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Microstructure of Crack Tip Plastic Zone and Fracture Toughness In Silicon Crystals

硅晶体裂纹尖端塑性区的微观结构与断裂韧性

基本信息

批准号：
14550656
负责人：
HIGASHIDA Kenji
金额：
$ 2.3万
依托单位：
Kyushu University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2003
项目状态：
已结题

项目摘要

In order to understand the dislocation process In the plastic zone and its relation to the fracture toughness In silicon crystals, microstructures of plastic zones around crack tips have been investigated using high voltage electron microscopy (HVEM) and atomic force microscopy (AFM). Cracks were Introduced Into (110) silicon wafers at room temperature by Vickers indentation method. The temperature of specimens indented was raised to higher than 823K to activate dislocation sources around a crack tip under the presence of residual stress due to the indentation. AFM study has revealed two types of fine slip bands : one type Is slip bands oblique to the direction of crack propagation, I.e., <110>, and another type is those parallel to this <110> direction. The former is corresponding to a hinge-type plastic zone, and the later is so-called 45゜-shear-type. HVEM study has also revealed the characteristic of dislocation structures developed in the both types of plastic zones. The correspond … More ence between AFM and HVEM results is verified, and the characteristics found in the both plastic zones are discussed. In addition to the HVEM and AFM studies, stress fields around a crack tip in silicon crystals have been investigated by using infrared photoelasticity with the aim of clarifying the shielding effect due to crack tip dislocations on the steep increase of fracture toughness in the brittle-to-ductile transition (BDT). first, compact tension tests were carried out at room temperature to make in-situ observation of elastic behavior of crack tip stress fields. The photoelastic images observed were In good agreement with those simulated for the usual elastic fields around the tip of a mode I crack. Next, to clarify the stress modification due to crack tip plasticity, three point bending tests were also made by using notched specimens at high temperatures around 1000K. After the high temperature test, in spite of the absence of the applied load, residual bright images were observed around the notch. Those images correspond to an internal stress due to dislocations multiplied around the notch, and they have an effect of shielding (accommodating) the stress concentration due to the applied load. The fracture toughness at room temperature was increased by the introduction of the residual stress. Less

为了了解硅晶体中塑性区的位错过程及其与断裂韧性的关系，用高压电子显微镜（HVEM）和原子力显微镜（AFM）研究了硅晶体中裂纹尖端塑性区的微观结构。用维氏压痕法在室温下对（110）硅晶片进行了裂纹的引入。压痕试样的温度升高到823K以上，在压痕产生的残余应力作用下激活裂纹尖端的位错源。AFM研究揭示了两种类型的细滑移带：一种是与裂纹扩展方向倾斜的滑移带，即，<110>另一种是平行于这个方向的<110>。前者相当于铰链型塑性区，后者相当于所谓的45度剪切型塑性区。HVEM研究还揭示了两类塑性区中位错结构的特征。相应 ...更多信息验证了AFM和HVEM结果之间的一致性，并讨论了两个塑性区的特征。除了HVEM和AFM的研究，应力场周围的裂纹尖端在硅晶体已被调查，通过使用红外光弹的目的是澄清屏蔽效应，由于裂纹尖端位错的断裂韧性急剧增加的脆韧性转变（BDT）。首先，在室温下进行了紧凑拉伸试验，对裂纹尖端应力场的弹性行为进行了原位观测。所观察到的光弹性图象与对Ⅰ型裂纹尖端通常弹性场的模拟结果符合得很好。接下来，为了阐明由于裂纹尖端塑性引起的应力修改，还通过使用缺口试样在1000K左右的高温下进行了三点弯曲试验。在高温试验后，尽管没有施加载荷，但在缺口周围观察到残留的明亮图像。这些图像对应于由于在缺口周围倍增的位错引起的内应力，并且它们具有屏蔽（容纳）由于施加的载荷引起的应力集中的效果。残余应力的引入提高了材料的室温断裂韧性。少