Development of a boron-free filler metal for brazing nickel-based superalloys utilizing the Cu–Mn–Ni system

A new material for boron-free brazing of nickel-based superalloys is described that utilizes a transient liquid-phase bonding (TLPB) mechanism. Commercially available AMS 4764 powder (52.8Cu–37.5Mn–9.7Ni) was mixed with pure Ni powder to increase Ni content in the filler metal. This alloy is a good candidate for TLPB in Ni superalloy applications because of its high strength, low liquidus temperature, low cost and the absence of brittle intermetallic phases. Analysis of in situ braze joint formation with IN625 base metal using differential scanning calorimetry measurements allowed for optimization of Ni content, braze temperature and hold time conditions of the brazing process. Calculated ternary phase diagrams coupled with EDS analysis of braze joints identified a low-temperature copper-rich segregated region in braze joints, which, through interdiffusion with the base metal, increases melting temperature with increasing hold time. This work concludes that a 50-µm half braze joint can be formed through full isothermal solidification with an 80-min hold at 1050 °C. Solidification occurs primarily through interdiffusion of base metal and filler metal.