日本機械学会論文集
Online ISSN : 2187-9761
ISSN-L : 2187-9761
材料力学,機械材料,材料加工
Ni基超合金Alloy718合金の疲労強度に及ぼす表面加工層の影響
蓮沼 将太磯崎 洋平桐谷 聡一波田野 明日可泉 聡志酒井 信介
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2015 年 81 巻 832 号 p. 15-00328

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The effect of processed surface condition on low cycle fatigue life of Ni based super alloy, Alloy 718, was investigated. Observation of turning surface indicates that the roughness is fairly small, i.e. Ra < 1 μm, however, many scratch are found. Compressive residual stress is measured on the surface. Specimen subsurface condition consists three characteristics including fine grained and plastically deformed layers and bulk material. Fine grained layer is divided into three layers. Specimens were prepared by electropolishing in order to remove the fine grained and plastically deformed layers. Low cycle fatigue tests were performed on these specimens. Under strain range Δε = 0.8 %, fatigue lives of the specimens with turned surface are longer than those of the electropolished specimens. On the contrary, the surface conditions have no effect on fatigue lives under Δε = 1.4 %. Fatigue cracks initiate from surface scratches and inclusions on the turned surface, while they are initiated from slip band for electropolished specimens. Under the test conditions in this study, residual stress has the strongest correlation with the low cycle fatigue lives affected by the surface conditions. To consider scratch, residual stress and microstructures are important to decide low cycle fatigue design and machining method.

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