Effect of current ratio on ceramic characteristics of ZrO2/Al2O3 coatings using plasma electrolyte oxidation

• Main Authors: Shang-Jung Wu, 巫尚蓉
• Other Authors: Chen-Chia Chou
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/48277046899560151495

碩士 === 國立臺灣科技大學 === 機械工程系 === 104 === In this paper,we try to adjust the positive and negative current ratio in plasma electrolytic oxidation(PEO) ceramic coating on 6061 alumibnum alloy. The electrolytes system contain NaAlO2 and K2ZrF6. The compositions, structure, morphologies and plasma behavior of the ZrO2/Al2O3 oxide coationgs formed in different working parameters were determined by scanning electron microscopy(SEM), X-ray diffraction(CRD), energy dispersive spectroscopy(EDS) and spectrometer. In the first part, using voltage constant to create a steable oxide coating layer and then adjust the positive and negative curent ratio(1.1、1.0、0.91、0.83、0.71 and 0.63) in reaction. When positive and negative current ratio is higher than 0.91, the oxide coatings thinkness can grow to more than 100μm and show volcanic morphology and denser. But, there are also easily become destroy when the voltage rises in ratio 1.1 and 1.0. On the other side, the positive and negative current ratio smaller than 0.83, the etching effect will stronger and make more pore on the surface. Coating layer will reduce or disappear because of damage. In the second part, we compare ratio 1.1, 1.0 and 0.91 data which thickness are higher than others. We can see increase and decrease in the coating layer. It shows growth and destruction at the reaction time. Especially in the ratio 0.91 part, the voltage suddenly drop about thirty miniutes to fourty minutes. The arc and reaction will become slowly and weakly in this time. But the oxide film also find relarively dense and stable in the slowly reaction. XRD analysis shows that the coatings contains ZrO2 and Al2O3 phase. It has been discovered from the surface 10 minutes to one hour. And zirconium oxide will increase with time(aluminum reduce). Tha average hardness value is 400Hv, which is not higher than pure alumina or zirconium. However, the toughness improvement made destructive decreased. It can make crack extension, not brittle fracture. 　　Plasma measurements found that the reaction of sodium ions can significantly relative to other elements spectrum. We will see OH peak and potassium ions peak after 30 minutes. And OH peak become weakly because of gas escape to the air. The potssium ions peak found obviously, which still clear and strong util the end of reation. It shows the potssiium ions not mainly reaction in electrolyte. Unfortunately, we expect to see the aluminum ions and zirconium ions spectrum peak, but is still not obviously. On the part of experimental spectrum may need to improve.