Dynamic high-temperature tensile characterization of an iridium alloy

Iridium alloys have been extensively utilized as structural materials in specific high-temperature applications, attributed to their superior strength and ductility at elevated temperatures. To enhance the understanding of high-speed impacts at elevated temperatures, it is imperative to characterize the mechanical properties of iridium alloys, including their failure response under high strain rates and elevated temperatures. In this study, the conventional split Hopkinson tension bar technique was modified to evaluate the tensile behavior of an iridium alloy at high strain rates and elevated temperatures. A dynamic high-temperature tensile testing technique for thin and flat specimens was established based on the high current heating method. A fixture with a slot was employed, enabling the specimen shoulder to bear the load and transmit it to the gauge section of the specimen. An integrated high current heater equipped with a self-controlled system was utilized to heat the iridium alloy specimen and maintain the desired high-temperature conditions. To prevent unintended heating of the bars, a pair of hollow water-cooled pillow blocks were installed. Moreover, to mitigate rapid cooling of the specimen, the cold contact time was meticulously controlled to be less than 1 ms. To elucidate the dynamic high-temperature properties of the iridium alloy, tensile tests were conducted using this technique at a strain rate of 103 s−1 and at temperatures of room temperature, 600, 900, and 1100 ℃. Experimental results revealed that as the temperature increased from room temperature to 900 ℃, the tensile strength of the iridium alloy decreased by 12%, while its ductility doubled. However, when the temperature was further elevated to 1100 ℃, the tensile strength decreased by 43%, and the ductility increased by a factor of 7.3. Macroscopic and microscopic analyses of the fracture morphologies were conducted to reveal the deformation mechanisms of the iridium alloy. It was found that with increasing temperature, the failure mode of the iridium alloy transitioned from predominantly intergranular fracture to plastic deformation and granular fracture. The dynamic fracture behavior of iridium alloy at high temperatures is governed by the competition between grain-boundary failure and granular softening.