Influence of alloy chemistry on microstructure and properties in NiCrBSi overlay coatings deposited by plasma transferred arc welding (PTAW)

The microstructures and performance of two NiCrBSi alloy overlays deposited by plasma transferred arc welding are studied. The coatings consist of a γ-Ni primary dendritic phase with harder Ni + Ni3B or Ni + Ni3Si eutectics and Cr-based particles (CrB, Cr3C2, and Cr7C3) situated at the interdendritic regions. It was found that the volume fraction of the soft primary dendritic phase drastically decreased and the proportion of chromium borides and carbides increased with an increase of C, B, Si, and Cr content. Microhardness testing revealed that the primary Ni dendrite, interdendritic, and Cr-particle phases had average hardness values of 405, 860, and 1200 HV respectively. An increase in the volume fraction of hard eutectics and Cr-particles lead to a substantial increase in hardness and wear resistance.