Koichi Takasawa

Single-phase interdiffusion in the B2 type intermetallic compounds NiAl, CoAl and FeAl

Abstract Interdiffusion coefficients, D , in the B2 type NiAl, CoAl and FeAl phases have been determined by single phase diffusion couples over a wide temperature range from 1073 to 1773 K. The value of D in the NiAl and CoAl phases shows a minimum at about 47 at.% Al deviating slightly from the stoichiometric composition, while the value of D in the FeAl phase has a weak minimum at about 41 at.% Al. The value of the activation energy, Q , for interdiffusion in the NiAl and CoAl phases shows a maximum at about 47 at.% Al, where the value of Q in the CoAl phase is much higher than that in the NiAl phase, while the value of Q in the FeAl phase is nearly constant and much lower than those in the other two phases. It is observed that the larger the lattice constant of the compounds becomes, the lower the activation energy for diffusion in the compounds becomes. Thus, the magnitude of activation energy for diffusion in the B2 type NiAl, CoAl and FeAl is probably related to the lattice constant of the compounds. Using the interdiffusion coefficient and the tracer diffusion coefficients of Ni and Fe with the help of Darkens relation, the diffusion coefficient of Al in the NiAl and FeAl phases has been estimated.

Internal Pressure Fatigue Test of Cr-Mo Steel in 45MPa Hydrogen Environment

Internal pressure fatigue properties of Cr-Mo steel (JIS G 4052, SCM435H) in high-pressure hydrogen or nitrogen atmosphere were investigated by the internal pressure fatigue test using a specially designed apparatus. Internal pressure was varied in the range from 0 to 40.5MPa, and test temperature was 20°C. The cycle length of internal pressure was varied up to 1000 seconds. We obtained the following results. 1. The number of fracture cycles in 45MPa hydrogen atmosphere was much less than those of in the 45MPa nitrogen atmosphere. 2. The number of fracture cycles was not depended on the cycle length. 3. In the fracture surface region where quasi-cleavage and intergranular surfaces are coexisting, the crack growth behavior is different from that of in the quasi-cleavage region.Copyright