Ming-Wen Chen

The interface morphology of a spherical crystal in the undercooled melt affected by a far-field uniform flow

The effect of the convective flow caused by the far-field uniform flow on the interface morphology of a spherical crystal is studied by using the matched asymptotic expansion method. For the case that the far-field uniform flow is far less than the characteristic velocity of the interface, we obtain the uniformly valid asymptotic solution of the spherical crystal in the entire melt region. The analytical results show that the far-field uniform flow has significant effect on the interface morphology of the spherical crystal. The convection flow makes the interface of the growing spherical crystal enhance growth velocity in the upstream direction of the far-field uniform flow, inhibit growth in the downstream direction and decrease growth velocity on the two sides of the spherical crystal. The drag effect of the far-field uniform flow makes the interface morphology of the spherical crystal evolve into a pearlike oval shape. Our analytical result is consistent with the experimental and simulation results.

Thermodynamic model for precipitation of carbonitrides in microalloyed steels and its application in Ti–V–C–N system

Based on mass balance and solubility product equations, a thermodynamic model enabling the calculation of equilibrium carbonitride composition and relative amounts as a function of steel composition and temperature was developed, which provides a method to estimate the carbonitride complete dissolution temperature for different steel compositions. Actual carbonitride precipitation behavior was further verified in Ti–V–C–N microalloyed steel system. The model suggests that for higher [V] and [Ti] dissolved in steels, it is available to decrease the addition of C and N during alloy composition design. The resultant longer fatigue life of the modified steel could be attributed to the more [V] and [Ti] dissolved in the matrix, inducing finer dispersion of carbonitrides. Therefore, this model is proved to be effective in determining better chemical composition for high-performance steels, leading to possible reductions in the cost of production and improvements in the combined mechanical properties of the steels.

Effect of anisotropy on deep cellular crystal growth in directional solidification

The effect of anisotropic surface tension and anisotropic interface kinetics on deep cellular crystal growth is studied. An asymptotic solution of deep cellular crystal growth in directional solidification is obtained by using the matched asymptotic expansion method and the multiple variable expansion method. The results show that as the anisotropic parameters increase, the total length of deep cellular crystal increases and the root depth increases, whereas the curvature of the interface near the root increases or the curvature radius decreases.