February AMP_Digital

iTSSe TSS A D V A N C E D M A T E R I A L S & P R O C E S S E S | F E B R U A R Y / M A R C H 2 0 1 9 3 9 iTSSe TSS the company’s promotional literature for this engine, the fol- lowing benefits are achieved by applying the coating: “ By using a highly advanced, thermally applied plas- ma fusion process on the cylinder walls, the V MAX SHO has no conventional steel cylinder sleeves, yet the cylinder walls are 60% harder than steel. That means larger cylinder bores for increased displacement, resulting in more power and torque, without increasing outer cylinder dimensions. It also results in dramatically lighter weight, better cooling, and the ‘micro-tex- tured’ cylinder walls help reduce friction loss, further increasing performance and enhancing reliability .” The “micro-textured” surface that Yamaha refers to is surface porosity that can be incorporated in the coating de- sign that helps retain oil for increased lubrication. This benefit is also realized by automotive manufacturers. The materials and processes used for creating bore coatings are mostly iron- based wire or metal powders. These economical materials are applied by plasma spray or plasma transferred wire arc (PTWA). The systems have been adapted to allow the engine block to remain stationary while the coating device rotates within the bore (Fig. 3). OIL AND GAS APPLICATIONS In the extraction of oil and gas, there are several com- ponents that require additional protection against wear and corrosion. Thermal spray coatings can be found on several of these devices to improve the performance of the appara- tus. Severe service gate valves are examples of components that are coated with the HVOF process. Coatings such as WC- 10%Co-4%Cr are used. Gates are coated and then ground to a smooth and flat finish to create a highly wear-resistant, gas- tight sealing surface that can hold up to abrasive and erosive wear. Figure 4 shows a gate valve gate being coated using the HVOF process. Pump components also use thermal spray coatings. For example, frac pumps used in hydraulic fracturing for well stimulation use thermal spray coatings to improve the perfor- mance and longevity of the pumps. These pumps use plungers to pump high volumes of sand and water at high pressures up to 15,000 psi. The plungers are coated and then heat treated to establish a strong metallurgical bond between the wear resis- tant coating and steel plunger. This metallurgical bond allows the coating to operate at high pressures without coating de- lamination. Figure 5 shows a coated plunger along with a well stimulation pump that the plunger is used in. AEROSPACE APPLICATIONS The aerospace industry and gas turbine power genera- tion applications are the largest consumers of thermal spray coatings. Coatings are used for different reasons such as abradable coatings that are applied to provide tight clearance control between compressor blades and shrouds. The tight clearance control helps maximize engine efficiency. Thermal barrier coatings such as yttria partially stabilized zirconia (YSZ) are used extensively to protect hot sections of the engines and allow themto operate at higher temperatureswhile protecting the components from oxidation. Increasing the operating temperatures of aerospace engines is a major focus for engine manufacturers. Devel- oping next-generation thermal barrier coatings (TBCs) and environmental protective coatings (EBCs) is a critical aspect FEATURE 5 Fig. 2 — Cold spray process. Courtesy of University of Wisconsin-Madison. Fig. 3 — Rotating thermal spray device for coating automotive cylinder bores.