Plasma Spraying Liquid Zinc Corrosion Resistance Mo And Mo/Al₂O₃-TiO₂Composite Coatings Technology Research

The Mo coating and Mo/Al₂O₃-TiO₂composite coating were prepared by plasmaspraying on the Q235steel in this thesis; the plasma spraying processing parameters wereoptimized by the orthogonal test with the bonding strength between the coating and thesubstrate as an indicator. Coatings prepared under the optimized process parameters, thebond strength and thermal shock test of prepared coatings was done,while study the effectsof ultrasonic impact treatment on the thermal shock resistance of coating; Themicrostructure and properties of these coatings were investigated by means of SEM、EDS、XRD and so on; Testing the hardness of the coatings and a single Mo coating residual stress;Test the friction characteristics of the coating and the substrate by the UMT-2CETRfriction and wear testing machine; The coating resistance to liquid zinc corrosion test wasdone under actual working conditions in this topic; The study suggests that:The key parameters on bonding strength of Mo coating are ranked as thesequence:Spray distance,Power, Primary gas flow rate and Powder feeding rate, Theoptimized process parameters were: Power25kw, Powder feeding rate20g/min, spraydistance100mm, primary gas flow rate60psi, the corresponding bonding strength was ashigh as71.53MPa,the thermal shock failure times is87,the coating thermal shock failurenumber increased to96times after ultrasonic impact treatment,found overall level ofresidual stress in the coating is low, the surface is the tensile stress, subsequently graduallyreduced, tensile stress begins to rise to the vicinity of the interface, the stress between thecoating and the substrate at the bonding interface mutations; The key parameters onbonding strength of Mo/Al₂O₃-TiO₂composite coating are ranked as the sequence：Spraydistance,Primary gas flow rate,Power and Powder feeding rate,The optimized processparameters were: Power25kw, Powder feeding rate30g/min, spray distance100mm,primary gas flow rate60psi, the corresponding bonding strength was as high as28.99MPa,the thermal shock resistance of it is superior to a single Mo coating, the thermal shockfailure times is116, but ultrasonic impact treatment has little effect on the thermal shockresistance of the composite coating,even a slight decrease.The friction coefficient of Mo and Mo/Al₂O₃-TiO₂coatings increased with increaseof linear speed, decreased with the increase of load or temperature, the friction coefficientof the Mo coating is gradually reduced as the friction time prolonged.The coefficient offriction of two coatings are low than substrate, and they can play a good antifriction effectat high temperature. The hardness values of two coatings are in line with Normally andWeibull distribution, and much higher than the steel substrate, combined with low frictioncoefficient,they can play a good wear-resistant protective effect on Matrix.Relative to the Mo coating, Al₂O₃-TiO₂coating has a lower porosity and morecompact, there is a phase transition for TiO₂and Al₂O₃reaction to Al₂TiO₅.In addition, made the resistant coating liquid zinc corrosion test in the actualconditions, the result is show that: Two coatings all have a good resistance to liquid zinccorrosion performance, particularly, Al₂O₃-TiO₂surface coating in the composite coating, it has low porosity, can cut off penetration of liquid zinc to protect the substrate from theliquid zinc corrosion.