Microstructural, Mechanical, and Damping Properties of a Cu-Based Shape Memory Alloy Refined by an In Situ LaB₆/Al Inoculant

In order to solve the problem of intergranular brittle fracture of Cu-based shape memory alloys (SMAs) and further improve their mechanical properties, an in situ LaB₆/Al inoculant was designed and used for the first time to significantly refine the grains of a CuAlMn SMA. Through phase analysis, microscopic observation, and theoretical calculation, it was confirmed that the LaB₆ particles in the inoculant could act as efficient heterogeneous nuclei of the CuAlMn SMA. The evolution of microstructures with grain refinement and its influence on the mechanical and damping properties were also investigated. It was found that with the decrease of the average grain size, the martensite structure of the CuAlMn SMA was also dramatically refined. Consequently, because of the increase of phase interface density, the damping capacity of the CuAlMn SMA was improved and the elongation, tensile strength, and yield strength were also significantly improved due to the principle of fine grain strengthening. After hot rolling, the average grain size of the refined CuAlMn SMA increased slightly, while the damping, tensile strength, and elongation were further improved, which has been ascribed to the elimination of casting defects and the increase of density.