Dynamic tensile properties of a single crystal Nickel-base superalloy at high temperatures measured with an improved SHTB technique

Abstract

In this study, to characterize the high-rate tensile properties of a Nickel-base single crystal superalloy at high temperatures, an improved technique for conducting split Hopkinson tensile bar (SHTB) tests at high temperatures (up to 1200°C) is developed. A Quick Hook Joint method to rapidly mount the specimen to the SHTB system is adopted in the technique. Firstly, the specimen is heated to target temperature while keeping the bars at the room temperature. Then the Quick Hook Joint method is used to quickly assemble the specimen to the SHTB by a synchronically dual-actuator assembled system, immediately before loading is imposed to the specimen. The cold contact time (CCT) experienced by the specimen is measured by laser sensors and the cold contact process is numerically simulated. The results show that no evident temperature decrease in the specimen gauge section and no significant temperature increase in the loading bars. Finally, tensile experiments of a single-crystal Nickel-base superalloy over a temperature range of 298–1473K and over a strain-rate range of 0.001–3000s−1 are conducted. Anomalous high temperature peak of flow stress is noticed in the experimental results, and the peak of the flow stress shifts to higher temperature as the strain rate increases. Anomalous temperature valley of the fracture strain is formed over the selected temperature range, and the valley of the fracture strain also shifts to higher temperature as the strain rate increases. A model is applied to quantitatively describe the strain-rate effect on the anomalous peak of the flow stress over a wide range of strain rates.