Microstructure of TiN/ carbon steel functionally gradient materials processed by high-energy electron beam irradiation

This article presents a microstructural study of TiN/carbon steel functionally gradient materials (FGM) processed by of high-energy electron beam irradiation. The mixtures of TiN powders and flux were deposited on a plain carbon steel substrate, and were irradiated using an electron beam accelerator. The microstructures of the irradiated surface layer consisted of surface region, melted region, interface, coarse-grained heat-affected zone (HAZ), fine-grained HAZ, and unaltered matrix. Residual pores and TiN powder agglomerates were found in the sample processed without flux, whereas these defects were hardly observed in the samples processed with a considerable amount of flux. As a result of irradiation, the Ti content decreased along the depth from the irradiated surface, thereby yielding the characteristics of FGM. Owing to the dissolved Ti and the formation of fine cuboidal Ti(C,N) particles, the hardness of the irradiated surface layer was greatly improved, reaching as much as twice or three times that of the original matrix, but the hardening effect was reduced along the depth from the surface.