Effect of heat treatment on acoustic emission in a nimonic alloy PE 16 during tensile deformation

Abstract

Acoustic emission (AE) monitoring during tension tests gives valuable information for the interpretation of mechanisms of deformation fracture etc. AE monitoring was done on the Nimonic PE-16 alloy with different microstructures, during tension to study the dynamic changes taking place during plastic deformation. The microstructures were imparted by various heat treatments. The microstructures with austenitic matrix (γ) with precipitates and carbides have been selected, and the effects of precipitation hardening on AE behaviour discussed. The tension tests were carried out in both solution annealed (1313 K/4 hrs.) and precipitation hardened (1073 K/1/2 hr. + 973 K/8 and 24 hrs.) conditions. A large increase in acoustic emission observed in the precipitation hardened specimens is explained in terms of the dislocation avalanche model. Generation of stronger AE events in the solution annealed specimens compared to those in the precipitation hardened specimens is explained as due to the operation of Frank-Read sources (mostly grain boundaries) having large dislocation mean free path.