Dynamic compressive behavior of a single crystal nickel-base superalloy at ultra-high temperature: mechanism investigation with a modified electric synchronous SHPB technique

Abstract

A novel experimental technique conducted at a modified automatic split Hopkinson pressure bar (SHPB) for measuring the dynamic compressive behavior at ultra-high temperature up to 1700 °C was developed. A bidirectional electric synchronous assembly system, two high-precision delay controllers and an automatic control mechanism were employed to automate each section in the whole experiment process with high precision and high reliability. The cold contact time (CCT) between specimen and loading bars can be accurately and stably controlled to be shorter than 5 ms and the effect of CCT on temperature distribution can be eliminated. Based on this automatic high-temperature SHPB technique, an experimental investigation into the responses of a new in-service single-crystal Nickel-base superalloy DD10 subjected to impact loading at high temperature was undertaken. The influence of strain rate and temperature on the flow behavior of DD10 was tested and analyzed over a wide range of strain rate (0.001/s-4000/s) and temperature (25°C–1200 °C). The high temperature has an evident effect on the flow stress, strain hardening and strain rate sensibility. An anomalous peak of stress in true stress–temperature curve can be found, and the peak temperature increases with strain rate increasing. Through the microstructural observation, the influence of strain rate and temperature on the compressive deformation and fracture mechanism was discussed. At the high temperature above 1000 °C, the shear deformation mechanism of both γ matrix phase and γ′ precipitate phase is the dominant deformation mechanism at high strain rate, instead of the rafting mechanism of γ′ precipitate phase of under quasi-static loading condition.