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在硫酸电解液中对致密Ti和梯度多孔Ti样品进行微弧氧化研究。分析了孔隙特性、电流密度和电解液组成对微弧氧化过程中起始电压、击穿电压、起弧时间、氧化膜形貌和厚度的影响,并测量了微弧氧化膜的物相组成。结果表明:与致密Ti样品相比,梯度多孔Ti样品的起始电压和击穿电压提高、起弧时间延长,氧化膜层厚度增加。随着电流密度的增加,梯度多孔Ti微弧氧化反应剧烈,表面膜层的微孔直径增大,孔洞变小,膜层表面粗糙度增加,膜层变厚。当在硫酸电解液中加入少量硝酸镧后,微弧氧化起始电压和击穿电压提高、起弧时间延长,表面氧化膜的平均孔径从200nm增加到2μm左右,膜层厚度从27.6μm增加到35.6μm,膜层表面粗糙度增加。XRD分析表明,微弧氧化膜主要由Ti、锐钛矿TiO2和金红石TiO2相组成,其中以锐钛矿TiO2为主。 相似文献
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溶质离子在镁合金微弧氧化膜形成过程中的作用 总被引:2,自引:1,他引:2
利用交流脉冲微弧氧化电源在NaF、NaCl和NaI三种电解液中对AZ31镁合金样品进行处理,采用SEM、XPD和XPS观察分析溶质离子对镁合金样品表面形貌、相组成及起弧前后微弧氧化膜层成分的变化。结果表明:微弧氧化现象只发生于NaF电解液中,起弧前样品表面的沉积膜为MgF2,起弧后膜层由MgF2和MgO两相组成;NaCl和NaI电解液中的两组样品既无微弧氧化现象发生,又未发现任何沉积膜层;微弧氧化初期阳极放电产生的金属阳离子与溶液中的阴离子形成沉积于样品表面的高阻抗膜层是微弧氧化过程进行的必要条件。 相似文献
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利用交流脉冲微弧氧化电源在氯化钠和不同浓度硅酸钠电解液中对LY12铝合金进行表面处理,对比研究了样品表面有无预制备膜对微弧氧化起弧及生长过程的影响规律。结果表明:铝合金样品表面形成较高阻抗值的膜层是微弧氧化起弧现象得以发生的必要条件;样品表面获取预制备膜抑制了活性电极放电并为后期电击穿提供一个易"失稳"的界面状态,有利于缩短微弧氧化起弧时间,降低起弧电压,但预制备膜厚度和阻抗值大小对起弧时间和电压影响均较小;样品表面有无预制备膜微弧氧化电压-时间曲线有着相似的变化规律,且预制备膜在后期生长过程中重新参与成膜,在相同能量输出条件下所得陶瓷层厚度明显大于无预制备膜铝合金。 相似文献
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AZ91D镁合金微弧氧化中电源脉冲宽度的影响研究 总被引:1,自引:0,他引:1
为研究带放电回路的微弧氧化电源脉冲宽度对镁合金微弧氧化的影响,设计了在恒电压增幅和频率为667 Hz的条件下,占空比在10%~90%之间的镁合金微弧氧化实验.研究发现,随着脉冲宽度的增加,起弧电压逐渐降低,大弧倾向增大;膜表面孔洞数量减少且孔径尺寸略有增大;微弧氧化的成膜效率随着脉冲宽度的增加先增大后减小;在占空比30%左右时成膜效率最高,并且膜层的耐蚀性最好.对于频率为667 Hz的镁合金微弧氧化,脉冲宽度控制在300~600μs时成膜效率最高且膜层质量较好. 相似文献
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《金属热处理》2017,(8)
采用阳极氧化和微弧氧化技术在2060-T8铝锂合金上分别制备出阳极氧化膜和微弧氧化膜,研究不同氧化工艺中不同参数对膜层微观结构及粘结性能的影响。结果表明:2060-T8铝锂合金在硫酸溶液中进行恒电压阳极氧化,生成一层硬质阳极氧化膜,膜层较薄不足以完全覆盖基体合金表面沟痕。合金在硅酸盐电解液中进行先恒流再恒压的微弧氧化,制备出一层含有大量突起和直径3~7μm微孔的陶瓷膜,膜层呈红棕色,较厚,则能够完全覆盖基体表面沟痕。在硫酸浓度为10%的电解液中制得的阳极氧化膜表面粗糙度为0.441μm,阳极氧化膜中粘结强度最高可达23.2 MPa,较基体提高73%;在氧化时间为45 min时制得的微弧氧化膜表面粗糙度为0.458μm,微弧氧化膜中粘结强度最高可达28.2 MPa,较基体提高111%。 相似文献
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溶质离子在铝合金微弧氧化陶瓷膜形成过程中的作用机理 总被引:2,自引:0,他引:2
利用交流脉冲微弧氧化电源在碳酸钠、硅酸钠和锡酸钠3种电解液中对LY12铝合金进行微弧氧化处理,通过SEM和XRD观察分析铝合金样品表丽形貌和相组成的变化,研究各溶质离了对微弧氧化起弧现象及生长曲线的作用规律.结果表明:在3种电解液中进行微弧氧化处理时,在硅酸钠溶液中铝合金易于起弧,能够在短时间、低电压下获得高阻抗膜;而在锡酸钠溶液中铝合金不能形成高阻抗膜,未发生起弧现象;铝合金样品表面预先制备高阻抗膜有利于发生微弧氧化起弧现象;在碳酸钠和硅酸钠溶液中,微弧氧化陶瓷膜的后期生长曲线有着相似的变化规律,在锡酸钠溶液中样品表面产生电化学溶解,不能形成陶瓷膜:铝合金样品表面形成高阻抗膜是微弧氧化现象得以进行的必要条件. 相似文献
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在原位锆溶胶和外加锆溶胶的磷酸盐电解液体系中,采用恒流模式对铝合金进行微弧氧化,通过分析氧化过程中电压和电解液参数的变化、氧化膜生长规律以及膜层表面形貌结构,研究锆溶胶对铝合金微弧氧化成膜过程的影响。结果表明,原位锆溶胶电解液氧化过程中pH值降低及电导率增加幅度较小,起弧电压、电解液温度较低,膜层生长速率较快,其厚度增长速率约为2.9μm/min。原位锆溶胶电解液制备的膜层表面呈多孔网状结构,内外膜层结合紧密,膜层较厚,可达85μm;外加锆溶胶电解液生成膜层表面有火山状沉积物,膜层疏松;微弧氧化膜主要由γ-Al2O3和t-ZrO2相组成。 相似文献
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The surfaces of amorphous Ni-18P, Ni-IOCr-20P, Ni-9Mo-19P and Ni-5W-18P alloys immersed or anodically polarized in 1 M HCl solution were analyzed in connection with their corrosion and anodic behavior. All alloys were more corrosion-resistant than crystalline nickel metal because of formation of phosphate-containing surface films on the Ni-18P, Ni-9Mo-19P and Ni-5W-18P alloys and because of spontaneous passivation due to formation of passive hydrated chromium oxyhydroxide film on the Ni-10Cr-20P alloy. The latter alloy was stable up to the transpassive region of chromium although intrusion of phosphate in the film was responsible for the higher passive current density in comparison to the amorphous Fe-Cr-13P-7C alloy of the same chromium content. The formation of thick porous phosphate films containing nickel, and molybdenum or tungsten by anodic polarization was not effective in passivating the Ni-18P, Ni-9Mo-19P and Ni-5W-18P alloys, and they suffered pitting corrosion by anodic polarization. 相似文献
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By using a rotating disc electrode and a new device for the control of interfacial polarization, an experimental study has been performed concerning the anodic dissolution and the passivation of iron in sulphuric medium. A model is given which interprets the Z-shaped current-potential curve and the impedance diagrams measured. As a matter of fact, it is proved and understood that a passive state and an active state can take place for a same potential. In the same way, active dissolution in localized corrosions at the surface of passive iron is due to the slowing down of the diffusion of passivating species in the hole. 相似文献
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The anodic polarization behaviour of iron whisker crystals was investigated in a neutral solution with or without the presence of chloride ion, with special attention to the role played by surface defects in the dissolution, the passivation and the pitting of iron. The grown whisker used was substantially dislocation-free and the defect density was varied by twisting of whisker. With increase in the angle of twisting, the anodic dissolution current increased in a chloride-free solution, whereas it decreased in a chloride-containing solution. The defect density in the substrate had no remarkable effect on passivation but the thickness of the passive film was slightly increased on twisted whiskers. The anodic polarization curve of a grown whisker in a chloride-containing solution did not exhibit a distinct pitting potential. By twisting of whisker, however, a current rise due to pitting appeared on the polarization curve and the apparent pitting potential shifted in the negative direction with increasing angle of twisting. Potentiostatic polarization experiments in a chloride-containing solution showed the emergence of random current pulses due to the breakdown of passive film and to repassivation. It is highly probable that the breakdown of the passive film occurs at the physical or chemical inhomogeneities in the passive film not associated with dislocation termini but that pitting occurs only when the breakdown occurs at emergent dislocation sites. 相似文献
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In this work, the electrochemical behaviors of SAM2 X5 Fe-based amorphous alloy coating and hard chromium coating were comparatively studied in 3.5 wt% Na Cl solution. In comparison with the hard chromium coating, the SAM2 X5 coating exhibited a wider and stable passive region with lower passive current density in the potentiodynamic polarization and showed a considerably lower current density at different anodic potentials in the potentiostatic polarization. In order to understand the passivation mechanism of the Fe-based amorphous coating, the components of the passive films formed at various polarization potentials were examined by X-ray photoelectron spectroscopy. The synergistic effect of Mo, W, Mn and Cr in the passive films was systemically analyzed. It has been revealed that Mo and W facilitate the formation of compact and stable Cr_2O_3 passive film at lower potentials, and the substantial enrichment of Mn in the passive film enhances the passivation ability at relatively higher potentials. The deep understanding of the passivation characteristics in multicomponent alloy systems could provide a guide for the design of corrosion-resistant amorphous alloy coatings for engineering applications. 相似文献
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H. C. K. Schwabe 《工业材料与腐蚀》1967,18(11):961-967
Origin of primary anodic passivation, in particular or ferrous metals It is shown, that a quantitative interpretation can be given of the characteristic current density decrease which accompanies increasing polarization in acid solutions and which is characteristic of the primary anodic passivation process on ferrous metals; the interpretation is arrived at when two concurring reactions are stipulated to take place with participation of water. One of these reactions yields active dissolution, the other one results in the formation of a passivating MeO layer. This passive layer increases in thickness until an oxide phase is formed; his process occurs with preference at surface defects and can be interpreted in terms of e.g. the theory developed by Mott and Cabrera for the growth of thin oxide layers. With high exchange current densities of the anodic dissolution, e.g. in hydrochloric acid, the direct formation of solid salt on the metal surface may produce the same current/potential characteristics. Since the passage of electric charges through the ion-conducting salt layer is efficiently inhibited up to high potentials, much larger passivity regions are found here. Reference is made to the influence of surface structure and pretreatment on the kinetic parameters of metal dissolution. 相似文献
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Comparative investigation of the anodic behavior of nickel in its own phase and in NiZn intermetallic compound in acidic sulfate solutions showed that the kinetics of anodic process is the same in both cases, but the partial anodic curve and the passivation potentials of nickel in NiZn phase are shifted in the negative direction by 140 mV. The passivation current is larger, and the dissolution rate of nickel from NiZn phase at the cathodic polarization is higher. The peculiarity of the behavior of nickel in NiZn phase is related to the activity of surface nickel atoms and the increase in the number of active sites of anodic dissolution. It is shown that introducing an electrochemically negative metal into an alloy can, under certain conditions, facilitate the passivation of the latter irrespective of the passivability of the former. 相似文献
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Investigations into the active/passive transition of 304 stainless steel in organic media containing water and hydrogen chloride Part 3. Results of the impedance measurements and passivation model of an alloy Steady state polarization curves and electrode impedances were measured during the active/passive transition of type 304 stainless steel in dearated ethanolic solution containing hydrogen chloride and different amounts of water. The passivation potential and the critical current density for passivation strongly depend on the water content of the solution. The impedance measurements in the active/passive transition show the same sequence of diagrams independent of the water content of the solution. They indicate the onset of passivation before the maximum current density and show two time constants related to two different passivating species on the alloy surface. The experimental results were interpreted on the basis of a reaction model with parallel dissolution and passivation mechanism of the iron and the chromium compound of the alloy. The resulting total surface composition (related to the steady-state polarization curves) can be described with a reaction model of iron–the alloy behaviour is that of pure metal. The fundamental passivation reaction is described as a potential dependent equilibrium between adsorbed Me(II)- and passivating Me(III)-hydroxide, water molecules being directly involved in the formation of this primary passivating film. In the case of stainless steel this primary passivating film mainly consists of chromium (III) adsorbates. Finally, a general model for the passivation is proposed: The passivation of a pure metal or of an alloy can be understood as the coupling of the stepwise deprotonation of the water molecules at the interface metal/solution and the formation of a high cation charge density in this adsorbed hydroxide/oxide film to build up the passive layer. The effect of water content, pH, adding of passivating species to the solution or the alloying with chromium on the passivation potential and the critical current density thus can be explained. 相似文献