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Author ORCID Identifier

https://orcid.org/0000-0001-7592-6404

AccessType

Open Access Dissertation

Document Type

dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Mechanical Engineering

Year Degree Awarded

2019

Month Degree Awarded

September

First Advisor

Jonathan P. Rothstein

Subject Categories

Mechanical Engineering

Abstract

The use of a cool supersonic gas flow to accelerate solid particles to form bonding upon impact on a substrate is known as cold spray deposition. The kinetic energy of the impacting particle dissipates resulting in the thermal softening and plastic deformation of the particle which leads to a strong bonding between the particle and the surface. The cold spray process has been commercialized for some metallic materials, but further research is required to unlock the exciting potential material properties possible with polymeric particles. In this research, a laboratory-scale cold spray system with the capability of accelerating 10 – 100µm polymer particles up to Mach 2 was used to study the deposition behavior of a series of polymers on both polymeric and non-polymeric substrates. A material-dependent window of successful deposition was determined for each particle/substrate combination as a function of particle temperature and impact velocity. Additionally, a study of deposition efficiency revealed the optimal process parameters for high-density polyethylene powder deposition which yielded a deposition efficiency close to 10% and provided insights into the physical mechanics responsible for bonding. The deposition windows of PA and PS were compared to those of the micro-ballistic single particle impact experiments. In the latter technique, an ablation laser pulse was used to accelerate a single polymer particle to over 400m/s while being tracked during flight and rebound from the substrate using ultrafast laser photography. Single particle impact studies provide a wealth of information about the particle impact dynamics including plastic deformation and energy dissipation that cannot be monitored during cold spray. In both the cold spray and single particle impact experiments, particles of both polyamide and polystyrene were found to deposit on LDPE substrate. The critical velocity required for successful deposition was similar in each case. However, unlike deposition on the soft LDPE substrate, like-on-like deposition was successful in cold spray but proved unsuccessful in single particle impacts. Additionally, when single particle impacts found deposition, the efficiency of deposition was close to 100% while for the cold spray processes the deposition was less than 5%. These results suggest multiple particle impacts and/or surface roughness can play a major role in the effectiveness and efficiency of the cold spray deposition process for polymers. Characterization of the deposited single particles by means of the scanning electron microscopy was conducted to further understand the differences between the single impact method and the cold spray process. Eventually in the proposed work, characterization of coating properties as a function of cold spray parameters, evaluating the peening effect using glass beads, the study of cold spray deposition of core-shell particles, UHMWPE, and PEEK as promising materials, high-speed camera direct velocity measurements, micro-ballistic single particle impact experiments for low-Tg polymers (HDPE and PU), and 3d printing were proposed as the completion steps for the study of polymeric cold spray.

DOI

https://doi.org/10.7275/15133752

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