Role of TiB reinforcement in the hydrogen embrittlement behavior of titanium matrix composites

The present work investigates the role of TiB reinforcement in hydrogen embrittlement (HE), with particular emphasis on hydrogen-assisted cracking (HAC) in titanium matrix composites (TMCs). TMCs containing 0, 1, and 4 vol.% TiB were investigated using in situ hydrogen charging tensile tests, Ag decoration, and microstructural analyses. Yield strength increased with TiB content, whereas HE resistance varied non-monotonically, with the 1 vol.% TiB-reinforced TMC showing the highest resistance. All hydrogen-charged specimens developed surface TiH 2 layers, from which HACs preferentially initiated. Cross-sectional observations revealed fewer HACs penetrating the matrix in the 1 vol.% TiB-reinforced TMC, whereas cracks were frequently associated with fractured TiB particles in the 4 vol.% TiB-reinforced TMC. Ag decoration revealed preferential hydrogen trapping at TiB–matrix interfaces, which reduced diffusible hydrogen ahead of crack tips and suppressed HAC propagation. However, premature TiB fracture can lead to the formation of TiB-fracture-associated cracks, which may coalesce with hydride-originated HACs and facilitate their propagation into the matrix. Thus, the HE resistance of TMCs is governed by the competition between the beneficial hydrogen-trapping effect of TiB–matrix interfaces and the detrimental effect of TiB particle fracture. These findings highlight the need to optimize TiB content by considering its non-monotonic influence on HE resistance when designing TMCs for hydrogen-containing environments.