High temperature microstructural and mechanical characterization of bulk materials and surface coatings utilizing hot micro-indentation techniques

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High temperature materials provide the basis for a wide variety of technology areas, including energy, electronic, photonic, and chemical applications. These materials are required to bear high stress and to combat severe corrosion and wear attack at high temperatures. Metallic materials change in microstructure with temperature because of phase transformations and crystal or grain alterations, as well as the occurrence of diffusion and homogenization. The change of microstructure will certainly affect the properties of the material. However, due to the limitations of many testing facilities/methodologies and due to the complexity of analytical approaches, studies in high temperature behaviour of materials have been rarely reported, which significantly limits the applications of these materials. The proposed research will be focussed on three issues: (1) In situ investigation of microstructural change of materials with temperature. (2) Study of mechanical behavior of materials at elevated temperatures. (3) Evaluation of fracture toughness of coatings at elevated temperatures. The research approach will use a hot micro indentation tester, which allows microstructural characterization of materials at elevated temperatures. This instrument also enables indentation to be made on individual phases of a microstructure, which provides the measuring of micro hardness. The most important feature of this test is that indentation generates cracks in brittle materials, thus allowing quantitative assessment of fracture toughness of the materials at elevated temperatures. Accurate measurement of the hardness and determination of the fracture toughness for a coating are a challenge because multiple factors may influence the results (for example, coating thickness, indentation load, interfacial bonding, substrate material and so on). The effects of these factors may become even more complex at elevated temperatures. However, these material properties are imperative for coatings in application. To this end, an attempt will be made in this research to develop an indentation based method and the associated fracture mechanics model for fracture toughness assessment of brittle coating/ductile substrate systems at elevated temperatures.