TC4钛合金复合涂层性能的研究

发布时间：2018-05-06 11:00

本文选题：热浸铝 + 微弧氧化　；参考：《沈阳理工大学》2017年硕士论文

【摘要】：TC4钛合金具有比强度高、加工技术成熟等优点,得到广泛的应用。但由于摩擦系数大、工作温度低限制了其应用范围。表面处理可以在保持TC4钛合金基体力学性能的同时,改善材料的表面性能。本文采用热浸铝和微弧氧化复合处理的方法在TC4合金表面制备复合涂层,并对涂层的氧化性能进行研究。TC4钛合金在750℃熔融铝液中浸镀3min后,表面形成一层纯铝镀层,800℃扩散退火3h后,纯铝层消失,转变为由Ti Al_3相组成的有许多孔洞的扩散层。微弧氧化后在Ti Al_3扩散层表面形成了一层Al_2Ti O_5陶瓷层。电解液中Na Al O_2含量越高,膜层厚度越大,超过4g/L后,表面质量变差。提高占空比和正向电压都有利于陶瓷层的生长。TC4基体和热浸铝试样在850℃和900℃进行循环氧化实验表明,热浸铝显著提高了钛合金的高温氧化性。热浸铝试样的氧化动力学曲线呈抛物线形。850℃高温氧化过程中,表面形成了一层致密的Al_2O_3保护层,在900℃高温氧化后,表面出现了由Al_2O_3和Ti O_2组成的较厚的混合氧化层。分别对在电解液1(Na_2Si O_(3 )8g/L、KOH 2g/L、Na Al O_2 4g/L)和电解液2(Na_2Si O_(3 )8g/L、KOH 2g/L)中复合处理的试样在850℃、900℃和950℃进行循环氧化实验,分析溶液成分对涂层高温氧化性的影响。实验结果表明,复合处理试样在850℃高温氧化性能优于热浸铝试样。900℃温度下,由于Al_2Ti O_5陶瓷层和Ti Al_3扩散层热膨胀系数不同,导致陶瓷层出现裂纹。氧化进行至一定程度后,陶瓷层脱落。950℃温度下,在溶液2中制备的试样陶瓷层更早脱落。对在电解液1中制备的试样在1000℃进行循环氧化实验,Al_2Ti O_5氧化分解为Al_2O_3和Ti O_2,弥合了陶瓷层产生的一部分裂纹,减缓了陶瓷层的脱落。氧化过程中伴随着Al元素的扩散现象,扩散层与基体之间出现了新的扩散层,扩散层中Ti Al_3相一部分转变为Ti Al_2,温度越高,此现象越明显。
[Abstract]:TC4 titanium alloy has many advantages, such as high specific strength and mature processing technology. However, because of the large friction coefficient and low working temperature, the application range of the titanium alloy is limited. The surface treatment can improve the surface properties of the TC4 titanium alloy and improve the surface properties of the materials. This paper adopts the method of compound treatment of Hot Dipping Aluminum and micro arc oxidation. A composite coating was prepared on the surface of TC4 alloy, and the oxidation properties of the coating were studied. After.TC4 titanium alloy was dipped in 750 C molten aluminum, a layer of pure aluminum coating was formed on the surface. After 800 C diffusion annealing for 3h, the pure aluminum layer disappeared and turned into a diffusion layer of many holes composed of Ti Al_3 phase. After micro arc oxidation, the surface of the diffusion layer on Ti Al_3 was on the surface of Ti Al_3. A layer of Al_2Ti O_5 ceramic layer is formed. The higher the content of Na Al O_2 in the electrolyte, the greater the thickness of the film, the higher the thickness of the film, the worse the surface quality. The increase of the duty ratio and the positive voltage are beneficial to the growth of the ceramic layer and the cyclic oxidation of the.TC4 matrix and the hot dipped aluminum sample at 850 and 900 C, indicating that the hot dipping aluminum greatly improves the high titanium alloy. The oxidation kinetic curve of the hot dipped aluminum specimen shows a dense Al_2O_3 protective layer during the high temperature oxidation process of parabolic.850 C. After oxidation at 900 C, the surface has a thicker mixed oxidation layer composed of Al_2O_3 and Ti O_2, respectively, to the electrolyte 1 (Na_2Si O_ (3) 8g/L, KOH 2g/L, Na Al) L) and the samples of the electrolyte 2 (Na_2Si O_ (3) 8g/L, KOH 2g/L) were treated by cyclic oxidation at 850, 900 and 950. The effect of the composition of the solution on the high temperature oxidation of the coating was analyzed. The experimental results showed that the high temperature oxidation performance of the composite treated samples was better than that of the hot dipped aluminum at the temperature of the hot dipped aluminum at 850 C, due to the Al_2Ti O_5 ceramic layer and the Al_2Ti O_5 ceramic layer. The thermal expansion coefficient of Ti Al_3 diffusion layer is different, which leads to the crack in the ceramic layer. After oxidation to a certain degree, the ceramic layer prepared in solution 2 at the temperature of.950 centigrade of the ceramic layer falls off earlier. The sample prepared in the electrolyte 1 is cyclic oxidation at 1000 C, and Al_2Ti O_5 is oxidized to Al_2O_3 and Ti O_2. A part of the crack produced in the ceramic layer slows down the falling of the ceramic layer. With the diffusion of Al elements in the oxidation process, a new diffusion layer appears between the diffusion layer and the matrix, and the Ti Al_3 phase in the diffusion layer is converted to Ti Al_2. The higher the temperature, the more obvious the phenomenon is.

【学位授予单位】：沈阳理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG174.4

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