Please enable JavaScript.

Coggle requires JavaScript to display documents.

Annealing, 分支補充 - Coggle Diagram

- - - - curvature induced growth by Gibbs Thompson effect is the chemical potential difference due to curvature
  - - - Ideal
      - Empirical
  - - - Mechanism
        
        in subgrain growth during recrystallization
        
        in a highly textured metal
      - for recovery, recrystallization, and grain growth
        
        其中recovery不牽涉到g.b. movement (在單晶當中subgrain boundary move)
  - - - similar to the solute atmosphere nearby a dislocation
      - 敘述
        
        grain boundary strain energy can be reduced by the migration of the foreign atoms to the vicinity of the grain boundary
        
        vicinity: the area near or surrounding a particular place
        
        retard the motion of g.b.
        
        Decreasing the rate of grain growth
        
        can use different elements to control the rate of the grain growth
      - T up and purity up, n approach 1/2
    - - The effect of second-phase inclusion up as size down and # up
      - T up, # of particles down, size up due to particle growth, then retarding effect of the inclusion down
      - Holes or pores in a metal can have a same effect
    - - Thermal grooving
        
        Problem
        
        phenomenon
        
        Grooves may form on the surface where g.b. intersect the specimen surface.
        
        When will free surface effect interact grain growth
        
        Grain size approach dimension of the thickness of the specimen
        
        grain growth rate down as grain size>1/10 thickness
      - Reduction of the net curvature of g.b. at a surface. Grain boundary near any free surface tend to perpendicular to the surface. Then cylindrical surface
    - - Free surface effects
        
        No curvature for g.b. to migrate under surface-tension force
        
        average grain size approaches the thickness of specimen, then grain growth will stop
      - Second phase inclusions can trap g.b.
        
        inclusion size小, volume fraction of the second phase密, grain size 小
    - - preferred orientation causes grain growth rate down
      - low angle g.b lowering g.b. mobility and the specific boundary energy(driving force)
  - - - some grains grow at the expense of their neighbors
      - usually induced by T up above the original grain growth temperature
      - driving force
        
        surface energy consideration
        
        curvature
      - 說明
        
        This effect starts after primary grain growth is inhibited.
        
        The process depends only on # of secondary nuclei.
        
        Factors control the grain growth do not control the secondary recrystallization
    - - like inverse gibbs thompson effect
      - 只有boundary movement，沒有長出新的crystal
      - As the movement occurs, the boundary leaves behind a crystalline region which is lower in its strain energy.
      - The boundary usually moves away from its center of curvatuure
        
        Rate of motion = f(strain)
        
        Boundary moves into the regions where the distortion has been the greatest
      - How?
        
        occurs after relatively small or moderate amounts of cold work
        
        induced in sheet specimen where the normal grain growth is inhibited by the size effects
        
        maybe free surface effects?
    - - The replacement of the secondary preferred orientation texture established during abnormal grain growth by a different preferred orientation texture during prolonged elevated temp anneals.
      - change texture by changing atmosphere
      - difference from other abnormal grain growth
        
        occurs after a secondary texture established by surface-induced abnormal grain growth in these sheets
        
        secondary texture
        
        Involves the growth of a few grains having the new orientation larger than the sheet thickness but smaller than secondary grains
        
        secondary grain size
      - due to the variation of surface energy. surface energy = f (grain orientation,annealing atmosphere)
- - - - k sensitive to T
      - n is independent of T
  - - - prestrain down, N down > G down so N/G down as prestrain down
      - N/G 大, grain size變小
      - N/G小, grain size大
    - - During cold-forming of sheet metal, if the average grain size is large, cold working produces a roughened and objectionable surface because of the anisotropic nature of plastic strain inside crystal
      - grain size
        
        小則加工困難
        
        大則orange peel effect
      - 廣泛的說法（對於全部材料）
  - - - Purity up, recrystallization temperature down
      - like solute atoms 偏析在dislocation旁邊 (Ch6)
    - - T up, growth up, driving force down
    - - initial size小, g.b. area多, nucleation rate up, final grain size小
- - - - dislocation movement
        
        climb
        
        slip
        
        focus on screw dislocation cross slip, partial disln combination
      - Arrhenius type law
        
        講義7-5
  - - - little change to hardness
        
        special case: HCP single crystal
      - resistance back to the original
      - Remove work hardening effects w/o movement of large angle g.b.
  - - - vacanies / interstitials absorbed by edge dislocation climbing
      - opposite sign of dislocation segments coming together
      - Vacancies + interstitials
    - - When a bent single crystal is annealed, the curved crystal breaks up into a number of closely related small perfect crystal segments. Rearrangement of the dislocations into cell walls
        
        講義7-7
      - lowering the strain energy and removing general lattice curvature
      - driving force for dislocation movement: decrease of the strain energy of the dislocations.
        
        dislocation movement (thermally activated)
        
        climb
        
        slip
        
        focus on screw dislocation cross slip, partial disln combination
        
        because CRSS down as T up
      - Polygonization develops sub-boundaries
        
        sub-boundaries lie inside grains
        
        sub-boundary is a low angle grain boundary.
        
        the original slip plane is perpendicular to the sub-boundaries
        
        boundary # down, strain energy down
  - - - Recovery at high T
        
        movement of the dislocations resulting from plastic deformation into subgrain or cell boundaries
        
        Polygonization, annihilation of dislocations
      - Recovery at low T
        
        reducing the number of point defects to their equilibrium value
        
        plastic deformations help
        
        mostly by cross-slip of screw dislocation
    - - Thermally activated process
      - lower the effective rate of work-hardening
        
        Dislocations move into cell walls, new dislocations are easier to nucleation. Fewer interactions in the middle.
      - Role of stacking fault energy
        
        High SFE, shorter distance, easier to recombine
      - thermal, stress help recombine partial dislocations
      - Comparison
        
        static recovery
        
        a result of interaction stresses between dislocations.
        
        dynamic recovery
        
        applied stress+stresses between dislocations