Oxygen embrittlement of vanadium alloys with and without surface oxide formation

Specimens of V-4Cr-4Ti have been exposed to low pressure oxygen and high purity He environments from 10⁵ Pa down to 10^-1 Pa in order to determine oxidation kinetics at 600-700 °C and effects on mechanical properties at 25 and 600 °C. At lower pressures (p(O₂)< 10^-5 Pa), linear reaction kinetics were measured for exposures up to 2000 h and the data was used to develop a mathematical expression for the oxidation rate as a function of temperature and oxygen pressure. At higher pressures, linear-parabolic reaction kinetics were measured associated with high oxygen uptake and the formation of an external oxide layer. Room-temperature and 600 °C tensile ductility was reduced by these exposures, but specimens which formed an external oxide retained some tensile ductility after exposure. However, similar specimens with an external oxide that were subsequently annealed for 2000 h at 700 °C were severely embrittled. These results suggest that a surface oxide on V-4Cr-4Ti can be a source of oxygen for further embrittlement and does not prevent embrittlement in extended exposures at 700 °C.