Infrared brazing Ti50Ni50 and Ti-6Al-4V using the BAg-8 braze alloy

Abstract

Microstructure evolution, reaction path and shear strength of infrared brazed Ti50Ni50 shape memory alloy and Ti-6Al-4V joints using BAg-8 braze alloy have been investigated. The braze alloy can readily wet on Ti-6Al-4V, but not on Ti50Ni50. Titanium dissolves from Ti-6Al-4V to enhance the wettability of braze alloy on Ti50Ni 50 during brazing. The joint is mainly comprised of hypoeutectic silver and copper for specimens infrared brazed below 850°C. Silver does not react with both substrates, but copper is readily alloyed with titanium and reacts vigorously to form TiCu4, Ti3Cu4, TiCu and Ti2Cu phases in Ti-6Al-4V side and form CuNiTi phase in Ti 50Ni50 side. The dramatic microstructure change of joint is observed for specimens infrared brazed at 900°C above 60s due to the extensive Ti2Ni presence. The average shear strength of the specimens infrared brazed below 850°C is about 200 MPa. Although the presence of interfacial CuNiTi phase is beneficial to the wettability of molten braze alloy on Ti50Ni50 substrate, it is detrimental to the bonding strength of the infrared brazed Ti50Ni50/BAg-S/Ti-6Al-4V joint. © 2005 The Japan Institute of Metals.