HYDROGEN PROPERTY IN LATTICE ASSOCIATED WITH THE EMBRITTLEMENT OF CO3TI ALLOYS

Some observations relating to solubility, diffusion and trap site of h ydrogen were performed on Co3Ti alloys in association with their embri ttlement. Hydrogen diffusivity at room temperature was evaluated to be low, similar to that of pure Ni. The desorption curve of hydrogen rea ched the maximum at similar to 430 K and the corresponding activation energy was estimated to be 48 kJ mol(-1). The fracture energy of the h ydrogen-precharged Co3Ti alloys measured by a small punch (SP) test wa s dependent on the hydrogen content and the alloy stoichiometry; it de creases with increasing hydrogen content and Ti content. It is suggest ed that the environmental embrittlement of the Co3Ti alloy requires th e hydrogen transport mode not via lattice diffusion. Also, the differe nce in the environmental embrittlement between the two tested alloy co mpositions is primarily due to the difference in the critical hydrogen content causing grain boundary fracture (i.e. intrinsic grain boundar y cohesion). (C) 1997 Elsevier Science Limited.