Title

Microstructure-sensitive models for predicting surface residual stress redistribution in PM Nickel-base superalloys

Date of Award

2017

Degree Name

Ph.D. in Materials Engineering

Department

Department of Chemical and Materials Engineering

Advisor/Chair

Advisor: Robert A. Brockman

Abstract

Compressive surface residual stresses achieved by mechanical surface treatments (shot peening, low-plasticity burnishing, or laser shock peening) typically extend component life under fatigue loading. Designers are unable to include this surface residual stress benefit in design life predictions due to the absence of detailed and accurate models of the behavior, and to the uncertainty of residual stress profiles that exist both before and after service. Generalization of coupled creep-plasticity models to incorporate microstructural features, size distributions, and volume fractions can provide an analytical description of the relevant relaxation mechanisms, allowing engineered residual stress to be taken into account in design. The current study combines observations from microstructural characterization and mechanical testing with the development of numerical models to predict surface residual stress relaxation following exposure to load and temperature. The grain size and γ' precipitate distributions are quantified for two different IN100 microstructures, and experimental measurements of the yield strength and creep behavior of the materials are obtained. The microstructural data are incorporated into a coupled creep-plasticity modeling framework which describes how the prior plastic deformation affects creep response. Residual stress relaxation predictions are validated against measured residual stress profiles from shot-peened laboratory scale experiments for both heat treatments of IN100 under service-relevant conditions. The resulting numerical model accurately predicts relaxation of engineered residual stresses under expected service conditions, using only data from standard mechanical tests and microstructural characterization methods, thereby enabling favorable residual stresses to be considered in the design process.

Keywords

Heat resistant alloys Testing, Stress relieving (Materials), Surfaces, Models of, Materials Fatigue, Residual stresses, Shot peening, Materials Science, nickel-base superalloy, residual stress, gamma prime precipitates, x-ray diffraction, hole drilling, x-ray elastic constant, shot peening

Rights Statement

Copyright 2017, author

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