Study On The Technology And Properties Of Detonation Gun Sprayed Cr₃C₂-NiCr Coatings

Thermal spray technology is widely used in national defense,aerospace and other important fields as well as people's livelihood because of its reusable coatings,resource saving and good performance.In view of the working conditions of flue gas turbine blades,detonation gun sprayed in the thermal spraying technology is adopted to further improve their surface performance and better protect the blade base.Because detonation gun sprayed is used in industrial applications,different gas will be selected due to production requirements and equipment.In this paper,propane is used as detonation gun sprayed gas,five kinds of oxygen-fuel ratio processes are selected to prepare Cr₃C₂-NiCr coatings.The properties of five kinds of oxygen-fuel ratio coatings are tested,the micro-morphology is characterized,and the influence rules of different oxygen-fuel ratio on the structure and properties of coatings are studied.Five groups of metal-ceramic composite coatings were prepared by using GH864as base material and Cr₃C₂-NiCr powder as coating material according to three kinds of explosion flames:oxidizing flame,neutral flame and reducing flame.According to the performance test requirements of flue gas turbine blades,the thermal shock resistance,hardness,toughness,friction and wear and oxidation performance of the coating were tested.The morphology and microstructure of the coating surface and section were characterized and analyzed,and the influence mechanism of oxygen-fuel ratio on the performance of the coating was explored.The thermal shock test results show that the oxidizing flame coating and the neutral flame coating can not guarantee the effective thickness of the coating under the same other conditions,and the coating is ineffective.The three coatings of the reducing flame are subjected to the repeated water quenching at 800?.It was satisfied with the requirements of thermal heat shock test of flue gas turbine blades,and with the increase of oxygen-fuel ratio,the thermal heat shock resistance are relatively beter when the oxygen-fuel ratio are 3.4 and 2.9.The results of hardness show that the hardness of the oxidizing flame,neutral flame and reducing flame coating increases begin and then decreases with the increase of oxygen-fuel ratio.When the oxygen-fuel ratio is 3.4,the hardness of the coating is the highest,reaching 686.5HV1.The results of cracking toughness test of reducing flame coating show that the cracking toughness of the coating is inversely proportional to its hardness.The poriness of the reducing flame coating showed that the poriness of the coating decreased first and then increased with the increase of oxygen-fuel ratio.When the oxygen-fuel ratio was 2.9,the porosity of the coating was 0.930%.The results of XRD and SEM of the coating surface show that when the spray atmosphere changes from reducing to oxidizing,the degree of decomposition of Cr₃C₂particles is intensified.When oxygen-fuel ratio reaches 5.1,it is almost completely converted to Cr₇C₃,and the diffraction peak of Cr₂₃C₆ is measured.The reducing flame coatings are composed of uniformly distributed black Cr₃C₂ particles and a small amount of Cr₇C₃ particles and a bonding?Cr,Ni??phase filled around the gap.The surface morphology shows that there is a flattened poorly concentrated area on the surface of the reducing flame coating,and with the increase of the oxygen-fuel ratio,the flattened poorly aggregated area tends to become smaller and smaller,when the oxy-fuel ratio is 2.4,the most flattened area is larger and the performance of the coating is relatively worse.However,when the oxygen-fuel ratio is increased from 2.9to 3.4,the surface morphology of the coating is not much different.The cross-section of coating SEM show that the cross-section of the reducing flame coating is a typical layered structure with no obvious defects,and similar to the surface structure,the binder phase and the hard phase are staggered and superimposed arrangement,and the flattened area can also be observed from the cross section.When the oxygen-fuel ratio is 3.4,the structure of the coating is the least,and the bonding ability of the coating is optimal.Through the cross-sectional SEM observation,the bonding form between the coating and the substrate is mainly in the form of mechanical bond.The friction properties show that the wear of the three reducing flame coatings are less than the wear of the basis,and the wear of the coating decreases with the increase of the oxygen-fuel ratio,but the friction coefficient of the coating increases with the oxygen-fuel ratio,it goes down and then it goes up.On the whole,the wear of the substrate is the most severity.When the oxygen-fuel ratio is 2.9,the overall high-temperature friction performance of the coating is the best.The morphology of friction show that the friction forms of the three reducing flame coatings are mainly fatigue wear and abrasive wear,accompanied by adhesive wear.But the form of the basis is mainly abrasive wear and adhesive wear,and its friction mechanism is the peeling wear mechanism,also the basis wear is serious.Compared with the wear results of the coating,the Cr₃C₂-NiCr coating can effectively protect the basis and improve its high temperature wear resistance.From the results of isothermal oxidation of the reducing flame coatings,the color of the coating surface did not change much.When the oxygen-fuel ratio was 2.4,the TGO layer gradually became thicker,so the high temperature oxidation resistance is the worst under this oxygen-fuel ratio and the oxidation results of the other two coatings are similar.Through comprehensive performance results and analysis,Cr₃C₂-NiCr coating can improve the hardness and high temperature friction performance of the basis.When the oxygen-fuel ratio is 2.9,the coating with the best comprehensive mechanical properties can be obtained.At the same time,protect the basis by preparing a coating,the use time of the flue gas turbine blade under severe working conditions can be effectively improved,the maintenance cost and the parking loss are saved,and have good economic and practical value.