Novel Ballistic Processing of Sn-0.7Cu Thick Films
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havior and structure of materials subjected to ultra-rapid (extreme) processing techniques are expected to be different than during conventional processing. Processes such as explosive compaction[1] and rapid solidification[2] have provided options for the processing of materials with unique characteristics and features. Thick films have been defined as those having thicknesses between 2 and 100 lm, whereas below 2 lm, they are considered thin films.[3] Processing approaches for films include splat quenching,[4,5] thermal spray[6] plasma physical vapor deposition (PVD),[7] flash evaporation,[8] sputtering,[9] electroplating[10] and sol-gel coating.[11] These are complex processes involving high vacuum, chemicals or multiple processing steps. For thick films, screen printing is fundamentally a cost-effective processing technique,[11] involving the use of bonding materials like glass or metallic oxides that usually reduce the conductivity of the film, or an active metal (that can increases the processing cost[12]). Amorphous films have also received a great deal of attention because of their promising applications in micro-electro-mechanical (MEMS) devices and biomedicine.[13]
D. CAVERO, Former MS Student, K. STEWART, MS Student, and K. MORSI, Professor, are with the Department of Mechanical Engineering, San Diego State University 5500 Campanile Dr. San Diego, CA 92182. Contact e-mail: [email protected] Manuscript submitted March 31 2016. Article published online November 1, 2016 46—VOLUME 48A, JANUARY 2017
Within the area of melt processing, planar-flow melt spinning (PFMS) is a common and effective process for manufacturing long ribbons of metallic glasses.[14] The process consists of flowing molten metal through a nozzle onto a rotating chilled (with water or other fluids) wheel, to increase the temperature gradients at the casting surface, which allows for undercooling of the material into an amorphous state. Wheel speed has strong effects on both cooling rate and ribbon thickness. Typical speeds investigated in the planar-flow melt spinning process for metals can range from 5 to 80 ms1 with typical thicknesses between 8 lm and a few hundred micrometers depending on material and process conditions.[15,16] The present paper discusses for the first time ballistic processing (BP), a novel ultrarapid processing technique with possibilities in thin, thick, and amorphous film processing, in addition to additive manufacturing. The process can be viewed as an extension of splat quenching[17] with the novelty being melt quenching on a rapidly moving substrate. A tin-copper (Sn-0.7Cu) alloy was used as a model material due to its low melting point‘; however, obviously, results are applicable to many other material systems. Although the present paper investigates processing velocities up to 36.1 m/s, higher ballistic velocities even above the speed of sound are possible with Ballistic Processing, which is the subject of a separate study. The present paper provides an initial insight into the capabilities of BP and the developed microstruc
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