Effects of Nb and W Additions on the Microstructures and Mechanical Properties of Novel γ/γ' Co-V-Ti-Based Superalloys

Microstructures, elemental partition behavior, phase stabilities and mechanical properties of Nb- and W-containing Co-V-Ti-based superalloys were investigated. Elemental partition coefficients (K-X = C-gamma/C gamma) of Nb and W in Co-V-Ti-based superalloys are 2.07 and 1.10, respectively. The gamma' solvus temperatures are determined as 1023 degrees C, 1055 degrees C and 1035 degrees C in Co-12V-4Ti, Co-10V-4Ti-2Nb and Co-10V-4Ti-2W alloys, which are higher than those of Co-9Al-9W alloy (1000 degrees C). The mass densities of quaternary Co-10V-4Ti-2Nb and Co-10V-4Ti-2W alloys are about 8.31 and 8.50 g.cm(-3), respectively, which are 15% lower than Co-Al-W-based superalloys (9.8 g.cm(-3)). All examined alloys exhibit an anomalous positive dependence on temperature rising from 600 to 750 degrees C. Strengths of all examined alloys are higher than those of MarM509 (traditional Cobalt-based superalloy) and Co-9Al-9W at all temperatures that we investigated. The maximum flow stress of Co-V-Ti-Nb alloy is about 638 MPa at 750 degrees C while that of Co-V-Ti-W alloy is about 588 MPa at 700 degrees C.