Experimental test of morphological stability theory for a planar interface during rapid solidification

Abstract

The Harvard community has made this article openly available. Please share how this access benefits you. Your story matters We report a parameter-free test of the theory predicting the critical solute concentration that destabilizes a planar solid-liquid interface in the high-velocity regime where nonequilibrium interface kinetics are important. Rapid solidification following pulsed laser melting was used to make metastable solid solutions of silicon-tin. Rutherford backscattering spectrometry and transmission electron microscopy were used to measure the breakdown concentration. Samples remained microsegregation free with near perfect crystallinity at tin concentrations up to 10 times the maximum equilibrium solubility and 100 times that predicted by linear stability theory with local interfacial equilibrium. These measurements, covering velocities from 1 to 10 m/s, agree with the predictions of linear stability theory when the latter incorporates a velocity-dependent partition coefficient and a thermodynamically consistent kinetic liquidus, and contains no adjustable parameters. We also report a systematic increase of the breakdown concentration with increasing deviation from steady-state conditions, which is not addressed by current stability theories, parametrized by the concentration gradient just prior to breakdown. ͓S0163-1829͑98͒07117-3͔

Supersaturating silicon with transition metals by ion implantation and pulsed laser melting

“…31 Transition metals leading to surface segregation at low concentrations and cellular breakdown at higher concentrations, as observed here, is consistent with previous investigations into PLM of transition metals ion implanted in Si. 14,15,20,28,32,33 As an example of typical cellular breakdown morphology, Figure 1 Table I are based on the maximum TABLE I. Summary of results and key experimental quantities for Si implanted with transition metals and melted with a XeCl þ excimer laser.…”

“…Using these parameters in steady-state interface stability theory, 28 we calculated the critical solute concentration for the stability of a liquid-solid interface traveling at 3 m/s, and found that a concentration of Au in the bulk liquid greater than 1.2 Â 10 18 cm À3 results in an unstable interface. However, if the velocity is increased to 7 m/s, the interface is stable for concentrations up to 9 Â 10 18 cm À3 .…”

“…The maximum melt depths were approximately 350 nm for the XeCl þ excimer laser and 150 nm for the Nd:YAG laser. Simulations suggest 28 that following one XeCl þ excimer laser pulse, the solidification speed peaks slightly above 5 m/s near the beginning of solidification and drops to under 3 m/s at the end of solidification; and that following a single Nd:YAG laser pulse, the solidification speed peaks at just over 10 m/s and drops to 7 m/s at the end of solidification.…”

“…Concentration-depth profiles were measured by Rutherford backscattering spectrometry (RBS) with 2 MeV 4 He þ ions for Fe and W and by SIMS for all other elements. 29 Where possible, concentration-depth profiles from SIMS were fit using models for PLM and solute diffusion 10,12,28,30 and these fits yielded best estimates of v D , a key parameter governing the amount of solute partitioning during rapid solidification. According to the continuous growth model for solute trapping, 9,10 …”

Parameter-free test of alloy dendrite-growth theory

“…34 In their samples an initially planar interface became unstable at approximately 50 nm below the surface, resulting in the laterally-averaged measured concentration profile diverging at this point from the profile simulated assuming a planar interface. In our case, the divergence between simulated and measured profiles starting at approximately 40 nm below the surface can be explained by interfacial breakdown commencing at this point.…”