Effect of cooling rates on solidification, microstructure and mechanical properties in tungsten

Abstract

Tungsten with its excellent high-temperature properties would be a most promising candidate as a plasma-facing material at the divertor in a nuclear fusion plant. However, homogeneous nucleation in melted tungsten remains unexplored at the nanoscale. Here, we investigate the effects of cooling rate on the microstructures and mechanical properties of tungsten using molecular dynamics simulations combined with experiment. The results reveal that an increasing cooling rate could reduce the degree of crystallization in tungsten. Specifically, an amorphous structure can be obtained at a cooling rate greater than 50 K ps⁻¹; the stable BCC phase and an amorphous phase can coexist at a cooling rate in the range of 20–50 K ps⁻¹; but for a cooling rate lower than 20 K ps⁻¹, only the stable BCC phase can exist. The arrangement with the BCC phase and the amorphous phase is observed in the solidification of tungsten under various cooling rates. Notably, a high cooling rate can inhibit crack nucleation in the cooling tungsten owing to faster stress relaxation, which consequently also leads to a low Young's modulus. Therefore, a high cooling rate could be employed to take advantage of the structural behavior of supercooled metallic liquids at the nanoscale. This work provides a way to optimize a promising processing route for preparing hybrid-structured tungsten with high mechanical performance by tuning the solidification rate.