Ni-Cr-Fe-Si-B-C hardfacing alloys (D-50) provide excellent resistance to abrasive and adhesive wear along with resistance to corrosion and high temperature oxidation. These alloys are candidate materials for hardfacing coatings on in-reactor components of fast breeder reactors.

Conventionally these deposits are made on steels through the welding route. Due to high fluidity of the molten alloy, generation of residual stress in the deposit (due to large difference in the thermal expansion between the deposit and the substrate) and significant dilution of the deposit (due to widely different melting points), achieving crack free deposits is often a very difficult and time-consuming task.

To address such issues arising out of conventional fabrication routes, compositionally gradient coatings have been tried through laser additive manufacturing.

A 3 layered compositionally graded deposit (D-50 /50D-50-50S/SS) was made on 316L SS build plate and examined using optical microscope, electron probe micro analyzer and Synchrotron XRD to identify the phase constituents and possible correlation with micro hardness.

Uppermost D-50 layer consisted γ-Ni, γ-Ni+Ni₃B and γ-Ni+Cr₅B₃ eutectics, CrB, Cr₇C₃, Cr₂₃C₆ and Cr₃C₂ precipitates. The middle layer consisted of γ-(Ni,Fe), γ-(Ni,Fe)+Cr₅B₃, Cr₅B₃ and Cr₃C₂.

The SS layer closest to the build plate had γ-Fe and Cr₃C₂ precipitates. Corresponding to the variation in microstructure a gradual change in hardness also can be seen starting from the top layer to SS build plate: 580±35 HV0.1, 532±17 HV0.1, 348±21 HV0.1 and 230±10 HV0.1, which is promising. Further, preferential formation of phases in various layers due to change in composition and effect of dilution will be discussed during the presentation.

This article is shared by S. Haribabu, C.P. Paul, V. Srihari, K.S. Bindra and C. Sudha.