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Diffusion Solids Fundamentals Diffusion Controlled Solid State Episode 3 Part 1

Tham khảo tài liệu 'diffusion solids fundamentals diffusion controlled solid state episode 3 part 1', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 504 29 Diffusion in Metallic Glasses Fig. 29.2. Structure of a binary metallic glass schematic They can be produced as homogeneous metastable materials in composition ranges where the equilibrium phase diagram requires heterogeneous phase mixtures of crystalline phases. Historical Remarks The first liquid metal alloy vitrified by cooling from the molten state to the glass transition was Au-Si as reported by Duwez AND COWORKERS in 1960 5 . These authors made the discovery as a result of developing rapid quenching techniques for chilling metallic melts at very high cooling rates of 105 to 106 Ks 1. The work of Turnbull and of Chen 6-8 was another crucial contribution to the field and illustrated the similarities between metallic and silicate glasses. This work clearly demonstrated the existence of a glass transition in rapidly quenched Au-Si glasses as well as other glass-forming alloys such as Pd-Si and Pd-Cu-Si synthesised initially by the Duwez group. Already around 1950 Turnbull and Fisher had predicted that as the ratio between the glass-transition temperature Tg and the liquidus temperature Ti of an alloy increased from Tg Tl 1 2 to 2 3 homogeneous nucleation of crystals in the undercooled melt should become very sluggish on laboratory time scales 6 . This Turnbull criterion for the suppression of crystallisation in undercooled melts is still today one of the best rules of thumb for predicting the glass-forming ability of a liquid. The field of metallic glasses gained momentum in the early 1970s when continuous casting processes for commercial manufacture of metal glass ribbons such as melt spinning were developed 10 . During the same period Chen 9 used simple suction casting methods to form millimeter diameter rods of ternary Pd-Cu-Si alloys at cooling rates in the range of 103 Ks . If one arbitrarily defines the millimeter scale as bulk then the Pd-based ternary glasses were the first examples of bulk metallic glasses. Experiments on Pd-Ni-P alloy melts using