Analysis of evolution law and mechanism of stacking fault density of M7C3 carbides under the action of the electric current pulse

Abstract

Stacking faults are often found in M7C3 carbides, and stacking fault density has an important impact on their properties. This study explores the evolution law and mechanism of the stacking fault density of M7C3 carbides under the action of an electric current pulse (ECP). ECP at different current densities was passed into the alloy melt during solidification. The results show that the Cr/Fe ratios in the carbides first decreased and then increased as the current density increased, and the stacking fault density first increased and then decreased. The high-density stacking faults cause the carbide microhardness to be approximately 200Hv0.3 higher than those with low stacking faults when the Cr/Fe ratio is the same. First-principles calculations show that the M7C3 stacking fault energy decreased with increasing Fe content. The increase in iron content was the thermodynamic factor leading to the evolution of stacking fault density. During alloy solidification, ECP led to rapid carbide growth and a decrease in the thickness of the solute diffusion layer at the solid-liquid interface, which induced a change in the Cr/Fe ratio of the carbides. This is the dynamic factor for the evolution of stacking fault density.