Changing the material's Phase (state)

Hi,

I am working on laser machining of metals and I am trying to model the process by COMSOL. What I have done is thermal modelling which shows the temperature distribution in the sample. I am wondering if it is possible to change the solid to melt when the T reaches Tm? and also same procesure for Tv? Is there anyway to define the Temperature dependent geometry and physics (I have to study the fluid flow when when the materials is molten)?

I will appreciate any help or tip.

Thanks,
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H. Alavi