Phase formation and properties of vanadium-modified Ni–Cr–B-Si–C laser-deposited coatings

A Ni–Cr–B-Si–C alloy powder was modified by addition of 2 and 5 wt% of vanadium to tackle the high cracking sensitivity of the original composition during laser deposition. The effects of vanadium on microstructure and phases were investigated by Scanning Electron Microscopy, Energy Dispersive Spectroscopy, and Transmission Electron Microscopy (TEM) and the changes in the hardness and cracking tendency of the deposits were evaluated. In comparison to the original composition, V-modified alloys produced deposits with lower hardness and moderately reduced cracking tendencies. Addition of vanadium transformed the nature and the morphology of the boride precipitates and added VC particles to the microstructure but did not induce a significant microstructural refinement. TEM characterizations confirmed that borides phases in the modified deposits consisted of alternating layers of CrB and (Cr_1−xV_x)B but the VC existed as independent particles which were formed on the boride precipitates. The final phase constitution of the modified alloys was dramatically influenced by the complete solid solubility between CrB and VB and the lack of solubility between Cr₇C₃ and VC. Addition of vanadium did not provide the phases which could act as nucleation sites to refine the microstructure of the deposits because VB had a tendency to dissolve in CrB and VC was formed at low temperatures on the boride phases. The outcomes of this study can be used to evaluate the effects of adding early transition metals such as vanadium on the microstructure and phase formations of the Ni–Cr–B-Si–C alloys.