Hydrogen Tolerance of gamma - TiAl Microstructures

摘要

The influence of hydrogen on the microstructure and mechanical properties ofgamma titanium aluminide alloys has been studied. Gas phase charging experiments have been conducted over the temperature range of 500 deg C to 1100 deg C with hydrogen pressures from 0.1 to 13.8 MPa. Following high pressure charging, two different hydrides have been observed: a newly identified tetragonal hydride and a FCC delta hydride. The new hydride, designated the theta phase, has a composition of approximately Ti2AlH and is body centered tetragonal with lattice parameters of a = 0.528nm and C = 2.848nm. At lower hydrogen pressures of 0.1MPa, both hydride phases have been observed only in near-surface regions in association with a series of reactions with trace gaseous impurities that result in complex mixtures of oxides and hydrides. Tension tests were conducted on samples that were pre-exposed to air, vacuum and 0.1MPa hydrogen environments prior to testing. Yield strengths were not significantly influenced by the hydrogen, air or vacuum exposures, but tensile ductility was reduced by both air and hydrogen exposures. Compression experiments following high pressure charging showed a substantial strengthening effect of the hydrides. No tension experiments could be conducted on high pressure charged materials, due to the extreme embrittling effect of these high pressure exposures.