Infrared brazing Ti–6Al–4V and Mo using the Ti–15Cu–15Ni braze alloy C.T. Chang a, * , R.K. Shiue b a Department of Materials Science and Engineering, National Dong Hwa University, Hualien 974, Taiwan b Department of Materials Science and Engineering, National Taiwan University, Taipei 106, Taiwan Received 1 November 2004; accepted 10 January 2005 Abstract Brazing Ti–6Al–4V and Mo using the Ti–15Cu–15Ni alloy has been extensively evaluated in the study. Both infrared and con- ventional furnace brazing are included in the experiment. Ti–15Cu–15Ni braze alloy demonstrates excellent wettability on Ti–6Al– 4V at 970 °C. In contrast, the wettability of the molten braze on the Mo substrate is significantly improved for the test temperature above 1000 °C. The brazed specimen is primarily comprised of the Ti-rich phase, and there is no interfacial reaction layer observed in the joint. Most of the brazed joints are fractured at the Mo substrate except for the joint infrared brazed at 970 °C for 180 s. For the specimen infrared brazed at 970 °C for 180 s demonstrates the average shear strength of 251 MPa, and quasi-cleavage fracture with sliding marks on facets is widely observed in the fractured surface. ABAQUS Ò stress simulations are also performed in order to illustrate the effect of residual stresses in the brazed joint during shear test. Based on the simulated result, there are two possible fracture locations in the brazed joint due to the presence of high Mises stresses, i.e., the braze alloy and Mo substrate. Additionally, the inherent low strength of the Mo substrate results in premature failure of the brazed joint during shear test for most brazed specimens. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Infrared brazing; Molybdenum; Ti–6Al–4V; Ti–15Cu–15Ni; Microstructure; Residual stresses; Shear test 1. Introduction The titanium alloy has been used as the structural material since 1952 [1]. For the titanium alloy, V is typ- ically added since it is an isomorphous b stabilizer. In contrast, the solubility of Al in Ti plays a crucial role of a stabilizer [2,3]. Accordingly, Ti–6Al–4V belongs to a type of a–b titanium alloys, which can be strength- ened by various solution and aging treatments. The equilibrium of a single b phase is stable at high temper- atures, and the a phase is transformed from the b phase at lower temperatures. With the proper heat treatment, the equilibrium phases for a wide composition range of a–b titanium alloys are mixture of a-Ti and b-Ti. Ti–6Al–4V has a large number of applications in the aerospace industry, mainly due to its superior strength to weight ratio [1]. Additionally, excellent corrosion resistance, good weldability, excellent elevated-tempera- ture mechanical properties greatly promote applications of the Ti–6Al–4V alloy. It is by far the most important and widely used titanium alloy, accounting for about 60% of the titanium market [1]. The molybdenum metal belongs to refractory metals with the high melting point of 2610 °C [1]. Molybdenum has been used in the nuclear, chemical and defense industries [4]. However, mechanical properties of most refractory metals are greatly affected by their ductile- to-brittle transition behavior [1,4]. For example, the molybdenum is brittle at room temperature, and it must be brazed in a stress-free condition. The recrystallization temperature range of the unalloyed Mo is between 1150 0263-4368/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijrmhm.2005.01.002 * Corresponding author. Tel.: +886 3 8634209; fax: +886 3 8634200. E-mail address: jct1028@ms41.hinet.net (C.T. Chang). International Journal of Refractory Metals & Hard Materials 23 (2005) 161–170 www.elsevier.com/locate/ijrmhm