High Temperature Nanoindentation of Ni-base Superalloys

Novel techniques for characterizing and assessing the properties of Ni-base superalloys are becoming increasingly important to the accelerated development of new structural alloys and the advancement of physics-based mechanical property models. Instrumented indentation techniques have long served as a useful approach for probing the mechanical response of a wide range of engineering materials. Nano and micro-indentation techniques are particularly well suited for measuring the properties of materials and structures in which the size or volume of the sample would make conventional mechanical testing methods cumbersome or cost prohibitive. Deformation volumes can be carefully controlled such that indentation can be applied to probe the properties of specific phases or features present within the microstructure. Moreover, recent developments in micromachining of micropedestal specimens via focused ion milling, chemical etching or femtosecond laser ablation allow for the direct assessment of compressive stress-strain responses using indentation equipment. Since high temperature structural materials, such as Ni-base superalloys, are primarily used in a variety of critical applications for turbine engines, materials development and usage of life prediction models has traditionally been extremely conservative. Predictive physics-based deformation models may increase the confidence of the property values and minimize some of the design conservatism, thus allowing more efficient materials usage and contributing to more efficient engine operation. Such predictive models may also accelerate the development of high temperature structural materials with improved temperature capability to further enhance engine performance. Recent developments have led to the ability to conduct instrumented micro/nano-indentation at elevated temperatures. Utilization of high temperature indentation techniques may potentially address some of these challenges associated with understanding the fundamental deformation mechanisms across limited length scales as well as establish new methods of utilizing combinatorial techniques for the design of structural materials.