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Through-Process Modeling of Aluminum Alloys for Cold Spray: EXPERIMENTAL CHARACTERIZATION and VERIFICATION of MODELS

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Through-Process Modeling of Aluminum Alloys for Cold Spray: EXPERIMENTAL CHARACTERIZATION and VERIFICATION of MODELS Through-Process Modeling of Aluminum Alloys for Cold Spray: EXPERIMENTAL CHARACTERIZATION AND VERIFICATION OF MODELS by Baillie McNally A Dissertation Submitted to the Faculty of the WORCESTER POLYTECHNIC INSTITUTE In partial fulfillment of the requirements for the Degree of Doctor of Philosophy in Materials Science and Engineering January 2016 Approved: Richard D. Sisson, Jr., Advisor Director of the Material Science and Engineering Program George F. Fuller Professor Mechanical Engineering ABSTRACT The cold spray process is a cost-effective process for repairing damaged parts or creating thin coatings and structural bulk materials for military vehicles and aircraft that require high maneuverability, durability, and energy efficiency. This process can be made even more robust with a predictive tool that would tailor the material and processing parameters to a variety of applications. A through-process model that includes powder production, powder processing, cold spray particle impact, and post-processing would benefit the current trial and error efforts immensely and would aid in the search for optimal cold spray alloys for different applications. The powder production stage addresses the microstructure, phases and strength that result from the gas atomization process. The powder processing stage takes into account microstructural effects from heat treating or degassing the powder before it is cold sprayed. The particle impact stage includes a finite element model that simulates the temperature generation and strain that occurs during cold spray. An additive strength model, which is applied to the powder and used as an input into the impact model, determines the contributions of solid solution, microstructural, and precipitation strengthening and is a function of particle diameter, and time and temperature of powder processing. The important parameters that are experimentally characterized to verify and enhance the described models are grain size, phase morphology and fraction, and nanohardness. Characterization techniques such as optical, scanning and transmission electron microscopy, focused-ion beam, x-ray diffraction, and nanoindentation are used to verify the various stages of the through-process model for aluminum alloys 6061 and 5056. 1 ACKNOWLEDGEMENTS The author would like to acknowledge and thank the Army Research Laboratory, and Victor Champagne in particular, for the continued support throughout this research project. I would not have been able to pursue my Ph.D. if not for this support. I would also like to sincerely thank my advisor, Prof. Richard Sisson, for his guidance dating back to my undergraduate career when I first decided that materials science and engineering was the field I wanted to pursue. I would also like to thank the other members of my committee, Prof. Jianyu Liang, Prof. Satya Shivkumar, and Dr. Timothy Eden for their support and guidance. I have to thank Dr. Danielle Cote for not only being a member of my thesis committee, but for all of the support for the last 5 years. In my senior year at WPI, Danielle was my Major Qualifying Project advisor, and that experience helped cultivate my love for research. Thanks goes to the MTE department and MPI faculty and staff, especially Rita Shilansky. I also would like to thank the lab manager Dr. Li for all his help learning how to use the tools I have grown to love. I must thank members of my research group, both past and present: Aaron Birt, Luke Bassett, Rachel White, Caitlin Walde, Derek Tsaknopolous, Rob DelSignore, Kyle Fitzpatrick, and Matt Gleason. I also thank my fellow graduate students in the department. Lastly, I have to thank my family. My parents, Dan and Donna, first and foremost for their support throughout this adventure. My sister, Brittany, for blazing the trail for my career at WPI and my brother, Taylor, for always backing me up. Finally, to my boyfriend, Brandon, thank you for your constant support while I worked towards this ultimate goal. 2 TABLE OF CONTENTS Abstract ......................................................................................................................................................... 1 Acknowledgements ....................................................................................................................................... 2 1.0 introduction & motivation ................................................................................................................ 5 1.1 Background ................................................................................................................................... 5 1.2 Current Project Needs ................................................................................................................... 7 1.3 Approach ....................................................................................................................................... 8 1.3.1 Modeling ............................................................................................................................... 8 1.3.2 Experimental Characterization ............................................................................................. 8 1.3.3 Alloys Studied ........................................................................................................................ 9 2.0 Literature review ............................................................................................................................. 11 2.1 Powder Characteristics for Cold Spray/Additive Manufacturing ................................................ 11 2.2 Microstructures of Al 6061 and 5056 ............................................................................................... 12 2.2.1 Aluminum 6061 ................................................................................................................... 12 2.2.2 Aluminum 5056 ................................................................................................................... 13 2.3 Thermal Processing of Aluminum Alloys ..................................................................................... 14 2.3.1 Degassing of Aluminum Powders ....................................................................................... 15 2.3.2 Microstructural Effects of Heat Treatment ......................................................................... 16 3.0 Through-Process Model for cold spray ........................................................................................... 19 3.1 Powder Production Stage ........................................................................................................... 19 3.1.1 Al 6061 & 5056 Solidification Model .................................................................................. 19 3.1.2 Experimental Grain Size ...................................................................................................... 20 3.1.3 Al 6061 Thermodynamic and Kinetic Modeling .................................................................. 23 3.1.4 Al 6061 Experimental Phase Identification ......................................................................... 26 3.1.5 Al 5056 Thermodynamic and Kinetic Modeling .................................................................. 31 3.1.6 Al 5056 Experimental Phase Identification ......................................................................... 34 3.1.7 Experimental Verification of the Powder Production Stage Models .................................. 37 3.2 Powder Processing Stage ............................................................................................................ 39 3.2.1 Al 6061 Heat Treatment Modeling ..................................................................................... 39 3.2.2 Al 6061 Experimental Comparison ...................................................................................... 40 3.2.3 Al 5056 Heat Treatment Modeling ..................................................................................... 45 3.2.4 Al 5056 Experimental Comparison ...................................................................................... 46 3.3 Additive Strength Model ............................................................................................................. 50 3.3.1 Model Description ............................................................................................................... 50 3 3.3.2 Experimental Comparison ................................................................................................... 51 3.4 Particle Impact Model ................................................................................................................. 56 3.4.1 Model Description ............................................................................................................... 56 3.4.2 Experimental Comparison ................................................................................................... 56 4.0 Recommendations for Future work ................................................................................................ 64 4.1 Powder Processing Stage ............................................................................................................ 64 4.1.1 Model Development ........................................................................................................... 64 4.1.2 Powder Processing Experimental Verification .................................................................... 64 4.2 Particle Impact Model
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