Effect of Ge addition on microstructural evolution and mechanical properties of quinary Nb-16Si-22Ti-2Al-2Cr alloy

In this study, the effect of Ge addition on microstructural evolution and mechanical properties of hypereutectic Nb-16Si-22Ti-2Al-2Cr (at.%) alloy was explored in detail. The microstructural evolution of these alloys containing Ge was characterized by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM). The mechanical properties including room-temperature fracture toughness and high-temperature compression strength were measured. Only Nbss and & beta;-Nb5Si3 were observed in all Ge-added alloys, which indicated that Ge intensively promoted the formation of & beta;-Nb5Si3 and restrained the formation of Nb3Si. Moreover, the volume fraction of & beta;-Nb5Si3 increased with Ge addition. Ge could improve the fracture toughness of Nb-16Si-22Ti-2Al-2Cr alloy. 1Ge (Nb-16Si-22Ti-2Al-2Cr-1Ge) alloy exhibited the max KQ of 18.47 MPa & BULL;m1/2. All alloys with added Ge, except 9Ge alloy, showed the higher toughness than that of Nb-16Si22Ti-2Al-2Cr alloy, owing to the presence of chaotic eutectics of Nbss/& beta;-Nb5Si3. In addition, Ge could not only improve the elastic modulus and nanohardness of constituent phases, but also elevate the high-temperature compression strength of the alloys. Moreover, some orientation relationships between Nbss and Nb5Si3 before and after high-temperature deformation were observed by EBSD method.