Effects of cooling rate and pouring temperature on microstructure and fracture toughness of the induction melted Nb-16Si-22Ti-2Hf-2Cr-2Al alloy

The effects of cooling rate and pouring temperature on microstructure and fracture toughness of the induction melted Nb-16Si-22Ti-2Hf-2Cr-2Al alloy were extensively investigated. The results revealed that with the decrease of cooling rates, the Nb_ss exhibits the dendrite-like morphology, the primary Nb₅Si₃ blocks form and the mean sizes of Nb ₅Si₃, Nb_ss and eutectic colonies increase; with the increase of the pouring temperature, the microstructure shows columnar structure and the particles of Nb₅Si₃ or Nb_ss become long and thin. Pouring temperature and cooling rate had little influence on the volume fractions of Nb_ss and Nb₅Si₃ and their compositions. The Nb₃Si phase eliminated in the case of high pouring temperature and slow cooling rate. Fracture toughness of the alloy prepared by induction melting is on the order of 13.7 to 15.3 MPa·m ^1/2. Similar fracture toughness value of each slab may be ascribes to the same volume fraction of the Nb_ss.