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

摘要

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 Nb_5Si_3 blocks form and the mean sizes of Nb _5Si_3, Nb_(ss) and eutectic colonies increase; with the increase of the pouring temperature, the microstructure shows columnar structure and the particles of Nb_5Si_3 or Nb_(ss) become long and thin. Pouring temperature and cooling rate had little influence on the volume fractions of Nb_(ss) and Nb_5Si_3 and their compositions. The Nb_3Si 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).