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

高温材料为广泛的技术领域提供了基础，包括能源、电子、光子和化学应用。这些材料需要承受高应力，并在高温下抵抗严重的腐蚀和磨损侵蚀。金属材料的显微组织随温度发生变化，这是由于相变、晶界或晶界的变化以及扩散和均匀化的发生。显微组织的变化必然会影响材料的性能。然而，由于许多测试设备/方法的局限性和分析手段的复杂性，关于材料高温行为的研究很少有报道，这大大限制了这些材料的应用。拟开展的研究主要集中在三个方面：(1)材料微观结构随温度变化的原位研究。(2)高温下材料力学行为的研究。(3)涂层高温断裂韧性的评定。研究方法将使用热微压痕测试仪，它允许在高温下对材料的微观结构进行表征。该仪器还可以在显微组织的各个相上进行压痕，从而提供显微硬度的测量。这种测试最重要的特点是压痕在脆性材料中产生裂纹，从而可以定量评估材料在高温下的断裂韧性。准确测量涂层的硬度和确定涂层的断裂韧性是一项挑战，因为多个因素可能会影响结果(例如，涂层厚度、压痕载荷、界面结合、基材等)。在温度升高的情况下，这些因素的影响可能会变得更加复杂。然而，这些材料的性能对于涂料在应用中是必不可少的。为此，本研究试图开发一种基于压痕的方法和相关的断裂力学模型，用于评估脆性涂层/韧性衬底系统的高温断裂韧性。

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.