Surface terraces in pure tungsten formed by high-temperature oxidation

TL;DR

This study investigates the formation of surface terraces in high-temperature oxidized tungsten, revealing orientation-dependent morphology influenced by preferential oxidation, with implications for tungsten's use in extreme environments.

Contribution

It introduces a new understanding that preferential oxidation of {100} planes, rather than diffusion, drives terrace formation in tungsten surfaces.

Findings

Terraces form predominantly on {111} grains.

Facets align with {100} planes, increasing surface energy.

Oxidation behavior varies with oxygen supply.

Abstract

We observe large-scale surface terraces in tungsten oxidised at high temperature and in high vacuum. Their formation is highly dependent on crystal orientation, with only {111} grains showing prominent terraces. Terrace facets are aligned with {100} crystallographic planes, leading to an increase in total surface energy, making a diffusion-driven formation mechanism unlikely. Instead we hypothesize that preferential oxidation of {100} crystal planes controls terrace formation. Grain height profiles after oxidation and the morphology of samples heat treated with limited oxygen supply are consistent with this hypothesis. Our observations have important implications for the use of tungsten in extreme environments.