Jounng o Titanium Using Ag-Cu Alloy Thin Film Deposited on Bonding Surface with Ion Beam Sputtering.

Abstract

A novel bonding process, which is a kind of diffusion bonding with cleaning the bonding surface followed by deposition of Ag-28mass% Cu alloy thin layer using ion beam sputtering, was applied to joining of commercial pure titanium (CPTi) under atmospheric pressure. The deposition of the Ag-Cu layer after removing the oxide film of the bonding surface successfully improve bondability of CPTi. The joint strengths depend on the thickness of the Ag-Cu deposited layer. A maximum joint strength close to the base metal strength is obtained using the optimum thickness of Ag-Cu deposited layer, 0.3μm, under the conditions of a bonding temperature of 1153K and bonding time of 300s or more. The thicker Ag-Cu deposited layer of 1.0μm in thickness results in a hardened microstructure including Ti2 (Cu, Ag) intermetallic precipitates and thereby lower strength and lower ductility after bonding at 1153K for 1800s. The joint with the thinner Ag-Cu deposited layer of 0.1μm in thickness is not bonded at all.The Ag-Cu deposited layers having 0.3μm or more in thickness become enriched in Ag during heating in the bonding process because of a greater diffusion coefficient of Cu than that of Ag in titanium. As a result a almost pure Ag layer is formed on the bonding surface after heating above 973K. The bonding is, therefore, considered to proceed via solid state diffusion bonding between the surface layers enriched in Ag and be completed after homogenization of the solute elements of Ag and Cu.