University:
McMaster University
Course:
MATLS 2H04 | Introduction to Materials Engineering
Academic year:

2023
Views:

402

Pages:

1
Author:

Sabrina S.

9.6 Grain Boundaries & Hall-Petch In polycrystalline materials, all the grains have the same crystal structure but different orientation Grain boundary - interfacial defect that separates 2 grains Grain boundary energy - as atoms in grain boundary are bonded less regularly, there is a grain boundary energy The magnitude of this energy is dependent on the degree of misorientation between the two adjacent grains -> high-angle boundaries higher grain boundary energy Fine-grained structure - total grain boundary length per unit volume is higher - total grain boundary energy is higher Other characteristics of grain boundaries - more chemically reactive - attract impurity atoms - grain growth is driven by the total grain boundary energy reduction Grain Boundaries as Barriers Act as barriers to dislocation motion (which causes plastic deformation!) Since 2 grains have different orientations, dislocation has to change its direction of motion The atomic disorder within a grain boundary results in a discontinuity of slip planes from one grain into the other - more stress is required to move a dislocation from one grain to another - the material becomes stronger Hall-Petch Fine grained material is stronger than a coarse one Yield strength - sigma y = sigma 0 + k_y / d^(1/2) Sigma y - yield strength Sigma 0 - constant K_y - constant d - grain diameter