Numerical Simulation And Experimental Study On Preparation Of Fe-Based Amorphous Coating By High Velocity Oxygen/Air Flame Spray

Fe-based amorphous alloy,which has excellent corrosion resistance and thermal stability,was widely used in coating field.However,Pores affect the corrosion resistance of the coating,which was inevitably in the coating prepared by thermal spraying.In this thesis,the analytical method of computer simulation and design verification experiment was used to study the physical and chemistry state of Fe-based powder particles during the spraying process by JP-8000 and AK-06 high velocity oxygen/air flame spraying system（HVO/AF）respectively.Then we optimized the spray process parameters to produce low porosity coatings and explore the correlation between spray parameters and coating porosity.The HVOF and HVAF computer grid model was build use the commercial computing software computing Fluent.The realizable k-εturbulence model,the eddy dissipation model and the discrete phase model was chosen as the control mathematical equation to research the temperature and velocity change rules of the flame before the addition of the Fe-based amorphous powder particles,the relationship between temperature and velocity change rules of the particles during the flight process and the impact on the substrate after the addition of the powder particles at different spray parameters,also designed the verification experiments based on simulation results.The samples were tested for SEM,XRD,DSC,oxygen content,cross-sectional porosity calculation and salt spray test,to verify the best spray parameters and preliminary study of the relationship between porosity and corrosion resistance.For the HVOF spraying process,the variation of the temperature and velocity change rules of the SAM2X5 Fe-based amorphous powder(Fe_49.7Cr₁₈Mn_1.9Mo_7.4W_1.6B_15.2C_3.8Si_2.4at.%)flight in the flow field were simulated on the basis of predecessors.The simulation results showed that when the spraying distance was range of 360-380mm,the particles would be in a semi-melting state with good fluidity when deposited on the substrate,and a coating with low porosity can be obtained.The XRD results in the verification experiment showed that the coatings prepared by different spraying distances were completely amorphous;the SEM imagines and porosity result showed that the porosity was the lowest 0.57%when the spraying distance was 370 mm.The optimized spray distance of the SAM2X5 Fe-based amorphous coating prepared by the JP-8000 spray gun and the effectiveness of the HVOF spray computer model was verified.For the HVAF spraying process,a computer model of the AK-06 spray gun was established,to research the variation of the temperature and velocity change rules of the self-developed Fe-based amorphous powder(Fe_48.9Cr₁₈Mo_8.2C_4.5B_16.3Ni₂P_2.1 at.%)in the model flow field.According to the simulated results,the optimal powder particle diameter of the Fe-based amorphous powder was range of 30-40μm,the optimal barrel type was 4E,and the optimal spraying distance was range of 200-210mm.The XRD results in the verification experiment indicated that all the coating samples were basically amorphous;The SEM results showed that the Fe-based amorphous coating prepared by AK-06 gun with the spray parameter that powder particles diameter ranging from 30-40μm,barrel type 4E,and spraying distance at a range of 200-210mm had the flat surface,the highest density of the cross section and the best bonding state between the coating and the substrate.Porosity statistics and salt spray test results showed that the Fe-based amorphous coating prepared by the combination of the best spray parameters had the lowest porosity 0.31%and a good surface morphology after 1000hours of salt spray test.It also indicated that the lower the porosity of the coating,the better the corrosion resistance of the coating.