Preparation and Properties of Cr₃C₂-25NiCr Thermal Spraying Powders and Coatings with Nano-Sized, Micro-Sized, and Bimodal Structures

Nano-sized, micro-sized, and bimodal Cr₃C₂-25NiCr feedstock powders were prepared using a spray drying and agglomeration sintering process and deposited by HVOF spraying. The microstructure and phase composition of the three powders and corresponding coatings were assessed along with coating hardness, toughness, and abrasive wear resistance. All three powders were nearly spherical in shape, but the bimodal powder had the best sphericity, the most uniform composition distribution, and the highest deposition efficiency. All three coatings were primarily composed of Cr₃C₂ and NiCr phases, although a small amount of Cr₂O₃ was detected in the nano- and micro-coatings due to oxidation. Compared with the micro-coating, the nano-coating has higher toughness but lower microhardness and abrasive resistance. The bimodal coating, however, integrates the advantages of the other coatings, has low porosity and a dense microstructure, and is tightly adhered to the substrate, thus displaying the best comprehensive performance.