交流窄脉冲占空比调制对钛合金微弧氧化陶瓷涂层的影响

Effect of the Duty Cycle Adjusting of Alternate Narrow Pulse on the Microarc Oxidation Coatings on Titanium Alloy

采用交流窄脉冲微弧氧化法于 Na2SiO3-KOH-(NaPO3)6溶液中在 Ti6Al4V 表面形成了陶瓷化涂层。用常压氧化方式(U=500 V),研究了正脉冲占空比对涂层生长速率、组织形貌和相组成的影响。为优化工艺,采用常流氧化方式(J=60 mA/cm2),并提出了占空比分级调节制度。结果表明:常压方式下,随正脉冲占空比的增大,涂层的生长速率增加,涂层的表面逐渐变得粗糙。涂层主要由 TiO2(锐钛矿相及金红石相)相组成,随占空比的增大,涂层中锐钛矿相 TiO2的相对含量减小,金红石相 TiO2的相对含量增加,并成为主晶相。正脉冲占空比为 8 %时可获得组织结构较致密且较厚的涂层。采用常流氧化方式,涂层的生长速率比常压方式明显增加,进而对占空比进行分级式调节可使涂层的表面结构得到改善。

Ceramic-like coatings were formed using alternate ultra-narrow pulse microarc oxidation method on alloy Ti6Al4V in Na2SiO3-KOH-(NaPO3)(6) aqueous solution. A constant voltage (U = 500 V) regime of microarc oxidation was applied to reveal the effect of positive pulse duty cycle on their growth rate, microstructure and phase composition. In order to obtain the optimum process, a constant current density (J = 60 mA/cm(2)) regime combined with the stepped adjusting of positive duty cycle during microarc oxidation process is also proposed. With the positive duty cycle increasing from 4 % to 20 %, the growth, rate of the coatings increases and the surface morphology becomes coarser. The as-deposited coatings are mainly composed of anatase and rutile TiO2. With the pulse duration increasing, the content of anatase decreases, while rutile increases and becomes the predominant phase. Considering the microstructure and growing thickness of the coatings, 8 % of positive duty cycle is suitable. When applying the constant current density regime, the growth rate of coatings is significantly increased compared with that by the constant voltage regime. And the morphology of the coatings is obviously improved by using the stepped adjusting of duty cycle furthermore.