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本文研究了不同组织形态Inconel 718合金在650℃高温低周疲劳过程中的裂纹萌生。实验结果表明:晶粒粗大并伴有部分长片状δ相沿孪晶界析出的合金,断口表面疲劳源处有明显的无任何特性的平的解理面,这些解理平面是孪晶面和孪晶界两侧的晶面,并发现疲劳裂纹很容易沿着这些晶面产生。这是由于粗晶组织合金中孪晶界上析出的长片状δ相阻碍晶体滑移,在δ相与孪晶的界面处造成了应力集中,降低了界面强度以及孪晶界两侧形成的无强化相析出带减弱了裂纹萌生抗力。晶粒细小,短片状δ相沿晶界析出的合金,断口表面疲劳源特性不明显,表面裂纹不易萌生。
In this paper, the crack initiation of Inconel 718 alloy with different microstructures during low cycle fatigue at 650 ℃ is investigated. The experimental results show that the grains with coarse grains and some long flake δ phase along the twin boundary precipitation of alloy, the fracture surface fatigue sources have obvious without any characteristics of the plane cleavage plane, the cleavage plane is the twin plane and Twins on both sides of the crystal plane and found that fatigue cracks are easily generated along these planes. This is due to the fact that the long sheet-like δ phase precipitated on the twin boundaries in the coarse-grained alloy obstructs the crystal slip, causing stress concentration at the interface between the δ phase and the twin, reducing the interfacial strength and the formation of Precipitation without strengthening phase weakens the crack initiation resistance. The alloy with fine grains and short δ phase precipitated along the grain boundary has not obvious characteristic of the fatigue source on the fracture surface and the surface cracks are not easy to sprout.