Probing the correlation between phase evolution and growth kinetics in the oxide layers of tungsten using Raman spectroscopy and EBSD

•A novel statistical method is adopted to analyse Raman spectra.•Oxidation kinetics correlates with crystallographic orientation of substrate grains.•Hexagonal WO3 initially formed on {001} substrate grains shows slowest growth.•External oxide layer dominated by orthorhombic WO3 on all substrate orientations.•Oxidation preference is preserved until tungsten blue oxide (TBO) is formed.•TBO has a pivotal role in late oxidation kinetics. Tungsten, a plasma-facing material for future fusion reactors, may be exposed to air during abnormal operation or accidents. Only limited information is available on the evolution of related oxide phases. This work addresses the effect of substrate orientation on structural variations of tungsten oxides. Annealing experiments in an argon-oxygen atmosphere have been conducted at T = 400 °C under varying oxygen partial pressure and oxidation time. A combination of EBSD, Raman spectroscopy and confocal microscopy shows preferential oxidation initially on {111} base material planes. The oxide scale changes its phase composition dynamically, influencing the kinetics of its growth.