To avoid self-welding and galling core structural materials in fast breeder reactors are hardfaced in Ni-based alloys.

In this work Ni-Cr-Fe-Si-B-C hardfacing alloy (D-50) deposited on 304L SS build plate by laser rapid manufacturing process.

Earlier studies on as-deposited specimen showed:

(a) only 60 μm wide dilution zone
(b) enhanced grain boundary (GB) precipitation on the SS side up to 10 μm, and;
(c) formation of interdiffusion zones with distinct microstructure, microhardness and microchemistry at the interface.

To understand the change in the interface microstructure due to interdiffusion, diffusion annealing experiments were carried out in the temperature range of 823-1123 K for 5-100 h.

At all annealing conditions structure of the additive manufactured coating changed from D-50 deposit consisting of various Cr rich borides and carbides to eutectic structures of y-Ni and Cr5B3 followed by precipitate lean dendritic solidification structure at the interface, then grain boundary precipitation on SS side to well annealed structure of SS.

Making use of the light element analysis capability of an electron microprobe the subtle variation in the microchemistry of carbides and borides and elemental segregation in interdendritic regions could be clearly brought out followed by phase analysis by XRD.

This article is shared by T.N. Prasanthi, C.P. Paul, K.S. Bindra and C. Sudha.