The development of deformation mechanism during tension at different strain rates for GH4169 superalloys quantified by in-situ acoustic emission

Abstract

The effect of strain rate on deformation has been an important issue involving material processing and service performance, where, however, the underlying mechanism is still an open question. Especially, the quantitative understanding of mechanism development during the deformation process remains unclear. In the present work, in-situ acoustic emission (AE) measurement has been performed on GH4169 superalloys at different strain rates ranging from 3.3 × 10−5 s−1 to 3.3 × 10−3 s−1, where a quantitative investigation on mechanism development during tension is achieved. The adaptive sequential k-means (ASK) algorithm has been used to extract deformation mechanisms from the AE signals. The main results show that the precipitates shearing and the slip bands are the dominating AE sources during the deformation process, which has been firmly supported by the ex-situ observation on microstructures. Furthermore, the average level of AE energy decreases with the strain rate, which suggests that the density of mobile dislocations is lower and the width of the slip band is narrower when superalloys are deformed at a relatively higher strain rate. The high-energy AE events are concentrated in the initial transitional stage with the appearance of a peak, which, however, decrease with the strain rate in the linear hardening stage. Meanwhile, the cumulative AE energy and AE number contributed from the precipitates shearing are predominant as compared with those from the slip bands, which gives a hint that the precipitates shearing plays the principal role in the deformation process. However, when the strain rate is relatively high, the effect of the slip bands becomes more significant, which leads to deteriorative ductility. Those findings might provide some insight into the deformation, strengthening and failure mechanisms for nickel-based superalloys.