Crystal Viscoplastic Modeling of Film Cooling Holes in Single Crystal Nickel-Based Superalloys

Abstract

Abstract. In the advancement of gas turbine technology, increasing thermal efficiency is a primary objective, and one of the most effective methods to achieve this is through elevating the turbine inlet temperature (TIT). Higher TIT enhances the specific power output by enabling greater energy extraction from combustion gases. In the initial turbine stages, blades are exposed to TITs of approximately 1500 °C, which significantly exceed the thermal limits of most structural materials. As a result, effective cooling strategies are crucial to mitigate blade surface temperatures. Various advanced techniques are employed for turbine cooling, among which one of the most widely utilized methods is film cooling, which will be the focus of this study. Coolant is introduced through discrete holes located at the leading and trailing edges of the turbine blade, forming a protective film that insulates the blade surface from extreme temperatures. However, the presence of film cooling holes has a significant negative impact on the structural integrity and service life of turbine blades. Nickel-based superalloys (NBSAs) have been widely employed in gas turbine components, such as turbine blades, due to their superior mechanical and thermal properties, such as higher strength and resistance to creep and cyclic fatigue. The inclusion of film cooling holes leads to the development of complex stress concentrations and plastic stress localization in the region of the cooling holes, which are further influenced by the thermomechanical loading experienced by the turbine blade and the anisotropic properties of single crystal (SX) and directionally solidified (DS) NBSAs. These factors often lead to fatigue crack initiation, predominantly around areas consisting of densely placed cooling film holes along the leading edge of the turbine blade, which eventually leads to failure. Therefore, it is essential to evaluate the evolution of stress in the vicinity of film cooling holes to accurately predict fatigue behavior and improve turbine blade design. The primary focus of this study is to utilize the crystal viscoplastic (CVP) material models for a generic SX NBSA, previously developed by the authors. Finite element analysis will be carried out at various temperatures and material orientations to assess the effects of anisotropy on generic SX and DS NBSAs. Specimen geometries comprising a thin plate and a thin plate with densely arranged multiple holes are utilized to compare the effects of these configurations on the material and to assess the performance of the SX-NBSAs.