Transient liquid phase diffusion bonding of oxide dispersion strengthened nickel alloy MA758

Transient liquid phase diffusion bonding has been used to join an oxide dispersion strengthened (ODS) nickel alloy (MA758) using an amorphous metal interlayer with a Ni-Cr-B-Si composition. A microstructural study was undertaken to investigate the effect of parent metal grain size on the joint microstructure after isothermal solidification. The ODS alloy rt as bonded both in line grain and recrystallised conditions at 1100 degrees C for carious hold times. The work shows that the final joint grain size is independent of the pal ent alloy grain structure and the bonding time. However, when the alloy is bonded in the recrystallised condition and given a post-bond heat treatment at 1360 degrees C, the joint grain size increases and a continuous parent alloy microstructure across the joint region is achieved. If MA758 is bonded in the fine grain condition and then subjected to a recrystallising heat treatment at 1360 degrees C, the grains at the joint appear to increase in size,with increasing bonding time. The joint grains are generally larger than those produced when the alloy is bonded in the recrystallised condition. The differences in microstructural developments across the joint are discussed in terms of stored str ain energy of the parent metal grains. (C) 1999 IoM Communications Ltd.