The Portevin-Le Chatelier Effect in the Ni-Based Superalloy IN100

Abstract

The Portevin-Le Chatelier (PLC) effect has been studied in the Ni-based superalloy IN100 which is currently used as a disk material in jet engines. A series of tensile tests was carried out at 588 K, 755 K, and 922 K (315 °C, 482 °C, and 649 °C) at plastic strain rates ranging from a low of 6.21 × 10−6 s−1 to a high of 4.92 × 10−2 s−1. The activation energy was determined using the slope of a line on a strain rate/temperature graph which divided the area of the graph into two regions: (1) “PLC behavior observed,” and (2) “No PLC behavior observed.” A new statistical approach was developed to objectively differentiate between a true PLC effect and experimental uncertainty (i.e., “noise”). The value of the activation energy was found to be 1.14 eV/atom, which strongly suggests that the rate controlling process was bulk diffusion of C in the lattice. A qualitative model, based on the Orowan equation and slip band dislocation mechanics, was proposed, which unifies the seemingly disparate ideas of the process being controlled by a single atom/dislocation interaction while at the same time exhibiting significant strains during PLC load drops.