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Phase transformation by mechanical milling

Phase transformation by mechanical milling. Partha Protim Chattopadhyay. Contents. Energy flow in materials Mechanically driven phase transformation Experimental techniques for mechanically driven phase transformation Mechanical milling Grain refinement by mechanical milling

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Phase transformation by mechanical milling

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  1. Phase transformation by mechanical milling Partha Protim Chattopadhyay

  2. Contents • Energy flow in materials • Mechanically driven phase transformation • Experimental techniques for mechanically driven phase transformation • Mechanical milling • Grain refinement by mechanical milling • Different types of phase transformation by mechanical milling • Some practical examples of mechanically driven phase transformation

  3. 1 TemperatureStress/Strain 2 3 4 5 6 Microstructure Energy flow in engineering materials 1. Thermal Stress 2. Heat generation due to mechanical work 3. Temperature dependent phase transformation 4. Latent heat 5. Transformation dilation 6. Stress induced phase transformation

  4. Mechanically driven microstructural evolution • Deformation localization in shear bands containing a high dislocation density • Annihilation/recombination/rearrangement of dislocation to form cell/subgrain structure with finer dimension • Random orientation of grains, i.e., low angle grain boundary  high angle grain boundary  grain boundary sliding rotation

  5. Experimental techniques for Mechanically driven phase transformation Equal channel angular extrusion Angular torsion Pack rolling Mechanical milling

  6. Grain refinement by mechanical milling Microstructure formation by ball milling Mechanics of a planetary ball mill Nanocrystalline structure Microcrystalline structure

  7. Effect of grain refinement in polycrystalline materials

  8. Polymorphic transformation in Nb Calculated lattice expansion in  3.7% Measured lattice expansion  4% Calculated stored energy 4.35 x 10-20J/atom Earlier reported value 1.46x 10-20J/atom

  9. Amorphisation by Mechanical Milling • Pioneered by Koch et al. in the case of Nb-Ni system • Most widely studied SSA technique • Achieved in the mixture of pure metal, intermetallics etc Defect induced disordering of the crystalline alloys Repetitive cold welding and fracture Alloying Amorphization

  10. Complete amorphization in Al65Cu20(TM)15

  11. Machining/wear

  12. Phase transformation in wear resistance coating material by mechanical milling

  13. 65 wt% Al 25 wt% Al 65 % El.SS 85 wt% Al Mechanical milling of Al and 316 stainless steel

  14. THANK YOU

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