Beneficial effects of hydrogen as a temporary alloying element in titanium alloys: An overview

Use of hydrogen as a temporary alloying element in titanium alloys (thermohydrogen processing, THP) is an attractive method for enhancing processability including working, machining, powder production, sintering, compaction, etc., and also for controlling microstructure and thereby improving final mechanical properties. In the case of near net shapes it is the only method for significant microstructural modification. In the present paper, the status of the THP technique and applications to titanium alloys is presented. The effect of hydrogen alloying on the phase composition, formation of metastable phases and kinetics of the phase transformations is described, The effect of hydrogen on hot workability, composite- and powder-metallurgy-product processing, and microstructure modification of cast-and-wrought and cast conventional alloys and intermetallics, including production of nanocrystalline structures, is reviewed.