Alloy 718の中高温下におけるき裂伝ぱ抵抗に及ぼす結晶粒径の影響

概要

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Rotating bending fatigue tests were carried out using specimens with a small blind hole for Alloy 718 with different grain sizes, about 18, 32, 88 and 276μm, at room temperature and 500℃ in order to invistigate the effects of grain size and temperature on the growth resistance of a fatigue crack. Crack growth rates were determined by the term σ^n_aa (σ_a: stress amplitude, a: surface crack length, n: constant), uniquely in all of the materials and at both temperatures. Resistance to crack growth considering the difference in static strength increased with increasing in grain size. This was mainly caused by the roughness induced crack closure effect. Both of the static strength and the resistance to crack growth were decreased by softening at 500℃. The decrease in the resistance to crack growth was larger than that in the static strength. This was mainly explained from the difference in Young's modulus at the both temperatures. Flat areas, facets, reflecting the grain size were observed in addition to striations on the fracture surface in all of materials and at both temperatures, and the ratio of facet on the fracture surface increased with increase in grain size.
社団法人日本機械学会の論文
2009-10-25