Dissimilar joining of P/M superalloy and single crystal superalloy using Ni–Cr–B brazing alloy

Abstract

An advanced technology for joining powder metallurgy (P/M) superalloy and single crystal (SC) superalloy is highly needed for fabricating a high-strength turbine bladed disk and the joints must meet the requirements of harsh working conditions. In the present paper, P/M superalloy FGH96 and SC superalloy DD6 were joined together using a Ni-Cr-B brazing alloy. The microstructure of the joint brazed at 1120°C for 10 min showed that massive Ni 3 B phase was formed in the central part of the brazing seam. In the FGH96 matrix near the brazing seam, a small bright phase which contained some element B, Cr, Mo, and W distributed along with grain boundary. The joints were subjected to a diffusion heat treatment at 1000°C for 1, 4, and 16 h, respectively. The results showed that the diffusion depth of B is increased from 80 μm at 1000°C/1 h to 140 μm at 1000°C/16 h. In addition, the bright phase was refined obviously, implying the homogenization of the joint microstructure. Compared with the joints treated for 1 and 4 h, the strength of the joints treated for 16 h was increased remarkably from 604∼630 to 913 MPa.