Study On The Microstructure And Tribological Properties Of Nanostructured Al₂O₃-TiO₂Composite Ceramic Coatings Prepared By Supersonic Plasma Spraying

Plasma-sprayed Al2O3-13wt.%TiO2composite ceramic coating has been put into useextensively in some fields such as aerospace, remanufacturing, light industry, auto industry,etc. because of its wonderful performance, including resistance to wear, corrosion, elevatedtemperature and oxidation. However, the poor fracture toughness of ceramic coatings limitsits application in more fields to a great degree. Nano thermal spraying technology is a newmethod in the field of surface engineering. Nanostructured ceramic coatings prepared bythis method improve their toughness due to the retained nanostructure during thesolidification, which makes up for its defect of the limited application range. Therefore,thorough investigation for plasma-sprayed nanostructured ceramic coating has vital theorysignificance and practical value in developing its properties and broadening its applicationrange.In this paper, nanostructured Al2O3-13wt.%TiO2(n-AT13) composite ceramic coatingswere deposited by high-efficiency supersonic plasma spraying technology (SPS) andconventional air plasma spraying technology (APS) on the substrate1045steel. Themicrostructure, porosity, phase composition, micro-hardness, elastic modulus, fracturetoughness and tribological properties of coatings were respectively experimented andanalysed by lots of equipments and methods. Finally the results showed that:(1) Fully melted regions and partially melted regions were alternately built-up to presenta lamellar feature, which was named bimodal distribution structure, and in some regionsthey were mixed together without distinct boundaries. The formation of structure wasmainly influenced by plasma jet temperature, the difference in melting points betweenAl2O3and TiO2and thermal conductivity.(2) The porosity and micromechanical properties (micro-hardness, elastic modulus,fracture toughness) followed Weibull distribution and micromechanical properties had acharacteristic of bimodal distribution. The distribution characteristic of porosity andmicromechanical properties were significantly influenced by bimodal distribution structure.(3) With the increase in argon gas flow rate (AGFR), the mean and characteristic valuesof porosity decreased and to a local minimum and then increased, the mean andcharacteristic values of micro-hardness and elastic modulus increased and reached a localmaximum and decreased, and those values of fracture toughness had a same trend with the porosity. With the increasing power, the porosity decreased gradually and remained finally,the micro-hardness and elastic modulus kept an increasing trend, but the fracture toughnesshad an opposite trend.(4) The numerical relationships of spraying parameters-porosity-micromechanicalproperties were built by regression analysis.(5) Under the dry friction, the wear mechanisms of supersonic plasma spraying (SPS)coatings were lamellar cracking caused by stress concentration and adhesive wear causedby pressure weld and friction hyperthermia; The conventional air plasma spraying (APS)coatings had same wear mechanisms with SPS coatings, but it had a lower critical load inmaking coating failure; Under the oil lubrication, the SPS coatings were lamellar crackingcaused by stress concentration under a low applied load and adhesive wear under a highapplied load.