Effect of carbide additions on the mechanical properties and microstructure of Nb-based multiphase alloy

The mechanical properties and deformation behaviors of Nbss, (Nb, Ti)C, Nb₃Al and the interface for as cast and heat treated Nb-21Ti-4C-xAl (x=0, 5, 10, 15 at%), Nb-35Ti-4C and Nb-25Ti-8C alloys were investigated using nanoindentation and atomic force microscopy (AFM). The results show that Ti and Al can effectively improve the hardness of Nbss and the capacity of solid solution strengthening of Al is better than that of Ti. The hard carbide and Nb₃Al which has a strong bonding with Nbss matrix can enhance the alloy before and after heat treatment. 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. After heat treatment, the hardness of Nbss matrix decreases due to the homogenization of matrix microstructure and the decrease in the dislocation density. However, the deviations of the elastic modulus are unconspicuous with the change of the Ti, Al, C fraction and heat treatment for all alloys.