| Non-skid coatings used in seawater environment has good properties of non-skid and corrosion resistance, effectively enhanced the safety of personnel and equipments and widely used in marine structures, such as, offshore oil rigs, drilling platforms and so on. However, since the service environment of these equipments is extremely harsh, the general single layer structure non-skid coatings can meet the demand of the properties of non-skid and wear resistance, while, they can not guarantee the property of corrosion resistance.So, these will lead to the the poor durability of these coatings and lay a huge risk to the safety of equipments and personnel. Therefore, the development of excellent wear and corrosion resistance non-skid coatings used in seawater environment can not only provide a technical support and conditions to protect the safety of offshore oil and gas equipment and the staff members. It has important scientific significance and practical value.Based on the extensive references and experimental work, the double layer structure of composite coating system, which consists of corrosion resistance coatings and wear resistance coatings, were selected ultimately. Ni-Zn-Al2O3 composite coatings as underlying coatings of corrosion resistance were prepared on Q235 carbon steel by low pressure cold spray and NiCr-Cr3C2 cermet coatings as wear non-slip surface material were prepared on underlying coatings of corrosion resistance by HVOF and SPS. The microstructure and phase composition of coatings were examed by using SEM, EDS and other failure analysis methods. The wear and corrosion behanior of composite coatings were studied by using the friction and wear test, electrochemical test and salt spray test, and the failure behavior and its mechnism in the marine environment were discussed.Dry friction and wear test results showed that, the dry friction coefficient of NiCr-Cr3C2 coarse powder coatings by SPS and flame spraying have reached U.S. military standard MIL-PRF-24667 C and showed good friction properties. The dry friction and wear mechanisms of NiCr-Cr3C2 coatings were mainly adhesive wear and abrasive wear.Electrochemical and salt spray test showed that, supersonic plasma sprayed NiCr-Cr3C2 coatings have poor corrosion resistant properties, and mainly due to the interfacial corrosion of the surface/bottom and bottom/substrate. Cold sprayed Ni-Zn-Al2O3 coatings and flame sprayed NiCr-Cr3C2 coatings demonstrated excellent corrosion protection properties.After salt spray corrosion, the friction coefficient of supersonic plasma sprayed NiCr-Cr3C2 coatings was lower than dry friction coefficient and the weight of the wear loss increased significantly. Therefore, seawater corrosion accelerated the deterioration of the tribological properties of coatings. The friction coefficient of flame-sprayed NiCr-Cr3C2 coatings after salt spray corrosion was slightly lower than the dry friction coefficient, but the weight of the wear loss was lower than that of dry condition. It is because the formation of the dense corrosion products Zn(OH)2 on the surface of these coatings significantly played the function of friction reducing and lubrication. But the wear losses under dry friction conditions was lower than that under salt spray corrosion conditions, which demonstrates that the corrosion of seawater accelerated the deterioration of coating’s tribological properties. The wear mechanism of NiCr-Cr3C2 coating after salt spray corrosion was corrosion fatigue wear.Therefore, we developed the composite wear resistant non-skid coatings which consist of Ni-Zn-Al2O3 corrosion resistant underlying coating and NiCr-Cr3C2 wear resistant surface coating. The composite wear resistant non-skid coatings can not only combine excellent corrosion and wear resistance, but also meet the demands of the conditions of marine environment sevice. |
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