Growth Behavior And Tribological Performance Of Microarc Oxidation Films Prepared With Composite Processes

Iron and steel are widely used in industry.To improve their wear resistance,micro-arc oxidation technology can be used to prepare a layer of ceramic film on their surfaces.However,the direct fabrication of micro-arc oxidation films on steel directly is difficult.The normal way is to first deposit a layer of valve metal on the steel before the micro-arc oxidation treatment.In this paper,two kinds of composite processes,including hot-dip aluminizing(HDA)/micro-arc oxidation(MAO)and arc ion plating(AIP)/micro-arc oxidation(MAO),were used to prepare ceramic films on the steel surface.And the effects of different process parameters on the growth behavior and tribological properties of the composite films were studied in depth.Using the HDA/MAO process,an alumina-based composite film was prepared under an aluminate electrolyte system.The composite film layer was composed of an oxide layer on the surface,an Al plated layer in the middle and a Fe-Al diffusion layer in the bottom.The results demonstrate that when the oxidation voltage was increased,more Al₂O₃ from the electrolyte was deposited on the surface of the film,promoting the outward growth of the composite film.When the oxidation time was prolonged,the oxygen ion content in the film layer was increased,promoting the inward growth.When the oxidation time reached45 min,the film layer was damaged by arc discharge and the thickness was decreased.With the duty cycle increasing,the composite film became thicker and the internal oxidation degree was increased.With the oxidation voltage increasing,the wear rate of the film layer was decreased;With the oxidation time increasing,the wear rate of the film layer was decreased first and then increased later;With the duty cycle increasing,the wear rate of the film layer continued to rise.When the oxidation voltage,the oxidation time and the duty cycle was 500 V,30 min,and 30%,respectively,the prepared composite film had the best wear resistance.Under the load of 7 N,the wear rate of the optimum composite film was reduced by 78.7%compared with the HDA substrate.Using the HDA/MAO process,an alumina-based composite film was prepared under a silicate electrolyte system.The results demonstrate that the duty cycle and frequency affect the distribution and content of Al and Si elements in the composite film.When the duty cycle was increased,the space density of micro-discharge became smaller.Less Al element participated in the reaction on the surface of the film layer,and the aggregated silicate increases,so the Al concentration was decreased and Si was concentrated in the outer layer of the film.As the frequency was increased,the pulse energy decreased,and the ion migration rate of Si slowed down,resulting in a reduction in the Si content on the film surface.As the duty cycle was increased,the wear rate of the film decreased first and increased later;With the frequency increasing,the wear rate of the film also decreased first and increased later.When the duty cycle was 40%and the frequency was 1000 Hz,the prepared composite film layer had the best wear resistance.AIP/MAO process was used to prepare titania-based composite film layer under the aluminate electrolyte system.The main phase composition of the film is Ti O₂ phase at low voltage and Al₂Ti O₅ phase at high voltage.The reason is that when the voltage increases,more Al₂O₃ deposits on the surface and reacts with Ti O₂ to form Al₂Ti O₅.With the growth of the composite film,cracks appear in the film,resulting in the local increased electric conductivity.The Fe matrix was melted by the high temperature caused by the strong current and erupted out of the surface of the film,and then solidified into a sphere when it condensed.