Crack Propagation in Powder Metallurgy Hot Isostatically Pressed Nickel-Based Alloy.
Annual rept. 1 Jan-31 Dec 84,
LEHIGH UNIV BETHLEHEM PA DEPT OF METALLURGY AND MATERIALS ENGINEERING
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The room temperature threshold fatigue behavior of PM HIPd L.C. Astroloy has been examined. Material with grain sizes ranging from 5 micrometers to 50 micrometers has been tested to investigate the influence of grain size on the threshold response. In disc compact tension specimens grain size is observed to have little influence on the threshold values in contrast tests conducted in four point bend specimens exhibit lower threshold values and display a dependence on grain size with larger grain sizes giving higher threshold values. Consideration has also been given to the growth of short cracks under cyclic loading at low stress intensities. The data reveal that under these conditions short cracks propagate at a consistently faster rate than long cracks subject to the same nominal stress intensity. Analytical work has been conducted which suggests that this behavior may be rationalized in terms of a more appropriate driving force for crack extension. Detailed microstructural information has been collected which identifies the major second phase particles present in the alloy. The effect of simple heat treatments on the distribution of these particles has been observed to be negligible. Keywords Fatigue crack propagation, nickel-based superalloys, powder metallurgy, crack length influence.
- Properties of Metals and Alloys