THE EFFECT OF ATMOSPHERE ON CREEP-RUPTURE PROPERTIES OF A NICKEL-CHROMIUM- ALUMINUM ALLOY

The role of ductility in the effect of environment om creep and rupture properties was investigated employing a 76% nickel, 19% chromium, and 4% aluminum alloy. Creep-rupture tests were conducted primarily in air and im vacuum at 1300, 1500, and 1900 deg F. It was found that at low temperatures and high stresses, timeto-rupture was longer in vacuum that in air, but that at high temperatures and low stresses the reverse was true. Generally, conventional minimum creep rates were unaffected by environment. An unusual creep curve was obtained in air at the higher temperatures, apparently due to oxidation; these specimens showed markedly greater than expected rupture time and ductility. The influence of atmosphere was related to the mode of crack formation in this relatively brittle material and can be explained by previously advanced mechanisms. (auth)