Tensile deformation behavior of a nickel based superalloy at different temperatures

Ni-based alloy Haynes 230 is of interest for high temperature applications (e.g. Intermediate Heat eXchanger (IHX)) because of its high temperature strength and oxidation resistance. In this work, the temperature dependence of the tensile behavior of the alloy and the strain rate effect was studied by tensile tests in the temperature range of 25–950 °C, at strain rates of 10−3 s−1, 10−4 s−1, and 10−5 s−1. The tensile strength decreased with increasing temperature regardless of the strain rate. The total elongation at rupture fluctuated more with temperature. The alloy showed an abnormal variation of the yield stress with increasing temperature i.e. the yield strength decreased slightly with temperature up to about 600 °C and then increased between 600 and 850 °C followed by a rapid decrease. This Yield Stress Anomaly (YSA) was however absent at the slowest strain rate of 10−5 s−1. SEM and TEM characterization was performed on fractured specimens to determine the predominant deformation mechanisms accounting for the observed Yield Stress Anomaly. serrations were observed in the stress–strain curves at temperatures above 300 °C, the shape and amplitude of which depended on temperature and strain rate. The analysis of the stress–strain curves coupled with the microstructure investigation of the fractured samples showed that two different deformation mechanisms occur depending on the temperature and strain rate. The saw-tooth type serrations at intermediate temperatures and higher strain rates were associated with dynamic strain aging whereas the oscillations with a sinusoidal shape were associated with dynamic recrystallization at temperatures higher than 800 °C and slower strain rates.