A novel Nb-W-C alloy with special microstructure and excellent mechanical property

Abstract

A new kind of Nb-W-C alloy with special microstructure and excellent mechanical property was designed and prepared by CVD subsequent with homogenizing heat treatment. Its microstructure is composed of columnar crystals with specific orientation, needle-like Nb2C second phase and layered structure with Nb/W composition segregation. By analyzing the effect of homogenizing heat treatment on the property and microstructure of the alloy, it was found that the as-deposited layered structure was retained in the microstructure after heat treatment at 1400 °C, but disappeared by treated at 1600 °C. The layered structure can effectively separate Nb2C and inhibit the size coarsening of Nb2C during carbide formation. During the homogenization process, needle-like carbides can maintain the strengthening effect under the condition of slight grain growth, but excessively high homogenization heat treatment temperature coarsens the grains and carbides, and ultimately weakens the strength of the alloy. The comprehensive strengthening effect of grain refinement and carbide pinning makes the room temperature strength of the sample reach 670 MPa after homogenizing treatment at 1400 °C for 6 h, which is about 35–45% higher than the as-deposited Nb-W-C alloy and the existing widely used Nb521 alloy produced by melting-forging-annealing technology.