Comparison of plasma sprayed NbB2-NbC coatings obtained by ex-situ and in-situ approaches

摘要

NbB2-NbC composite coatings were fabricated on the surface of TC4 by plasma spraying NbB2-NbC and Nb-B4C composite powders. The microstructure and properties of the as-prepared coatings were investigated, and the reaction mechanism of the Nb-B4C composite powder in the plasma jet and the formation mechanism of the NbB2-NbC coatings were revealed. During the plasma spraying process, NbB2-NbC composite powder underwent melting-depositing and no phase transformation occurred. The formation mechanism of the coating by plasma spraying Nb-B4C composite powder was solid phase diffusion-reaction-melting-deposition, and NbB2 and NbC were formed in situ by the solid phase diffusion reaction between Nb and B4C in the plasma jet. The coating obtained by reactive plasma spraying Nb-B4C composite powder has obvious lamellar structure, low porosity, high density, higher microhardness, good toughness, and better wear resistance compared with the coating prepared by NbB2-NbC composite powder, which is attributed to the exothermic reaction between Nb and B4C.