DIFFUSION BONDING OF TiAl TO Ti AND TC4 ALLOY

TiAl was diffusion bonded to Ti and TC4 alloy in vacuum furnace. Results showed,at the TiAl-Ti interface,the reaction layer of stratification Ti3Al was formed closest to TiAl base,and the a phase and the α + βphase arised closest to Ti base at 1173K and 1573K respectively. The phase structure of TiAl/ and the phase structure of TiAlwere observed be- tween AiAl and TC4 under respetive bonding temperature.The fiacture at tensile testing occurred in the bond - line, producing very flat fracture surfaces with some pull-out of the TiAl materials.The ultimate tensile strengths of the joint were approximate to γ-TiAl base marterial.

Interface structure and formation mechanism of diffusion-bonded joints of TiAl-based alloy to titanium alloy

Vacuum diffusion bonding of a TiAl based alloy (TAD) to a titanium alloy (TC2) was carried out at 1 273 K for 15～120 min under a pressure of 25 MPa . The kinds of the reaction products and the interface structures of the joints were investigated by SEM, EPMA and XRD. Based on this, a formation mechanism of the interface structure was elucidated. Experimental and analytical results show that two reaction layers have formed during the diffusion bonding of TAD to TC2. One is Al rich α(Ti)layer adjacent to TC2,and the other is (Ti 3Al+TiAl)layer adjacent to TAD,thus the interface structure of the TAD/TC2 joints is TAD/(Ti 3Al+TiAl)/α(Ti)/TC2.This interface structure forms according to a three stage mechanism,namely(a)the occurrence of a single phase α(Ti)layer;(b)the occurrence of a duplex phase(Ti 3Al+TiAl)layer;and(c)the growth of the α(Ti)and (Ti 3Al+TiAl)layers.

Analysis of diffusion bond interface of TiAl base alloy with Ti, TC4 alloy and 40Cr steel

TiAl is diffusion bonded with Ti, TC4 Alloy and 40Cr Steel by heating in vacuum, and analysis of interfaces shows stratified Ti 3Al forms in TiAl/Ti interface closest to TiAl base, and the α phase and the α+β phase arise closest to Ti base at lower temperature and higher temperature respectively; Structure of TiAl/TC4 interface is TiAl/γ+α 2/Ti 3Al/α-Ti/TC4 at lower temperature and TiAl/γ+β+α 2/TC4 at high temperature; in TiAl/40Cr steel interface, obvious decarbonised layer on steel side while TiC and reaction phase with Fe Al Ti system form on TiAl side.

Diffusion Bonding of Dissimilar Intermetallic Alloys Based on Ti_2AlNb and TiAl

Direct diffusion bonding of an orthorhombic Ti2AlNb base alloy to a TiAl base alloy, Ti-22Al-23Nb-2Ta and Ti-46.2Al-2Cr-2Nb-0.15B （at. pct）, was carried out and the interface microstructure, formation of new phase at the interface and joint strength were characterized. At low temperature, a new phase with AlNb2-structure, Al（Nb, Ti）2, was formed in the interface region adjacent to the O base alloy. The α2 was found to be the major reaction product and developed in the interface region adjacent to the TiAl alloy as well as in the region adjacent to the O base alloy accompanying the formation of Al（Nb, Ti）2. The occurrence of Al（Nb, Ti）2 has been attributed to the different diffusivity of Nb and Al, leading to a eutectoid-like reaction. At relatively high temperature, Al（Nb, Ti）2 did not form due to enhanced diffusion of Nb but a B2-enriched zone formed on the O alloy side instead after long holding time. Only when an appropriate interface microstructure was achieved by optimizing the bonding parameters, could the shear strength of the joint reach 80% of that of the TiAl base alloy.

以Ti/V/Cu、V/Cu为中间层的TiAl合金与40Cr钢的扩散连接

用真空扩散连接方法对TiAl/Ti/V/Cu/4 0Cr钢及TiAl/V/Cu/4 0Cr钢进行了研究。结果表明 ,以Ti/V/Cu作中间层的接头拉伸强度高于以V/Cu作中间层的接头强度。界面分析显示 ,Ti/V、V/Cu、Cu/4 0Cr钢的各个结合界面处未形成金属间化合物 ,而TiAl/Ti的结合界面上有Ti3Al产生 ;在TiAl/V的界面上有Ti3Al、Al3V两种金属间化合物产生 ;界面上脆性金属间化合物的产生是接头发生断裂的原因。

TiAl/40Cr扩散连接接头的界面结构及相成长

在 1173～ 1373K、0 .3～ 5 .4ks的接合条件下对TiAl金属间化合物与 4 0Cr钢进行了真空扩散连接。采用扫描电镜 (SEM )、电子探针微区成分分析 (EPMA)、X射线衍射分析 (XRD)等方法确定了反应相的种类和界面结构。研究结果表明 ,在 1373K的接合温度下 ,TiAl/ 4 0Cr接头生成了TiC ,Ti3 Al,FeAl和FeAl2 4种反应相 ,形成了 3个反应层 ,界面结构为TiAl/Ti3 Al+FeAl+FeAl2 /TiC/脱碳层 / 4 0Cr钢。界面总反应层的厚度随接合温度和接合时间按抛物线方程成长 ,成长的活化能Q为 2 11.9kJ/mol,成长常数k0 为 4 .6× 10 -5m2 /s。当脆性反应层厚度为 3μm时 ,TiAl/ 4 0Cr钢接头的室温拉伸强度达到 183MPa的最大值。

S_3iN_4/Ni/TiAl扩散连接接头界面结构及性能

采用厚度为80μm的镍中间层实现了Si3N4陶瓷和TiAl合金的扩散连接.采用扫描电镜(SEM),能谱检测(EDS)等分析方法确定了TiAl/Ni/Si3N4扩散焊接头的典型界面结构为TiAl/Al5Ni2Ti3/AlNi2Ti/Ni3(Ti,Al)/Ni(s,s)+Ni3Si/Si3N4.重点分析了连接温度对接头界面结构及力学性能的影响规律.结果表明,随着温度的升高,TiAl/Ni界面处元素互扩散速率逐渐加快,导致各化合物层厚度增加.同时,Si3N4与镍的反应加快致使在Si3N4/Ni界面处出现孔洞;连接温度过高时,易在该孔洞区产生裂纹.当连接温度1 000℃,保温时间2 h时接头抗剪强度达到最大为104.2 MPa.压剪过程中,裂纹起裂于SiN/Ni界面处,随后向SiN侧扩展并最终断裂于陶瓷母材.

SiC/TiAl扩散连接接头的界面结构及连接强度

对常压烧结的 Ｓｉ Ｃ 陶瓷与 Ｔｉ Ａｌ 金属间化合 物进行了真空扩散连接。采用扫描电镜、电子探针和 Ｘ 射线衍射分析等手段确定了反应产物的种类和接头的界面结构，并用拉剪试验评价了接 头的连接强度。研究结果表明， Ｓｉ Ｃ 与 Ｔｉ Ａｌ 扩散连接中生 成了 Ｔｉ Ａｌ２ 、 Ｔｉ Ｃ 和 Ｔｉ５ Ｓｉ３ Ｃｘ 三种新相，接头的界 面结构为 Ｓｉ Ｃ／ Ｔｉ Ｃ／（ Ｔｉ Ｃ＋ Ｔｉ５ Ｓｉ３ Ｃｘ）／（ Ｔｉ Ａｌ２ ＋ Ｔｉ Ａｌ）／ Ｔｉ Ａｌ 。在１５７３ Ｋ 和１ ．８ ｋｓ 的连接条件下，接头室温剪切强度达到２４０ Ｍ Ｐａ ，高温（９７３ Ｋ） 剪切强度达到２３０ Ｍ Ｐａ 。

TiB_2金属陶瓷与TiAl金属间化合物的扩散连接

对TiB2 金属陶瓷与TiAl金属间化合物进行了扩散连接试验 ,研究了直接扩散连接和采用Ni为中间层进行扩散连接的接头界面结构及工艺参数对界面结构和连接性能的影响。直接扩散连接时 ,连接界面处生成了Ti(Cu ,Al) 2 金属间化合物 ,采用Ni为中间层进行扩散连接时 ,界面处生成了单层TiAlNi2 金属间化合物层和两层Ti,Al,Ni扩散层共三层结构。直接扩散连接时 ,连接温度T =12 2 3K ,时间t=1.8ks,压力p =80MPa时接头强度为 10 3MPa ;采用Ni为中间层时 ,连接温度T =12 73K ,时间t=1.8ks,压力p =80MPa时接头强度为 110MPa。

Microstructure evolution and diffusion mechanism of Nb/TiAl alloy diffusion-bonded joints

The interdiffusion behavior in Nb/TiAl alloy diffusion couples was studied.The process was carried out in the temperature range of 950-1400℃for 8 h in the vacuum hot-pressure sintering furnace.The microstructural evolution was observed by optical microscopy(OM),electron backscattered diffraction(EBSD),X-ray diffraction(XRD)technique and transmission electron microscopy(TEM).The element concentration distribution at the bonded interface was obtained by scanning electron microscopy with an energy-dispersive X-ray spectroscopy(EDS)apparatus.The thickness of reaction interface increases with bonding temperature increasing.The formed phases in diffusion interface are found to be O-Ti_(2)AlNb,σ-Nb_(2)Al,δ-Nb_(3)Al and Nb solid solution(Nbss)at 1350℃.The average interdiffusion coefficient of the interface elements was calculated by the theory of Dayananda.The results indicate that Al diffuses faster than Nb and Nb diffuses faster than Ti in the Ti-Al-Nb system.Meanwhile,it is found that Ti promotes the diffusion of Al and Nb and Nb inhibits the diffusion of Ti and Al in the process of diffusion.