Alumina-based Coatings Research Articles

In-situ densification of combustion synthesized coatings

Dense intermetallic and ceramic (alumina based) coatings can be formed in situ during simultaneous combustion synthesis and densification in the field of centrifugal forces. Both microstructure and composition of alumina-based coatings formed during alumino-thermal reduction of oxides can be altered by an introduction of additives such as ZrSiO 4 , SiO 2 , Na 2 CrO 4 , and carbon. The activation energy and frequency factor for the Ni-Al reacting system consisting of equal atomic amounts of Ni and Al powders with an average particle size of 5 μm were measured using a nonisothermal technique, which were equal to 1.05 X 10 5 J/mol and 1.017 x 10 8 s -1 , respectively. A mathematical model of in-situ densification of a single-phase combustion product (NiAl) in the field of centrifugal forces was developed and explored.

Properties of alumina-based coatings deposited by plasma spray and detonation gun spray processes

Properties of alumina-based coatings deposited by plasma spray and detonation gun spray processes

Properties of alumina-based coatings deposited by plasma spray and detonation gun spray processes

Alumina, Al2O3 + 3 to 40 wt% TiO2, and Al2O3 + 40 wt% ZrO2 coatings were deposited by atmospheric plasma spraying (APS) and detonation gun spraying (DGS). The coatings were evaluated by optical microscopy, microhardness measurements, and X- ray diffraction. Wear resistance of the coatings was evaluated by rubber wheel sand abrasion and particle erosion test methods. Detonation gun- sprayed coatings exhibited more homogeneous microstructures and somewhat higher microhardness than corresponding plasma- sprayed coatings. Small additions of TiO2 (3 wt%) improved both the abrasion and erosion wear resistance, whereas 40 wt% TiO2 significantly decreased the erosion wear resistance of both APS and DGS coatings. Alumina + 40% ZrO2 coatings exhibited the best abrasion wear resistance of both APS and DGS coatings, but the erosion wear resistance of these coatings was lower than that of the Al2O3 and Al2O3 + 3 wt% TiO2 coatings. The best abrasion wear resistance of the coatings studied was obtained with DGS Al2O3 + 40 wt% ZrO2 and Al2O3 + 3 to 40 wt% TiCh coatings. These coatings exhibited lower wear rates than bulk Al2O3. The best erosion wear resistance was obtained with the DGS Al2O3 + 3 wt% TiO2 coating; however, it exhibited a higher wear rate than bulk Al2O3. In general, detonation gun- sprayed coatings showed significantly enhanced abrasion and erosion wear resistance than the corresponding plasma- sprayed coatings.