Effects of high-temperature air and vacuum exposure on tensile properties and fracture of ODS alloy MA6000

The effects of air and vacuum exposure at 1100 degrees C on tensile mechanical properties, notch fracture toughness, and fracture toughness at room temperature of MA6000 were investigated. By air exposure in the range of 2-1000 h, yield strength and ultimate tensile strength were decreased slightly, while fracture strain decreased significantly (40-50% of the as-received (as-rec.)). Also, notch fracture toughness was reduced by air exposure to similar to 75% of the as-rec. This decrease in strain and toughness was due to the occurrence of subsurface void formation zones, where fractures initiate. The mechanical properties and notch fracture toughness of the MA6000 vacuum-exposed for 24 and 240 h were almost the same as the as-rec., even though there were slight subsurface void formations. Fracture toughness of the pre-fatigue-cracked compact tension specimen was not reduced by either air exposure or vacuum exposure. (C) 1997 Elsevier Science S.A.