Insights into Dynamic Hardness of B2 Iron Aluminide using Ultra-high Constant Indentation Strain Rate Testing
This project aims to investigate the dynamic hardness of B2-iron aluminides at high strain rates using an in situ nanomechanical tester capable of indentation up to constant strain rates of up to 100000 s−1 and study the microstructure evolution across strain rate range.
Binary and multicomponent iron-aluminides are envisioned as potential replacements for various high-end structural and aviation applications and have been rigorously investigated in the past. The investigation of potential applications demands next to high-throughput synthesis also a quick assessment of the mechanical properties of newly designed alloy compositions under a wide variety of service-relevant loading conditions including extremely high strain rates. However, owing to the limitations of classical micro/nanomechanical instruments and necessary complex protocols, rate-dependent dynamic hardness measurements at constant indentation strain rates are typically limited to maximum rates of 100 s-1. In the current study, we have successfully expanded the constant strain rate regime to 100,000 s-1 and applied it to B2 FeAl samples (~45 at% Al). In-house-built high-speed piezo-based micromechanical testing instrumentation involves custom-modified electronics hardware and testing protocols to obtain the high-fidelity load-displacement signals and subsequently, hardness values from it. A linear trend in strain rate sensitivity of hardness for single-crystal FeAl grains was identified, which was also found to be independent of the grain orientation. Post-deformation orientation mapping beneath the indent using TEM showed a more pronounced formation of dislocation substructures at higher strain rates.
