Microstructure and High-Temperature Strength in Cr-Si Binary Alloys

Cr-based alloys have potential as heat-resistant materials due to the higher melting point and lower density of Cr. Although oxidation and nitridation at high temperatures are one of the drawbacks of Cr and Cr-based alloys, addition of Si has been reported to enhance the oxidation and nitridation resistance. This study focuses on the microstructure and mechanical properties in the Cr-Si binary alloys with the Cr_ss + Cr₃Si two-phase structure. The Cr-16at.%Si alloy showed an eutectic microstructure and hypoeutectic alloys with the lower Si composition exhibited a combination of the primary Cr_ss and the Cr_ss/Cr₃Si eutectic microstructure. Compression tests at elevated temperatures were conducted for the hypoeutectic and the eutectic alloys in vacuum environment. Among the investigated alloys, the Cr-13at.%Si hypoeutectic alloy including the Cr₃Si phase of about 40% was found to show the highest 0.2% proof stress of 526 MPa at 1000 °C. Its specific strength is 78.1 Nm/g which is roughly twice as high as that of Ni-based Mar-M247 alloy. It was also confirmed that the 0.2% proof stress at 1000 °C depends on not only the volume fraction of the Cr₃Si phase, but also the morphology of the Cr_ss + Cr₃Si two-phase microstructure.