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

高温材料为各种各样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。随着温度的升高，金属材料的显微组织会发生变化，主要是由于相变、晶体或晶粒的变化，以及扩散和均质化的发生。微观结构的变化必然会影响材料的性能。然而，由于许多测试设备/方法的局限性以及分析方法的复杂性，材料高温行为的研究很少被报道，这极大地限制了这些材料的应用。研究方向主要集中在三个方面：(1)原位研究材料的微观组织随温度的变化。(2)材料在高温下的力学行为研究。(3)涂层高温断裂韧性评价。研究方法将使用热微压痕测试仪，它允许在高温下对材料进行微观结构表征。该仪器还可以在微观结构的各个相上进行压痕，从而提供显微硬度的测量。该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。涂层硬度的精确测量和断裂韧性的确定是一个挑战，因为多种因素可能会影响结果（例如，涂层厚度、压痕载荷、界面结合、基材材料等）。这些因素的影响在高温下可能会变得更加复杂。然而，这些材料性能对于涂料的应用是必不可少的。为此，本研究将尝试开发一种基于压痕的方法和相关的断裂力学模型，用于脆性涂层/韧性基体系统在高温下的断裂韧性评估。

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.