Microstructure and performance of NiCrBSi coatings prepared by modulated arc currents using powder plasma transferred arc welding technology

Abstract

This study examines the impact of varying plasma arc currents 70 A, 80 A, 90 A, and 100 A on NiCrBSi coatings applied to 15HM steel substrates using powder plasma transferred arc welding (PPTAW). Finite element analysis identifies two thermal cycle zones: the coating middle and coating/substrate transition. Microstructural analysis reveals dendritic structures in all samples, primarily rich in Cr. At the transition zone, various solidification modes are observed, accompanied by a coarse-grained heat-affected zone and minor macrosegregation. Energy-dispersive X-ray spectroscopy (EDS) confirms metallurgical bonding, while electron backscatter diffraction (EBSD) and X-ray diffraction indicate grain refinement as current decreases, with γ-Ni, Cr23C6, and Cr3C2 strengthening phases. PTA current of 70 A emerged as the optimal fabrication current within the tested range of currents, producing coatings exhibiting superior properties over the others. The results show improved corrosion resistance and tribological properties as current drops from 100 A to 70 A. Notably, corrosion current density decreases from 23.6 µA/cm2 to 12.8 µA/cm2, and average microhardness increases from 488 HV to 832 HV, reducing wear rate from 2.9 × 10−2 m3/m to 1.8 × 10−2 m3/m.