Type
Text
Type
Dissertation
Advisor
Welch, David | Sampath, Sanjay | Johnson, Curtis | Lara-Curzio, Edgar.
Date
2016-12-01
Keywords
Coefficient of Thermal Expansion, Linear Expansion, Thermal Expansion, Thermal Shakedown, Thermal Spray Coatings, Thermal Stresses and Strain | Materials Science -- Engineering
Department
Department of Materials Science and Engineering
Language
en_US
Source
This work is sponsored by the Stony Brook University Graduate School in compliance with the requirements for completion of degree.
Identifier
http://hdl.handle.net/11401/76131
Publisher
The Graduate School, Stony Brook University: Stony Brook, NY.
Format
application/pdf
Abstract
Thermal Spray (TS) is a very versatile manufacturing process to deposit thick coatings on a variety of substrates. Coatings are used in protective (i.e. wear, chemical attack, high temperature, etc.) and functional (i.e. sensors) applications. TS coatings have a unique lamellar microstructure as a result of the overlapping of millions of molten and partially-molten particles. During processing, high deformation by impact, high temperature, and rapid solidification lead to a complex hierarchical material system that contains a high amount of microstructural defects. The presence of defects in the microstructure contribute to differences in property values in comparison to bulk materials. Thermal stresses and residual strains arise from processing, thermal gradients and thermal exposure. Evaluation of thermal properties, in this case, the coefficient of thermal expansion (CTE) is of vital importance to enhance coating performance. In this dissertation, expansion measurements of various metals, alloys, ceramics, and cermet coatings; were carried out using various techniques (push rod dilatometry, x-ray diffraction XRD, digital image correlation DIC, and curvature method) to determine the dilation behavior at the atomic, micro- and macro-scale levels. The main results were. 1) Mathematical models (Turner and Kerner) used for composite materials, successfully predicted the CTE property of a TS coating where the primary phase is the coating material and the secondary phases can be oxides, precipitates, etc. (formed as a byproduct of the spraying process). CTE was found not to be affected by porosity 2) Despite the anisotropic behavior characteristic of TS coatings, the experimental results shown that CTE results to be reasonable isotropic within the scope of this study. 3) The curvature method was found to be an alternative technique to obtain the CTE, as well as the Young´s modulus of coating in a bi-material strip, with good approximation 4) An anomalous expansion behavior during the first heating exposure was exhibited by all coatings. The effect was named here, as “thermal shakedown†, and is magnified in metals and alloys 5) Non-isothermal rapid annealing of defects was correlated to this first irreversible contraction or expansion behavior. Although observed in most thermal spray materials, two material systems, pure Al and Ni-5Al were evaluated in-depth to quantify the mechanisms contributing to this behavior: vacancy formation, dislocation annealing, grain boundaries annihilation, residual stress relief, inelastic mechanical effects, etc. Correct determination of CTE values are important for design to assure integrity and functionality of coatings. Considerations of appropriate measurements are described in this dissertation. | 124 pages
Recommended Citation
Bejarano, Miryan Lorena, "Dilation Behavior of Thermal Spray Coatings" (2016). Stony Brook Theses and Dissertations Collection, 2006-2020 (closed to submissions). 2081.
https://commons.library.stonybrook.edu/stony-brook-theses-and-dissertations-collection/2081