Effect of Temperature and Strain during Forging on Subsequent Delta Phase Precipitation during Solution Annealing in ATI 718Plus® Alloy

Abstract

ATI 718Plus ® alloy relies upon grain boundary precipitation of the delta phase in order to achieve good resistance to notch failure. Delta phase precipitation can occur when forging at subsolvus temperatures or during solution annealing. Precipitation of delta phase during solution annealing can be affected by the interaction of forging temperature and strain during hot working whereby the combination of high forging temperature and low strain can result in unsatisfactory delta phase precipitation. Additionally, delta phase precipitation can be affected by exposure to supersolvus temperatures after forging is complete. This paper describes the effect of thermal mechanical processing history on delta phase precipitation in ATI 718Plus alloy and provides guidance on best practices to achieve optimum microstructure.

Grain boundary precipitation in Inconel 718 and ATI 718Plus

“…Similar to Inconel 718, increasing the level of strain also causes increased η phase precipitation within ATI 718Plus [54,55]. Casanova et al [56] found that within the microstructure of components made with ATI 718Plus, two main morphologies co-exist together; coarse plates and thin lamellae, and the origin of these were investigated by the author.…”

“…However, it would be of interest to obtain experimental volume fraction data at lower temperatures to see if these discontinuities can be validated. McDevitt [54] investigated the effect of thermomechanical processing on η phase precipitation in ATI 718Plus, and found that the kinetics of precipitation are increased as the level of residual strain is increased. Casanova et al [57] also reached the same conclusion in that areas with higher levels of residual strain produced faster precipitation kinetics.…”

“…Casanova et al [57] also reached the same conclusion in that areas with higher levels of residual strain produced faster precipitation kinetics. McDevitt [54] also found that η phase precipitation is inadequate during annealing after deforming the material at temperature above the η solvus temperature.…”

Effect of Strain Hardening on Precipitation Kinetics in ATI 718Plus

“…Although relatively little literature exists regarding the effect of deformation on precipitation kinetics within nickel superalloys, some authors have found that increasing the level of strain also causes increased η phase precipitation within ATI 718Plus [13,14]. Casanova et al [15] found that within the microstructure of components made with ATI 718Plus, two main morphologies co-exist together; coarse plates and thin lamellae, and the origin of these were investigated by the author.…”