Dynamic deformation mechanism of a single-crystal nickel-based superalloy at various temperatures

Abstract

The demand for engineering materials that can work under high temperatures has never stopped since the invention of jet turbine engines. During their operations, some engine components experience high stress states under high temperatures and severe corrosive environments. Materials have been specially designed to make these components, which are called superalloys. Single-crystal nickel-based superalloys are some of the most commonly used superalloys nowadays. They have been extensively studied, and a lot of their properties were well understood, such as their creep, fatigue, and corrosion resistance properties. However, their deformation mechanism at high temperatures and strain rates has been seldomly studied and reported in the literature. It is problematic, since the superalloys can experience such deformation during their applications. It is dangerous to use them when there is the major flaw in our understanding in them. In light of the situation, this research project focused on the dynamic deformation mechanism of a single-crystal nickel-based superalloy at high temperatures.

This report consists of two major sections. The first section focuses on the design of a new high temperature Split-Hopkinson tensile bar (SHTB) setup. SHTB is an equipment used to perform high strain rate tensile tests. Many of the existing high temperature SHTB setups are not well-developed yet. Therefore, a new and improved setup was proposed in this report. It would be used to perform high temperature tensile tests on a single-crystal nickel-based superalloy. The second section of this report focuses on the mechanical behavior and microstructural evolution of the superalloy deformed at various temperatures and strain rates. At high temperatures, it was found that as strain rate increased, the superalloy’s strength decreased. Through microstructural analysis, it was revealed that the dislocation structures of the superalloy deformed at these two conditions are significantly different. The difference in dislocation structure may suggest different deformation mechanisms, which may in turn explain the difference in strength.