Mechanical properties of beryllium fabricated by powder metallurgy

A general survey of the mechanical properties of commercially pure beryllium fabricated from powder by vacuum hot pressing and other consolidation methods is presented. The effect of fabrication method, grain size, strain rate, and directionality upon both room and elevated temperature tensile properties is reported.     

快速凝固/粉末冶金制备高硅铝合金材料的组织与力学性能

采用空气雾化水冷与真空包套热挤压工艺相结合的方法,制备了Al-30Si和Al-40Si过共晶高硅铝合金材料,采用扫描电镜与金相显微镜进行了显微组织分析,检测了其力学性能.研究表明:所制备的高硅铝合金粉末颗粒尺寸在2～10 μm之间;挤压后的材料具有组织十分细小且均匀弥散分布的Si相;在370℃热挤压条件下,其抗拉强度高达239 MPa,比相同成分的铸轧态试样提高了77%,随着挤压温度的升高以及Si含量的增加,硅相颗粒增大,抗拉强度下降.     

粉末冶金W/Re合金靶材的显微结构及磁控溅射沉积性能

为了研制高品质W/Re合金靶材,采用机械混料、压制成形和真空烧结致密化工艺路线制备了纯钨及铼含量分别为1％、5％、10％(质量分数)的钨/铼(W/Re)合金,测试了W/Re合金的致密度、晶粒度及晶粒取向、磁控溅射沉积等性能.研究表明,W/Re合金致密度及纯度均随Re含量增加而逐渐提高,而晶粒逐渐细化.W/10％Re合金...     

Mechanical properties of Mo-Si-B alloys fabricated by using core-shell powder with dispersion of yttria nanoparticles

In recent years, refractory materials with excellent high-temperature properties have been in the spotlight as a next generation’s high-temperature materials. Among these, Mo-Si-B alloys composed of two intermetallic compound phases (Mo₅SiB₂ and Mo₃Si) and a ductile α-Mo phase have shown an outstanding thermal properties. However, due to the brittleness of the intermetallic compound phases, Mo-Si-B alloys were restricted to apply for the structural materials. So, to enhance the mechanical properties of Mo-Si-B alloys, many efforts to add rare-earth oxide particles in the Mo-Si-B alloy were performed to induce the improvement of strength and fracture toughness. In this study, to investigate the effect of adding nano-sized Y₂O₃ particles in Mo-Si-B alloy, a core-shell powder consisting of intermetallic compound phases as the core and nano-sized α-Mo and Y₂O₃ particles surrounding the core was fabricated. Then pressureless sintering was carried out at 1400 °C for 3 h, and the mechanical properties of sintered bodies with different amounts of Y₂O₃ particles were evaluated by Vickers hardness and 3-point bending test. Vickers hardness was improved by dispersed Y₂O₃ particles in the Mo-Si-B alloy. Especially, Mo-3Si-1B-1.5Y₂O₃ alloy had the highest value, 589 Hv. The fracture toughness was measured using Mo-3Si-1B-1.5Y₂O₃ alloy and the value indicated as 13.5 MPa·√m.     

熔渗法制备C/C-Cu复合材料的力学性能

以炭纤维(Cf)针刺整体毡为预制体,分别采用化学气相渗透(Chemical vapor deposition,CVI)和浸渍炭化(Impregnation and carbonization,I/C)制备不同密度和基体炭的C/C坯体;通过添加Ti元素改善熔融Cu与C/C坯体的润湿性.采用真空熔渗法制备C/C-Cu复合材料.对复合材料的力学性能及其与坯体之间的关系进行研究,并与常用滑板材料的力学性能进行比较.结果表明:随着坯体密度的增加,复合材料的抗弯强度下降,而坯体密度为1.4 g/cm3的复合材料的冲击韧性达到最大值.与用I/C坯体制备的复合材料相比,用CVI坯体制备的复合材料具有更高的强度和韧性,其弯曲曲线呈“假塑性”断裂特征,断裂时纤维从热解炭层或熔渗金属相中拔出,熔渗金属相呈“韧窝状”的塑性断裂形貌.冲击断裂时,复合材料倾向于沿TiC/熔渗金属界面断裂.C/C-Cu复合材料的抗弯强度为180～300 MPa、冲击韧性高于3.5 J/cm2,优于常用滑动电接触材料的性能,是一种极具潜力的新型滑动电接触材料.     

Microstructure and mechanical behavior of NiAl-based alloy prepared by powder metallurgical route

Rapidly solidified NiAl–28Cr–6Mo–B–Dy prealloyed powder doped with Nb powder was consolidated by hot pressing under 1250 °C for 30 min at 30 MPa. The consolidated material exhibited a different microstructure from the original powder, i.e. the NiAl and Cr(Mo) plates in the eutectic cell tend to break down into short platelets or even particles during hot pressing process. The mechanical behaviors at room temperature and at high temperature of consolidated sample from powder alloy were evaluated by three-point bending technique, tensile test and compressive test. The results showed that the hot pressing alloy possessed a reasonable combination of room temperature ductility and toughness, and elevated temperature strength.     

Investigations on processing powder metallurgical high-Nb TiAl alloy sheets

In this work, high Nb-containing TiAl alloy sheets were hot rolled starting from powder metallurgical billets. The prealloyed powder prepared by the plasma rotation electrode process (PREP) was characterized. Results show that there are two typical morphologies of powders: martensitic (M) and dendritic (D) powders, which are formed due to different local cooling conditions. The two PREPed powders lead to the formation of different microstructures in HIPing. The coarse D powder will introduce defects, such as residual primary particle boundaries and interfacial porosity in the as-HIPed microstructures. The deformation behavior of PM high-Nb TiAl alloys largely depends on γ phase. Besides the dynamic recrystallization and the superplastic deformation, due to the large amount of the γ phase in PM high-Nb TiAl alloy and the high rolling rate, the mechanical twinning in γ phase plays a critical role in the hot rolling process. The mechanical properties of high-Nb TiAl alloys can be significantly improved by the hot rolling, through the refinement of microstructures and the elimination of primary particle boundaries. However, a large deformation may introduce defects and coarsened microstructures, and thus 60% deformation may be suitable for the purpose of improving mechanical properties.     

粉末热挤压Al-Zn-Mg-Cu系合金的热处理工艺

通过XRD衍射分析、光学和透射电镜观察以及力学性能测试,研究了固溶和时效处理对粉末热挤压法制备的Al-Zn-Mg-Cu高强铝合金组织性能的影响.结果表明:挤压态合金中析出大量MgZn_2相;合金适宜的T6热处理制度为460℃×2.5h水冷+120℃×24h空冷;在此条件下合金的抗拉强度、屈服强度和伸长率分别为731MPa、670MPa和6.2%;晶粒细化是合金T6组织与铸锭挤压Al-Zn-Mg-Cu合金回归再时效(RRA)组织类似的主要原因.     

Mechanical properties and corrosion resistance of low rigidity quaternary titanium alloy for biomedical applications

Electrochemical corrosion of Ti-35Nb-5Ta-7Zr alloy fabricated by arc melting and heat treatment process was studied in 0.9% NaCl at (37±1) °C. Phase and microstructure of the fabricated alloy were investigated using X-ray diffractometer and scanning electron microscope. Mechanical properties such as yield strength and elastic modulus of the alloy were determined by tensile test. Potentiodynamic polarization technique and impedance spectroscopy were employed to study the corrosion behavior. The results of the study were compared with those obtained for Ti-6Al-4V commercial alloy. The result of the study supports feasibility of Ti-35Nb-5Ta-7Zr alloy for implant applications.     

Fabrication and compressive properties of porous TiAl-Mn intermetallics by powder metallurgical route

We investigated the effects of process parameters on the microstructure and compressive properties of reactive-sintered porous TiAl-based intermetallics. Different extrusion ratios were selected in order to change the as-extruded microstructure and thus obtain various types of porous structures (unidirectional and spherical pores) after reactive sintering. In addition, different environmental conditions, such as vacuum and air, were used during the reactive sintering stage. It was revealed that the compressive strength is influenced by the unidirectionalty of the pores. High unidirectionalty led to higher yield strength at room temparature and at 1073 K. The compressive properties of the porous TiAl intermetallics were also influenced by the environment where reactive sintering is carried out.     

注射成形Mo/Cu合金脱脂及烧结工艺

采用粉末注射成形工艺制备电子封装用Mo/Cu合金,重点研究了脱脂和烧结工艺,以喂料的热差分析为指导,制定出合适的热脱脂工艺路线,并分析了烧结过程中的温度和时间对烧结密度和热导率的影响规律.研究结果表明,利用溶剂脱脂可以除去粘结剂中81%左右的石蜡,缩短了热脱脂时间;材料密度随着烧结温度的升高不断增加,但当温度大于1 450℃时,密度反而下降,材料在1 450℃烧结3 h后,相对密度达到了98%;影响热导率的主要因素是烧结密度,实验获得的热导率最大值为158 W/mK.     

Mechanical behavior and microstructure of Al-10wt.%Nb alloy fabricated by Mechanical Alloying

Al-10%Nb alloy powders were fabricated by mechanical alloying and their mechanical behavior and microstructure were investigated by means of tensile testing, differential scanning calorimetry, X-ray diffraction and electron microscopy. An intermetallic compound of Al₃Nb was partially formed in the mechanically alloyed powders. The grain size was 50 run after mechanical alloying for 20 hours, and increased to 500 nm after hot extrusion at 400°C. However the 20 size of the intermetallic compounds of precipitated Al₃Nb in an Al matrix, did not vary with hot extrusion. The density of the consolidated Al-Nb alloy was over 97% relatively with hot extrusion. Both the tensile strength and elongation decreased at the elevated temperature. As the temperature increased, the dimples in the fracture surface were large and of coalescent shape, and the fracture was caused by the precipitated phases of Al₃Nb.     

Hot deformation behavior and microstructural evolution of powder metallurgical TiAl alloy

The hot deformation behavior of powder metallurgical(PM) TiAl alloys was investigated on Gleeble-3500 thermomechanical simulator, at a temperature range of 1050–1200 °C with an interval of 50 °C and a strain rate range of 0.001–1.000 s~(-1). The results show that the flow stress of PM TiAl alloy is sensitive to deformation temperature and strain rate, the peak stress decreases with the increase in deformation temperature and decrease in strain rate, and dynamic recrystallization occurs during the hot compression. The deformation active energy was calculated and the flow stress model during high-temperature deformation was established based on the Arrhenius equations and Zener–Hollomon parameter. The deformed microstructure consists of refined homogeneous γ and ɑ_2/γ grains.     

Mechanical properties of β-SiC fabricated by spark plasma sintering

The consolidation of SiC nanopowder synthesized by the mechanical alloying method was subsequently accomplished by spark plasma sintering of 1700 °C for 10 min under an applied pressure of 40 MPa. The SiC sintered compact with relative density of 98% consisted of nano-sized particles smaller than 100 nm. This phenomenon resulted in the ordering process of stacking disordered structure formed by mechanical alloying. In this work, the effect of grain size and relative density on the mechanical properties were studied. The mechanical properties of sintered compacts were evaluated and compared with the reference samples fabricated from the commercial SiC powder (β-SiC, 0.3 μm, IBIDEN Co., Gifu, Japan) with sintering additive (B–C mixture). The Vickers hardness and bending strength of those sintered compacts increased with the increment of the density. However, the mechanical properties were lower than those of reference samples in case of lower density, even though the mechanical property was close to that of reference sample in case of higher density. This phenomenon was considered for the difference of bond strength between grains because those sintered compacts were fabricated without any sintering additives, while those reference samples were fabricated by accelerating the grain bonding with a sintering additive of B–C mixture. In other words, those results indicated that the effect of sintering additive affected on mechanical properties directly. This paper was presented at the International Symposium on Manufacturing, Properties, and Applications of Nanocrystalline Materials sponsored by the ASM International Nanotechnology Task Force and TMS Powder Materials Committee on October 18–20, 2004 in Columbus, OH.     

氢化脱氢法制备Nb-Ti基合金粉末

采用氢化-脱氢法制备了微细轻质Nb-Ti基合金粉末,并研究了吸氢/解吸行为。300℃时,氢吸收明显,400℃时吸氢量达到饱和值1.12%(质量分数)。氢化后形成二元和三元氢化物(Nb0.803V0.197H,Nb0.696V0.304H,TiHx)。由于氢致脆化效应,吸氢后的粉末破碎后得到细粒径的氢化粉末。在脱氢过程中,氢含量在300℃时有效降低至0.001%,实现了从铌或钛氢化物到单相固溶体合金(β相)的相转变。由于组分元素与氧反应活性高,粉末中氧含量随吸氢或脱氢温度的升高而增加。为了防止杂质氧的污染,氢化和脱氢温度都选择为400℃。实验最终得到了主要粒径小于10μm,氧含量为2980μg/g的微细Nb基合金粉末,且粉末表面的氧杂质主要以Nb2O5和TiO2的形式存在。     

Preparation ofAZ91 alloy by powder metallurgy method

Magnesium alloy AZ91 was prepared by powder metallurgy method, and the effect of sintering temperature on the densities and microstructures of the alloys was investigated. The results show that tight control of the sintering temperature within a narrow range around the liquidus level generates structures with high integrity and reduces some of the disadvantages caused by the higher temperatures. The matrix consists of α-Mg grains/cells surrounds by discontinuous precipitates of Mg17Al12 intermetallics which are normally located at the grain boundaries and triple junction.     

Mechanical properties and microstructures of magnesium alloy AZ31B joint fabricated by resistance spot welding with cover plates

Abstract

The authors welded magnesium alloy AZ31B sheets using the technique of resistance spot welding with cover plates, and investigated the effects of welding parameters on the tensile shear strength of joints and shape characteristic of nugget. The joints with high tensile shear strength were obtained under relatively low welding current. The equiaxed grains with the many intragranularly precipitated particles Mg₁₇Al₁₂ in the nugget were observed.     

新SIMA法制备AZ80合金半固态坯料的组织与性能(英文)

借助新应变诱导熔化激活方法制备AZ80合金半固态坯料。在新应变诱导熔化激活方法中,首先利用等通道角挤压对铸态AZ80镁合金进行预变形,然后将预变形的AZ80镁合金进行半固态等温处理。结果表明:利用等通道角挤压能够使AZ80合金获得很好的应变诱导效果。这是由于等通道角挤压能够使AZ80合金微观组织细化,力学性能提高。新应变诱导熔化激活方法能够制备晶粒细小且球化程度高的半固态坯料。利用新应变诱导熔化激活方法制备的半固态坯料触变锻造的零件具有高的力学性能,其屈服强度达到216.9MPa,抗拉强度达到312.4MPa,伸长率达到26%。触变成形实验结果也证明,新应变诱导熔化激活方法是一种非常理想的AZ80半固态坯料制备方法。