Abstract
Investigation was made on the effect of the working degree on the creep-rupture strength of molybdenum coated with Nickel-base heat-resistant alloy of Nimonic 90 and cobalt-base heat-resistant alloy of S-816 subjected to casting and 25% to 80% hot-working at 1000°C and 1150°C. The creep-rupture strength was improved as the working degree was increased, but it was deteriorated adversely by heavy working such as 80% reduction, due to the lowering of the recrystallization temperature of molybdenum, and this tendency became marked with lowering working temperature. When the working degree is small, the high stress and short-time strength is low but the deterioration of the low stress and long-time strength is small. Molybdenum coated with S-816 alloy has usually a superior short-time strength, but an inferior long-time strength compared with molybdenum coated with Nimonic 90 alloy under the same reduction by working. Molybdenum shows ductile fracture under the high stress and short-time test, but shows brittle fracture through the grain boundary of molybdenum under the low stress and long-time test because of the recrystallization of molybdenum.
The recrystallization temperature of molybdenum worked at 1000°C is around 1100°C at 80% working and around 1150°C at 65% working, and the strain of molybdenum worked heavily is recovered easily by heating until 1150°C and molybdenum is softened, but the worked properly can be sustained up to a considerably high temperature. Accordingly, for improving the long-time creep-rupture strength of the composite materials, hot workings of 30% to 40% at 1000°C and 40% to 60% at 1150°C are optimal.
