The Dynamics of Deposit Formation in Thermal-Spray Processes

Abstract

In thermal spraying, coatings are formed by particles flattening and piling up on the substrate. At impact, the sudden deceleration of the particle causes a pressure buildup at the particle-surface interface; the high pressure inside the particle forces melted material to flow laterally and ductile material to deform. The particle spreads outward from the point of impact and forms a “splat.” The arresting of spreading results from the conversion of particle kinetic energy into work of viscous deformation and surface energy. Solidification constraint (when the solidification front is advancing from the substrate surface fast enough to interact with the liquid during spreading) and mechanical constraint (due to the roughness of the substrate surface) can interfere with the flattening process.

In Situ Characterization of Small-Particle Plasma Sprayed Powders

“…However, the offset, disc speed, angle-carrier interaction, and angle-disc interaction also affect velocity. The model possesses a high R 2 value (93%) and a large number of DOF (9). Because the variance in the test is relatively low (S test = 8.1 m/s) compared to the full range of observed velocities, the adjusted R 2 is also high at 98.0%.…”

“…All the other factors that entered the model (i.e., offset, disc speed, and angleoffset interaction) played a less significant role. The high R 2 value (98.6%) and the large number of DOF (9) indicate that the model describes the majority of the data without overfitting. The average variance in the test is relatively low (S test = 0.031 mm) compared to the full range of position values that was measured.…”

“…For example, particles with low temperature and velocity deform less on collision, resulting in increased coating porosity [8] or poor coating adhesion. [9] However, superheated particles can experience a high degree of splashing on impact. The resultant debris can affect defect formation, as well as the final surface roughness.…”

Ethylene Methacrylic Acid (EMAA) Single Splat Morphology

“…The coating formation process is generally determined by the prime processing variables, which include substrate roughness, substrate temperature, impact velocity, stand-off distance (SOD), and the nature of the local atmospheric environment [3][4][5][6]. Many of these factors are inter-related.…”

Spreading Behavior and Morphology of Ethylene Methacrylic Acid (EMAA) Deposits via the Flame Spray Process

“…The physical properties of thermal conductivity and the wettability at impact between the thermal sprayed particle and the substrate influence the individual splat geometry [1,2] and the coating build-up and, consequently, the coating properties. The coating formation process is generally determined by the prime processing variables, which include substrate roughness, substrate temperature, impact velocity, stand-off distance (SOD), and the nature of the local atmospheric environment [3][4][5][6]. Many of these factors are inter-related.…”