Hydride formation during cathodic charging and its effect on mechanical properties of a high Nb containing TiAl alloy

Abstract

Due to their high specific strength and modulus at evaluated temperature, high Nb containing TiAl alloys have attracted extensive interest as prospective structural material for aerospace. However, low ductility as well as long-term expose to hydrogen still impedes its wide application in aerospace industries. This work focuses on hydrides' formation during cathodic charging and its effect on microstructure and mechanical properties of a high Nb containing TiAl alloy with the composition of Ti45Al8.5Nb-(W, B, Y). A hydride (TiAl)Hx with tetragonal crystal structure has been observed in alloys charged at 20, 100 and 500 mA/cm2 for 24 h. With the increase of current intensities, the thicknesses of hydride layer are around 2, 6 and 20 μm in samples charged at 20, 100 and 500 mA/cm2 for 24 h, respectively. The hydride layer exhibits loose and polyporous structure. The hydrogen diffusion coefficient of the alloy charged at 20 mA/cm2 for 24 h has been evaluated to be 6.33 × 10−16 m2/s by the nano-hardness from the distribution of the hydride layer. The tensile strengths of the alloys charged at 20, 100 and 500 mA/cm2 are 485, 476 and 405 MPa, while the strains are 0.699, 0.659 and 0.558, respectively.