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Kinetic Competition During Duplex Partitionless Solidification in Ni-V Alloys
Published online by Cambridge University Press: 21 February 2011
Abstract
A structure composed of both partitionless face-centered cubic (α-fcc) and body-centered cubic (β-bcc) phases has been observed following high undercooling solidification of nickel-vanadium (Ni-V) alloys in the composition range 47-51.7 at.% V. Containerless processing and rapid solidification suppresses the formation of the equilibrium σ phase and results in the simultaneous formation of partitionless fcc and bec phases. Transmission electron microscopy analysis has identified regions in which 0.1-1 μηι a and β grains co-exist in a duplex structure. A nucleation and growth kinetics analysis has been developed to describe the conditions under which this structure may form. Thermodynamic and kinetic arguments have been used to provide bounds on various kinetic parameters. These bounds indicate that the nucleation rates for a and β must be larger than about 1027 m−3 s−3 to account for the number of grains observed in the time available for nucleation, and the growth rates are constrained to be larger than about 1 m/s to account for complete solute trapping.
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- Copyright © Materials Research Society 1998
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