An Investigation Of The Formation Mechanism Of Ti-6Al-4V Alloy Micro Arc Oxidation Composite Film

Using the DC pulse mode,the second phase particles??-Al₂O₃,ZrO₂,W?were added into the silicate phosphate electrolyte system to prepare the corresponding TC4titanium alloy micro arc oxidation composite film.SEM micro morphology observation and EDS energy spectrum analysis of micro arc oxidation composite films were carried out respectively.In the?-Al₂O₃ composite film,some regions contain?-Al₂O₃ particles.In the region of the?-Al₂O₃ composite film without?-Al₂O₃ particles,the content of Al is 6.89%,and the content of Al₂O₃ is 13.01%.The content of Al in the original film is1.52%,and the content of Al₂O₃ is 2.87%.The content of Al₂O₃ in the?-Al₂O₃composite film is 10.14%more than that in the original film.It is shown that the fusion of the?-Al₂O₃ particles with the effect of the high temperature of the film formation leads to the disappearance of the particles.In theZrO₂ composite film,some regions contain ZrO₂ particles.In the ZrO₂ composite film,the content of Zr element in the region without ZrO₂ particles is 31.81%.It is shown that the ZrO₂ particles melt under the high temperature of the film formation.In the W-composite film made of W powder with medium particle size of 50nm,the content of W element in the region without W powder is 6.69%.It is indicated that the W powder particles melt because of the high temperature of the film formation,which results in a certain amount of W elements in the film.According to the results of SEM and EDS detection,the second phase particles in the film are melted and it is known that the highest temperature of micro arc oxidation film is higher than W melting point of 3410?.The micro arc oxidation coatings were labeled with Na₂WO₄,after micro arc oxidation reaction for a period of time,mixed solution containing Na₂WO₄.,marking on the film with W elements.After SEM morphology observation and EDS spectrum detection were carried out on the film,it is concluded that the growth of micro arc oxidation film is in the form of molten pool growth.Using Na₂WO₄ markers and combining with EDS energy spectrum analysis,it is known that how much the film thickness increased by a spark after the voltage is stable.Na₂WO₄ labeling method and EDS energy spectrum analysis were used to find out the time of molten pool regeneration.Combination the observation with long distance working microscope,the time required for the first generation formation of the weld pool to cover the sample is12min.The time required for the second generation formation of the weld pool to cover the sample again is 7min.The micro arc oxidation process was observed by using long distance microscope.It is found that when the voltage is low and the stable value is not reached,the spark exists in the form of spark clusters and the spark is easy to walk after it is produced.Then,as the voltage increases,spark appears in a single one,and the spark is relatively stable,not easy to walk.With the increase of voltage,the frequency of spark appears to decrease gradually and the exist time and the size of the spark increase gradually.Bubbles and breakdown always occur at the weak point of the film.The relationship between the reaction time and the film thickness is y=152.4*x^0.06-161.The relationship between reaction time and the molten pool size is y=88.65*x^0.112-103.The relationship between the size of the molten pool and the thickness of the film is y=15.35*x^0.35-18.49,and all of them are exponential function.