Laser pulse crystallization of Pd-Si metallic glasses

Abstract

A novel method of laser pulse crystallization (LPC) capable of revealing and quantifying crystallization in amorphous ribbons is presented. It is used to study the morphology of crystallization and, indirectly, surface crystallization (SC) of Pd-Si amorphous alloys in the composition range Pd77Si23-Pd85Si15. The laser-induced, frozen-in fronts of crystallization are studied by optical metallography and X-ray diffraction. The shapes of these fronts are determined by the initial degree of SC, which depends on alloy compositions, their thermal history and/or the surface of the ribbon being analysed. SC is inactive in alloys of eutectic composition (Pd85Si15) and is most pronounced for compositions near the border to the amorphous region on the silicon-rich side (Pd77Si23). For as-quenched ribbons, a stronger tendency to SC exists on the shiny surface of the ribbon. Low-temperature furnace annealing as well as room temperature ageing over a period of 2 years equalizes the degree of SC on both surfaces. The X-ray diffraction patterns taken from the regions containing frozen-in fronts of crystallization only reveal the presence of metastable phase II, independently of composition and/or thermal history of the given sample.