chapter 7: dislocations and strengthening edge dislocations

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CHAPTER 7: DISLOCATIONS AND STRENGTHENING EDGE DISLOCATIONS

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  • CHAPTER 7: DISLOCATIONS AND STRENGTHENINGEDGE DISLOCATIONS

  • SCREW DISLOCATIONS

  • CHARACTERISTICS OF DISLOCATIONS

  • SLIP SYSTEMS

  • SLIP IN SINGLE CRYSTALSResolved Shear Stress

  • Example ProblemConsider a single crystal of BCC iron oriented such that a tensile stress is applied along [010] direction.Compute the resolved shear stress along a (110) plane and in a [ 11] direction when a tensile stress of 52 MPa is applied

  • STRENGTHENING BY GRAIN SIZE REDUCTION

  • SOLID SOLUTION STRENGTHENING

  • SOLID SOLUTION STRENGTHENING

  • COLD WORKING-Forging-Rolling-Extrusion-Drawing

  • COLD WORKING

  • New crystals are formed that: --have a small disl. density --are small --consume cold-worked crystals.33% coldworkedbrassNew crystalsnucleate after3 sec. at 580C.Fig. 7.19 (a),(b), Callister 6e. (Fig. 7.19 (a),(b) are courtesy of J.E. Burke, General Electric Company.)0.6 mm0.6 mmRECRYSTALLIZATION

  • All cold-worked crystals are consumed.After 4secondsAfter 8secondsFig. 7.19 (c),(d), Callister 6e. (Fig. 7.19 (c),(d) are courtesy of J.E. Burke, General Electric Company.)0.6 mm0.6 mmFURTHER RECRYSTALLIZATION

  • GRAIN GROWTH Empirical Relation:After 8 s,580CAfter 15 min,580Celapsed timecoefficient dependenton material and T.grain diam.at time t.exponent typ. ~ 20.6 mm0.6 mmFig. 7.19 (d),(e), Callister 6e. (Fig. 7.19 (d),(e) are courtesy of J.E. Burke, General Electric Company.)