| Confronting the problems that the chrome-plated screw rotor used for Daqing Oilfield easily scaling and wear serious in ASP flooding environment, a study on the nanostructured AT 13/CaF2 coating which was prepared by plasma spraying on the screw rotor was carried in this paper. SEM, XRD, EDS, wear tester and universal tensile testing machine were used to characterize the microstructure, mechanical property and wear resistance of nanostructured AT13/CaF2 coating respectively. The antifriction mechanism of nanostructureed AT13/CaF2 coating was discussed in detail. Moreover, a stimulation of residual stress in coating was calculated with ANSYS finite element software. The main conclusions are as followes:(1) Two featured area in the nanostructured AT13/CaF2 coating were scaned by SEM. one is fully melted area and another one is mostly melted area. In the fully melted area, the nanostructured AT13/CaF2 particles may grow in size. However, in mostly melted area, amounts of nano particles still been in original size. With the increase of CaF2, lots of fine particles are founded on the surface of nanostructured AT13/CaF2 coating. The mainly composites of nano AT13/CaF2 coating are ?-Al2O3?CaF2 and Rutile-TiO2,and few ?-Al2O3 and Al2TiO5 also detected.(2) According to mechanical test, the microhardness, bonding strength and thermal shock resistance of nanostructured AT13/CaF2 coating were much better than that of microstructured AT13/CaF2 coating. With the increase of CaF2, the hardness and bonding strength were impaired, while the thermal shock resistance improved. Clearly, the porosity in nanostructured AT13/CaF2 coating contributed to thermal shock resistance.(3) The contact angles of nanostructured AT 13/CaF2 coating were measured by contact angle measurement. The result showed that contact angle is improved compared with the microstructured AT13/CaF2 coating. The porosity of nanostructured AT13/CaF2 coating increased with the increasing CaF2. A composite liquid-solid contact is formed and the contacting transited into Cassie state which led to the increasing contact angle. A stimulation of scaling resistance of nanostructured AT13/CaF2 coating was carried. The data indicated that contact angle had no connection to scaling resistance of nanostructured AT13/CaF2 coating even in ASP flooding surrounding. But the surface energy did contribute to the fouling capability. The mainly composites of scaling are mainly CaSO4, CaCO3 and the crystalline hydrate of calcium sulfate.(4) As for the result of wear test, the coefficiency of friction decreased as more load carried on the the coefficiency of friction consisting of same composite. Additionally, the coefficiency of friction decreased either as more CaF2 added into the composite coating under unchanged load. As 200N loading on the nanostructured AT13/CaF2 coating, the friction coefficiency was 0.66. The coefficiency of friction arranged from 0.33 to 0.63 when more CaF2 added. Within the process of wear, the CaF2 formed into a self-lubricating film which alleviated the wear damage between the coating and milling ring. When 10wt% CaF2 added into the film, the wear loss of nanostructured AT13-10%CaF2 coating is least.(5) The analysis of ANSYS infinite software stated that the highest inner tensile stress in the radial bearing is along the boundary of nanostructured AT13-10%CaF2 coating which may result in striping from the matrix. In the axial bearing, stress distributed between the matrix and film. Because of the Ni/Al layer, the radial stress of coating is reduced. |
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