Accelerating Hardening Response of Martensitic Stainless Steel by Copper-Rich Cluster Formation Under Pulsed Electric Current

Abstract

The pursuit of excellent comprehensive mechanical properties with rapid aging process is practically significant across aging strengthening field. The pulsed electric current assisted aging process could effectively accelerate the aging and reduce the energy consumption provoked by long-term thermal aging. Here, the enhancement of pulsed electric current on Cu-rich cluster formation was investigated to better understand the accelerating behavior. The size and structure of Cu-rich cluster was characterized using transmission electron microscopy and the results showed the pulsed electric current could not change the mechanism of aging strengthening, but accelerated the process. The time to attain the peak aging become shorter due to the athermal effect (interaction between atoms and electrons) induced by pulsed electric current. Nevertheless, The athermal effect decreases as the temperature increases, and the relationship between athermal effect and temperature is obtained. When the current density of 7×10 7 A/m 2 was applied, the precipitation activation energy of Cu-rich clusters decreased by 91 kJ/mol, which is embodied in the following two aspects: (1) The pulsed electric current lowers the vacancy formation energy, resulting in the increase of vacancy concentration. (2) The current density gradient caused by the difference in conductivity between the matrix and the Cu-rich clusters accelerates the substitution of Cu atoms and vacancies and reduces the atomic migration energy. These results provide insight into the effect of pulsed electric current on the kinetics of precipitation in martensitic stainless steels and elucidate the mechanism for the rapid growth of Cu-rich clusters.

Keywords: Pulsed electric current, Peak aging, Precipitation activation energy, athermal effect, Atomic drift rate