The formation of intermetallics in dissimilar Ti6Al4V/copper/AISI 316 L electron beam and Nd:YAG laser joints I. Tomashchuk * , P. Sallamand, H. Andrzejewski, D. Grevey Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 5209 CNRS-Université de Bourgogne, 12 rue de la Fonderie, F-71200 Le Creusot, Saone et Loire, France article info Article history: Received 19 February 2010 Received in revised form 25 March 2011 Accepted 19 May 2011 Available online 13 July 2011 Keywords: A. multiphase intermetallics C. welding D. microstructure F. electron microscopy, scanning F. diffraction (X-ray) F. mechanical testing abstract The welds of titanium alloys with steels suffer from the brittleness of resulting intermetallic compounds. In present study, we report the feasibility of Ti6Al4V to stainless steel AISI 316L welding through pure copper interlayer carried out by electron beam and pulsed Nd:YAG laser. The nature and the localization of intermetallic phases in these welds have been studied by SEM, EDS, XRD and microhardness measurements. The simplified scenario of weld formation has been proposed in order to understand the mechanism of weld formation and to explain the way local phase content determines the mechanical properties. It can be concluded that the insertion of 500 mm pure copper interlayer allows reducing but not sup- pressing the formation of brittle TieFe and TieCr-based phases. The local accumulation of CueTi and CueFe eTi-based phases is less detrimental to the strength of the welds, which makes joining possible. The thickness of brittle regions is reduced due to short lifetime of the melt and compensated by the ductilizing effect of copper. The tensile strength of the welds is limited by brittleness of CuTi 2 þ FeTi þ a-Ti layer sit- uated next to the solid Ti6Al4V. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction The major metallurgical problem of joining titanium alloys with steels consists in formation of brittle intermetallic phases, which make impossible direct joining by conventional welding methods. According to FeeTi phase diagram [1], the solubility of Fe in a-Ti is very small (0.1 at.%), and when exceeded, the phases FeTi and then Fe 2 Ti (600 HV and >1000 HV respectively [2]) start to form. The presence of these phases increases the strength of the joint and decreases its plasticity. During fusion welding with steel, it’s impossible to maintain the melted zone in the ranges of the solu- bility of steel in titanium. Chemical inhomogeneity of melted zone often leads to local accumulation of brittle phases. Consequently, resulting welds are very brittle and do easily crack. The task is even more complex in case of joining of titanium and its alloys with austenitic steels. In this case, complex intermetallic compounds form between Ti, Fe, Cr and Ni which made the weld even more brittle [3]. Titanium demonstrates good weldability with very limited number of metals which do not form intermetallics with it: zirco- nium, niobium, molybdenum, tantalum, vanadium and hafnium. But high cost of these materials forced the using of more accessible metals (Ag, Cu, Ni etc.) and its alloys as potential interlayers between titanium and steel. As those materials form intermetallic phases with titanium, the strength of such welds depends on brittleness of Ti x M y (M e metal of interlayer) comparing with Ti x Fe y and of spatial distribution of intermetallics in the weld. The use of copper as an interlayer material for solid state joining of Ti alloys with steels has allowed improving mechanical resis- tance. It does not form intermetallic compounds with steel elements, has high ductility allowing the compensation of the difference in thermal expansion coefficients of base materials and has low price comparing with other usable interlayers (Ag, V, Nb etc). However, the mechanical resistance of such joints is limited by the brittleness of CueTi intermetallics. Kundu and Chatterjee [4] report the successful diffusion bonding of titanium with steel through copper interlayer. The strength of the joints was deter- mined by the content of diffusion interfaces between Ti and Cu, which contained various intermetallic phases (CuTi 2 , CuTi, Cu 3 Ti 2 , Cu 4 Ti 3 , FeTi, Fe 2 Ti, Cr 2 Ti, s 2 , s 3 and s 5 ). The maximum bond strength of w318 MPa was obtained for the couple bonded at 900  C. Further the rise of temperature induces the decrease in bond strength due to formation of brittle FeeTi based intermetallics. Lee et al. [5] report that the insert of copper interlayer during friction welding of TiAl to AISI 4140 structural steel has allowed increasing the tensile strength of the welds from 170 to 370 MPa. In this case the * Corresponding author. Tel.: þ33 3 85 73 10 56; fax: þ33 3 85 73 11 20. E-mail address: Iryna.Tomashchuk@u-bourgogne.fr (I. Tomashchuk). Contents lists available at ScienceDirect Intermetallics journal homepage: www.elsevier.com/locate/intermet 0966-9795/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.intermet.2011.05.016 Intermetallics 19 (2011) 1466e1473