Surface exafs study of the crystallization of a metallic glass

• Published in: Journal of non-crystalline solids 1989-07, Vol.110 (1), p.111-117
• Main Authors: Guo, Tie, denBoer, M.L
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; Materials science; Metals, semimetals and alloys; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; Specific materials; Specific phase transitions
• ISSN: 0022-3093; 1873-4812
• DOI: 10.1016/0022-3093(89)90188-9

The crystallization of an amorphous solid on high-temperature annealing may occur progressively from the surface into the bulk or uniformly throughout the whole sample. We have studied crystallization by means of surface EXAFS in the metallic glass Fe 40Ni 32Cr 8P 12B 8. Samples were annealed at various temperatures and times ranging from 240°C for 10 min to 400°C for 42 h; X-ray diffraction showed the gradual formation of crystalline phases. EXAFS measurements were made from the surface to about 4000 Å deep, with a depth resolution of a few hundred Å. The EXAFS results were quite sensitive to the crystallization, an effect quantified by model fitting in which the Debye-Waller factor σ 2 was varied as a parameterization of the local static disorder. We find that for partly crystallized samples σ 2 increases at the surface compared to deeper inside the sample. Since σ 2 is a direct measure of local static disorder (thermal vibrations are not important here as all measurements were made at room temperature), in this sytem these results imply that crystallization begins at the surface before it occurs in the bulk.