Microstructural modification and hardness improvement of titanium-base surface-alloyed materials fabricated by high-energy electron beam irradiation

The present study is concerned with the microstructural modification and the hardness improvement of Ti-base surface-alloyed materials fabricated by high-energy electron beam irradiation. The mixtures of TiB2 or TiC powders and flux were deposited on a CP Ti substrate or a Ti-10V-2Fe-3Al alloy substrate, and then an electron beam was irradiated on these mixtures using an electron beam accelerator. Cracks, pores and powder agglomerates were found in the melted region of the specimen fabricated without flux. In the specimens processed with a flux mixing ratio of 50%, the melted region of 1.2∼1.5 mm in thickness was homogeneously formed without defects, and contained a large amount of titanium borides or titanium carbides. This microstructural modification including the formation of TiB or TiC greatly improved hardness, especially high-temperature hardness up to 450°C. These findings suggested that the surface-alloying using high-energy electron beam irradiation was economical and useful for the development of titanium alloys with improved high-temperature hardness.