Contrast of color-changing metallic glasses reveals the glass properties beneath the surface.

• 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]