Instrumented indentation of transforming and no-transforming phases in Cu-Al-Be shape-memory alloys

Abstract

The behavior of Cu-Al-Be alloys under instrumented indentation using a Berkovich tip was studied. The pseudoelastic effect was evidenced in the transforming β Cu-Al-Be phase as a closed hysteresis loop between the unloading-reloading paths in the P-h curves and high depth recovery ratios. From series of indentations conducted in the (β + γ 2) specimens, it was found that the indentation response of the two phases is remarkably different. Unlike the pseudoelastic β phase, γ 2 precipitates present an elastic-plastic behavior, obtaining a complete coincidence between the unload and reload path in the load-displacement curves, and a lower recovery capacity. An average contact pressure versus the penetration depth curve was estimated for each indentation curve, and results suggest that 8 GPa and 3 GPa can be considered an elastic limit for γ 2 and β phase respectively under Berkovich indenter stress state. The elastic modulus and the hardness of both phases were estimated from load-displacement curves using the Oliver and Pharr method.