TC4钛合金微弧氧化成膜机理研究

发布时间：2018-03-04 15:27

本文选题：Ti-6Al-4V合金　切入点：微弧氧化　出处：《南昌航空大学》2017年硕士论文　论文类型：学位论文

【摘要】：在8g/L Na_2SiO_3·9H_20-6g/L(NaPO_3)_6-4g/L Na_2WO_4·2H_2O-2g/L Na5P3O10电解液体系中,采用直流脉冲模式,以电流密度为10A/dm2,频率为500HZ,占空比为50%的电参数对TC4钛合金进行微弧氧化。通过第二相颗粒(β-SiC、γ-Al_2O_3、κ-Al_2O_3、m-ZrO_2)的相变和分解探索了熔池温度;并通过第二相颗粒的分布寻找放电通道;首次通过长距离显微镜观察了火花和熔池的对应关系;探索了TC4钛合金微弧氧化膜的生长方式及成膜机理与模型。研究结果表明:氧化电压是微弧氧化膜层生长的驱动力。微弧氧化前10min电压随时间的增长速率明显高于10-120min。前十分钟电压随时间的变化呈Logistic S型指数曲线递增规律,10min-120min内电压随时间呈低斜率线性变化规律,方程为:(1)V=541.2749-571.9594/(1+t/1.49761)~(1.10423)(0t10min)(2)V=486.83797+0.2615t(10≤t120min)膜层厚度、粗糙度及熔池尺寸随终止电压的增加而增加,熔池的尺寸随着膜层厚度的增加服从二次多项式y=-114.99725+7.85254x-0.06728x~2,其中x为膜层厚度,y为熔池尺寸。通过γ-Al_2O_3、κ-Al_2O_3、m-ZrO_2的相变,β-SiC的相变及分解判定微弧氧化过程中熔池温度分布不均,存在一个温度范围:最低温度小于1223K,最高温度大于3143K。氧化过程中,火花和熔池呈一一对应的关系,随着微弧氧化的进行,火花击穿膜层产生熔池,火花尺寸与熔池尺寸的变化规律一致,都在不断增大,两者尺寸相当,但熔池的尺寸略小于火花尺寸。随着氧化时间的增加,火花密度不断减少,火花持续的时间不断增加。电压快速增长阶段、电压转折阶段、电压稳定增长阶段的火花尺寸分别为9.9μm、23.8925μm、108.46μm,熔池的直径分别为12.645μm、28.84μm、112.56μm,火花密度分别为132个/cm~2、18个/cm~2、4个/cm~2,火花持续的时间分别为0.07s、0.55s、3.315s。微弧氧化成膜过程中,膜层与基体是通过犬牙交错方式结合的,在膜层与基体的交界面,能明显观察到放电通道的存在,尺寸约为0.6nm。微弧氧化过程中火花等离子体对膜层的击穿首先发生在膜层的薄弱处,放电类型分为三种,分别发生在膜层表面,膜基交界面,膜层中间。火花对膜层的击穿方式是环环相扣式击穿,火花沿放电通道放电直达基体,使熔融基体和氧化物沿放电通道火山式喷发、流淌,并在电解液骤冷作用下凝固,从而使新旧熔池不断翻新重组,近而使膜层通过熔池重组的方式进行生长。微弧氧化成膜模型为图5-8e。
[Abstract]:In the system of 8g / L Na_2SiO_3 路9H S / L / 20 ~ 6g / L / L Na_2SiO_3 / T / T _ 6-4g / L Na_2WO_4 路2H _ 2O-2g / L Na5P3O10 electrolyte, the phase transition and decomposition temperature of the TC4 titanium alloy was investigated by the phase transition and decomposition of the second phase particle (尾 -SiC, 纬 -Al2O3, 魏 -Al2O3mZrO2) with electric parameters of current density of 10A / dm2, frequency of 500HZ, duty cycle ratio of 50%. The phase transition and decomposition of TC4 titanium alloy were investigated by means of the second phase particle (尾 -SiC, 纬 -Al2O3, 魏 -Al2O3ZrO2). The discharge channel was found by the distribution of the second phase particles, and the corresponding relationship between the spark and the molten pool was observed by the long distance microscope for the first time. The growth mode, film forming mechanism and model of TC4 titanium alloy microarc oxide film were studied. The results show that the oxidation voltage is the driving force of the micro arc oxide film growth. The change of voltage with time in the first ten minutes was an increasing rule of exponential curve of Logistic S-type, and the voltage changed linearly with time at a low slope in 10 min-120 min. The equation is that the thickness of the film, the roughness and the size of the melting pool increase with the increase of the termination voltage. With the increase of the thickness of the coating, the size of the molten pool is changed from the quadratic polynomial y1-114.99725 7.85254x-0.06728xm2, in which x is the thickness of the film, and y is the size of the molten pool. The phase transition of 纬 -AlAl2O3, 魏 -AlSn2O3- ZrOSn2, the phase transition of 尾 -SiC and the decomposition of 尾 -SiC are used to determine the uneven temperature distribution of the molten pool in the process of micro-arc oxidation. There is a temperature range: the lowest temperature is less than 1223K, and the highest temperature is more than 3143k.in the oxidation process, the relationship between the spark and the molten pool is one-to-one. With the development of micro-arc oxidation, the spark breaks through the film layer to produce the molten pool. The size of the spark and the size of the weld pool are all increasing, but the size of the pool is slightly smaller than the size of the spark, and the density of the spark decreases with the increase of the oxidation time. The duration of sparks continues to increase. The period of rapid voltage growth, the phase of voltage transition, The spark size of the voltage stable growth stage is 9.9 渭 m ~ 23.8925 渭 m ~ (-1) 108.46 渭 m, the diameter of the melting pool is 12.645 渭 m ~ (28. 84) 渭 m ~ (-1), the spark density is 132 / cm ~ (2), 18 / cm ~ (2), 4 cm / m ~ (2), and the duration of the spark is 0.07 s-1 ~ (0.55) s ~ (3) ~ (315) s, respectively. In the interface between the film and the substrate, the discharge channel can be observed obviously. In the process of micro-arc oxidation, the breakdown of the film by spark plasma first occurs in the weak part of the film, and the discharge type is divided into three types, which occur on the surface of the film and at the interface between the film and the substrate, respectively. In the middle of the film layer. The way of the spark breakdown to the film is the annular breakdown, the spark discharge along the discharge channel to the matrix, so that the molten matrix and the oxide erupt along the discharge channel, flow, and solidify under the action of electrolyte sudden cooling. Thus, the new and old molten pools are continuously renovated and reorganized, and the film layer is grown through the recombination of the molten pool. The model of micro-arc oxidation film formation is shown in figure 5-8 e.
【学位授予单位】：南昌航空大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG174.4

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