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Development of high-functional materials by surface treatment and its evaluation of gigacycle fatigue strength

表面处理高功能材料的开发及其千兆周疲劳强度评价

基本信息

批准号：
12650077
负责人：
SHIOZAWA Kazuaki
金额：
$ 2.37万
依托单位：
Toyama University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2002
项目状态：
已结题

项目摘要

Some surface modifications are applied to the surfaces of mechanical elements and engineering components for the purpose of increasing fatigue strength and extending lifetime of engineering materials in various kinds of environments, because the surface is usually the most sensitive part for strength and failure resistance. In this study, gigacycle fatigue behavior of metals surface-treated with ceramics thin film, nitriding and shot-peening is investigated through the cantilever-type rotary-bending fatigue tests and discussed the rules of surface layer on fatigue strength. Main results are summarized as follows :(1) The S-N curve obtained for a high carbon-chromium bearing steel, JIS SUJ2, high speed tool steel, JIS SKH51, and low-alloy steel, JIS SNCM439, clearly classified the fracture modes into two groups each with a different crack origin. One was governed by crystal slip on the specimen surface at high-stress amplitude level and low number of cycles and the other was governed by … More a non-metallic inclusion at subsurface at high number of cycles. The remarkable shape of the S-N curve was named a 'duplex S-N curve'.(2) Fatigue crack initiation site changed from the surface of untreated specimen to the subsurface of the specimen because of hardening and compressive residual stress with surface treatment in the region of high-stress amplitude. On the other hand, no difference in fatigue life controlled by the subsurface crack initiation between untreated specimen and surface treated one was observed in high-cycle region. It was suggested that the S-N curve corresponding to the internal fracture mode is inherent in the material, as compared with the S-N curve of surface fracture mode, which is affected by surface conditions, environmental conditions and so on.(3) A distinctive feature of the fracture surface, named as a granular-bright facet (GBF), was observed in the vicinity of a non-metallic inclusion at the subsurface fracture origin inside the fish-eye zone. From the discussion based on fracture mechanics, it is pointed out that an internal crack is able to grow after formation of the GBF during the long fatigue process. Mechanisms of the GBF formation was proposed as 'disperse decohesion of spherical carbide' model.(4) The effect of anodized coating on fatigue strength of aluminum alloys was investigated under repeated tensile fatigue test. Fatigue strength of the anodized specimens decreased as compared with uncoated one, because the fracture of anodized coating film occurred at the critical strain formed by the accumulation of plastic deformation of substrate metal and crack was induced in the substrate at the flaw of the anodized film. Less

为了提高工程材料在各种环境下的疲劳强度和使用寿命，通常对机械零件和工程零件表面进行一些表面改性，因为表面通常是强度和抗毁性最敏感的部位。通过悬臂式回转弯曲疲劳试验，研究了经陶瓷薄膜、渗氮和喷丸处理的金属表面的千周疲劳行为，并探讨了表层对疲劳强度的影响规律。(1)高碳铬轴承钢JISSUJ2、高速工具钢JISSKH51和低合金钢JISSNCM439的S-N曲线明确地将断裂模式分为两组，每组具有不同的裂纹来源。一种是高应力幅值和低循环次数下试件表面的晶体滑移，另一种是由…控制的。在高循环次数下，更多的是地下的非金属夹杂物。S-N曲线的显著形状称为“S-N双曲线”。(2)在高应力幅值区域，疲劳裂纹的萌生位置从未处理试件的表面转移到试件的亚表层，这是由于表面处理的硬化和残余压应力造成的。另一方面，在高周区，未处理试件和表面处理试件的亚表面裂纹萌生所控制的疲劳寿命没有差别。与受表面条件、环境条件等因素影响的表面断裂模式的S-N曲线相比，S-N曲线是材料固有的内部断裂模式。(3)在鱼眼区内的亚表面断裂起始处的非金属夹杂物附近观察到了明显的颗粒亮面特征。从断裂力学的角度进行了讨论，指出在长期疲劳过程中，内部裂纹在GBF形成后能够扩展。在反复拉伸疲劳试验条件下，研究了阳极氧化膜对铝合金疲劳强度的影响。与未涂膜的试件相比，阳极氧化后的试件疲劳强度降低，这是因为阳极氧化膜的断裂发生在基材金属塑性变形累积所形成的临界应变处，并在氧化膜的缺陷处在基材上产生裂纹。较少