Effect of Ru additions on microstructure and mechanical properties of Cr-TaCr2 alloys

Early work indicated that Ru reduced the ductile-to-brittle transition temperature of Cr even at small concentrations. To evaluate the potential of Ru as a beneficial alloying element in the two-phase Cr-TaCr2 alloys, a number of Cr-8 at.%Ta alloys with 0-10 at.%Ru were prepared, and their microstructures and mechanical properties were evaluated. The Ru addition was found to move the eutectic point of Cr-TaCr2 to a higher Ta level, as compared to the binary Cr-Ta system. Ru partitioned preferentially in the Laves phase over in the Cr matrix, with a partitioning ratio of 2-5:1, depending on the Ru addition level. Ru was also found to mainly occupy the Cr site in the TaCr2 Laves phase. The hardness of both the primary Cr matrix and the eutectic microconstituent increased slightly with the increase in Ru addition. At a higher Ru addition level (i.e. 10 at.%), the hardness of the primary Cr matrix increased significantly, probably due to the precipitation of extremely fine Laves-phase precipitates. The Ru addition did not noticeably affect the fracture toughness of the two-phase alloys.