The Effect of Defects on the Fatigue Initiation Process in Two P/M Superalloys.
Final rept. Nov 77-Nov 79,
AIR FORCE WRIGHT AERONAUTICAL LABS WRIGHT-PATTERSON AFB OH
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A metallurgical investigation was performed to determine the effect of defect size, shape, and population on the fatigue initiation process in two high strength PM superalloys, AF-115 and AF2-1DA. The specific alloy heats tested had contrasting defect populations the AF-115 alloy contained a large population of spherical pores, and a lesser number of elliptical ceramic inclusions and plate-like hafnium oxide inclusions, and the AF2-1DA material contained only a small population of the elliptically shaped inclusions. Strain controlled fatigue tests were performed on uniform section specimens at 760 C, 649 C, and 22 C using both continuously cycling and cyclic dwell waveforms. Microscopic examination of the failed specimens showed that for the high temperature tests there was a transition in the nucleation site of the cracks that caused failure from a surface to a subsurface location as the strain range was reduced. This surface-subsurface transition SST occurred at approximately the same strain range for both alloys.
- Properties of Metals and Alloys