The Micromorphology And Mechanical Properties Of Plasma Sprayed Splats

Plasma spraying technology,as an important technology to prepare coatings,is widely used in the fields of machinery,aviation,aerospace,metallurgy,petrochemical,et al.The YSZ material is widely used in the thermal barrier coating due to its high melting point and excellent high temperature stability,and the Ni60 material is often used as an interlayer in thermal barrier coating because it can alleviate the difference of thermal expansion coefficient between top coating and substrate in thermal barrier coating system.As the basic unit of the coating,the micro-morphology and mechanical properties of the splat affect the structure and properties of the coating greatly.Therefore,the further research of the splat is expected to provide a key method for improving the properties of the coating.In this paper,Ni60 and YSZ splats and coatings were prepared by plasma spraying on nickel-based alloy and copper substrates.The micromorphology was observed by optical microscope,3D microscope with super wide depth of field and scanning electron microscope.The results showed that the spray power and the type of substrate had a great influence on the morphology of splat.With the increase of the power,the thickness and diameter of Ni60 splats decreased,the splash became more severe,and the splats transformed from regular circular shape to irregular shape gradually.At the same time,the deposition number of Ni60 splats on the substrate first increased and then decreased,and the coverage rate of Ni60 splats decreased with the increase of the power.On the other hand,the YSZ splats on copper substrate were more rounded and were of less spatter than that on nickel-based alloy substrate at the same power.There was basically no crack and hole in the center of splats.In this paper,the hardness of the coatings was measured by microhardness tester,the hardness,fracture toughness and elastic-plastic properties of the splats were measured by nanoindentation tester,and the residual stress of the splats was measured by Raman spectrometer.The results showed that the hardness of Ni60 splats were8.0¹2.4 GPa.The hardness of the corresponding coating was 8.6¹0.9 GPa.The hardness of YSZ splats was 13.0²2.4 GPa,and the hardness of the corresponding coating was 8.2¹2.3 GPa.The relationship between the hardness of the coatings and the splats was established to predict the maximum hardness of the coatings with little defect according to the nanohardness of the splats.The elastic recovery range of Ni60splats was smaller than YSZ splats,and their elastic modulus was 240⁴00 GPa higher than YSZ splats.Ni60 splats had more uniform plastic deformation resistance in the thickness direction,while YSZ splats had less plastic deformation resistance near the substrate.The fracture toughness of YSZ splats was from 0.15 MPa·m^1/2 to0.29 MPa·m^1/2,which was quite different from that of traditional coatings of 0.8¹.7MPa·m^1/2.The possible reason was the suppression of coating pores and surrounding splats on the extension and propagation of cracks.The residual stress of YSZ splats was from 16.8 MPa to 40.5 MPa,which indicated the tendency of increasing with the decreasing size of splats.