而导致合金的塑性降低。粉末粗细搭配相比于原始粗粉,有助于提高合金的塑性,从而有效降低粉末钛合金的成本。     

热处理对Ti-6Al-4V ELI合金厚板组织与性能的影响

研究了热处理对Ti-6Al-4V超低间隙（ELI）合金厚板组织与性能的影响。结果表明，Ti-6Al-4V ELI合金经α＋β区热处理后得到双态组织，强度、塑性都较高；经β区热处理后得到片层组织，细片层组织强度较高。片层粗化后，强度降低。当片层尺寸小于某一临界值（-5μm）时，延伸率随着片层的粗化升高，当片层继续粗化时，延伸率反而下降。     

粉末粒形对Ti-6Al-4V注射成形喂料显微形貌及流变性能的影响

采用粒度分析、显微形貌分析及流变性能分析等方法,研究了不同粒形Ti-6Al-4V注射成形喂料的显微形貌和流变性能。实验结果显示,球形粉喂料与氢化脱氢粉喂料的临界装载量分别为67%和52%。在最佳装载量下,球形粉喂料的粘度值（η）和流动行为指数（n）均小于氢化脱氢粉喂料,表明球形粉喂料具有更好的流动性。粒形分析显示,降低粉末比表面积有利于提高金属粉末注射成形喂料的临界装载量;理论研究及能谱分析则指出,氢化脱氢粉喂料的低流动性与小颗粒粉末的分布密切相关,小颗粒粉末是影响喂料流动性能的关键因素。     

采用氢化钛粉制备Ti-6Al-4V合金

研究了以氢化钛粉和Al-V合金粉为原料，采用粉末冶金方法，在真空炉中脱氢烧结一次完成的生产工艺，制备了Ti-6Al-4V合金．其合金性能为：烧结密度4．4g／cm^3，抗拉强度854．89MPa，延伸率3.8％，达到国外相同水平．该方法简化了钛粉制备工艺，有利于降低最终产品杂质含量和节能．     

两种3D打印用雾化Ti-6Al-4V粉末的对比研究

本研究分别利用水冷铜坩埚真空感应熔炼气雾化(VIGA-CC)和等离子旋转电极(PREP)两种技术制备出球形Ti-6Al-4V合金粉末,作者利用SEM、同步辐射CT扫描-三维重建和氩气含量测试等分析手段对不同粒径的Ti-6Al-4V合金粉末的孔洞缺陷和氩气含量、硬度值进行了表征。实验结果表明, VIGA-CC粉末粒度分布宽,细粉收得率较多,粉末粒度分布在40~180 μm之间, PREP粉末的粒度分布较窄,主要集中在110~180 μm之间;金属粉末内部的孔隙率、气体含量和孔尺寸随着粉末粒度的增大而增大,且同一粒径范围内VIGA-CC粉末的气孔概率多于PREP粉末;随着粉末粒径减小,粉末截面组织逐渐细化,其硬度值逐渐升高,整体上VIGA-CC粉末硬度值高于PREP粉末。     

热处理温度对Ti-6Al-4V耐腐蚀性及力学性能的影响

为了改善Ti-6Al-4V合金的性能,将Ti-6Al-4V合金在90％氮气和10％氧气组成的气氛中进行化学热处理以达到表面强化的目的.试验通过扫描电子显微镜(SEM)对涂层形貌进行表征、X射线衍射(XRD)确定涂层的化学组成、利用极化曲线(Tafel)和显微硬度(HV)测试涂层的耐腐蚀性能和力学性能.测试结果显示涂层和基体结合良好,涂层由TiO2和TiN构成,在800℃处理时具有最高的硬度和最强的耐腐蚀性能.     

注射成形Ti-6Al-4V合金的显微组织和力学性能

采用金属注射成形方法制备Ti-6Al-4V合金坯体,然后利用溶剂脱脂和热脱脂工艺脱除坯中粘结剂,研究了合金在真空烧结和热等静压烧结条件下的显微组织和力学性能.结果表明:真空烧结Ti-6Al-4V合金具有典型的魏氏体组织,其初始的β晶粒粗大,β晶粒内为次生片状α和薄β相片,空隙较多,合金的强度和塑性较低;合金经热等静压处理后,组织明显细化且均匀,空隙很少或几乎没有,从而强度和塑性都有所提高.     

Diffusion Bonding of Ti-6Al-4V Sheet with Ti-6Al-4V Foam for Biomedical Implant Applications

Advanced metallic bone implants are designed to have a porous surface to improve osseointegration and reduce risks of loosening. An alternative approach to existing surface treatments to create a porous surface is to bond separately produced metallic foams onto the implant. To assess the feasibility of this approach, a Ti-6Al-4V foam was diffusion bonded onto bulk Ti-6Al-4V in an argon atmosphere at temperatures between 1173 K and 1223 K (900 °C and 950 °C) for times between 45 and 75 minutes. These specimens were tested in tension to determine bond quality: failures occurred in the foam, indicating a strong diffusion-bonded interface. The quality of the bond was confirmed by metallographic studies, indicating that this approach, which can also be applied to creating of sandwich with porous cores, is successful.     

射频等离子体制备球形Ti—6Al—4V粉末性能表征

以不规则形状的Ti-6Al-4V(TC4)粉末为原料,通过射频等离子体球化处理制备了球形TC4粉末,并研究了球化处理对粉末特性及加料速率对粉末球化率的影响.利用扫描电子显微镜、激光粒度分析和霍尔流速计分别对其粉末微观结构、粒度分布和粉体性能进行了测试和分析.结果表明:TC4粉末经等离子球化处理后得到表面光滑、球形度好及球化率可达到100%的球形粉末;球化处理后,粉末的松装密度、振实密度和粉末流动性得到明显改善,粒度略微增大;随着加料速率的增加,TC4粉的球化率逐渐降低.     

Cavitation-Induced erosion of Ti-6Al-4V

Cavitation-induced erosion has been examined in Ti-6A1-4V in the mill annealed, solution-treat and aged, and beta annealed conditions. Weight loss data show only small differences between heat treatments with the solution-treat and aged microstructure exhibiting the lowest weight loss rates. Sequential micrographs of the same specimen area as a function of erosion time show that initial fracture occurs along the α-β interfaces and along crystallographic slip bands in the α-phase. The early stages of erosion are also dependent on the orientation of the Widmanstatten colonies in the beta annealed condition. These observations strongly suggest that fatigue fracture is important, at least in the early stages of the cavitation erosion process. Depression of the softer α- phase also occurs at short exposure times, and this facilitates fracture and removal of the exposed material;i.e., β-phase or tempered martensite. Examination of the eroded surfaces in the later stages where considerable material has been removed shows little evidence of the underlying microstructure, despite the distinct differences in the micro-structures of the samples tested. Formaly Undergraduate Students at Michigan Technological University     

High-temperature mechanical behavior of Ti-6Al-4V alloy and TiC p /Ti-6Al-4V composite

Mechanical behaviors at 538 °C, including tensile and creep properties, were investigated for both the Ti-6Al-4V alloy and the Ti-6Al-4V composite reinforced with 10 wt pct TiC particulates fabricated by cold and hot isostatic pressing (CHIP). It was shown that the yield strength (YS) and ultimate tensile strength (UTS) of the composite were greater than those of the matrix alloy at the strain rates ranging from approximately 10⁻⁵ to 10⁻³ s⁻¹. However, the elongation of the composite material was substantially lower than that of the matrix alloy. The creep resistance of the composite was superior to that of the matrix alloy. The data of minimum creep strain rate vs applied stress for the composite can be fit to a power-law equation, and the stress exponent values of 5 and 8 were obtained for applied stress ranges of 103 to 232 MPa and 232 to 379 MPa, respectively. The damage mechanisms were different for the matrix alloy and the composite, as demonstrated by the scanning electron microscopy (SEM) observation of fracture surfaces and the optical microscopy examination of the regions adjacent to the fracture surface. The tensile-tested matrix alloy showed dimpled fracture, while the creep-tested matrix alloy exhibited preferentially interlath and intercolony cracking. The failure of the tensile-tested and creep-tested composite material was controlled by the cleavage failure of the particulates, which was followed by the ductile fracture of the matrix.     

Low temperature creep of Ti-6 Al-4 V

Creep tests were conducted at 295 K on Ti-6 Al-4 V in the solution treated and aged (4 h at 815 K) condition, and in the as-welded condition. Some aged specimens were tested after pre-straining. Creep stresses ranged from 40 to 90 pct of the aged material yield strength. Results showed that creep was of the primary or transient kind in all cases, and was much greater in welded than in aged material. In general, pre-strains reduced creep, although a strain larger than 10^-3 was needed to do this at the highest creep stress. Activation areas A* were between 10 and 20 b², and thus were similar to tensile results on titanium and its alloys. The microstructural rationale applied to Ti-5 Al-2.5 Sn in earlier work, based on the character of dislocation sources, proved successful in understanding the effects of prestrain in this work. Formerly with Sandia Laboratories, Livermore, Calif.     

Superplastic deformation of Ti-6Al-4V alloy

The alloy Ti-6-Al-4V deforms superplastically in the temperature range 750 to 950° The most important factor which is responsible for superplastic behavior was found to be the very fine grain size. Strain rate has no direct effect on superplasticity, however when the strain rate is very low (approximately 2 × 10 s), prolonged exposure to high temperature causes grain growth and early failure. The strain rate sensitivity factorm = 0.5 and the apparent activation energyAH = 45,000 cal/mole, which is approximately the same as the activation energy for grain boundary self diffusion of titanium. Both values are independent of strain rate within the range 10 - 2.5 × 10 s. All the experimental points fall in a straight line when plotted as log (εkTd* ²/D_gbGb³) vs log (σ/G) with a slopen = l/m = 2. This is in excellent agreement with the theory of grain boundary sliding accommodated by dislocation motion.     

Fretting wear behaviour of plasma nitrided Ti-6Al-4V fretted against unnitrided Ti-6Al-4V and alumina counterbodies

Ti-6Al-4V samples were plasma nitrided at 520°C in two environments (nitrogen and a mixture of nitrogen and hydrogen in the ratio of 3:1) for two different time periods (4 h and 18 h). Fretting wear tests were conducted on unnitrided and nitrided samples for 50,000 cycles using two counterbody materials (unnitrided Ti-6Al-4V and alumina). Gross slip prevailed at a normal load of 4.9 N while mixed stick-slip prevailed at 9.8 N. Tangential force coefficient values of plasma nitrided samples were lower than those of unnitrided samples. The tangential force coefficient nearly stabilised after thousand cycles in case of samples tested against Ti-6Al-4V counterbody. On the other hand, it showed a continuously increasing trend in case of specimens tested against alumina counterbody. The samples nitrided for 4 h exhibited higher hardness and lower tangential force coefficient compared to the specimens nitrided for 18 h. The samples nitrided in nitrogen-hydrogen mixture environment exhibited higher hardness and lower tangential force coefficient compared to the specimens nitrided in nitrogen. The samples plasma nitrided in nitrogen-hydrogen mixture for 4 h exhibited the highest hardness and the lowest tangential force coefficient. The wear volume of the plasma nitrided samples was lower than that of the unnitrided samples. Owing to tribochemical reactions, the wear volume of unnitrided and nitrided samples fretted against alumina ball was higher than that of the samples fretted against Ti-6Al-4V. A consistent trend was not observed regarding which nitriding condition would result in lower wear volume at different loads.     

Hydrogen in β transformed Ti-6Al-4V

The internal reactions associated with hydrogen absorbed at ambient temperature by Ti-6A1-4V having a transformedβ microstructure were determined by using X-ray diffraction analysis. Below 650 ppm, the absorbed hydrogen was concentrated primarily in theβ phase causing an increase in the d(200) spacing and considerable X-ray line broadening. The a phase, however, was not significantly affected by the absorbed hydrogen showing no change in the d(1120) and d(1012) spacings and only a finite amount of line broadening. At approximately 650 ppm H, hydride precipitation began at thea-β interface. With increasing hydrogen content, theβ phase d(200) spacing continued to increase, the (200) X-ray line broadening reached a limiting value, and massive hydrides were formed. The data indicates that low concentrations of hydrogen absorbed by a-β titanium alloys can be detected by examining the X-ray line profile of theβ phase. W. D. HANNA, formerly with the McDonnell Douglas Astronautics Co.     

Producing basal textured Ti-6Al-4V sheet

This study determined the conditions under which Ti-6Al-4V sheet with a strong basal plane texture can be produced on a commercial basis. Texture development during all stages of processing starting with the forged sheet bar was followed using pole figures. The influences of sheet bar forging temperature, rolling temperature, rolling procedures and prior texture were examined. The deformation mechanisms by which a basal plane texture can form are discussed and it is shown that (1120) slip principally on {1010} prism planes can account for it. To demonstrate that texture can be controlled on a production basis, two 1.2 m×2.4 m×1.5 mm sheets from each of six heats of Ti-6Al-4V were rolled with a uniform basal plane texture.