Precipitation evolution of M5B3 boride in diffusion affected zone and its effect on mechanical properties of TLP bonded Mar-M247 superalloys

Abstract

Boron is usually added in the bonding interlayer as the melting point depressant element in the transient liquid phase (TLP) bonding of Ni-based superalloys, which inevitably leads to the precipitation of borides and therefore has an important impact on the mechanical properties of the joints. M5B3-type borides (where M is a mixture of Cr, W and Mo) are the predominant borides in diffusion affected zone (DAZ) of the Mar-M247 bonded joints. In present work, the precipitation and evolution of M5B3 in the joints with different bonding time have been systematically investigated by multi-scale methods. Three kinds of crystallographic orientation relationships between M5B3 and matrix have been observed, and the morphologies and precipitation positions of M5B3 borides are found to have certain characteristics in specific bonding time joints. These crystallographic orientation relationships are consistent with the predictions based on calculations of coincidence of reciprocal lattice points (CRLP) model. The effect of the precipitation of borides on mechanical properties has been evaluated by means of microhardness and micropillar compression testing.