3 Additionally, it is hypothesized that the dispersoids prevent impurity (O, N, etc.) trapping at the grain boundaries, which leads to brittle fracture, by re-distributing the impurity concentrations. 5 Although the brittle character of W has often limited its application to wire and thin film geometries, experimental studies have found that adding carbide dispersoids (TiC, TaC, and ZrC) to W can lower the ductile-to-brittle transition temperature to that of a thin film. 4 Taking into account off-normal events like edge-localized modes (ELMs), it is predicted that the divertor surface will need to withstand up to 2573 K in realistic operating conditions. 1,2 However, W has a high brittle-to-ductile transition temperature (≤473 K) 3 and has been observed to undergo recrystallization and grain growth at ITER temperatures (≥1000 K). High-purity, nano-crystalline Tungsten is a leading candidate for the divertor material in future fusion reactors and ITER due to its high melting temperature, thermal conductivity, and sputtering threshold. Meanwhile, the W(110)–ZrC(111) Zr-terminated bicrystal has the highest UTS at 2500 K. At 2500 K, the terminating C layer diffuses into the W, resulting in a weaker W–Zr interface. Tensile tests of W/ZrC bicrystals show that although the W(110)–ZrC(111) C-terminated bicrystal has the highest ultimate tensile strength (UTS) at room temperature, observed strength decreases with increasing temperature. Validation of lattice parameters, surface energies, bulk moduli, and thermal expansion is confirmed on the optimized potential. Further accuracy and stability tests of the potential were achieved using objective functions for both material properties and high temperature stability. In order to construct a potential suitable for large-scale atomistic simulations at fusion reactor temperatures, it is necessary to train on ab initio data generated for a diverse set of structures, chemical environments, and temperatures.
We present a machine learned Spectral Neighbor Analysis Potential for W–ZrC that can now be used to study these materials. Dispersion-strengthening W with zirconium carbide (ZrC) can improve ductility and limit grain growth, but much of the effects of the dispersoids on microstructural evolution and thermomechanical properties at high temperatures are still unknown.
However, W has a very high brittle-to-ductile transition temperature, and at fusion reactor temperatures (≥1000 K), it may undergo recrystallization and grain growth. Tungsten (W) is a material of choice for the divertor material due to its high melting temperature, thermal conductivity, and sputtering threshold.
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