Mechanism of hydrogen-restrained crack propagation and practical application research of thermohydrogen treatment in a TiAl-based alloy

Abstract

The mechanism of hydrogen-restrained crack propagation and practical application of thermohydrogen treatment in a TiAl-based alloy was investigated in this study. Hydrogenated and unhydrogenated alloys were subjected to high-temperature compression test, with a temperature range 1050–1200 °C and strain rate range 0.001–1 s−1. The results showed that crack propagation was restrained due to hydrogen addition. The main mechanism of hydrogen-restrained crack propagation of such alloy was revealed that hydrogen-promoted lamella bending and hydrogen-decreased Young's modulus induced inter-lamellar cracks transforming into trans-lamellar cracks, decreasing cracks in the hydrogenated alloy. Additionally, hydrogen-induced mechanical twinning in γ-phase lamellae partly restrained inter-lamellar crack propagation. In the two-step forging process, the optimum forging parameters were determined. It was found that hydrogen could effectively restrain crack propagation during the two-step forging process. Hydrogen refined grains of the forged billets, which improved toughness of such billets. The hydrogen content of the forged hydrogenated billets could be decreased to a desired value, and the phase composition and content were basically identical to those of the initial unhydrogenated alloy.