Identifier

etd-11152006-102208

Degree

Master of Science in Mechanical Engineering (MSME)

Department

Mechanical Engineering

Document Type

Thesis

Abstract

Grain-boundary (GB) diffusion creep (Coble creep) is the dominant deformation mechanism for the fine-grained materials under low stress and at elevated temperature. During creep deformation the grains become elongated in the tensile direction because of atoms diffusion along GBs from places in compression to those in tension. Consequently, the GB diffusion rate depends on the normal stress gradient along the boundaries. It is widely accepted that the GB migration generally plays two important roles during Coble creep: one leading to the decrease of the creep rate due to the increase of the grain size by GB migration mediated grain growth and the other one leading to the relaxation of the stress concentrations along the GBs and at the triple junctions. In this study we use mesoscopic simulations to investigate the influence of the external stress and grain-boundary migration (static grain growth) on creep deformation of polycrystalline materials. Our simulation methodology is based on the variational principle of dissipated power and the simulation results reveal that the grains comprising the microstructure remain almost equiaxed during grain-boundary diffusion creep with accommodation by GB migration. In addition, the average grain size of the evolving microstructure is controlled by the interplay between the static and dynamic grain growth and depends strongly on both the externally applied stress and the strain.

Date

2006

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Dorel Moldovan

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