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 Ti₅₀Ni₅₀ 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 Ti₅₀Ni₅₀ side. The dramatic microstructure change of joint is observed for specimens infrared brazed at 900°C above 60 s 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-8/Ti–6Al–4V joint.