Effects Of Different Al Particle Size On The Micro Structure, Mechanical Properties And Oxidation Resistance Of The Composite Micro-arc Oxidation Coating Formed On Pure Titanium

This paper mainly studied the effect of different particle sizes of Al particles on the micro-arc oxidation, friction and wear properties and high temperature oxidation resistance of pure titanium micro-arc oxidation composite coating, which prepared in electrolyte(Na2SiO3 6 g/L, NaOH 0.5 g/L,(NaPO3) 65 g/L) with adding Al particles in different size.The micro structure, composition, wear weight loss and the micro structure before and after high temperature oxidation, oxidation weigh gain and hardness of pure titanium micro-arc oxidation composite coating were characterized by scanning electron microscopy(SEM), energy disperse spectroscopy(EDS), X-ray diffraction(XRD), micro hardness meter and electronic balance. the impact of different particle sizes of Al particles on the micro structure, mechanical properties and oxidation resistance of pure titanium micro-arc oxidation composite coating were investigated.The technological parameters of MAO were as follows: Na2SiO3 6 g/L, NaOH0.5g/L,(NaPO3)6 5g/L, temperature: room temperature, current density: 4.2A/dm2.Adding nano-Al particles, micro-Al particles, 200 mesh-Al particles into the electrolyte,the grain sizes were 50 nm, 10μm, 74μm. The friction and wear properties were studied by friction test machine under the load of 3.1N for 20 min. The studies on the high temperature resistance properties of the coatings were carried out by the high-temperature oxidation weight gain tests and surface morphology at 750 oC for100h.(1)With the content of nano-Al particles changed from 0g/L to 5g/L,The termination voltage of micro oxidation increased from 448 V to 528 V, the hardness increased from 811 HV to 1368 HV. The number of holes decreased and coating became smooth. the average friction coefficient decreased from 0.68 to 0.39, and the wear weightlessness reduced from 1.0 mg to 0.58 mg when the content of nano-Al particles was 3g/L.After 100 h oxidation at 750℃, the mass gain reduced from 2.9mg/cm2 to 0.024mg/cm2, the surface morphology had no significant change.(2)With the content of micro-Al particles changed from 0g/L to 5g/L, the termination voltage of micro oxidation increased from 448 V to 472 V, many micro-bulge could be found at the MAO coating and increased the surface roughness. the hardness increased from 811 HV to 920 HV. the average friction coefficient decreased from 0.68 to0.5 with adding 1g/L micro-Al particles, there are some fragile on the micro-crack wearsurface, the wear weightlessness would increase, the wear weightlessness is up to 1.4mg when the content of micro-Al particles was 5g/L. the mass gain reduced from 2.9mg/cm2 to2.3 mg/cm2 after high temperature oxidation test, when the content of micro-Al particles was 1g/L. The oxidation coating would be peeling off, if the content continued increasing.(3)With the content of 200 mesh-Al particles changed from 0g/L to 5g/L,The termination voltage of micro oxidation increased from 448 V to 467 V, there are some mushroom shape micro-bulge at the MAO coating surface. The hardness increased first and then decreased with the increasing of content of 200 mesh-Al particles, the hardness was 1067 HV when the content was 1g/L. The average friction coefficient and wear weightlessness were decrease. The oxidation mass gain reduced to 1.9mg/cm2, big holes and agglomeration could be found at MAO coating surface after high temperature oxidation test.