Study On Preparation And Tribological Properties Of Nano Ceramic Coating Applying To High-speed Conditions

In modern industrial production, more components used in high speed condition,such as shaft, roller, brake disc,and etc. Which is extremely extensive in industrialapplications. Higher friction velocity may cause serious wear within a short time,reducing the production efficiency. Now the surface treatment is expected to solve thisproblem.In this paper, through controlling the spraying process parameters, the coatingswere deposited by plasma spraying on20steel substrate who has a Ni/Al base coat,and the coats use micrometer Al₂O₃-13%TiO₂, nano-Al₂O₃-13%TiO₂aftergranulation and La₂O₃powders as raw material. There are Al₂O₃-13%TiO₂coating（AT）, nano-Al₂O₃-13%TiO₂coating（NAT）, nano-Al₂O₃-13%TiO₂-1%La₂O₃coating（NAT-1）, nano-Al₂O₃-13%TiO₂-3%La₂O₃coating（NAT-3） and Al₂O₃-13%TiO₂-5%La₂O₃coating（NAT-5）. The microstructure and phase composition ofcoatings were represented with XRD、SEM、EDS and so on, testing the friction andwear performance of the coatings utilize different friction testing machines.The SEM observation of the coating structure shows that the coatings weretypical of layered structure, there were molten zone, partial melting zone, unmoltenzone, micro-cracks and porosity in the coatings, mechanical bond in interface regions.In this paper experimental conditions, NAT-1coating is the most uniform,compactness is the best, and coating porosity as low as9.19%. Mechanics performancetest results of coatings show microhardness of NAT-1coatings reach841.3HV0.1, inaddition, with the porosity decreasing and increasing, microhardness of coatingsshowed a trend of increase and decrease. Nano-coating`s fracture toughness are betterthan the AT coating, the crack extension of NAT-3coating force up to7.89J/m2. Thetensile bond strength of NAT-1coating is the highest reaching15.97MPa.The α-Al₂O₃phase transform into metastable γ-Al₂O₃phase in the process of plasma spraying. Reaction producting in conventional coating is Al₂TiO5. Nanocoating generated the Al3Ti alloy due to the catalytic effect of La₂O₃, cause there is asmall amount of metallurgy combined in the coating. In the NAT-1and NAT-3coatings, existing LaTiO₃.4compound, which make the effect of solid solutionstrengthening and grain refinement on nano-coatings, and add excessive La₂O₃candisturb structure property of nano-coatings.Results of the friction and wear testing, which indicate friction and wearproperties of nano-coatings is superior to20steel substrate and AT coating, both inlow-speed and high-speed friction conditions. With the increase of velocity, thefriction coefficient of coatings were significantly reduced, addition of La₂O₃optimizedcoating performance, and then decrease the friction coefficient. Under the condition offriction and wear at low speed, the wear rate of coating increase with rotational speedincreasing, when the La₂O₃content more than3%, friction and wear performance ofcoating fell sharply, the wear performance is good while less than3%content. Coatingwear rate decreased under the condition of high-speed friction and wear, NAT-1added1%La₂O₃have the lowest wear rate, and less curve fluctuations. GCr15materialtransferred to the coating surface, together with abrasive dust of the coating to formthe transfer film which has the effect of protecting coating.At low-speed and high-speed friction conditions, the wear mechanism of thecoating is based in adhesive wear of GCr15material and crack growth leading tofatigue spalling wear of coatings. In high-speed friction, there is a slight abrasive wearin the transfer layer of the surface of coating. La₂O₃content influence coating porosity,hardness and fracture toughness, was an important factor affecting the friction andwear properties of nano-ceramic coating.