Year

2021

Season

Spring

Paper Type

Master's Thesis

College

College of Computing, Engineering & Construction

Degree Name

Master of Science in Mechanical Engineering (MSME)

Department

Engineering

NACO controlled Corporate Body

University of North Florida. School of Engineering

First Advisor

Dr. Paul Eason

Second Advisor

Dr. Stephen Stagon

Rights Statement

http://rightsstatements.org/vocab/InC/1.0/

Third Advisor

Dr. Grant Bevill

Department Chair

Dr. Osama Jadaan

College Dean

Dr. William Klostermeyer

Abstract

Cold gas dynamic spraying commonly known as cold spray is a process currently used for restoration, re-tolerancing, and application of coatings. With additional resources allocated towards the development of a through process model aimed at predicting the properties of bulk material produced via the Cold Spray process, more lab testing and investigation must be done to capture the effects of the varying microstructure in CS materials. The properties of ultra-fine-grained materials are derived from data collected from coarse grained materials and processes that do not accurately capture the effects as elevated strain rates and ultra-fine-grained materials. The lack of property data in the is made worse by the complete absence of studies on the fracture behavior of bulk CS components.

This study aims to investigate the underlying microstructure and its effect on fracture morphology in cold sprayed 6061 Al. Samples excised from bulk consolidated material were subsequently subjected to low temperature heat treatment for various time lengths prior to characterization to gain understanding of the possible benefits of low temperature heat treatment. After heat treatment samples were notched and subjected to mode 1 failure. Microstructure is investigated through metallographically prepared samples as well as on bulk samples in orthogonal directions as well as perpendicular cross sections of fracture surfaces. The correlation of fracture features, microstructure, and electron back scattered diffraction techniques presented in the research are shown to provide a method for optimizing the investigation of the failure behavior close to primary, secondary, and tertiary cracking. It was observed that low temperature heat treatment of 6061 CS aluminum drives recrystallization within the regions of higher deformation in the microstructure and alters crack path propagation through these fine-grained regions. These fine-grained regions coarsen into textured regimes after low temperature, resulting in failure occurring along the boundaries of high misorientation between regions.

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