Chapter 9_Part_5

Chapter 9_Part_5 - Development of microstructure in...

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MSE 2090: Introduction to Materials Science Chapter 9, Phase Diagrams Development of microstructure in isomorphous alloys Fast (non-equilibrium) cooling • Compositional changes require diffusion in solid and liquid phases • Diffusion in the solid state is very slow. The new layers that solidify on top of the existing grains have the equilibrium composition at that temperature but once they are solid their composition does not change. Formation of layered (cored) grains and the invalidity of the tie-line method to determine the composition of the solid phase. • The tie-line method still works for the liquid phase, where diffusion is fast. Average Ni content of solid grains is higher. Application of the lever rule gives us a greater proportion of liquid phase as compared to the one for equilibrium cooling at the same T. Solidus line is shifted to the right (higher Ni contents), solidification is complete at lower T, the outer part of the grains are richer in the low-melting component (Cu). • Upon heating grain boundaries will melt first.
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Chapter 9_Part_5 - Development of microstructure in...

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