The influence of test atmosphere on creep-rupture properties was determined for plain and notched bars of nickel, Nichrome V, Udimet 500, and Inconel X. The rupture life of nickel and of Nichrome V was shorter in air than in vacuum at relatively low temperatures, but at high temperatures it was longer in air. While both types of specimen geometry were generally affected alike by atmosphere, a larger atmosphere effect was observed for notched bars of the two materials in the air-strengthened region. The Udimet 500 and the high-strength Inconel X alloys at 1500 deg F were slightly stronger in vacuum than in air. However, the Inconel X with a modified heat-treatment displayed a reversal in the atmosphere effect. It was observed that all the materials generally develop intergranular cracks more readily in air than in vacuum.

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