Preparation And Tribological Study Of Composite Materials Based On Layered Structures

Under special environment of petroleum/gas well with slurries composing of water and abrasive sands,sliding bears in downhole tools have harsh working conditions,friction and wear causes damage of the bearings,leading to the failure of the whole system.Ceramic materials have high strength,high hardness,good wear resistance,good corrosion resistance,stable performance and other excellent performances.Ceramic materials are widely used in the automotive industry,oil drilling process,aerospace and other fields.Shell pearl has layered structure from macro to micro grading and high toughness and strength.Therefore,ceramic composite with shell-like layered structure can be prepared as sliding bearings under special environment of petroleum/gas well.In view of the above reasons,this paper uses nano-powder to prepare porous alumina?Al₂O₃?ceramic scaffolds by directional solidification,freeze-drying and high temperaturesinteringthroughthefreezingcastingmethod.Then,the polymethylmethacrylate?PMMA?is filled into the porous ceramic body by prepolymerization,filling,polymerization,and stripping through polymerization method,and the biomimetic lamellar Al₂O_3/PMMA composites with lamellar structure are prepared.In order to study the mechanical properties and tribological properties of the composites,fracture toughness and friction and wear experiments were carried out respectively.The fracture properties of the composites are analyzed by using the chevron notch method?CN method?.The friction coefficient of the composites under different load and rotational speed is studied.The surface of the material after friction and wear is analyzed by scanning electron microscopy and three-dimensional laser morphology.The results are used to summarize the effects of various factors on the friction coefficient and wear resistance.The main results of the sudy are as follows:?1?Using the freezing casting technology,nanometer Al₂O₃ powder and after sintering at 1650°C for 4 h,the ceramic scaffolds with obvious lamellar structure are successfully prepared.With the increase of the initial solid content,the viscosity of the ceramic slurry becomes larger,the pore size become smaller.?2?Layered Al₂O₃/PMMA composites with obvious lamellar structure are prepared by filling the polymer PMMA into the porous ceramic scaffolds by bulk polymerization method.The matrix ceramic and the reinforced phase polymer are combined well.The prepared composites have high fracture toughness.?3?Under the condition of water-based drilling fluid lubrication,the friction coefficient of different solid content composites descend first and then rise with the increase of load and the friction coefficient change with the speed is not obvious.Under the dry friction condition,the friction coefficient of the five different solid content composites decreases with the increase of load and rotational speed.?4?Under the condition of water-based drilling fluid,the wear scar diameter increases with the increase of the rotational speed,which is the same as the change of the wear marks diameter with the speed.Under the dry friction condition,the wear marks diameter increases with the increase of the load and the change of the wear scar diameter with the load is the same.From the experimental data,it can be seen that there is a positive correlation between wear scar diameter and wear marks diameter in ball-plate friction experiment.?5?Under the condition of water-based drilling fluid,the wear forms of steel balls grinding one the lamellar Al₂O₃/PMMA composites with different solid content are corrosion wear and abrasive wear.