Study On Microstructure And Properties Of Plasma Sprayed Coatings Using Nb₂O₅-Al Powders On Aluminum Alloy Substrate

Based on the aluminum thermal reaction:10Al+3Nb₂O₅=6Nb+5Al₂O₃,composite coatings were fabricated on Al substrate by plasma spraying using Al-Nb₂O₅ composite feedstock prepared by spray-drying with fine Nb₂O₅ and Al powders.The constituent phase,microstructure and grain size of the coatings were analyzed by XRD,SEM and EDS,and the mechanical property and wear property were evaluated as well.（1）Thermodynamic analysis of Al-Nb₂O₅ system was made and it was shown that theΔG of the reaction between Al and Nb₂O₅ was negative,indicating the reaction between Al and Nb₂O₅ was feasible in thermodynamics.Self-propagating reaction of Al-Nb₂O₅ system is available because the adiabatic temperature of this system is between 2700 K and 2800 K,higher than 1800 K.On this basis,composite feedstock for plasma spraying were prepared by spray-drying with Al and Nb₂O₅ raw powders.（2）Process optimization of plasma spraying of composite coating was carried out,with the optimal parameters:the mass ratio of aluminum to niobium oxide 2.5:10 and the spray power 30 kW.The structure of plasma sprayed composite coating is uniform and very dense.There were few microscopic defects in the coating.The composite coatings have a lamellar structure composed of AlNbO4,Al2O3 and NbO2.The layers of the composite coatings bonded very well to each other.The spray power and the ratio of Al and Nb₂O₅have some effect on the microstructure of the composite coating.（3）The results of the mechanical properties test showed that the composite coating exhibits higher microhardness(889.8 HV_0.1),good toughness,and high crack expansion energy（14.14 J/m²）,The bonding strength between the composite coating and the aluminum substrate was about 21.33 MPa with bonding layer.The coating and the substrate are combined by mechanically bond.（4）The friction coefficient of the composite coating was low.The worn surface of the coating was flat and showed less peeling area.The wear mechanism of the composite coating was abrasive wear and fatigue wear,and the plasma spraying condition and wear condition of the composite coating affected the proportion of abrasive and fatigue wear relative to the wear mechanism.