Effect of Ti/Nb content on microstructure evolution and wear properties of in-situ (Ti,Nb)C reinforced composite coatings by plasma spray welding

Abstract

Due to their superior wear resistance, multi-particle reinforced composite coatings have caught the interest of numerous researchers. In this research, a method of preparing composite coatings containing in-situ (Ti,Nb)C particles was proposed using plasma spray welding with a mixture of Fe-based alloy, pure Ti, and pure Nb powders. The research involved a detailed analysis of the nucleation mechanism, particle shape and strengthening behavior of (Ti,Nb)C particles in the composite coatings with different atomic ratio of Ti/Nb. The microstructure and phase were examined, and the wear resistance was tested and examined. The phase analysis results manifested that the composite coatings had primarily (Ti,Nb)C reinforcing phase and α-Fe matrix. The (Ti,Nb)C particles were not added in the raw powders, but in-situ generated via the reactions between the powders. The microstructure analysis results indicated that the reinforced particles transformed from irregular dendritic particles into lumpy and spherical particles, and then into an interspersed distribution of laths and spheres as the atomic ratio of Ti/Nb decreased. The microhardness value of these composite coatings when the Ti/Nb ratios were different were 550 HV–650 HV, while the microhardness value of the steel was 174 HV. However, with the increase of Ti/Nb atomic ratio, the change of wear resistance showed the trend: increase → decrease → increase. In-situ (Ti,Nb)C particles were uniformly distributed in the coatings and beneficial to improving the wear resistance. When Ti/Nb ratio is 1:1, the mass loss of the composite coating was only 0.6 mg, which was a quarter of the steel substrate (2.4 mg).