Mechanical properties of Nb based multiphase alloy studied by nanoindentation and atomic force microscopy

The mechanical properties and deformation behaviours of as cast and heat treated Nb-21Ti-4C- xAl (x: 0, 5, 10 and 15 at-%) alloys are comprehensively investigated using nanoindentation and atomic force microscopy. For the Nb-21Ti-4C alloy, nanoindentation tests are performed for the Nb solid solution (Nbss) matrix, carbide and the interface between them. The results show that the hard carbide, which has a strong bonding with the Nbss matrix, can enhance the alloy before and after heat treatment, and the eutectoid transformation of the large sized carbide after heat treatment leads to less possibility for the forming of cracks on the carbide surface, which in turn improves the toughness. For the Nb-21Ti-4C-(0, 5, 10, 15)Al alloys, the hardness of the Nbss matrix increases significantly with increasing Al fraction for both as cast and heat treated alloys. However, deviations of the elastic modulus are inconspicuous with the Al fraction for the as cast and heat treated alloys.