Improvement of high-temperature hardness of (TiC, TiB)/Ti–6Al–4V surface composites fabricated by high-energy electron-beam irradiation

Abstract

The objective of this study is to investigate microstructure, hardness and high-temperature hardness of five kinds of (TiC, TiB)/Ti–6Al–4V surface composites fabricated by high-energy electron-beam irradiation. Mixtures of TiC, Ti+C, TiB 2, Ti+B 4C and TiC+TiB 2 powders and CaF 2 flux were deposited on a Ti–6Al–4V substrate, and then a high-energy electron beam was irradiated on these mixtures. The surface composite layers of 0.9–1.6 mm in thickness were homogeneously formed, and contained a large amount (30–44 vol.%) of hard precipitates such as TiC and TiB in the martensitic matrix. This microstructural modification improved the hardness and high-temperature hardness of the surface composite layer two to three times greater than that of the substrate. Particularly, the surface composite fabricated with Ti+B 4C powders had a larger volume fraction of TiB and TiC homogeneously distributed in the martensitic matrix, and thus showed the best hardness even at high temperatures. These findings suggested that the fabrication of the (TiC, TiB)/Ti–6Al–4V surface composites using high-energy electron-beam irradiation held significant implications for the economical development of new structural aerospace materials requiring excellent thermal resistance.