Effect Of Stacking Fault Energy On The Mechanical Behaviour Of Metallic Materials At Cryogenic Temperatures

Abstract

As science and society continue to advance, new metallic materials are being developed to meet increasing demands for environmental safety, reduced material consumption, improved life cycle performance, and cost-effectiveness. In many industries, a crucial requirement for materials is their ability to withstand extremely cold temperatures while maintaining good strength and ductility. Materials used for cryogenic applications must remain tough at low temperatures since any failure in such systems could have catastrophic consequences. Strength and ductility are essential prerequisites for materials in any structural application to ensure their effectiveness. It is widely acknowledged that metallic materials typically exhibit poor ductility when subjected to cryogenic temperatures. However, recent studies have shown that the ductility of high-entropy alloys can be improved at such low temperatures due to their ability to facilitate twinning behaviour, resulting in enhanced ductility. This research demonstrates that the same concept can be applied to simple binary alloys with a face-centred cubic structure to achieve high strength and excellent ductility at cryogenic temperatures. Copper-aluminium (Cu-Al) alloys were utilized as model materials, with aluminium contents below 12 atomic percent (at.%). Increasing the Al content significantly reduces the stacking fault energy that promotes deformation twinning. By adding different amounts of aluminium element solute, the strength and ductility of the alloys were improved to varying degrees, with the most significant improvement in ductility observed in Cu-7Al. Electron microscopy characterization revealed that high densities of deformation twins are responsible for the outstanding mechanical properties at cryogenic temperatures. Lowering the temperature promotes deformation twinning propensity, which benefits dislocation accumulation, leading to high strain hardening rates and excellent ductility. The research results provide a general guideline for future materials design for applications at cryogenic temperatures.