MECHENG 382 Lecture Notes - Power Law, Microstructure, Glide Plane

• School: U of M
• Department: Mechanical Engineering
• Course: MECHENG 382
• Professor: All

Document Summary

Energy of atoms on grain boundary b < energy on grain boundary a . Atoms diffuse from a b : creep is a shear driven process. Lecture 31 - creep mechanisms (ii) grain-boundary creep: also known as coble creep (1963, atoms move along the grain boundaries. Width of diffusion path = region of disorder of width b between grains: key points for modeling. Both diffusion routes contribute simultaneously to creep: modeling gives the following equation for diffusional creep. H = where lattice creep. = atomic volume (m3) k = boltzmann"s constant (1. 38 x 10-23 j. atom-1. k-1) d = grain size (m) Ql = activation energy for lattice diffusion (j. mol-1) Qb = activation energy for boundary diffusion (j. mol-1) Lattice diffusion tends to dominate at higher temperatures. Boundary diffusion tends to dominate at lower temperatures. Caution in extrapolating creep data: shear stress drives dislocations.