Atomic Species Associated with the Portevin–Le Chatelier Effect in Superalloy 718 Studied by Mechanical Spectroscopy

Abstract

In many Ni-based superalloys, dynamic strain aging (DSA) generates an inhomogeneous plastic deformation resulting in jerky flow known as the Portevin-Le Chatelier (PLC) effect. This phenomenon has a deleterious effect on the mechanical properties and, at high temperature, is related to the diffusion of substitutional solute atoms toward the core of dislocations. However, the question about the nature of the atomic species responsible for the PLC effect at high temperature still remains open. The goal of the present work is to answer this important question; to this purpose, three different 718-type and a 625 superalloy were studied through a nonconventional approach by mechanical spectroscopy. The internal friction (IF) spectra of all the studied alloys show a relaxation peak P 718 (at 885 K for 0.1 Hz) in the same temperature range, 700 K to 950 K, as the observed PLC effect. The activation parameters of this relaxation peak have been measured, E a (P 718) = 2.68 ± 0.05 eV, s 0 = 2AE10 À15 ± 1 s as well as its broadening factor b = 1.1. Experiments on different alloys and the dependence of the relaxation strength on the amount of Mo attribute this relaxation to the stress-induced reorientation of Mo-Mo dipoles due to the short distance diffusion of one Mo atom by exchange with a vacancy. Then, it is concluded that Mo is the atomic species responsible for the high-temperature PLC effect in 718 superalloy.

Effect of ZrH2 particles on the microstructure and mechanical properties of IN718 manufactured by selective laser melting

“…In the latter case, DSA was reported in specimens deformed at high temperature (>550ºC) but not at room temperature. It was attributed to the interaction of substitutional atoms (mainly Nb) in solid solution with dislocations [32][33][34]. The lack of DSA at ambient temperature (Fig.…”

“…However, it was obvious that the heat treatment enhanced this mechanism, which could also contribute to the excellent strength retention at 550ºC. DSA has been observed in IN718 manufactured by traditional routes [32][33] as well as by additive manufacturing [34]. In the latter case, DSA was reported in specimens deformed at high temperature (>550ºC) but not at room temperature.…”

Experimental and numerical analysis of the Portevin–Le Chatelier effect in a nickel-base superalloy for turbine disks application

“…At low temperature the PLC effect is attributed to the interaction between carbon atmosphere and mobile dislocations during plastic deformation (Chen and Chaturvedi, 1997;Hale et al, 2001). The occurrence of jerky flow has been ascribed to the effect of Cr, (Hale et al, 2001), Nb (Hayes, 1983;Nalawade et al, 2008) and Mo (Max et al, 2014(Max et al, , 2018.…”

Physics-Based Flow Stress Model for Alloy 718

“…In addition, several researchers investigated the dynamic strain aging (DSA) behavior of the alloy when deformed between 400 °C and 700 °C at low strain rates in the range of 10 -3 to 10 -1 s À1 . [2][3][4][5][6][7] The deformation behavior of alloy 718 in the medium and high strain rate domain (~10 2 s À1 and above) has mostly been studied at temperatures up to 800 °C. [8][9][10][11][12][13][14] Research about dislocation density-based plasticity models have been published for fifty years.…”