Influence of Feedstock and Thermal Spray Process on the Phase Composition of Alumina Coatings and Their Sliding Wear
Omar M. Ali, Rehan Ahmed, Filofteia-Laura Toma, L.‐M. Berger, Björn Matthey, Nadimul Haque Faisal, Khalid Ahmed
Abstract
Abstract Suspension thermal spraying is an emerging coating technology that enables the deposition of dense-structured ceramic coatings. As wear resistance is a main application field of alumina (Al 2 O 3 ) coatings, this study aimed to evaluate the dry reciprocating sliding wear resistance of suspension sprayed high velocity oxy-fuel (S-HVOF) alumina coatings and to compare it with atmospheric plasma sprayed (APS) and HVOF coatings. Coatings were analyzed in the as-sprayed state and post-treated at 910 °C (hot isostatically pressed, HIPed) conditions. Wear tests were conducted using a tribometer, following the ASTM G133-02 standard and a sintered WC-6 wt.% Co ball as the counterbody. Coating characterization was done using scanning electron microscopy, x-ray diffraction and nanoindentation technique. Results indicate that the HVOF, HVOF-HIP and S-HVOF coatings had a high α-Al 2 O 3 content, whereas the APS and APS-HIP coatings had a high γ-phase content together with high porosity. Sliding wear resistance was an order of magnitude higher for the S-HVOF and HVOF coatings than the APS and APS-HIPed coatings. This difference in wear performance was attributed to the high nanohardness, elastic modulus, dense microstructure and relatively high α-Al 2 O 3 content in the HVOF, S-HVOF and HVOF-HIP coatings. Results are discussed in terms of the wear mechanism and structure-property relationship.