Cold rolled versus sputtered Ni/Ti multilayers for reaction-assisted diffusion bonding

Abstract

Reaction-assisted diffusion bonding of TiNi to Ti6Al4V was carried out using two types of filler materials: (i) Ni/Ti multilayer foils produced by accumulative roll bonding (ARB) and (ii) Ni/Ti multilayer thin films prepared by magnetron sputtering. In ARB, nanostructures were produced through severe plastic deformation by stacking alternated Ni and Ti foils and rolling at a strain rate of 20 s−1 up to 16 cycles, attaining a total thickness close to 300 μm. Using ARB Ni/Ti ultrafine multilayers, it was possible to achieve sound joints at undemanding conditions for a solid-state joining process (800 °C/10 MPa/60 min), with a shear strength of 35 MPa. The layered structure of the foil transforms into TiNi with small regions of Ti2Ni and TiNi3; a continuous layer of Ti2Ni is observed close to the Ti6Al4V base material. Ni/Ti multilayer thin films with nanometric modulation periods have also been successfully used to produce sound joints at 750 and 800 °C, under 10 or 50 MPa during 60 min, with a shear strength of 88 MPa. The interface is very thin (less than 10 μm) and exhibits several zones; comprising a Ti2Ni layer close to the Ti6Al4V alloy, followed by TiNi and Ti2Ni phases.