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SUPPRESSION MECHANISM OF FATIGUE CRACK INITIATION OF NICKEL-BASE SURERALLOY AT ELEVATED TEPERATURE

镍基合金高温疲劳裂纹萌生的抑制机制

基本信息

批准号：
09650109
负责人：
KAWAGOISHI Norio
金额：
$ 2.11万
依托单位：
KAGOSHIMA UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1999
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09650109/
关键词：
FATIGUE NiCKEL-BASE SUPERALLOY ELEVATED TEMPERATURE CRACK INITIATION CRACK PROPAGATION SURFACE INTEGRITY

项目摘要

In the present study, the initiation and early propagation behavior of the small fatigue crack for Ni-base superalloy. Inconel 718, is investigated at the elevated temperature. The influence of temperature on the fatigue strength is examined and the results are discussed from the viewpoints of the softening of matrix and the surface oxidation of specimen at elevated temperature. It is concluded that the initiation and propagation mechanism of a small fatigue crack and the significance of the fatigue limit of a plain specimen are not influenced by the temperature. However, the initiation and propagation of the small fatigue crack is promoted at the elevated temperature owing to the softening of matrix and suppressed at the same time owing to the formation of oxide films on the surface of specimen, which effect is dominant will depend on the temperature and the stress level. As result, the fatigue limit of plain specimen is much higher at elevated temperature than at room temperature because the growth of small cracks in the length of 20-30μm, which occupies about 90% of the fatigue life of plain specimen, is greatly suppressed at elevated temperature.The effect of grinding on the fatigue strength is examined from the viewpoints of residual stress, surface roughness and surface hardening. The surface layer of CBN ground specimen is hardened through CBN grinding and a great compressive residual stress is generated in the layer. As the result, the fatigue strength is increased by CBN grinding.The fatigue strength of notched specimen and the influence of temperature on the notch sensitivity are investigated by using the 60 degree V-grooved specimen. The notch sensitivity of Inconel 718 is relative low when considering its high static strength, but it becomes a little notch sensitive at higher temperature.

研究了镍基高温合金疲劳小裂纹的萌生和早期扩展行为。Inconel 718在高温下进行了研究。研究了温度对疲劳强度的影响，并从高温下基体软化和试样表面氧化的角度对结果进行了讨论。结果表明，温度对疲劳小裂纹的萌生和扩展机制以及平面试样疲劳极限的意义没有影响。高温下基体的软化促进了疲劳小裂纹的萌生和扩展，同时试样表面氧化膜的形成抑制了疲劳小裂纹的萌生和扩展，其作用主要取决于温度和应力水平。结果表明，在高温条件下，平面试样的疲劳极限远高于室温，这是因为在高温条件下，长度为20-30μm的小裂纹（约占平面试样疲劳寿命的90%）的扩展受到了很大的抑制。CBN磨削试样的表面硬化，并在磨削层中产生较大的残余压应力。采用60 ° V型槽试样，研究了CBN磨削对缺口试样疲劳强度的影响以及温度对缺口敏感性的影响。Inconel 718合金由于静强度高，缺口敏感性较低，但在较高温度下，缺口敏感性变小。