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Metallurgical Engineering and Materials Science Department IIT Bombay

Dislocation Dynamics Studies of dislocation interaction in multilayers UROP 03 – Stage II Presentation by Rajlakshmi Purkayastha ( 04011013) under the guidance of Prof. Prita Pant. Metallurgical Engineering and Materials Science Department IIT Bombay. Outline. Introduction and Background

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Metallurgical Engineering and Materials Science Department IIT Bombay

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  1. Dislocation Dynamics Studies of dislocation interaction in multilayersUROP 03 – Stage II PresentationbyRajlakshmiPurkayastha(04011013)under the guidance ofProf. Prita Pant Metallurgical Engineering and Materials Science Department IIT Bombay

  2. Outline • Introductionand Background • Image Forces • Interface Strength • Strengthening Mechanisms in Multilayers • Conclusions

  3. Introduction : Multilayers • A series of thin films of different materials deposited on top of each other • Extraordinary strength, hardness, friction and wear, higher temperature operation, corrosion resistance, fracture toughness, low electrical resistivity, heat-resistance • E.g. NiCrAlY bondcoat used as a thermal coating for turbine blades • Higher strength-to-weight ratios Co-Ni Multilayers (http://cms.tnw.utwente.nl/magnetic_multilayers/magn_mult.htm)

  4. Introduction : Experimental vs Simulation • Experimental Results [A. Misra, M. Verdier, Y.C. Lu, H. Kung, T.E. Mitchell, M. Nastasi, J.D. E Embury. Scripta Materialia, 39(4/5):555-560, 1998.] • Simulation Results [F. Akasheh ,H. M. Zbib, J. P. Hirth, R. G. Hoagland, and A. Misra. Journal of Applied Physics, 101:08414, 2007.]

  5. Introduction : Problem Formulation • Two layers each 400 nm thick • Each having different moduli (Cu =41.35 GPa , Ni = 80.15 GPa) • Sharp interface with misfit dislocations Nickel • Factors to be considered while determining strengthening mechanism • Image forces • Interface Strength • Dislocation Interactions Copper

  6. Outline • Introductionand Background • Image Forces • Interface Strength • Strengthening Mechanisms in Multilayers • Conclusions

  7. Image Forces : Theory • Origins :Motion of a dislocation towards a free surface • Violate laws of conservation • Concept of an image dislocation, from electrostatics • On left side : • On right side : (a) A screw dislocation placed at distance -x from the interface, along the z axis. (b) Dislocation and its image which produce the stress for x<0.. (c) Image dislocation which gives the stress for x>0..

  8. Image Forces : Koehler Barrier • Screw Dislocation • Edge Dislocation • Net stress where, 1

  9. Image Forces : Simulation Results Screw Dislocation • Mixed Dislocation

  10. Image Forces : Simulation Results • Mixed Dislocation Screw Dislocation

  11. Outline • Introductionand Background • Image Forces • Interface Strength • Strengthening Mechanisms in Multilayers • Conclusions

  12. Interface Strength : Misfits • Misfit dislocations at the interface of two crystal lattices with a 0.05 mismatch • [ www.tf.uni-kiel.de/matwis/amat/semien/kap5/illustr/mistdislocations.gif ] • Spacing of dislocation array is

  13. Interface Strength : Results • Loop percolating through

  14. Interface Strength : Results • Cu-Ni interface • Interface Strength vs Misfit Dislocation Spacing • Cu-Cr interface

  15. Interface Strength : Comparison • Array of Misfit Dislocations • Strength arrived at = 975 MPa • Literature : 1100 MPa from atomistics simulations • Comparison with literature • [Hoagland RG, Mitchell TE, Hirth JP, Kung H. Philos Mag A 2002;82(4):643.]

  16. Outline • Introductionand Background • Image Forces • Interface Strength • Strengthening Mechanisms in Multilayers • Conclusions

  17. Strengthening Mechanisms • Self stress due to curvature of the loop • Image forces • Repulsion due to the array of misfit dislocations at the interface • Interactions between different dislocations in the same layer

  18. Strengthening Mechanisms • All factors combined

  19. Strengthening Mechanisms: Dislocation Interactions • Ordered System • Semi-Random System

  20. Strengthening Mechanisms: Dislocation Interactions • 20 loops completely random • (a) Initial configuration • (b) Some loops start shrinking • (c) Some loops have already begun to merge with each other • (d) activity starts to take place at the interface • (e) Loops merge at the interface • (f) More loops collide

  21. Strengthening Mechanisms: Dislocation Interactions • A close up the interface interactions • (a) The blue loop in the Copper layer is very close to the red loop in the Nickel layer. • (b) The loop is so close that the motion of the red loop is hindered. However the blue loop in the Nickel layer advances. • (c) The two blue loops merge • (d) As the merged loop starts moving away , the red loop can now advance.

  22. Strengthening Mechanisms: Image Forces • Comparison to see the effect of Image forces

  23. Outline • Introductionand Background • Image Forces • Interface Strength • Strengthening Mechanisms in Multilayers • Conclusions

  24. Conclusions

  25. Thank You ! Metallurgical Engineering and Materials Science Department IIT Bombay

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