Benard–Marangoni Instability as Possible Modifier of Surface Alloy Composition

Thermophysical properties of amorphous alloys represent the features of a given material specimen, and, as such, they are dependent, in general, on their elemental composition. Some properties are measured at surfaces, and others are measured for the bulk as a whole. Complications arise when the elemental composition varies as a function of position within the material specimen, as demonstrated by simultaneous measurements of thermal diffusivity and elemental composition by time-resolved spectroscopy of laserproduced plasma (LPP) plume emissions. To further understand the source of a rather common near-surface elemental composition anomaly, the evolution of the surface composition of Wood’s alloy under the influence of thermal cycling with, and without, a temperature gradient over the specimen has been investigated. Surface composition modifications have been found to take place by accumulation of irregularly spaced gray patches of an inhomogeneous composition on the surface in the presence of a temperature gradient. Determination of elemental composition by LPP spectroscopy shows the three-dimensional structure of the patches.