Kahn H, Ballarini R, Bellante J J, Heuer A H
Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106-7204, USA.
Science. 2002 Nov 8;298(5596):1215-8.
In the absence of a corrosive environment, brittle materials such as silicon should be immune to cyclic fatigue. However, fatigue effects are well known in micrometer-sized polycrystalline silicon (polysilicon) samples tested in air. To investigate the origins of this phenomenon in polysilicon, we developed a fixed-grip fracture mechanics microspecimen but could find no evidence of static stress corrosion cracking. The environmental sensitivity of the fatigue resistance was also investigated under cyclic loading. For low-cycle fatigue, the behavior is independent of the ambient conditions, whether air or vacuum, but is strongly influenced by the ratio of compressive to tensile stresses experienced during each cycle. The fatigue damage most likely originates from contact stresses at processing-related surface asperities; subcritical crack growth then ensues during further cyclic loading. The lower far-field stresses involved in high-cycle fatigue induce reduced levels of fatigue damage. Under these conditions, a corrosive ambient such as laboratory air exacerbates the fatigue process. Without cyclic loading, polysilicon does not undergo stress corrosion cracking.
在没有腐蚀性环境的情况下，像硅这样的脆性材料应该不会出现循环疲劳。然而，在空气中测试的微米级多晶硅样品中，疲劳效应是众所周知的。为了研究多晶硅中这种现象的起源，我们开发了一种固定夹式断裂力学微试样，但没有发现静态应力腐蚀开裂的证据。在循环加载下，还研究了抗疲劳性的环境敏感性。对于低周疲劳，其行为与环境条件无关，无论是空气还是真空，但受到每个循环中压缩应力与拉伸应力之比的强烈影响。疲劳损伤很可能源于与加工相关的表面粗糙度处的接触应力；随后在进一步的循环加载过程中会发生亚临界裂纹扩展。高周疲劳中涉及的较低远场应力会导致疲劳损伤水平降低。在这些条件下，像实验室空气这样的腐蚀性环境会加剧疲劳过程。没有循环加载时，多晶硅不会发生应力腐蚀开裂。
