The Effect Of Layered Phase Distribution And Cermet Transition Zone On The Mechanical Properties Of The Coating

Al2O3-40wt%TiO2 coating are widely applied in mechanical,textile and metallurgy.The Al2O3-40wt%TiO2 coatings deposited with atmospheric plasma spraying have high hardness,wear resistance and stable chemical properties.With the development of industry,the application area of Al2O3-40wt%TiO2 coating is become widely than before and the apply condition also become more severe.Therefore,improve the properties of coating is ergency.It is believed that nano-structure coating have excellent properties due to their nano-structure.Although nano-structure coating has excellent properties,the depositing process and parameters is difficult to control.Graded Al2O3-40wt%TiO2 coating and multilayer Al2O3-40wt%TiO2 coating could decrease the stress gradient in the coating,which is benefit to prolong the service time of coatings.There are many interface in the graded and multilayer coating system.It is believe that defects tend to initiate at the interface.The addition of another phase also can improve the properties of coatings.The influences of Y2O3 on the structure and properties of Al2O3-40wt%TiO2 have not been deeply researched.As we known,the properties of materials are depend on the structure.In my experiment,we designed a new structure of Al2O3-40wt%TiO2 coating with metal-ceramic trasition region and add Y2O3 into the Al2O3-40wt%TiO2 coating.The cracks propagation mechalnism is studied.We also researched the properties of Al2O3-40wt%TiO2 coating with different quanlity Y2O3 addition.Following are some conclusions of our experiments:(1)The Al2O3-40wt%TiO2 coating with metal-ceramic transition region have been successfully diposited.The metal-ceramic transition region could decrease the stress gradient in the coating and changed the fatigue mechanism of coatings under thermal shock test and three points bend test.The metal-ceramic transition region improve the mechanical properties through hindering the propagation of cracks.(2)Plasma spraying parameters and pre-exist morphology are the main factor affect the lamellar phase distribution in the Al2O3-40wt%TiO2 coating.R/h?a<1 is the essential condition to form the scattered phase.Slope of the pre-exist morphology(?)affect the location of the scattered phase.(3)Interface defects play an important role in the stress release mechanism.When the diamond indenter loading on the coating,cracks will generate near the indentation and the interface defects.Cave-in will occure when the cracks conect each other.In the coating with many interface defects,cracks generation and propagation and cave-in are the main stress release methods.However,in the coating with compact lamellar structure,cracks and spallation are the main stress release mechanism.(4)In the ceramic region,cracks propagate along the intergranular interface of columnar grain.Cracks could be deflected by NiAl alloy splats and cross the NiAl alloy splats with large plastic deformation.(5)The addition of Y2O3 could decrese the homogeneity of coatings and improve the mechanical property of Al2TiO5.Because the mechanical property improving of Al2TiO5,the 8wt0%Y2O3 addition greatly decrease the wear rate of Al2O3-40wt%TiO2 coating.(6)In conclusion,The optimal parameters for achieving good wear resistant coating are a spraying current of 550 A,an N2 flow rate of 2400 L/h,a stand-off distance of 110 mm,and a power feed voltage of 8 V.Furthermore,the range values demonstrate that wear rate is mainly affected by the N2 flow rate,stand-off distance and spraying current.