Quantitative evaluation of the effect of process-induced defects on the fatigue limit of additively manufactured Ni-based superalloy in a hydrogen environment

氢环境下工艺缺陷对增材制造镍基高温合金疲劳极限影响的定量评估

• 批准号: 22J12181
• 负责人: PARK SUNGCHEOL
• 金额: $ 0.58万
• 依托单位: Kyushu University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for JSPS Fellows
• 财政年份: 2022
• 资助国家: 日本
• 起止时间: 2022-04-22 至 2023-03-31
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-22J12181/
• 关键词: Additive manufacturing; Ni-based superalloy 718; Fatigue limit; Small crack; Fatigue threshold

During this year, I have examined the fatigue limit of an additively-manufactured, Ni-based superalloy 718 in terms of the small, fatigue-crack growth-threshold, using samples with various small defects and microstructures. Based on the macro- and microscopic analyses, the determining mechanism of the fatigue limit, the effects of small defects and the factors impacting fatigue resistance were all thoroughly explored. The principal conclusions are summarized as follows:1) Fatigue tests revealed that small-crack behavior was governed by maximum shear stress under both cyclic torsional loading and push-pull loading. This implied that the fatigue limit of all the samples was the threshold condition of a shear-mode, small fatigue-crack propagation, similar to the findings related to wrought materials.2) In each case, the shear-mode, small fatigue-crack growth-threshold was estimated to quantify the effects of small defects. As a result, the relationship between the fatigue threshold and defect size was acquired, showing not only a crack-size dependence consistent with the results of wrought materials, but also a substantially low fatigue resistance of additively-manufactured materials.3) Through the comprehensive examination of the effects of potential determining factors on small fatigue crack-growth resistance, it was concluded that the twist angle between two favorable slip planes in neighboring grains was the most influential factor in the inferior fatigue threshold of the additively-manufactured material.

在这一年中，我研究了增材制造的镍基高温合金718在小疲劳裂纹增长阈值方面的疲劳极限，使用了具有各种小缺陷和微观结构的样品。通过宏观和微观分析，深入探讨了疲劳极限的确定机理、小缺陷的影响以及影响疲劳抗力的因素。主要结论如下：1）疲劳试验表明，无论是在循环扭转载荷下还是在推拉载荷下，小裂纹的行为都是由最大剪应力控制的。这意味着所有样品的疲劳极限是剪切模式小疲劳裂纹扩展的阈值条件，与锻造材料相关的发现相似。2）在每种情况下，估计剪切模式小疲劳裂纹扩展阈值以量化小缺陷的影响。结果，获得了疲劳阈值与缺陷尺寸之间的关系，不仅显示出与锻造材料的结果一致的裂纹尺寸依赖性，而且还显示出增材制造材料的显著较低的疲劳抗力。3）通过全面检查潜在决定因素对小疲劳裂纹扩展抗力的影响，得出结论，相邻晶粒中两个有利滑移面之间的扭转角是增材制造材料的劣疲劳阈值的最有影响的因素。

项目成果

Shear-mode threshold of small fatigue crack in Ni-based superalloy 718 fabricated by additive manufacturing

增材制造镍基高温合金718小疲劳裂纹的剪切模式阈值

• 发表时间: 2022
• 作者: 陳思楠;中村匡秀;Sinan Chen and Masahide Nakamura;Sinan Chen and Masahide Nakamura;Sungcheol Park
• 通讯作者: Sungcheol Park