Microstructure of TiB2/carbon steel surface-alloyed materials fabricated by high-energy electron beam irradiation

The processing and the microstructural analysis of TiB2/carbon steel surface-alloyed materials using the irradiation of a high-energy electron beam were investigated in this study. The mixtures of TiB2 powders and flux were deposited on a plain carbon steel substrate, and then electron beam was irradiated on these mixtures using an electron beam accelerator. The microstructure of the irradiated surface layer was composed of a melted region, an interfacial region, a coarse-grained heat-affected zone (HAZ), and a fine-grained HAZ. A few residual micropores were found in the melted region of the specimen processed without flux because of irregular thermal transfer, but their number was decreased in the specimens processed with a considerable amount of flux. As a result of irradiation, the Ti content was homogeneously maintained throughout the melted region, whose hardness was greatly improved. This was associated with the microstructural modification including the segregation of Ti and B along solidification cell boundaries and the formation of fine Ti(C, N) particles. The proper flux mix ratio was 15 to 30 pct to obtain excellent surface alloying and a homogeneous microstructure.