The average lamellar spacing and interface undercooling in steady-state irregular eutectic growth were estimated based on the Jackson and Hunt’s analysis by relaxing the isothermal interface assumption.At low growth rates,the average lamellar spacing and average interface undercooling are dependent only on the characteristic thermo-physical properties of a binary eutectic system. For a general Al-Si eutectic,it is found that the eutectic characteristic length based on the present non-isothermal analysis is consistent with that obtained from isothermal analysis;however,the average interface undercooling is remarkably different between them,and such discrepancy in average interface undercooling increases with increasing of growth rate.The measured interface undercooling obtained from literature is reasonably interpreted by present non-isothermal analysis.
Directional solidification of rod-like eutectic is an important route to produce in situ composites.The rod-like phase spacing of composites is a crucial parameter in determining the properties of the materials.In this study,the rod-like phase spacing of melt-grown in situ eutectic composites is estimated by the method that is established based on the classical Jackson-Hunt theory and completed by considering the minimum undercooling principle in eutectic solidification at steady state.The density difference between the solid phases is also considered when calculating the diffusion field in the liquid.It is found that the rod-like phase spacing of in situ eutectic composites is generally a not unique value but displays a finite range under fixed growth conditions.Also,the range width,which decreases with increasing growth rate and vice versa,is only dependent on the intrinsic properties of an alloy at a given growth rate.By comparing with the experimental observations,the results show that the predicted spacings are in reasonable agreement with experimental data for nonfaceted-nonfaceted Succinonitrile-(D)camphor,MnSb-Sb,and Al-Al3Ni alloys and faceted-nonfaceted MnBi-Bi system when growing in a coupled manner.
Considering the local linear superposition of the species and combining the calculation of phase diagram, the columnar and equiaxed growth behaviours are investigated systematically during solidification of multicomponent alloys. A theoretical model is developed to describe the columnar to equiaxed transition during multicomponent alloy solidification by taking account of the competition between nucleation and growth ahead of a dendrite array, which shows a good agreement with the experimental results.
