Controllable Preparation And Performance Tuning Of Aluminum Matrix Composite Coatings Via Low Pressure Cold Spray Technology

Low-pressure cold spray technology?LPCS?is a new type of surface treatment technology.Compared with the conventional thermal sprayed aluminum coating,the LPCS aluminum coating has the advantages of a low degree of oxidation,high density and good resistance to uniform corrosion.However,the inert aluminum coating is not stable in marine environment,it is prone to localized corrosion,which leads to coating failure.In addition,the aluminum coating has the inherent disadvantages of low strength and hardness.When the aluminum coating is exposed to high-speed,strong friction,seawater lubrication and other harsh service environments,its tribological performance has improved significantly but still cannot meet the demands of long-term safety and reliability.Therefore,in order tosolve the key common problems of corrosion and wear,which are common in offshore oil and gas equipments,such as deep-sea drilling rigs,platforms and on-line storage and offloading devices.In this paper,on-demand design,controllable preparation and performance tunning of low pressure cold sprayed abrasive corrosion-resistant coatings were carried out.In this study,the performance characteristics of three different types of coating systems were first comparatively studied.It was found that cathode phase Ni in the cold spraying Zn-Ni-Al₂O₃ coating would accelerate the dissolution of zinc and corrosion of carbon steel substrate,while Al-Al₂O₃ coating had a relatively better corrosion resistance;the addition of ceramic phase Al₂O₃ and Cr₃C₂ is helpful to improve the abrasion resistance of thermal spraying NiCr and Zn-Ni coating system,but the corrosion protection performance of all these four thermal spraying ceramic coatings on steel substrate was poor;compared with the Zn-Ni-Al₂O₃ coating system,Al-30 vol%Al₂O₃ coating had a better wear resistance,but its friction coefficient is relatively high.After a systemic comparison of the performance characteristics of the metal-based coating systems,the Al-30 vol%Al₂O₃ was finally selected as the main component of the low pressure cold sprayed abrasive corrosion-resistant coating.And by adding a proper amount of solid lubricant?MoS₂/WS₂ powder?and alloying elements?Y/Mg?to adjust and improve the wear resistance and corrosion resistance of the coating.The corrosion resistance of aluminum matrix composite coatings shows that the addition of an appropriate amount of Y/Mg element is very important to improve the corrosion resistance of the coating.Whether the addition amount of Y/Mg is too low or too high,the improvement can be negligible or even negative.The optimal amount of Y is 0.2 wt%,and for Mg,the optimal amount is either 0.2 wt%or 0.5 wt%,by which the corrosion resistance of the coating is very good.The corrosion process of Al?Y?-30 vol%Al₂O₃ coating includes four stages:the surface uniform corrosion,the interfacial erosion-infiltration diffusion,the localized corrosion and the corrosion inhibition.The corrosion process of coatings with different Mg contents also have four aspects:the surface uniform corrosion,the selective dissolution of Mg,the Al corrosion and the corrosion inhibition.Under the dry friction condition,the wear weight loss of the coating is shown to decrease with the increasing content of MoS₂/WS₂.The wear mechanism of the coating mainly includes the lubrication of MoS₂/WS₂ and the oxidation-adhesive wear and abrasive wear.Under the seawater conditions,the wear volume of coatings with different amount of MoS₂/WS₂ decreases with the increase of MoS₂/WS₂ content,which indicates that the increaseof MoS₂/WS₂ content improves the wear resistance of the coating.The wear mechanism of the coating is mainly consists of MoS₂/WS₂ lubrication,corrosion wear caused by adhesive wear and a small amount of abrasive wear.The finite element method is used to simulate the collision deformation process of single particles and multi-component particles hitting the substrates.The results show that the MoS₂ particles cannot be deposited on the steel substrate individually,only if the MoS₂ particles have been encapsulated by Al power.Finally,a secondary regression model of the corrosion resistance and wear resistance of Al?Y?-Al₂O₃-MoS₂ coating with three parameters,including the spray temperature,the powder feeding rate,the mass ratio of Al-Y alloy powder and MoS₂ powder,were obtained by ternary quadratic orthogonal regression tests.The results showed that the influential factor on the corrosion resistance of the composite coating was as follows:the spraying temperature>the mass ratio of Al-Y powders to MoS₂ powders>the powder feeding rate,and the optimal preparation conditions were as follows:the spraying temperature of 350⁴00?,the powder feeding rate of 7⁸ gears,the mass ratio of Al-Y alloy powder and MoS₂ powder of 2.5³.0.The influential factor on the wear resistance of the composite coating was as follows:the mass ratio of Al-Y alloy powders to MoS₂ powders>the spraying temperature>the powder feeding rate,and the optimal preparation conditions were as follows:the spraying temperature range of 350⁴00?,the powdering rate of 5⁶ gears and the mass ratio of Al-Y alloy powder and MoS₂ powder of 2².5.Based on the regression model of single target corrosion resistance and wear resistance,the optimal preparation conditions and composition ratios of the coating under different practical working conditions were obtained by adjusting the different weight coefficients.When the weight coefficients are 0.2,0.5 and 0.8,respectively,the optimal preparation conditions and composition ratios of the coating are the spraying temperatures of 366/373/383?,the powder delivery rate of 5.8/6.3/7.0 gears,w?Al-Y?:w?MoS₂?of 2.0/2.5/2.7,respectively.