电解质对钛合金微弧氧化放电方式和耐磨性能的影响

Effect of Electrolyte on Micro-arc Oxidation Discharge Mode and Wear Resistance of Titanium Alloy

目的通过比较添加微量磷酸盐对放电方式的影响,表征各膜层的微观结构与成分组成,研究分析放电方式差异对膜层耐磨性能的影响。方法在3组电解液中分别进行TC4钛合金微弧氧化,以磨损率为指标判定每组的最优配比。通过扫描电子显微镜(SEM)观察膜层表面与截面微观形貌。使用X射线能量色散谱仪(EDS)分析膜层表面和磨损区域的元素分布情况。使用X射线衍射仪(XRD)表征膜层物相结构组成,通过维氏显微硬度计测量膜层的硬度,使用摩擦磨损试验机进行膜层摩擦学性能测试,并通过三维形貌仪分析磨痕轮廓。结果在铝酸盐电解液中添加磷酸盐电解质后会增强A、C型放电,减弱B型放电,使制得膜层的缺陷(微孔与微裂纹)明显增多,产生了较厚的疏松层,并且随着电解液中磷酸根离子的增多,放电方式进一步受影响,膜层磨损率也大幅增加。而不添加磷酸盐的20 g/L铝酸盐浓度制备的钛合金微弧氧化膜层在15 N高载荷滑动干摩擦下的摩擦系数为0.6~0.7,磨痕窄且浅,磨损率仅为基体的7.22%。结论磷酸盐电解质极易引起杂质放电,导致微弧氧化反应时B型放电显著减弱,A、C型放电大幅增加,导致膜层致密性显著降低,严重降低了微弧氧化膜层的耐磨性能。20 g/L铝酸盐电解液制备的钛合金微弧氧化膜层缺陷少、硬度高、厚度大,显著改善了高载荷下钛合金的耐磨性能。

Micro-arc oxidation technology is an advanced surface treatment technology for in-situ growth of oxide ceramic coating on the substrate surface.It can improve the surface properties such as wear resistance,corrosion resistance and high temperature oxidation resistance without changing the properties of the substrate material.Because different discharge modes produce different structures,the difference of structural defects significantly affects the wear resistance of the coating under high load.In this paper,the effects of different electrolytes on the discharge mode and wear resistance of titanium alloy micro-arc oxidation were studied.Using wire cutting,TC4 titanium alloy was cut into rectangles of 15 mm×15 mm×5 mm as the substrate,and the surface oxide coating and oil were removed by grinding the 600#,1000#and 1500#water sandpaper in turn,and then ultrasonic cleaning with absolute ethanol and deionized water.For electrolyte,a high concentration aluminate electrolyte and a high concentration aluminate-low concentration phosphate composite electrolyte with a total of 3 electrolyte systems were used.The MAO-10HB micro-arc oxidation complete sets of equipment were used for micro-arc oxidation,the power mode was constant current mode.Relevant electrical parameters were as follows:current density-7 A/dm2,frequency-200 Hz,and duty cycle-30%.The wear rate index comprehensively determined the optimal ratio of each group of electrolyte system.The microscopic morphology of the coating and wear area was observed by a scanning electron microscopy(SEM).An X-ray energy dispersion spectrometer(EDS)was used to analyze the distribution of elements and changes in the surface and wear area of the coating.An X-ray diffractometer(XRD)was used to characterize the structural composition of the coating.The hardness of the dense layer of the coating was measured with a Vickers microhardness tester.The tribological performance of the coating was tested by a friction and wear tester,and the abrasion profile was analyzed by a three-dimensional morphological microscope.B-type discharge was a strong electric field dielectric discharge throughout the coating,forming a dense coating structure,which was the main reason for the dense coating,and could make the electrolyte react with the substrate to form a new phase;A,C-type discharge was only breakdown on coating surface or in the middle of weak electric field during gas discharge.The coating structure was loose.It was the main cause of coating loose.When the titanium alloy was micro-arc oxidized in high concentration aluminate electrolyte,AlO2-ions participated in the coating-forming reaction to form Al_(2)O_(3),and a secondary reaction occurred under the action of high temperature and high pressure plasma:Al_(2)O_(3)+TiO2→Al2TiO5,forming a large number of aluminum titanate hard ceramic phase.In the phosphate electrolyte,micro-arc oxidation was very likely to cause impurity discharge,resulting in micro-arc oxidation reaction B-type discharge was significantly weakened,A-type and C-type discharge increased significantly,resulting in a significant reduction in coating density,seriously reducing the wear resistance of micro-arc oxidation coating.The Al2TiO5/γ-Al_(2)O_(3)/R-TiO2 oxidation ceramic coating with good wear resistance was prepared in the micro-arc oxidation of TC4 titanium alloy(the optimal electrolyte ratio was:NaAlO2-20 g/L,NaOH-1 g/L).The hardness was as high as HV0.981100,and the wear rate was only 7.22%of the titanium alloy substrate.The main reason for the excellent wear resistance of the coating prepared in the optimal ratio electrolyte and the significant improvement of the wear resistance of the coating is the large number of hard phases of aluminum titanate,and the second reason is the dense coating generated by the micro-arc oxidation reaction led by B-type discharge.The defects are significantly reduced,effectively avoiding the failure of the coating due to the expansion of defects when high load friction is effectively avoided.