Microstructure and mechanical properties of Nb–Si alloys fabricated by spark plasma sintering

This paper deals with microstructural evolutions and mechanical properties of Nb–Si binaries containing dual-phase Nb/Nb5Si3 with Nb to Nb5Si3 fraction ratios of 90:10, 80:20, 70:30 and 50:50, prepared by spark plasma sintering (SPS). Dense Nb/Nb5Si3 samples with a relative density larger than 99.5% were obtained by SPS processing. The SPS samples consist of the Nb and Nb5Si3 phases with less than 3% fraction of NbO oxide. Hv at room temperature, and compressive strength at 1150 °C and 1250 °C of the bulk SPS alloys increase monolithically by enhancing fraction of the stiffening Nb5Si3 phase. For example, 0.2% yield strength, σ0.2, increases from 175 MPa to 420 MPa at 1150 °C and from 110 MPa to 280 MPa at 1250 °C, when the Nb5Si3 fraction increases from 10% to 50%. It is interesting that the fracture toughness, KQ, of the bulk SPS samples seems not to be sensitive to phase fraction. Heat treatment, however, plays a key role on the KQ as compared with that of the as-sintered state, at the corresponding Nb5Si3 fraction and considerably improves the KQ by about 100% for samples with the Nb5Si3 fractions of 10%–30%, and by about 50% for the sample with 50% Nb5Si3 fraction.