CHAPTER 7: DISLOCATIONS AND STRENGTHENING

CHAPTER 7: DISLOCATIONS AND STRENGTHENING EDGE DISLOCATIONS

SCREW DISLOCATIONS

CHARACTERISTICS OF DISLOCATIONS

SLIP SYSTEMS

SLIP IN SINGLE CRYSTALS Resolved Shear Stress

Example Problem Consider 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

COLD WORKING -Forging -Rolling -Drawing -Extrusion

COLD WORKING

RECRYSTALLIZATION • New crystals are formed that: --have a small disl. density --are small --consume cold-worked crystals. 0.6 mm 0.6 mm Fig. 7.19 (a),(b), Callister 6e. (Fig. 7.19 (a),(b) are courtesy of J.E. Burke, General Electric Company.) 33% cold worked brass New crystals nucleate after 3 sec. at 580C.

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

GRAIN GROWTH 0.6 mm Fig. 7.19 (d),(e), Callister 6e. (Fig. 7.19 (d),(e) are courtesy of J.E. Burke, General Electric Company.) 0.6 mm After 8 s, 580C After 15 min, 580C coefficient dependent on material and T. • Empirical Relation: exponent typ. ~ 2 elapsed time grain diam. at time t.

CHAPTER 7: DISLOCATIONS AND STRENGTHENING