Abstract
The influence of Nb and Nb5Si3 powder sizes (Nb: 83.8, 37.4, 4.9 μm; Nb5Si3: 86.4, 43.6, 2.9 μm) on microstructure and fracture behavior of an Nb-16Si alloy fabricated by spark plasma sintering (SPS) was investigated. The results revealed that all as-sintered samples consisted of Nb and Nb5Si3 phases, with no new phases formed during SPS. The morphologies of the Nb and Nb5Si3 phases in the as-sintered samples depended on the original Nb and Nb5Si3 powder sizes. Large Nb5Si3 powders 86.4 and 43.6 μm in combination with Nb powder of described sizes resulted in an Nb matrix plus Nb5Si3 island biphase microstructure, which supplied excellent fracture toughness. The microstructure made from the finest Nb powder (4.9 μm) and the largest Nb5Si3 powder (86.4 μm) had a high fracture toughness of 12.4 MPa m1/2 through a mixed fracture mechanism of dimple, tear, and cleavage from the small Nb grains. When the Nb5Si3 powder size was decreased to 2.9 μm, the sample tended to form an Nb5Si3 matrix plus Nb island biphase microstructure, which exhibited a poor fracture toughness value of between 5.6 and 8.0 MPa m1/2 due to the crack propagation mainly within the brittle Nb5Si3 phase.
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