Shear Strength of Reactive Resistance Welded Ti6Al4V Parts with the Use of Ni(V)/Al Multilayers
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RODUCTION
WELDING of titanium-based alloys, like a Ti6Al4V, poses a significant challenge due to a high affinity of titanium for oxygen as well as its high melting temperature. The former may be overcome by applying an argon protective atmosphere, while the latter by a local heating with an electron or a laser beam.[1] The strength of obtained joint is therefore compromised not only by a coarse grain present in melted and solidified material, but also by a large heat-affected zone softened by recovery processes. On the other hand, diffusion brazing process is most frequently performed at temperature below the a fi b transition at ~ 1000 C.[2] However, it requires relatively long processing times necessary to activate the solid-state diffusion across the interface between filler material and base material.[3] Therefore, new alternative techniques of joining titanium alloys are still sought. Reactive metallic multilayer foils, releasing a large amount of heat during self-propagating high-temperature synthesis (SHS), open new possibilities in joining materials. Initiated by an external energy pulse, they
ŁUKASZ MAJ, JERZY MORGIEL, and ANNA TARASEK are with the Institute of Metallurgy and Materials Science, Polish Academy of Sciences, 25 Reymonta St., 30-059 Krako´w, Poland. Contact e-mail: [email protected] KRZYSZTOF MARS and _ ELZBIETA GODLEWSKA are with the Faculty of Materials Science and Ceramics, AGH University of Science and Technology, 30-059 Krako´w, Poland. Manuscript submitted February 23, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
produce fast local temperature raise (even up to 1500 C for the Ni(V)/Al system[4]) and results in the melting of at least one of reactants. However, the heat released at fast moving SHS front is insufficient to melt surfaces to be joined. Up till now, obtaining a firm connection with the use of reactive multilayers has been possible only either through deposition of an additional braze alloy coating[5] or by supporting the heat pulse produced during SHS reaction in other ways.[6] The approach taking advantage of braze alloy good wetting properties has been already applied by commercializing NanoFoil product. It consists of freestanding Ni(V)/Al multilayer foil covered with IncusilTM (Ag-Cu-In-Ti) alloy Ignited Ni(V)/Al multilayer releases enough heat to melt the Ag-Cu-In-Ti layer, securing good wetting of pieces of titanium alloy. It was reported that such a joint can be obtained in a very short time, but its shear strength barely reaches ~ 40 MPa.[5] The other way is realized by passing strong electric currents through elements to be joined with multilayers, what helps to attain high-temperature activating diffusion processes necessary for good connection. Therefore, this joining process is called a ‘reactive resistance welding’ (RRW). Although not fully worked out as yet, theoretically it should secure not only fast but also much stronger connection, compared with the brazing technique. The RRW method was originally applied to join elements made of refractory metals, including tungst
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