Development of high-temperature hardness and fracture toughness models for superalloy coatings based on micromechanics theory

术语超级合金用于描述通常在工作温度超过约540ºC时使用的镍基或钴基合金。这些合金还含有高铬、中等量的钨和/或钼以及少量的碳或硅。由于其独特的化学成分和微观结构，这些合金具有优异的耐磨性、高温下的机械强度和抗蠕变性、良好的表面稳定性以及抗腐蚀和抗氧化性。近年来，随着工业应用中许多机械部件（例如，燃气涡轮机发动机中的热段部件）的工作温度和磨损/腐蚀严重程度的提高，以及涂层沉积技术的进步，高温合金更常用作表面涂层以保护能源和航空航天工业中的机械免受高温环境中的磨损和腐蚀攻击。然而，由于现有的测试设备和方法的限制，这些涂层的高温力学性能很难评估，因此很少有报道。这些性能的缺乏极大地限制了这些合金的应用。为此，拟议的研究的目的是开发高温硬度和断裂韧性模型，用于评估或评估基于微观力学理论的高温合金涂层的强度。高温微压痕为基础的方法，结合微断裂力学理论，在模型的开发。硬度和断裂韧性之间的关系将建立揭开神秘的机制，管理的高温合金涂层的断裂/失效。此外，本研究还试图以较少的试验误差，为高温合金涂层的设计和制备提供参考，从而节省试验成本，缩短设计和制备周期。所提出的高温合金涂层高温硬度测定和断裂韧性评估方法可推广到陶瓷、金属陶瓷复合材料等一系列涂层系统。

The term superalloy is used to describe nickel- or cobalt-based alloys that are generally employed when operating temperatures are beyond about 540ºC. These alloys also contain high chromium, moderate tungsten and/or molybdenum, and minor carbon or silicon. Because of their unique chemical compositions and microstructures, these alloys possess excellent wear resistance, mechanical strength and creep resistance at high temperatures, good surface stability, and corrosion and oxidation resistance. In more recent years, with the increasing of operation temperature and wear/corrosion severity for many mechanical components in industrial applications, for example, the hot-section components in gas turbine engines, and the advance of coating deposition technologies, superalloys are more often used as surface coatings for protection of machinery in energy and aerospace industry against wear and corrosion attacks in high-temperature environments. However, due to the limitations of the existing testing facilities and methodologies, the high temperature mechanical properties of these coatings are difficult to assess, and hence have been rarely reported. The lack of these properties has significantly limited the application of these alloys. To this end, the proposed research is aimed to develop the high temperature hardness and fracture toughness models for evaluating or assessing the strength of superalloy coatings based on micromechanics theory. High-temperature microindentation-based approaches will be employed, combined with microfracture mechanics theory, in the model development. The relationship between hardness and fracture toughness will be established to demystify the mechanisms that govern the fracture/failure of superalloy coatings. Furthermore, this research also attempts to contribute to the advance of design and fabrication of superalloy coatings with less trial and-error, thus saving the experimental cost and shortening the design and fabrication cycle. The proposed methods for high temperature hardness determination and fracture toughness assessment of superalloy coatings can be extended to a range of coating systems such as ceramics, metal ceramic composites, etc.