Semester

Spring

Date of Graduation

2001

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Bruce S. Kang.

Abstract

Under high temperature and stress (as in the front of the crack tip) oxygen can diffuse to the grain boundaries and react with the constitutive elements of the alloy producing brittle oxide layers, which cause the embrittlement of the material, and a brittle elastic, intergranular failure. Crack growth tests were performed on INCONEL 783 three-point-bend specimens in air and controlled oxygen atmosphere at 650°C and 538°C on two types of specimens, with and without beta-phase. Initial elastic crack growth was observed at test specimens without beta-phase. The specimens with beta-phase didn't reveal elastic crack growth. Based on the results of this research SAGBO embrittlement could be explained by the diffusion of oxygen under high stress levels in front of the crack tip combined with the formation of a brittle oxide layer on the grain boundary surface. The damage zone is a linear function with time, environmental oxygen and stress intensity factor for a given temperature. Specimens with beta-phase, which is an aluminide phase, showed improved resistance to SAGBO embrittlement. Oxidation studies indicate that the beta-phase is oxidation resistant and hence may cause increased SAGBO resistance.

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