Influence of coherent γ on acoustic emission generated during tensile deformation in Nimonic alloy PE16

Abstract

The influence of Ni₃(Al,Ti)-type γ precipitates in a Nimonic alloy PE 16 on the acoustic emission (AE) generated during room temperature tensile deformation has been studied. Various time domain AE parameters have been used to characterize the AE signals associated with particle shearing and Orowan looping processes in microstructures containing γ' with a mean radius of 6-20 nm. The presence of γ' led to a large-scale increase in acoustic activity compared with solution-annealed specimens. Particle shearing and Orowan looping processes generated AE events with higher peak amplitudes, energy and ringdown counts, longer event duration and higher rise time those generated in solution-annealed specimens. The generation of stronger AE signals from the particle shearing process compared with those with the Orowan looping process is attributed to the irreversible energy change associated with the former. It is possible to determine the predominant deformation process operating in a material having γ' precipitates with a mean radius of 10-50 nm using AE parameters, particularly the r.m.s. voltage near the yield region.