Microstructure And Properties Of Plasma Sprayed Al₂O₃-13wt%TiO₂ Composite Coating

Experiments using atmospheric plasma spraying technique?APS?over NiGrAl coatings system through orthogonal experiment on Q235 steel substrate,micron Al₂O₃-13wt%TiO₂coating prepared by single factor method,by detecting the morphology and properties of the transition layer and Al₂O₃-13wt%TiO₂ ceramic coating,coating optimization.Research results:?1?NiGrAl small holes on the surface of coating and coating due to droplet collision in overlapping formation,no obvious cracks and holes through the coating,high current powder particles in the plasma flow in excessive heating,when reaching the substrate or coating surface easily when sintering,on the formation of coating is useless.Based on the orthogonal experiment to evaluate the adhesion of the coating scratch test,the primary and secondary factors of NiGrAl coating spraying process are current,powder feeding rate and spraying times.The coating thickness may be mainly related to the number of spraying and powder feeding rate.The results of orthogonal test and coating thickness,current 350 A,powder feeding rate of 53g/min,spraying 2 times are the best parameters of Ni/Al coating.Vivtorinox hardness NiGrAl coating average in the same cross section at the depth of 325 HV along the thickness direction,cross-sectional coating hardness value unchanged,showed that the coating microstructure is compact with a good combination of Al₂O₃-13wt%TiO₂coating.?2?the current affects the melting state of the powder particles,the current is too high and the powder particles burn too much.The better the melting,the better the coating of the molten droplet stack,the better the spraying current is on the surface of 400 A coating.The argon flow rate is mainly affected by the particle velocity and the time in the plasma plume.When the argon flow rate is higher,the kinetic energy of the droplet is larger.When the droplet and substrate collision speed,lead to the formation of stress within the coating is large,easy to crack;speed is smaller and produce more due to less energy will lead to deformation of the droplet is not fully pore.Because of the typical lamellar structure of the micro Al₂O₃-13wt%TiO₂coating,the pores and cracks in the coating can not be avoided.The bestprocess parameters of spraying Al₂O₃-13wt%TiO₂coating are current 450 A,argon flow rate1800L/h.?3?in the coating forming part of a-Al₂O₃ into a non stable phase gamma-Al₂O₃ process,a part of TiO2 transformed into anatase rutile TiO₂ stable,there is a part of a chemical reaction between alumina and titania Al₂TiO₅.When the argon flow rate is constant,the increase of current will lead to the decrease of-Al₂O₃ phase.In the scratch test,when the current is too high and the argon flow is large,there are obvious brittle fracture in the scratch.It is mainly due to the increase of the residual stress in the coating,which results in brittle fracture.The average hardness of coating is 1295 HV.SEM and EDS analysis show that the fracture position is the fracture between the Al₂O₃-13wt%TiO₂ coating,which indicates that the coating failure,the bonding strength of the coating is 23.2MPa.?4?the surface morphology of the coating was optimized by experiment,and the thickness of the coating was uniform,which was about 300 m,and the average hardness of the coating was 1307.9HV.The composition of the coating is mainly alpha-Al₂O₃,gamma-Al₂O₃,Al₂TiO₅ and a small amount of rutile TiO2.The increase of the content of alpha-Al₂O₃ in the optimized coating leads to the improvement of the hardness and wear resistance of the coating.?5?the erosion angle is small,the destruction of the coatings is mainly due to the target of cutting stress,when the angle increases,due to the brittle material plastic deformation,crack expansion mainly leads to brittle fracture,the erosion angle of 90 degrees of erosion is most obvious,the cutting effect is weakened,brittle fracture phenomenon is most obvious.