Transient liquid phase bonding of Ni3Al based superalloy using Mn-Ni-Cr filler

new 70Mn 25Ni 5Cr (wt. %) filler with no traditional melting-point depressants (MPDs) of Si/B was used for transient liquid phase (TLP) bonding a directionally solidified (DS) superalloy based on Ni3Al intermetallic compound (IMC) at 1150 degrees C, a pressure of 2 MPa for 10-120 min. Experimental results show that the joint can be divided into 3 zones, isothermally solidified zone (ISZ), athermally solidified zone (ASZ) and diffusion-affected zone (DAZ), which was similar to microstructure of typical TLP joint bonded by Ni based filler. The joint microstructures were mainly composed of gamma-Ni, gamma'-Ni-3(Al, Ta), MC and M23C6 carbides. Besides, in the ISZ, due to the enrichment of Al, which diffused from the base metal (BM), strip-shaped Ni(Mn, Al) phases formed in such region. The ASZ included g-Ni and compounds of equiaxed Ni(Mn, Al) + acicular Ni3Ta owing to the composition segregation during the later stage of solidification. Moreover, as the bonding time increased, the volume fraction of Ni(Mn, Al) and MC carbides decreased owing to homogenization of alloying elements. After bonding for 120 min, sufficient isothermal solidification (IS) of filler can also decrease segregation of Mn/Al in front of the S/L interface and the Ni(Mn, Al+Ni3Ta compounds were eliminated almost. Thus, the highest tensile strength was 816.9 MPa of the TLP joint of 120 min, which has been equivalent to that of BM (812 MPa). However, due to the existence of a few residual large MC carbides in the joint, which can induce the stress concentration and decreased the ductility of the joints, the highest joint elongation of 4.4% was only about 40% of the BM. (c) 2021 The Author(s). Published by Elsevier B.V.

Automated summary

A new filler material without traditional melting-point depressants was used in transient liquid phase bonding of a directionally solidified superalloy. The joint was composed of three zones with different microstructures and the isothermal solidification of the filler helped to eliminate segregation and improve tensile strength.