Abstract
The arrest function in fatigue crack propagation at 25 and 550°C in air was investigated for Fe-20Cr alloys containing dispersed oxide particles of Al2O3, ZrO2 and Y2O3 in weight percents from 0.3 to 1.2. The Pmax-constant ΔK-decreasing test, where the minimum load, Pmin, increased with increasing crack length while the maximum load, Pmax, remained constant, was employed in order to avoid crack closure. The main conclusions obtained are as follows : (1) Fatigue crack propagation properties including the threshold were independent of the material at room temperature under the closure-free condition. The fatigue threshold values at 550°C were higher than those at room temperature for all materials. In addition, the threshold values at 500°C were about 50% higher for Y2O3-dispersed alloys than those for the base alloy and Al2O3-or ZrO2-dispersed alloys. (2) The increase of threshold level at 550°C for Y2O3-dispersed alloys was explained in terms of suppression of the spalling of the oxide layer formed at the fatigue crack tip by dispersed Y2O3 particles. Accordingly, we concluded that Y2O3 dispersion could show the arrest function of the fatigue crack propagation at elevated temperatures.
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