HfCo 2 Laves phase intermetallics—part II : elastic and mechanical properties as a function of composition

Abstract

In efforts to establish and understand structure–property relationships in Laves phase intermetallics, elastic and mechanical properties are studied as a function of composition in the C15 HfCo 2 system. Elastic constants and Debye temperatures are determined by resonant ultrasound spectroscopy (RUS) at room temperature. A maximum near the stoichiometric Laves composition is revealed with the Young's modulus, bulk modulus, and Poisson's ratio. In addition, a slight drop in shear modulus is found with Co-rich compositions, and the Debye temperature increases with Co-content. Room temperature Vickers indentation is performed to assess the microhardness and fracture toughness of the HfCo 2 alloys. A maximum in hardness occurs near the stoichiometric composition, which is contrary to the behavior displayed in most other classes of intermetallics. Slight improvements in the toughness are found with the Co-rich compositions of the Laves phase. Compositional trends of the properties are attributed to defect structures, and are analyzed with respect to the bonding of the structure and the ease in which the synchroshear deformation process proceeds. Toughening strategies and methodologies are then developed based upon these results.