3 research outputs found
Microstructure and Phase Formation in a Rapidly Solidified Laser-Deposited Ni-Cr-B-Si-C Hardfacing Alloy
In this study, microstructural evolutions and phase selection phenomena during laser deposition of a hardfacing Ni-Cr-B-Si-C alloy at different processing conditions are experimentally investigated. The results show that even minor variations in the thermal conditions during solidification can modify the type and morphology of the phases. Higher undercoolings obtained at faster cooling rates suppressed the primary borides and encouraged floret-shape mixtures of Ni and Cr5B3 via a metastable reaction. Variations in the boride phases are discussed in terms of nucleation-and growth-controlled phase selection mechanisms. These selection processes also influenced the nature and proportion of the Ni-B-Si eutectics by changing the amount of the boron available for the final eutectic reactions. The results of this work emphasize the importance of controlling the cooling rate during deposition of these industrially important alloys using laser beam or other rapid solidification techniques. (C) The Minerals, Metals & Materials Society and ASM International 201
Diffusion-limited aggregation: A relationship between surface thermodynamics and crystal morphology
We have combined the original diffusion-limited aggregation model introduced
by Witten and Sander with the surface thermodynamics of the growing solid
aggregate. The theory is based on the consideration of the surface chemical
potential as a thermodynamic function of the temperature and nearest-neighbor
configuration. The Monte Carlo simulations on a two-dimensional square lattice
produce the broad range of shapes such as fractal dendritic structures, densely
branching patterns, and compact aggregates. The morphology diagram illustrating
the relationship between the model parameters and cluster geometry is presented
and discussed.Comment: 5 pages, 6 figure