Processing, microstructure, and mechanical properties of (Nb)/Nb5Si3 two-phase alloys

It has been shown that a fine lamellar structure composed of Nb solid solution, (Nb), and Nb5Si3 is formed through eutectoid decomposition in the Nb-Si binary system and its ternary derivatives. Such alloys would exhibit a high strength at over 1400 K, yet showing room-temperature toughness of over 10 to 20 MPa m(1/2) if a proper lamellar spacing is chosen. In the present work, effects of processing on the microstructure evolution and mechanical properties are investigated on the Nb-18 at. pct Si alloys prepared by hot pressing (HP) and spark-plasma sintering (SPS). The powders used in the present work are of pure Nb and Nb5Si3 in order for the fabrication to become possible at temperatures higher than the melting point of Si and to reduce the formation Of SiO2. The results show that the SPS yields more uniform two-phase microstructure but the alloy fabricated through HP tends to provide higher elevated temperature strength.