Thermal-induced evolution of microstructure as a plasma arc coating Direction-Dependent phenomenon

This study elucidates the effects of different directed energy deposition trajectories on the microstructure and properties of powder plasma transferred arc welding (PPTAW) fabricated coatings. Two trajectories, straight (STT) and complex (CXT), were explored to deposit NiCrBSi powders onto a low alloy steel substrate. Finite element thermal analysis revealed distinct heat distribution zones, the middle zone (MZ) and transition zone (TZ), showing temperature variations between the STT and CXT coatings. Microstructural examination indicated lower dendrite arm spacing (DAS) in the STT coating (11 μm) than in the CXT coating (16 μm). Electron backscatter diffraction (EBSD) analysis demonstrated significant grain refinement in the STT coating (17.4 μm) versus the CXT coating (68.7 μm). X-ray diffraction phase analysis identified three reinforcing phases − γ-Ni, Cr₂₃C₆, and Cr₃C₂ – enhancing corrosion resistance and tribological properties. The STT coating exhibited superior corrosion resistance with a corrosion current density (i_corr) of 12.8 µA/cm², while the CXT coating showed i_corr of 34.3 µA/cm². Additionally, the STT coating exhibited higher hardness (832 ± 33 HV_1.0) and better wear resistance with a wear rate of 10.46 ± 0.29 × 10^-3 m³/m, over the CXT coating (hardness: 450 ± 36 HV_1.0; wear rate: 12.67 ± 0.54 × 10^-3 m³/m).