Surface concentration and microscale distribution of hydrogen and the associated embrittlement in a near α titanium alloy

Abstract The hydrogen embrittlement of near α Ti-2.5Al-2Zr-1Fe alloy is demonstrated by the decreasing of impact toughness when increasing the charged H content in the near surface layer. In order to get knowledge of the role of hydrogen and the possible embrittle mechanisms, a series of experiments are performed. First, the fracture mode was analyzed by scanning electron microscope and optical microscope. Then the deuterium charge and secondary ion mass spectroscope (SIMS) study was carried out to obtain the precise distribution of H in microstructure scale. The transmission electron microscope (TEM) study was performed to identify whether hydride formation occurs. Both Focused Ion Beam (FIB) lift out and conventional grinding methods were used to prepare the TEM sample. No hydride was observed in the sample prepared by FIB lift out method, while hydrides appeared in the sample prepared by conventional method. The results suggest that hydride formation relates with the TEM sample preparation process rather than the H charge process. The charged deuterium was found to concentrate in β phase at α grain boundaries by SIMS, which should be the cause of crack growth along β phase. Among the hydrogen embrittle mechanisms, the weakening of β phase was most probably caused by hydrogen enhanced decohesion.