Nanostructured and Conventional Cr 2 O 3 , TiO 2 , and TiO 2 -Cr 2 O 3 Thermal-Sprayed Coatings for Metal-Seated Ball Valve Applications in Hydrometallurgy Luc Vernhes, Craig Bekins, Nicolas Lourdel, Dominique Poirier, Rogerio S. Lima, Duanjie Li, and Jolanta E. Klemberg-Sapieha (Submitted August 11, 2015; in revised form March 12, 2016) A detailed characterization project was undertaken by Velan, an international industrial valve designer and manufacturer, in collaboration with the National Research Council of Canada, Boucherville, and Polytechnique Montre´ al. The purpose was to assess the mechanical and tribological resistances of promising ceramic coatings for hydrometallurgy applications, including a novel n-TiO 2 -Cr 2 O 3 blend. Hardness and shear strength were determined using microhardness indentation testers and universal tensile testing equipment. Wear resistance of the coatings under sliding wear, abrasion, and galling conditions were measured by standard pin-on-disk tests, abrasion tests, and custom-designed galling tests. The main result is that the synergy between Cr 2 O 3 and n-TiO 2 produced abrasion performance exceeding that of these materials alone. Also, an optimized balance between the hard and brittle Cr 2 O 3 phases and the soft and ductile n-TiO 2 phases resulted in higher abrasion, sliding, and galling resistance. The novel n-TiO 2 -Cr 2 O 3 blend is therefore considered as a promising evolution of the current TiO 2 - Cr 2 O 3 blend. Keywords air plasma spraying (APS), ceramic coating, gal- ling, high-pressure acid leaching (HPAL), pres- sure oxidation (POx), tribomechanical properties 1. Introduction Over the last two decades, metal-seated ball valves (MSBVs) have become the industry standard for hydrometallurgy applications. They ensure tight, reliable shut-off, a critical service that facilitates maintenance and contributes to a safe working environment. The typical MSBV design for hydrometallurgy applications consists of a floating ball in contact with a fixed seat. The ball and seats consist of either titanium or duplex stainless steel substrates protected by a ceramic coating. The primary function of the ceramic coating is to enhance the load- carrying capacity and tribological performance of the base material, thus extending the in-service life of the equip- ment, especially during ball motion phases (Ref 1). Twenty years ago, conventional Cr 2 O 3 applied by air plasma spraying (APS) was the preferred coating for protecting MSBVs used in gold processing. Extreme abrasion, pressure, and elevated temperature are inherent to the pressure oxidation (POx) recovery process in which gold ore is mixed with oxygen and sulfuric acid in an autoclave. Over time and based on field experiments, sil- icon dioxide (SiO 2 ) and titanium dioxide (TiO 2 ) were added to the original Cr 2 O 3 blend to improve the ductility and toughness. VelanÕs Cr 2 O 3 blend has proven effective in gold extraction at sites such as the NERCO Con Mine (Canada) and the Barrick Goldstrike and Lone Tree mines (USA). The Lihir and Porgera gold mines (Papua New Guinea) have also reported good results with VelanÕs Cr 2 O 3 blend applied to MSBVs (Ref 2). Similar to POx, high-pressure acid leaching (HPAL) is used in the nickel recovery process, whereby laterite ore is leached in a sulfuric acid environment in an autoclave at 0.41 MPa (600 psi) and temperatures above 240 °C (464 °F). Unlike POx, HPAL operates at high pressure, which, combined with a higher chloride content, produces a more corrosive environment (e.g., titanium is susceptible to crevice corrosion in HPAL). Based on VelanÕs experi- ence with different coating blends at Falconbridge Mines (Canada), the Cr 2 O 3 blend optimized for POx corrodes prematurely when used in HPAL (Ref 3). Because it is relatively inert in this environment, TiO 2 would appear to be a promising choice for HPAL (Ref 3). However, the mechanical and tribological performances of conventional TiO 2 are significantly lower than those of Cr 2 O 3 , resulting Luc Vernhes, Craig Bekins, and Nicolas Lourdel, Velan, Montreal, QC, Canada; Dominique Poirier and Rogerio S. Lima, National Research Council of Canada, Boucherville, QC, Canada; and Duanjie Li and Jolanta E. Klemberg-Sapieha, Department of Engineering Physics, Polytechnique Montreal, Montreal, QC, Canada. Contact e-mail: luc.vernhes@velan.com. JTTEE5 DOI: 10.1007/s11666-016-0405-9 1059-9630/$19.00 Ó ASM International Journal of Thermal Spray Technology Peer Reviewed