Effect of N on microstructure, nucleation mechanism and mechanical performance of (Ti, Nb) C particles in Fe-based composite coating via plasma spray welding

Abstract

Compared with the coating of Ti-Nb-C system, the coating of Ti-Nb-C-N system shows better mechanical properties, especially wear resistance. Therefore, this investigation was focus on the in-situ (Ti, Nb) C reinforced Fe-based composite coatings (D1 composite coatings) and in-situ (Ti, Nb) (C, N) reinforced Fe-based composite coatings (D2 composite coatings) which were created on high strength steel via plasma spray welding (PSW) technology in the environment with nitrogen and without nitrogen, respectively. The two coatings were compared to explore nucleation mechanism of nitrogen on (Ti, Nb) C particles, grain size, particle morphology and the influence on the mechanical performance of coatings. The findings showed that the changes in the typical microstructure morphology and the shape of the reinforced particles of the two coatings were not obvious. However, the heterogeneous nucleation sites of (Ti, Nb) C were provided by introducing nitrogen. In addition, the introduction of nitrogen could refine the grains of D1 composite coatings. As a result, the average grain size of D1 composite coatings decreased by an order of magnitude, and the crystal orientation of the grains in the composite coatings showed better isotropy. The average microhardness of D2 composite coatings was 967.52 HV1, which was 1.5 times of the average microhardness of D1 composite coatings. The wear loss of D2 composite coatings was 0.4 mg, which was only half of that of D1 composite coatings (0.8 mg).