Characterizations on the microstructure and micro-mechanics of cast Be-Al-0.4Sc-0.4Zr alloy prepared by vacuum induction melting

The cast Be-Al-0.4Sc-0.4Zr alloy is attractive for potential applications in numerous fields owing to the advantageous performance closely related to its microstructure and mechanical properties. This work investigates the microstructure and micro-mechanical properties of this alloy using various characterizing methods. In addition to the pronounced microstructure modifications, it was determined that both the scandium (Sc) and zirconium (Zr) preferentially formed intermetallic compounds with Be in the melt, and the majority of secondary phases existed in the Al matrix rather than the Be matrix. The calculated disregistry of lattice spacing, all greater than 15%, for the Al3Sc/Be and Be13Sc/Be couples indicated the secondary phase particles (SPs) did not act as effective nucleation sites for the Be. The calculated Gibbs energy and thermal analysis results both revealed, for the first time, that the Be13Sc formed spontaneously in the melt below the temperature of 1350 °C. Micro-mechanics including the reduced modulus and micro-hardness of the dispersed SPs (approximately 300 GPa and 16 GPa), the Be (approximately 320 GPa and 5.2 GPa) and Al (approximately 166 GPa and 0.6 GPa) matrices were determined by nano-indentation. The pop-in events at the depth near 10 nm on the load–depth curves for the SPs and the Be phase were attributed to the surface oxide layer, whereas those near 30 nm were due to their intrinsic properties. The true micro-hardness of the SPs and the Be phase were determined to be 4.68 GPa and 15.46 GPa via material pile-up corrections. The mechanism embodied by the homogeneous dislocation nucleation and propagation for the SPs was facilely concluded with the critical shear stress of 6.0 GPa and dislocation loop radius of 2.7 nm obtained.