A Study on Method for Evaluating Fracture Strength of Brittle Thin Films Using a Small Spherical Indentation

本研究的目的是研究用小球形压痕评价脆性薄膜断裂强度的方法。本文的主要研究成果总结如下：采用十字形微试样对厚度为2mum的permaloy - SiO_2薄膜的Young's E和断裂强度sigma_f进行了评价。结果表明，E和sigma_f几乎可以用所提出的方法求得。采用球形压头压痕法，对WC基板上涂覆厚度为2mum的TiN膜或Al_2O_3膜的微断裂强度进行了评价。结果表明，球形压头越小，环形裂纹起裂强度越大。本文尝试用有效面积的概念，从环形裂纹起裂强度来估计块状材料的弯曲断裂强度。得到了合理的弯曲断裂强度值。在评价用球形压头压痕涂覆在基材上的薄膜的断裂强度之前，用Si_3N_4球形压头对Si_3N_4块状板进行了压痕试验。利用有效面积的概念，研究了压痕试验评价的环形裂纹起裂强度与弯曲断裂强度之间的关系。结果表明，环形裂纹起裂强度大于弯曲断裂强度，且球形压头越小，环形裂纹起裂强度越大。利用有效面积的概念，发现环裂纹起裂强度不能与常规弯曲断裂强度相关联。为了找出用球压痕法评价的Si_3N_4块板的环形裂纹起裂强度与常规弯曲断裂强度不能相关联的原因，采用有效面积的概念，建立了表面微裂纹的环形裂纹起裂模型。验证了环形裂纹起裂强度与弯曲断裂强度的差异可以定性解释。少

The aim of this research is to study the method for evaluating fracture Stregth of brittle thin films using a small spherical indentation. The principal results of the research are summarized as follows.1. An attempt was made to evaluate Young's E and fracture strength sigma_f of a thin film of permaloy and SiO_2 with a thickness of 2mum using cross-shaped micro-specimens. It was found that E and sigma_f could be evaluated nearly using the proposed method.2. The microfracture strength of TiN film or Al_2O_3 film with a thickness of 2mum coated on a WC substrate was evaluated by indenting a spherical indenter. It was found that as spherical indenter was smaller, the ring crack initiation strength was large. An attempt was made to estimate the bending fracture strength of the bulk materials from the ring crack initiation strength using the concept of effective area. A reasonable value was obtained for the bending fracture strength.3. Before evaluation of fracture strength of a thin film … More coated on a substrate by indenting a spherical indenter, indentation tests on Si_3N_4 bulk plates using a Si_3N_4 spherical indenter were carried out. The relationship between the ring crack initiation strength evaluated from indentation tests and bending fracture strength was examined using the concept of effective area. It was found that the ring crack initiation strength was larger than the bending fracture strength and as spherical indenter was smaller, the ring crack initiation strength was larger. It was found that ring crack initiation strength could not be related to conventional bending fracture strength, using the concept of effective area.4. To find the cause that the ring crack initiation strength of Si_3N_4 bulk plates evaluated by the sphere indentation method could not be related to conventional bending fracture strength, using the concept of effective area, a ring crack initiation model of a surface microcrack was applied. It was confirmed that the difference between the ring crack initiation strength and bending fracture strength could be interpreted qualitatively. Less