Microstructure and mechanical properties of a hot-extruded Al-based composite reinforced with core-shell-structured Ti/Al3Ti

An Al-based composite reinforced with core-shell-structured Ti/Al₃Ti was fabricated through a powder metallurgy route followed by hot extrusion and was found to exhibit promising mechanical properties. The ultimate tensile strength and elongation of the composite sintered at 620℃ for 5h and extruded at a mass ratio of 12.75:1 reached 304 MPa and 14%, respectively, and its compressive deformation reached 60%. The promising mechanical properties are due to the core-shell-structured reinforcement, which is mainly composed of Al₃Ti and Ti and is bonded strongly with the Al matrix, and to the reduced crack sensitivity of Al₃Ti. The refined grains after hot extrusion also contribute to the mechanical properties of this composite. The mechanical properties might be further improved through regulating the relative thickness of Al-Ti intermetallics and Ti metal layers by adjusting the sintering time and the subsequent extrusion process.     

Effects of gadolinium addition on the microstructure and mechanical properties of Mg-9Al alloy

This research aims to study the significance of Gd addition (0wt%-2wt%) on the microstructure and mechanical properties of Mg-9Al alloy. The effect of Gd addition on the microstructure was investigated via X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The Mg-9Al alloy contained two phases, α-Mg and β-Mg17Al12. Alloying with Gd led to the emergence of a new rectangular-shaped phase, Al₂Gd. The grain size also decreased marginally upon Gd addition. The ultimate tensile strength and microhardness of Mg-9Al alloy increased by 23% and 19%, respectively, upon 1.5wt% Gd addition. We observed that, although Mg-9Al-2.0Gd alloy exhibited the smallest grain size (181 μm) and the highest dislocation density (5.1×1010 m-2) among the investigated compositions, the Mg-9Al-1.5Gd alloy displayed the best mechanical properties. This anomalous behavior was observed because the Al₂Gd phase was uniformly distributed and present in abundance in Mg-9Al-1.5Gd alloy, whereas it was coarsened and asymmetrically conglomerated in Mg-9Al-2.0Gd.     

Microwave sintering effects on the microstructure and mechanical properties of Ti-51at%Ni shape memory alloys

Ti-51at%Ni shape memory alloys (SMAs) were successfully produced via a powder metallurgy and microwave sintering technique. The influence of sintering parameters on porosity reduction, microstructure, phase transformation temperatures, and mechanical properties were investigated by optical microscopy, field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), compression tests, and microhardness tests. Varying the microwave temperature and holding time was found to strongly affect the density of porosity, presence of precipitates, transformation temperatures, and mechanical properties. The lowest density and smallest pore size were observed in the Ti-51at%Ni samples sintered at 900℃ for 5 min or at 900℃ for 30 min. The predominant martensite phases of β2 and β19' were observed in the microstructure of Ti-51at%Ni, and their existence varied in accordance with the sintering temperature and the holding time. In the DSC thermograms, multi-transformation peaks were observed during heating, whereas a single peak was observed during cooling; these peaks correspond to the presence of the β2, R, and β19' phases. The maximum strength and strain among the Ti-51at%Ni SMAs were 1376 MPa and 29%, respectively, for the sample sintered at 900℃ for 30 min because of this sample's minimal porosity.     

Microstructure s and mechanical properties of Ti3Al/Ni-based superalloy joints arc welded with Ti –Nb and Ti– Ni – Nb filler alloys

Dissimilar joining of Ti3Al-based alloy to Ni-based superalloy has been carried out using gas tungsten arc(GTA) welding technology with Ti–Nb and Ti–Ni–Nb filler alloys.The joint welded with the Ti–Nb filler alloy contained much less interfacial brittle phases than the one using the Ti–Ni–Nb filler alloy.The average room-temperature tensile strength of the joint welded with Ti–Nb was 202 MPa and the strength value of the one welded with Ti–Ni–Nb was 128 MPa.For both fillers,the weak links of the dissimilar joints were the weld/In718 interfaces.The presence of TiNi,TiNi3 and Ni3Nb intermetallic compounds in the joint welded with Ti–Ni–Nb induced microcracks at the weld/In718 interface and deteriorated the mechanical properties of the joint.And the adoption of the Ti–Nb filler alloy decreased the formation tendency of interfacial brittle phases to some extent and thus enhanced the tensile strength of the joint.     

Interfacial microstructure and mechanical properties of Ti-6Al-4V/Al7050 joints fabricated using the insert molding method

Ti-6Al-4V/Al7050 joints were fabricated by a method of insert molding and corresponding interfacial microstructure and mechanical properties were investigated. The interfacial thickness was sensitive to holding temperature during the first stage, and a good metallurgical bonding interface with a thickness of about 90 μm can be obtained at 750°C. X-ray diffraction, transmission electron microscopy, and thermodynamic analyses showed that the interface mainly contained intermetallic compound TiAl_3 and Al matrix. The joints featured good mechanical properties, i.e., shear strength of 154 MPa, tensile strength of 215 MPa, and compressive strength of 283 MPa, which are superior to those of joints fabricated by other methods. Coherent boundaries between Al/TiAl_3 and TiAl_3/Ti were confirmed to contribute to outstanding interfacial mechanical properties and also explained constant fracture occurrence in the Al matrix. Follow-up studies should focus on improving mechanical properties of the Al matrix by deformation and heat treatment.     

Microstructure and mechanical properties of a hot-extruded Al-based composite reinforced with core-shell-structured Ti/Al3Ti

An Al-based composite reinforced with core-shell-structured Ti/Al3Ti was fabricated through a powder metallurgy route followed by hot extrusion and was found to exhibit promising mechanical properties. The ultimate tensile strength and elongation of the composite sintered at 620°C for 5 h and extruded at a mass ratio of 12.75:1 reached 304 MPa and 14%, respectively, and its compressive deformation reached 60%. The promising mechanical properties are due to the core-shell-structured reinforcement, which is mainly composed of Al3Ti and Ti and is bonded strongly with the Al matrix, and to the reduced crack sensitivity of Al3Ti. The refined grains after hot extrusion also contribute to the mechanical properties of this composite. The mechanical properties might be further improved through regulating the rela-tive thickness of Al-Ti intermetallics and Ti metal layers by adjusting the sintering time and the subsequent extrusion process.     

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.     

HA/YSZ/Ti6Al4V生物复合材料的制备与界面特性

采用磁控溅射法制备出HA／YSZ／Ti6Al4V生物复合材料,利用X-射线衍射仪（XRD）、扫描电镜（SEM）和能谱分析（EDXA）研究复合涂层的相组成、表面微观形貌和界面微观形貌,并用划痕仪测定复合涂层与基体的界面结合力．结果表明：溅射的复合涂层中主要含有HA、ZrO2和Y2O3物相,此外还有少量的TCP和CaO相;该复合涂层表面凹凸不平,呈现网状微孔结构,其孔隙直径约为0．5～2μm,孔隙面积占薄膜表面积的30％～40％．划痕试验表明,复合涂层与Ti6Al4V基体结合力约为80N．复合涂层拉伸试样横断面分析显示,在涂层与基体界面处无裂纹,界面处存在Ti6Al4V基体成分Ti与复合涂层成分Ca、P问互扩散的扩散层,该扩散层厚度为0．5～1．5μm,复合涂层界面的结合机制为机械齿合和扩散结合．     

Ti6Al4V和Al2A12的扩散连接界面组织及力学性能

采用热等静压(HIP)工艺连接Al2A12和Ti6Al4V两种不同的航空航天用材料.利用扫描电镜、能谱仪和X射线衍射仪观察连接过渡区的微观组织和组成的演化,并测试其主要的力学性能.结果表明:采用热等静压制备这两种材料的界面连接好;Ti/Al反应层界面处形成了不同的金属间化合物,例如,Al3Ti、TiAl2和TiAl;连接接头处硬度为163HV,界面连接处剪切强度达到了23MPa,比只添加镀层而无中间层的连接强度提高了约17.9%,但低于带有中间层的连接强度.由于过烧和孔隙的形成使得断裂方式是脆性断裂.由此可知,在热等静压成形过程中异种材料的元素发生了相互扩散,在扩散连接处形成了不同的金属间化合物,这些金属间化合物影响连接处的力学性能.     

Nb对Ti/Al_2O_3复合材料力学性能的影响

研究了热压烧结条件下Nb元素对Ti/ [φ(Al2 O3 ) =80 % ]复合材料相对密度、抗弯强度、断裂韧性及维氏硬度等力学性能的影响 ,分析了其影响机理。结果表明 ,在Ti/ [φ(Al2 O3 ) =80 % ]的Al2 O3 复合材料中掺入Nb元素 ,材料的微观组织形貌得以细化 ,性能有了较大提高。随Nb掺量的增加 ,材料的相对密度、维氏硬度与抗弯强度先增大后减小 ,当掺量为 φ =1.5 %时 ,其相对密度、抗弯强度、维氏硬度达到最高 ,分别为 98.13%、5 0 1.0 6MPa和 2 0 .31GPa ,断裂韧性随Nb掺量的增加而增大 ,当掺量为 φ =2 %时 ,其断裂韧性为5 .2 4MPa·m1/ 2 。     

铝热反应制备YAG/Al2O3复相陶瓷的组织和性能

利用铝热反应熔化法制备YAG/Al2O3复相陶瓷材料,研究配料中Y2O3含量对复相陶瓷显微组织和力学性能的影响.结果表明:复相陶瓷的相组成为YAG和Al2O3,合有少量的Fe相.随着Y2O3含量的增大,Al2O3颗粒分布越均匀,复相陶瓷的维氏硬度先减小后增加,而相对密度是增加的,在x=0.90时达到最大值分别10.9 ...     

Nb对Ti/Al2O3界面微观结构与显微硬度的影响

在放电等离子烧结 (SPS)工艺条件下 ,运用SEM、XRD、EDX等测试手段对 12 0 0℃高温处理后的Ti Al2 O3复合材料界面反应区的显微结构及外加金属Nb对其界面特性的影响进行了研究。结果表明 ,不掺加金属Nb时界面反应产物为Ti3Al、TiAl,掺加金属Nb后界面生成TiAl和AlNb2 化合物 ;界面处生成的AlNb2 能有效的阻止Al、O原子向金属Ti中扩散 ,使Ti Al2 O3材料界面反应得到抑制 ,扩散层厚度减少到 5 μm以下 ;Nb的加入使界面扩散区的显微维氏硬度提高近 5 0 % ,金属Ti侧的显微维氏硬度提高 6 0～ 80 %。     

焊接电流对镁/镀锌钢 TIG熔--钎焊接头显微组织与力学性能的影响

采用TIG熔-钎焊焊接方法,以镁合金焊丝为填充材料,对镁合金与镀锌钢进行连接实验,并分析热输入量对接头显微组织和力学性能的影响.热输入量过小会阻碍镁/钢界面反应层的形成而使得焊缝难以焊合,热输入量过大又会促进焊缝内部脆性第二相的长大,降低接头力学性能.接头强度随着焊接电流和焊接速度的增大都呈现先上升后下降的趋势,电流为70 A时强度达到最大,该值接近AZ31B母材的88．7%.此时断裂发生于焊缝熔焊区,断面出现大量韧窝和撕裂棱,呈现出塑性断裂特征.     

Ni/Ti原子数比值对NiTiAlHf合金微观组织和力学性能的影响

采用扫描电镜、室温和高温压缩实验等方法研究了Ni/Ti值对Ni42+xTi50-xAl4Hf4(x=0～7)合金的微观组织和力学性能的影响.Ni42+xTi50-xAl4Hf4合金由NiTi基体和Ti2Ni相组成,随着Ni/Ti原子数比值的增加,Ti2Ni相的尺寸和数量急剧减少,析出强化效果减弱.室温时,随着Ni/Ti值的增加,NiTiAlHf合金的压缩屈服强度和显微硬度逐渐降低,塑性提高.高温下,当Ni/Ti<1时,Ti2Ni相的析出强化起主要作用,合金的屈服强度随Ni/Ti值增加而降低;当Ni/Ti>1时,Hf固溶强化作用的影响提高,并且Ti2Ni相趋于均匀弥散分布,使合金的屈服强度随Ni/Ti值增加而升高.在化学计量比(Ni/Ti=1)两侧,合金的屈服强度变化不对称.