Wear-resistant ceramic and ceramic composite coatings are significant to provide durability and support long-duration missions to the moon's surface for rovers, landers, robotic systems, habitats, and many other components. On the Lunar surface, structural components are continuously exposed to lunar dust projectiles that can cause protective coating delamination around the affected area, of protective coatings and this may not be physically visible. Ceramic coatings, composed of alumina, present excellent resistance to different types of wear due to their high strength and hardness as well as the ability to protect structural components from regolith impacts, wear, and abrasive damage. Air Plasma Spray (APS) already plays a vital role in the aerospace industry by protecting engine structures against wear, friction, corrosion, high temperatures, and harsh environments. In this study, an Inconel 738 substrate was grit blasted, following a 100-μm layer bond coat, and a 200-μm layer of alumina was deposited using APS. Prior to performing destructive experiments, the microstructure and characteristics of the APS alumina coating were studied and analyzed. Scanning electron images were collected to observe the anisotropic properties of the APS alumina coating. The X-Ray diffraction measurements demonstrated that α-phase and γ-phase are the dominant phases present in the APS alumina coating. The roughness of the APS alumina coating was measured with a profilometer, resulting in an average of 4.063 μm. The surface energy plays a role in enhancing the adhesion of the regolith particles to the surface of the components and systems used for lunar exploration. In this study, the surface energy had an average advancing contact angle of 61.13°, relating to low surface energy. Artificial damage was introduced by indenting the coating using Rockwell and Vickers indenters. The hardness of the APS alumina coating was measured around the different indentation locations. The measured Vickers hardness values at 1000 gf and 2000 gf were found to be 0.2913 GPa and 0.5677 GPa, respectively. An initial Rockwell hardness value of 38.9 was found and was reduced to 22.5 after two surrounding indentations were applied to the coating. Results showed that the Rockwell hardness value decreases as the number of indentations around the initial indent increases. The fracture toughness of the APS alumina coating was calculated using the cracks formed during the last two Rockwell indentations and was found to be 2.48 and 2.95 MPa√ m. Considering the optical properties of the alumina, piezospectroscopic (PS) measurements were taken to detect the underlying coating delamination and determine the mechanical properties of the APS alumina coating. The peak shifts from the characteristic alumina peaks revealed the underlying damage, quantifying the effect of projectiles on the overall coating integrity. The multifunctional properties of alumina, utilized in the studies performed here, have offered a unique means for understanding the durability of a material with high spatial and stress resolution.


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Graduation Date





Raghavan, Seetha


Master of Science in Aerospace Engineering (M.S.A.E.)


College of Engineering and Computer Science


Mechanical and Aerospace Engineering

Degree Program

Aerospace Engineering; Space System Design and Engineering


CFE0009557; DP0027566





Release Date

May 2023

Length of Campus-only Access


Access Status

Masters Thesis (Open Access)