Can electric heating replace contact heating in high-temperature test for nickel base single crystal superalloy?

Abstract

Compared with contact heating or environmental heating in high-temperature test, electric heating has the advantage that it can realize in-situ high-temperature heating in SEM. Especially, it can simplify the heating and loading equipment and clearly obtain surface microstructure information of small scale specimens. However, due to the positive feedback characteristic of Joule thermal effect and other electro-induced effects in materials, such as the influence of electromigration and electric field on dislocation motion, etc. the effectiveness of high temperature mechanical properties of materials obtained under electric heating needs further study. In this paper, the tensile properties of nickel-based single crystal superalloy at room temperature to 950 ℃ were conducted using by electric heating and contact heating modes. The results show that when the heating temperature is below 600 ℃, the fracture mode and dislocation evolution of nickel base single crystal superalloy do not change significantly under two heating modes; When the heating temperature exceeds 600 ℃, the macroscopic mechanical properties change gradually, but the elastic modulus has no obvious difference. Through the distribution of two-phase elements, it is found that the relevant differences are mainly related to element migration. In addition to the thermal effect caused by electric current, the athermal effect promotes dislocation movement and element migration, which leads to the increasing difference of mechanical properties at high temperature under the two heating modes. These results show that at the temperature exceeds 600 ℃, the electric heating method is no longer suitable for studying the high-temperature mechanical properties of nickel-based single crystal superalloy.