Effects of microstructure on the evolution of dynamic damage of Fe50Mn30Co10Cr10 high entropy alloy

Abstract

The Fe50Mn30Co10Cr10 high-entropy alloy (HEA) was subjected to plate impact loading with a single-stage light gas gun and the Doppler pin system (DPS) was used to measure the velocity of free surface particles of the sample during loading. The effects of microstructure on the evolution of spallation of the Fe50Mn30Co10Cr10 HEA were investigated by means of electron back scattered diffraction (EBSD), optical microscope (OM) and X-ray diffraction (XRD) techniques. The results showed that the voids are neither nucleated at the martensite (M)/matrix interface nor nucleated in the M aggregated area (M area) with high impact resistance as predicted by impact dynamics, instead, voids nucleated inside the matrix phase with low impact resistance. The reason is that the lattice expansion during M transformation leads to the formation of compressive residual stress at the M/matrix interface as well as M area and tensile residual stress in the matrix, which promoted the preferential nucleation of voids in the matrix. Void nucleation in the matrix was not random: the tri-junction of general high angle grain boundaries (HAGBs) and the grain boundaries of adjacent grains with a large difference in Taylor Factor (TF) value were prone to stress concentration under tensile loading, which were the priority position for void nucleation. The void nucleation was inhibited by twin boundary (TB) due to its stable structure and low energy. However, the intersections of HAGBs and termination TB are the possible position for void nucleation due to its high interface energy. The compressive residual stress at the M/matrix interface and inside of M area has a closure effect on the microcrack, which caused the microcrack avoided the M area and propagated in the matrix and finally stopped at the M/matrix interface.