Ribbon-Substrate adhesion dynamics in chill block melt-spinning processes
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I.
INTRODUCTION
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widely used method for the fabrication of rapidly quenched metallic ribbons and tapes is chill block meltspinning (C.B.M.S.). 1,2 The process involves streaming of molten alloy onto a rapidly moving substrate surface, thereby forming and chilling a continuous metallic ribbon. A ribbon thus formed typically remains in contact with the substrate surface for some constant sticking distance, d , prior to being flung from the substrate by centrifugal force. The ribbon-substrate adhesion distance is found to increase in a catastrophic fashion at some time into a run.3'4 The run time required for transition o f the ribbon adhesion distance from constant to catastrophic depends on the process parameters and materials used. The substrate track on which ribbon is formed heats up during C.B.M.S. and results in a concurrent increase in the ribbon adhesion distance. The ribbon-substrate sticking distances observed in the present investigation have been indirectly correlated with the results of a reiterative point source heating calculation, summarized in the Appendix. Substrate surface isothermal maps generated by these calculations are discussed in relation to observed ribbon-substrate sticking distance dynamics in a given run and also with differences in C.B.M.S. process variables.
this investigation had nominal compositions Fe4oNi4oB2o (liquidus temperature ~ 1100 °C) and Fe8~.sB 14.55i4 (liquidus temperature ~ 1 2 0 0 °C). Unless otherwise specified, all C.B.M.S. runs were conducted using a 0.5 mm round orifice clear fused quartz crucible and a 20 kPa Ar gas ejection pressure. The effect o f ribbon width on sticking distance dynamics has been monitored for samples having widths 1 -< w -< 20 mm. Ribbon width and thickness have been measured for all samples made.
III. A.
RESULTS AND DISCUSSION
Experimental Observations
Ribbon-substrate sticking distance measured as a function o f substrate w h e e l revolutions (run time) is shown in Figures 2 through 6. The data in Figure 2 show that the onset of catastrophic ribbon-substrate sticking occurs sooner for the Fe4oNi4oB2o than for the FeB1 sB~4 ~Si4 amorphous alloy on the copper wheel used. This presumably results from the
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II.
EXPERIMENTAL PROCEDURE
Several series of C.M.B.S. runs were conducted using various combinations of process conditions and materials. Each of these runs was filmed by high speed movies taken at 3000 pictures per second and the ribbon-substrate sticking distance recorded as a function o f elapsed substrate wheel revolutions (run time) in frame-by-frame measurements, as schematically shown in Figure 1. Substrate wheel materials tested include O.EH.C. copper, Cu-2Mn alloy, H-12 tool steel, 304 stainless steel, and 2024 aluminum. Diameters of some o f these substrate wheels were 2.5 ~
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~ ~200 ~150
~'i20 n = 50
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n=l (c)
Fig. 7--Calculated isothermal maps of a 2.5 cm diameter O.F.H.C. copperwheel substrate surfaceahead of t
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