Nanoscale segregation behavior and high-temperature stability of nanocrystalline W-20 at.% Ti

Abstract

Nanocrystalline W powders with ∼20 nm average grain size are produced by high-energy ball milling and exposed to a target consolidation temperature of 1100 °C. After 1 week, unalloyed W exhibits substantial grain growth, whereas a W alloy with 20 at.% Ti retains its nanoscale structure. A heterogeneous distribution of Ti is observed by independent characterization methods, including scanning transmission electron microscopy, energy dispersive spectroscopy and atom probe tomography. This heterogeneous solute distribution is different from the expected homogeneous solid solution based on bulk W–Ti phase diagrams. Using a Monte Carlo simulation that includes the possibility of grain boundary segregation and allows grain boundaries as potential equilibrium states, a complex nanoscale structure of Ti around W-rich crystallites is explicitly reproduced. This simulated structure has both grain size and extrema in local Ti content in line with the experimental observations.