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• Contrast of color-changing metallic glasses reveals the glass properties beneath the surface. • Color contrast reflects inhomogeneous distribution of enthalpy, structure, and chemistry of metallic glass. • Color contrast provides a new way of surface defect inspection. Recently, color-changing glasses have been developed from a series of Ce-based metallic alloys. The functionality originates from fast and spontaneous surface oxidation. In most cases, single-color glasses have been obtained, but in a few cases, multicolor glasses that have spatially-dependent color contrast have been found. The natural color contrast mostly results from the interference effects on the oxide layer. The present work investigates factors that influence and control the variable oxidation rate observed at different locations on the surface, and what manufacturing steps and processing history lead to the rate variation. It is found that cooling rate, residual strain, and precipitation in melt-spun ribbons are the effects controlling the oxidation rate giving the enhanced color contrast. Therefore, the final surface color contrast reflects the non-uniform distribution of enthalpy (glassy state), microstructure, and chemistry of the metallic glass beneath the surface. The inspection of natural color contrast also represents technologically useful method for early surface flaw detection in color-changing metallic glasses. [ABSTRACT FROM AUTHOR]

Abstract The precipitation processes during the peak-aged and over-aged stages of the as-extruded Mg-11.9Gd-1Y-0.44Zr (wt.%) alloy were investigated in detail by transmission electron microscopy. We revealed that, in addition to the dominant precipitate β′, both β T and β F ' precipitates were also found from the peak-aged stage. The transformation from β T to β F ' gives rise to the formation of neck morphology that connects different β-phases. The lengthening rate of precipitate in the <10 1 ¯ 0> α is larger than the thickening rate in the <1 2 ¯ 10> α. In the over-aged condition, self-stress orienting phenomenon leads to the reduction of the variants of precipitates. The age-hardening of this alloy strongly depends on the formation of the size of the near-continuous network composed of the {11 2 ¯ 0} α prismatic precipitates. The near-continuous precipitate network was formed in the peak-aged condition while the breakdown of the near-continuous precipitate network results in the significant decrease of hardness. Highlights • The origin of β F ′ was clarified and the transformation from β T to β F ′ was observed. • The lengthening rate of precipitates is larger than the thickening rate. • The breakdown of the near-continuous precipitate network results in the decrease of hardness. [ABSTRACT FROM AUTHOR]