LONG TIME CREEP RUPTURE OF HAYNESTM ALLOY 188

The creep of Haynes Alloy 188 sheet in air was studied at temperatures of 790”, 845” and 900 “C for times in excess of 30,000 h as part of a program to assure that Haynes Alloy 188 could be used in critical components of a solar dynamic power conversion system for Space Station Freedom. The rupture life and time to 0.5 and I .O percent creep strain of creep rupture specimens which had lives from about 6,000 to nearly 59,000 h are reported. Both welded and as-received specimens were tested. The welded specimen had essentially the same lives as the as-received specimens. Comparison of this data with previously published results suggests that this material was similar in behavior to that previously studied by Haynes except at 790 “C where the current sheet is somewhat stronger in stress rupture. Therefore the previously published data for Haynes Alloy 188 may be used in conjunction with this data to estimate the lives of components for a long life solar dynamic power system. Three creep rupture tests were discontinued after 16,500 to 23,200 h and tensile tested at room temperature or 480 ‘C. The elongation of all three specimens was substantially reducedcompared to the as-received condition or as aged (without applied stress) for 22,500 h at 820 ‘C. The reduction in elongation is thought to be caused by the presence oxidized pores found across the thickness of the interrupted creep specimens. The implications of the severe loss of ductility observed in tensile tests after prolonged creep test needs further study.