solidification of a ternary alloy composition

dendritic solidification, eutectics, peritectics,....
Bernd
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Joined: Mon Jun 23, 2008 9:29 pm

Re: solidification of a ternary alloy composition

Post by Bernd » Mon Feb 15, 2016 5:53 pm

Hi Johann,

I think both scenarios how you try to calculate the velocity do not apply to the experimental (and also to the simulation) conditions:

In your first scenario, there are two problems:
1.) The nucleation undercooling is not identical to the driving force for steady state growth of the lamellae. It could be a rough estimate only in the case that you have continuous nucleation (and not only at the beginning)
2.) You assume the velocity of the interfaces to be limited by the interface mobility. However, in reality the velocity is limited by lateral diffusion in the liquid!

The second scenario assumes that you have steady-state growth over long distances like in directional solidification. But in the simulated scenario (and I assume also in reality), the temperature gradient has no significant influence. It is rather like quenching, the temperature of the interface is continuously decreasing until the eutectic grains grow together.

What is missing in the simulation - and you may remember that we talked about that at the beginning - is release of latent heat which could compensate cooling and keep the interface at constant temperature during solidification. But, even if we would try to do that, we would not have enough information on the exact thermal conditions which is needed to exactly predict the velocity of the interfaces by simulation.
However, if we get the correct morphology and lamellar distances from simulation, we can know that the simulated velocity was correct (assuming we know the diffusion coefficients and interface energies). That means, that we only need one fitting parameter to reproduce the correct morphology (either cooling rate or interface energies or diffusion coefficients).

Best wishes

Bernd

mogeritsch
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Re: solidification of a ternary alloy composition

Post by mogeritsch » Wed Feb 17, 2016 9:01 am

Dear Bernd,

I see, I was on the wrong track. Now, it is clear for me.

Thank you and best regards,

Johann

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