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SOLIDIFICATION (Growth Mechanism (Type of Growth Mechanism (Planar Growth,…

- - - - Temperature of the liquid metal is greater than freezing temperature
      - Temperature of the solid formed is at or below the freezing temperature
      - Latent heat of fusion must be removed by conduction from solid-liquid interface through solid to surrounding for solidification to continue.
  - - - Specific Heat of the Liquid
        
        Heat required to change temperature of unit weight of the material by one degree.
        
        Specific heat must be removed either by radiation into surrounding atmosphere or by conduction into surrounding mold until liquid cools to the freezing temperature
      - Latent Heat of Fusion
        
        heat generated when solid crystals form from a liquid.
        
        Latent heat must be removed from solid-liquid interface before solidification completely.
- - - - The difference between these two morphologies
        • Due to a distinctly different atomic mechanism by which the liquid atoms attach themselves to the solid interface.
  - - - The example (A) above show the supercooling with a negative temperature gradient (from solid to liquid) for non-faceted materials
      - The amount of supercooling be defined as S= Tf - T
      - It has been determined experimentally that when ds/dz > 0, the planar interface becomes unstable and degenerates into a dendritic interface
      - Dendrite – treelike projections that form on the solid surface after it becomes unstable
      - When the supercooling is quite small, interface morphologies intermediate between planar and dendritic are obtained. These morphologies are called cellular
      - Each dendrite is a single crystal
      - Dendrite exhibits a preferred orientation, frequently in <100> direction for almost metal alloy
- - - - -Consider a bar of metal solidifying under condition of unidirectional flow.
      - -The temperature of the liquid is higher than the solid.
      - -The interface is undercooled by finit amount, ∆Tk in order to drive the interface reactions.
      - -The temperature gradient in the liquid is always positive.
    - - -Assume a bar of metal solidifying under condition an undercooling of ∆T to be attained so that the liquid temperature is less than freezing temperature.
      - -Due to the heat transfer through solid to liquid a negative gradient is formed.
      - -When the liquid atoms start to join solid structure the latent heat is release at the interface.
      - -The interface temperature will increase higher than the temperature of solid-liquid.
      - -The temperature profile is known as temperature reversible