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 %。     

含金属间化合物的Al基合金半固态加压连接Si3N4陶瓷

用含金属间化合物Al3Ti或Al3Zr的Al基合金作连接材料,研究了半固态加压连接Si3N4陶瓷时接头的形成,以及Al基合金种类和连接压力对接头组织与强度的影响。结果表明:半固态连接可获得性能良好的陶瓷接头;连接过程中加压能提高连接层金属中耐高温金属间化合物的含量,达到提高接头高温性能的目的;连接压力适当时,接头在室温和600℃下的剪切强度可分别达到126～136MPa和32～34MPa,明显比用纯Al连接的接头强度高;在结合界面形成过程中,第二活性元素Ti和Zr也参与了界面反应。     

AgCu28对Be/HR-1不锈钢热静压接头组织性能的影响

以AgCu28合金作为中间层材料,进行Be/HR—I不锈钢热静压扩散连接。利用光学金相、扫描电镜(SEM)、俄歇电子能谱(AES)和X射线衍射仪(XRD)及材料试验机分析了热静压扩散连接接头的显微组织、元素和物相分布以及力学性能,探讨了扩散区成分、组织结构与性能的关系,以及AgCu28合金作为中间层材料的作用。研究表明:采用AgCu28合金作为中间层材料,能够实现Be/HR—I不锈钢的扩散连接,能有效地减少铍、不锈钢间的元素互扩散,减少了Be与Fe和不锈钢中其他合金元素的脆性金属间化合物的大量生成,接头质量较好。     

Al膜和衬底Ti间的反应和互扩散

本文研究了厚度为1.25μm Al 膜与 Ti 衬底间在580～800℃反应时,金属间化合物TiAl 及 Ti_3Al 的生长规律,并用 Boltzmonn—Matano—Heuman 和 Wagner 方程计算了Al 在化合物中的互扩散系数及扩散激活能,找出了扩散系数随温度和时间的变化规律.Al 在TiAl 及 Ti_3Al 中的扩散激活能 Q_r 及 Q_a,分别为0.73+0.1eV 和 0.59+0.1eV.     

扩散连接Al/Ni/0Cr18Ni9Ti复合材料的界面组织

选取纯Ni箔作过渡层,采用真空热压扩散工艺,在加热温度480℃、压力10 MPa、真空度1.0×10-2Pa的工艺条件下,制备了变形铝合金2024和不锈钢0Cr18Ni9Ti双金属复合材料.利用扫描电子显微镜、能谱仪、X射线衍射仪和显微硬度仪等测试分析方法,对双金属复合材料的2个连接界面及基体进行了组织、性能分析.结果表明:不锈钢/纯Ni界面形成了宽约8μm的互扩散区,但其过渡区无金属间化合物生成;Al/Ni界面生成了宽约4μm的扩散过渡区,过渡区的相组成为金属间化合物Al3Ni2、Al3Ni及Al3Ni5.     

Be/Cu/HR-1不锈钢扩散连接界面特性

以Cu为中间层材料,采用Greeble1500热模拟试验机对Be/HR-1不锈钢进行扩散连接试验,利用PME Olympus Tokyo光学显微镜、扫描电镜(SEM)、显微硬度计(HV-1000)、X射线衍射仪研究分析了其界面特性.研究表明,Cu层过渡材料能有效阻碍Be和Fe之间的互扩散以及阻挡不锈钢中合金元素Ni、Cr等向铍基体的扩散,从而阻碍了它们之间金属间化合物在扩散区内的形成,但它也带来了新的金属间化合物如Be2Cu;金属间化合物优先沿晶界生成,呈三维网状分布;元素的扩散主要沿晶界进行,且扩散不是各个部位均等的向前推进,也没有单一的金属间化合物薄层形成;试样的断裂位置在Be/Cu界面处.     

三元合金及金属间化合物中各组分活度系数的计算

根据Kohler三元溶体模型和Miedema二元系统生成热模型，建立了计算三元合金及金属化合物中各组分活度系数的方程。计算了三元合金Ti-5Al-2.5Sn,Ti-6Al-4V及不同温度下金属间化合物TiAl,Ti3Al和Ti2AlNb中各组分的活度系数。并与有关实验值进行了对比.计算结果表明此公式的计算结果与实验值吻合较好，解决了固态二元、三元合金及金属间化合物中各组分的活度系数的计算问题，Ti与A1活度系数均小于1，对Raoultl定律产生负偏差。根据所计算的活度系数和活度值，预测了SiC/TiAl,SiC/Ti3Al和SiC/Ti2AlNb复合材料的界面反应，表明SiC/Ti3Al界面反应较为严重。     

表面纳米化0Cr18Ni9Ti/TA17加镍中间层扩散连接

采用高能喷丸(HESP)对TA17钛合金与0Cr18Ni9Ti不锈钢棒材端面表面进行自纳米化(SSNC)处理;采用镍箔作为中间层,在不同温度(800～875℃)下对处理后的钛合金／不锈钢进行脉冲加压扩散连接(PPDB).对接头剖面组织进行金相观察;在拉伸试验机上测试接头拉伸强度,对断面进行SEM,EDS和XRD结构物相分析.研究结果表明:在850℃时接头拉伸强度达到最高,为322.8 MPa;连接后接头界面处纳米晶粒没有完全长大,存在细晶粒区;镍箔有效地阻止了Fe-Ti脆性金属间化合物的形成,在接头处形成β-Ti,(Fe,Ni)固溶体和Ti-Ni金属间化合物(Ti2Ni,TiNi,TiNi3);断裂发生在Ni层与Ti-Ni金属间化合物界面处.     

Mn含量对铸造高铌TiAl合金组织和性能的影响

选择两种Mn含量不同的高铌TiAl合金Ti46Al8Nb2Mn0.2B和Ti46Al8Nb1.3Mn0.2B,通过热等静压(HIP)及后续热处理,结合组织和力学性能的分析,研究了Mn含量对高铌TiAl合金的组织和性能的影响.XRD和SEM背散射电子实验结果表明:Mn含量较高的Ti46Al8Nb2Mn0.2B合金,经热等静压及循环热处理,得到的双态组织较粗大,并且有少量脆性β相存在;Mn含量较低的Ti46Al8Nb1.3Mn0.2B合金,经热等静压后直接在双相区长时间保温处理,得到了细小的双态组织,并且完全消除了β相.室温拉伸实验表明,Mn含量的降低提高了Ti46Al8Nb1.3Mn0.2B合金的力学性能,其延伸率、屈服强度和断裂强度分别达到2.4%、548MPa和660MPa.断口形貌分析表明,室温下两种合金都属于解理断裂.     

Mg/Al异种材料瞬间液相过冷连接工艺研究

采用瞬间液相过冷连接工艺对AZ31镁合金和5083铝合金进行连接实验,研究保温扩散时间t2对焊缝微观组织及力学性能的影响。利用SEM,EDS,XRD和微观硬度计对接头剖面的微观组织和力学性能进行表征;在拉伸试验机上测试接头拉伸强度,利用SEM对断口形貌进行分析。研究结果表明:采用瞬间液相过冷连接工艺可以实现Mg/Al异种材料的有效连接;随着保温扩散时间t2的增加,接头的抗拉强度随之提高,当t2=30 min时,接头抗拉强度最高达到20.5 MPa;拉伸断口形貌具有明显的脆性断裂的特征,铝合金侧主要有解理面和撕裂棱组成,而镁合金侧属于典型的沿晶断裂形貌;在接头处形成MgAl,Mg2Al3,Mg0.44Al0.56和Mg17Al12金属间化合物,结合界面的微观维氏硬度最高达320。     

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℃. X-ray diffraction, transmission electron microscopy, and thermodynamic analyses showed that the interface mainly contained intermetallic compound TiAl₃ 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/TiAl₃ and TiAl₃/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.     

基于原位合金化的SiCp/Al复合材料等离子弧焊接

为了抑制SiCp/Al基复合材料在焊接过程中的界面反应,补充烧损元素,同时原位产生新的增强颗粒,分别以Al-Ti-Si和Al-Ti-Mg两种药芯焊丝作为填充材料,向熔池中直接添加Al,Si,Ti和Mg等金属元素,用氩氮混合等离子气对SiCp/Al基复合材料进行等离子弧原位焊接.对比分析了两种药芯材料对焊缝组织和性能的影响.结果表明:以两种药芯焊丝作为原位反应填充材料进行等离子弧原位焊接时,均可以有效抑制针状脆生相Al4C3的生成,形成了稳定熔池,得到了以TiC,TiN,AlN,Ti5 Si3,MgAl2O4和细小棒状的Al3Ti等新生增强相的焊缝;焊缝组织致密结合良好,最大抗拉强度分别为232和196 MPa.     

钢/铝回填式搅拌摩擦点焊接头界面形貌和组织研究

采用回填式搅拌摩擦点焊实现了钢和铝合金板的连接。利用光学显微镜、扫描电子显微镜和电子探针X射线显微分析仪等设备观察了钢/铝点焊接头的界面形貌,并分析了钢/铝点焊接头的力学性能与界面形貌的关联机制。结果显示,钢/铝点焊接头的断裂类型为钮扣断裂,力学性能较好。钢/铝点焊接头结合良好,未见明显的焊接缺陷。在钢/铝点焊接头界面处可以观察到钩状结构和漩涡结构,这些结构提供机械互锁效果,有利于母材的结合。钢/铝点焊接头界面处形成了主要元素为Al、Fe和Si的金属间化合物层。有效的冶金结合和机械结合是钢/铝点焊接头性能良好的主要原因。     

Microstructural characterization of Cu/Al composites and effect of cooling rate at the Cu/Al interfacial region

Cu/Al composites are of vital importance in industrial applications because of their numerous advantages. The influence of bonding temperature and cooling rate on the microstructure and morphology of Cu/Al composites was investigated in this paper. The interfacial morphology and constituent phases at the Cu/Al interface were analyzed by optical microscopy and field-emission scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy. The results indicate that effective Cu-Al bonding requires a higher bonding temperature to facilitate interdiffusion between the two metals. The microstructural characteristics are associated with various bonding temperatures, which impact the driving force of interdiffusion. It is observed that cooling rate exerts a significant influence on the morphology and amount of the intermetallic compounds at the interfacial region. Meanwhile, microhardness measurements show that hardness varies with the bonding temperature and rate of cooling.     

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.     

Interface microstructure and formation mechanism of ultrasonic spot welding for Al–Ti dissimilar metals

The present study focuses on interface microstructure and joint formation. AA6061 aluminum alloy (Al) and commercial pure ti-tanium (Ti) joints were welded by ultrasonic spot welding (USW). The welding energy was 1100–3200 J. The Al–Ti joint appearance and in-terface microstructure were observed mainly via optical microscopy and field emission scanning electron microscopy. Results indicated that a good joint can be achieved only with proper welding energy of 2150 J. No significant intermetallic compound (IMC) was found under all con-ditions. The high energy barriers of Al–Ti and difficulties in diffusion were the main reasons for the absence of IMC according to kinetic ana-lysis. The heat input is crucial for the material plastic flow and bonding area, which plays an important role in the joint formation.     

Reinforcing effect of laminate structure on the fracture toughness of Al_3Ti intermetallic

Metal/intermetallic laminate composites can improve the mechanical properties of intermetallic materials using metal layers. In recent years, titanium aluminide intermetallics have received increasing attention due to their excellent performance properties, such as high melting point, high specific strength and stiffness, and good corrosion resistance. However, the low fracture toughness of Al_3Ti alloys at room temperature has greatly limited their application, and fiber or particle reinforcement has not shown a significant toughening effect. Research into the reinforcing effects of the interface and near-interface zone on the fracture behavior of Al_3Ti is lacking. Ti/Al_3Ti metal/intermetallic laminate composite was synthesized from titanium and aluminum foils using vacuum hot-pressed sintering technology. The microstructure of the prepared material was analyzed by scanning electron microscope and electron backscattered diffraction. Results illustrate that both Ti and Al_3Ti were single-phase and there was a noticeable stress concentration on the interface. To obtain indentation and cracks, loads were applied to different locations of the composite by a microhardness tester. The growth path of the cracks was then observed under microscope, showing that crack propagation was prevented by the interface between the Ti and Al_3Ti layers, and the cracks that propagated parallel to the laminate shifted to the interface. Fracture toughness of the different areas, including Al_3Ti layers, interface, and near-interface zone, were measured by the indentation fracture method. The fracture toughness at and near the interface was 1.7 and 2 times that of the Al_3Ti layers, respectively. Results indicate that crack blunting and crack front convolution by the laminate structure was primarily responsible for increased toughness.     

Effect of preheat on TIG welding of AZ61 magnesium alloy

The effects of preheat treatments on the microstructures and mechanical properties of tungsten inert gas (TIG)-welded AZ61 magnesium alloy joints were studied by microstructural observations, microhardness tests and tensile tests. The results showed that the volume fraction of the lamellar β-Mg₁₇(Al,Zn)₁₂ intermetallic compound of in fusion zone (FZ) increased from 15% to 66% with an increase in preheat temperature. Moreover, the microhardness of the FZ and the ultimate tensile strength of the welded joints reached their maximum values when the preheat temperature was 300℃ because more lamellar β-Mg₁₇(Al,Zn)₁₂ intermetallic compounds were distributed at the α-Mg grain boundaries and no cracks and pores formed in the FZ of the welded joint.