In-situ EBSD study of deformation behavior of Inconel 740H alloy at high-temperature tensile loading

Abstract

Plastic deformation behavior of Inconel 740H superalloy during uniaxial tension at high temperature was investigated. The self-developed in-situ high-temperature tensile stage provides a better method for the study of tensile deformation of materials under different conditions. By a joint application of in-situ SEM and EBSD techniques, the tensile mechanical properties, microstructure, orientation, and grain boundary evolutions under near-service conditions (650 °C) were experimentally investigated. The results obtained show that due to the different grain orientations of polycrystalline metals, the grains with preferable orientation begin to slip first under the external force, while those orientation of harder grains will slip until they rotate to favorable orientation. In order to ensure the continuity of the matrix, the deformation between grains must be coordinated. Meanwhile, in-situ observation of the grain rotation at high temperature shows that rotation angles and paths of different grains are related to the initial orientation. By tracing typical grains and analyzing the grain rotation during in-situ EBSD testing, it was found that some grains with randomly distributed orientation at the initial state gradually changed to the direction between [001] and [111] poles with the stress increasing. This complies with the overall trend of a single grain rotation. However, after that the grains tend to reach the [101] pole rather than the stable orientation [112]. During the total deformation process, low-angle boundaries form and accumulate at the grain boundaries with concentration of stresses. While high-angle boundaries are slightly affected by the tensile deformation, and the density of twin boundary (TB) decreases.