マグノックス合金の冶金学的挙動に関する研究, (II)

クリープ中におこるcavitationとcracking現象

抄録

Creep tests have been carried out on Magnox, Mg-1% Al and Mg-1% Zr alloys at several temperatures in the range from 300° to 500°C under several stresses in the range from 0.15 to 0.38kg/mm². After the creep test specimens were cut out to investigate the phenomenon of cavitation in these alloys during creep test.
Average creep rates of Magnox alloys under the condition described above are the order of 10^-310^-1%/hr and Magnox A12 possesses higher creep strength than other Magnox alloys. Creep specimens show ductile fracture at the temperature of 400°C or above and brittle fracture at the temperature of 300°C or below. The surface of the specimen becomes rough by creep deformation.
Cavities are formed preferentially in grain boundaries normal to the stress axis at early stage of secondary creep mainly caused by grain boundary sliding. In the case of higher stress cavities and cracks are mainly created at triple points of grain boundaries. At constant temperature, for a given amount of strain the number of cavities increases with decreasing strain rate and for a given strain rate it increases with total amount of strain. Cavities are formed easily at the temperature range from 300° to 400°C and they are not formed at the temperature of 500°C and above.