5 research outputs found
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Nonequilibrium Partitioning During Rapid Solidification of Si-As Alloys
The velocity dependence of the partition coefficient was measured for rapid solidification of polycrystalline Si-4.5 at% As and Si-9 at% As alloys induced by pulsed laser melting. The results constitute the first test of partitioning models both for the high velocity regime and for non-dilute alloys. The continuous growth model (CGM) of Aziz and Kaplan fits the data well, but with an unusually low diffusive speed of 0.46 m/s. The data show negligible dependence of partitioning on concentration, also consistent with the CGM. The predictions of the Hillert-Sundman model are inconsistent with partitioning results. Using the aperiodic stepwise growth model (ASGM) of Goldman and Aziz, an average over crystallographic orientations with parameters from independent single-crystal experiments is shown to be reasonably consistent with these polycrystalline partitioning results. The results, combined with others, indicate that the CGM without solute drag and its extension to lateral ledge motion, the ASGM, are the only models that fit the data for both solute partioning and kinetic undercooling interface response functions. No current solute drag models can match both partitioning and undercooling measurements.Engineering and Applied Science
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Time-Resolved Temperature Measurements during Rapid Solidification of Si-As Alloys Induced by Pulsed-Laser Melting.
The solidification of Si-As alloys induced by pulsed-laser melting was studied at regrowth velocities where the partition coefficient is close to unity. The congruent melting temperatures T0 of Si-As alloys were determined using a temperature measurement technique developed for this work, and was confirmed with T0 measurements using three other methods. The time-resolved temperature measurement uses a thin-film platinum thermistor, below and electrically isolated from the Si-As alloy layer, to directly measure the temperature during solidification. The other techniques compared the results of heat flow simulations with the fluence dependence of the peak melt depth obtained by transient conductance, the fluence dependence of the melt duration determined from time-resolved reflectivity and transient conductance, and the fluence threshold for the initiation of melting. This combination of measurements in conjunction with Rutherford backscattering spectrometry permitted the determination of the solid-liquid interface temperature, velocity and partition coefficient, the latent heat of fusion and T0 for Si-4.5 at. % As and Si-9 at. % As alloys. The values of T0 determined by all four independent methods were consistent, indicating overall agreement between the direct experimental measurements and the analyses based on heat flow simulations. T0 was determined to be 1565±25 K for 4.5 at. % As and 1425±25 K for 9 at. % As. In addition, the enthalpy of fusion was determined to be independent of composition for the range studied. The values obtained in this work are compared with previous measurements.Engineering and Applied Science