Galvanic corrosion of Al alloys—III. The effect of area ratio

The Al alloys 2024 and 7075 have been electrically coupled to Cu, stainless steel 304L, 4130 steel, Ti-6Al-4V, Cd or Zn in 3–5%NaCl. Galvanic current and weight loss data have been obtained for area ratios A^C/A^A = 0·1, 1 and 10 in 24 h tests. Experimental results confirm theoretical calculations based on mixed potential theory, according to which the galvanic c.d. i_g^A with respect to the anode is directly proportional to the area ratio: i_g^A = k₁A^C/A^A, while the dissolution rate r_A of the anode is related to the area ratio by: r_A = k₂(1 + A^C/A^A). The galvanic current I_g is independen t of anode area A^A and directly proportional to the cathode area A^C: I_g = K₁A^C. The galvanic c.d. i_g^A can be converted into dissolution rates r_A according to:

$r_A=k_3{i}_g^A\left(1+\frac{A^A}{A^C}\right).$

     

SiCp/Al复合材料在Cl~-作用下初期腐蚀行为

通过室内浸泡模拟实验方法,采用扫描Kelvin探针技术研究了SiCp/Al复合材料在Cl~-介质下初期腐蚀行为。结果表明,SiC颗粒与Al基体界面结合处是复合材料在Cl~-介质下初期腐蚀的优先发生位置,Cl~-和界面相是促进初期腐蚀发展的主要原因。随腐蚀的不断进行,复合材料先形成钝化膜,表面电位先整体正移,后钝化膜破损,表面电位整体负向移动。复合材料初期腐蚀过程表现为其钝化膜形成和逐渐破损的腐蚀特征,腐蚀产物主要为Al(OH)_3、Al_2O_3和AlCl_3。     

The effect of recrystallization on corrosion and electrochemical behavior of 7150 Al alloy

By weight loss, potentiodynamic polarization, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS) techniques complemented by optical and scanning electron microscopy observations, the effect of recrystallization on the corrosion, and electrochemical behavior of 7150 Al alloy was studied. The results indicated that the high recrystallization fraction 7150‐1# was worse than the low recrystallization fraction 7150‐2# on corrosion resistance. The analysis of EIS indicated that 7150‐1# exhibited obvious pitting corrosion at 5 h immersion time, whereas 7150‐2# showed no obvious pitting corrosion even at 33 h. The corrosion route developed along the grain boundary of recrystallization grains, not along the grain boundary of unrecrystallization grains.     

Cu/Ti在模拟海水中的电偶腐蚀行为(英文)

采用电化学阻抗谱、电化学噪声和扫描电镜等技术研究了纯铜、铜/钛耦合电极在模拟海水中的腐蚀行为。结果表明:纯铜的腐蚀过程分2个阶段,其腐蚀阻抗和点蚀参数SE均遵循先增后降的规律,而其腐蚀参数SG的变化规律则正好相反;铜/钛耦合电极的腐蚀过程则由3个阶段组成,其腐蚀阻抗和点蚀参数SE均遵循先降后升到最后再降的规律,而其腐蚀参数SG则同样反向变化。铜和钛之间的电势差加速了纯铜的点蚀萌生,同时铜/钛耦合电极的腐蚀电位总是正于纯铜的腐蚀电位。     

核电汽轮机焊接转子接头在氯离子环境中的电偶腐蚀行为

为了研究焊接接头的尺寸效应对焊接接头的电偶腐蚀行为的影响,采用宏观电化学、微区电化学（SVET）、浸泡试验等试验研究了25Cr2Ni2MoV转子钢焊接接头在氯离子溶液中的电偶腐蚀行为.结果表明,焊缝的腐蚀电位最低,腐蚀电流密度最大,焊缝区作为阳极优先发生腐蚀,而母材和热影响区作为阴极区被保护.进一步运用三维形貌仪（IFM）和扫描电镜（SEM）观察腐蚀表面形貌,发现随着焊接接头尺寸的增加电偶腐蚀效应更显著,但是当接头尺寸增大到一定程度后,电偶腐蚀效应又有所减弱.     

热解碳涂层对Cf/Al复合材料热膨胀性能的影响

采用真空挤压吸渗工艺制备了不同厚度热解碳（PyC）涂层的碳纤维增强铝基（C_f/Al）复合材料,研究了热解碳涂层对C_f/Al复合材料热膨胀性能的影响。结果表明,热解碳涂层均匀而致密,可有效地保护碳纤维;对C_f/Al复合材料的热膨胀性能进行测试表明,与碳纤维表面无涂层的C_f/Al复合材料相比,当热解碳涂层的厚度约为70 nm时,碳纤维表面具有热解碳涂层的C_f/Al复合材料的热膨胀系数减小了24%;在一定的厚度范围内（70~250 nm）,随着热解碳涂层厚度的增加,碳纤维表面具有热解碳涂层的C_f/Al复合材料界面结合强度和滑移阻力逐渐减小,热膨胀系数逐渐增大。     

Galvanic Corrosion of Al Alloys

In a systematic study of galvanic corrosion of Al alloys the effects of the dissimilar metal, the solution composition and area ratio have been studied using galvanic current and weight loss measurements, In 3.5% NaCl, galvanic corrosion rates of the Al alloys 1100, 20324,2219, 6061 and 7075 decrease with the nature of the dissimilar metal in the order AG>Cu> 4130 steel ?stainless steel ≈Ni>>Inconel 718?Ti-6A1-4V≈?Haynes 188>Sn>Cd. Coupling to zinc did not lead to cathodic protection of all A1 alloys. The potential difference of uncoupled dissimilar metals have been found to be a poor indication of galvanic corrosion rates. Dissolution rates of A1 alloys coupled to a given dissimilar material are higher in 3.5% NaCl than in tapwater and distilled water where they are found to be comparable. In assessing the galvanic corrosion behavior of a given A1 alloy as a function of environment, one has to consider the effect of the dissimilar metal. The dissolution rate of Al 6061 is, for example, higher in tapwater with Cu as cathode than in 3.5% NaCl with SS304L or Ti-6AI-4V as cathode. The effect of area ratio \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{A^C }}{{A^A }} $\end{document} has been studied in 3.5% NaCl for area ratios of 0.1, 1.0 or 10. The galvanic current was found to be independent of the area of the anode, but directly proportional to the area of the cathode. The galvanic current density \documentclass{article}\pagestyle{empty}\begin{document}$ i_{^g }^A $\end{document} with respect to the anode has been found to be directly proportional to the area ratio (\documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{A^C }}{{A^A }} $\end{document}), while the dissolution rate r_A of the anode was related to area ratio by \documentclass{article}\pagestyle{empty}\begin{document}$ r_A = k_{_2 } (1 + \frac{{A^C }}{{A^A }}) $\end{document}. The results obtained have been explained in terms of mixed potential theory.     

Galvanic reactions during localized corrosion on stainless steel

During localized (crevice and pitting) corrosion, a local cell is established between an anode within a crevice or pit and a cathode on the surrounding passive surface. Data are presented to show that concentrated acidic chloride solutions, simulating corrosion product hydrolysis within a crevice or pit, produce potentials which are active (negative) to the normal surface passive potential. This behaviour explains the previously observed active drift of corrosion potential after initiation of crevice or pitting attack in dilute chloride solutions. The active state in concentrated chloride solutions was quite noble (positive) compared to the active state in more dilute solutions. Thus, there is no need to invoke ohmic resistance effects to account for the active state within a crevice or pit.Experiments were devised in which the local anode within a crevice was physically separated from the nearby passive-surface cathode. When the two were coupled together electrically, the cathode surfaces were polarized nearly to the unpolarized local anode potential, with only a few millivolts anodic polarization at the anode within the crevice. The rate of localized corrosion appears from the data to be limited by the rate of dissolved-oxygen reduction on the cathode surfaces. Thus, localized corrosion in dilute chloride solutions will be increased by (a) raising the temperature, (b) adding an oxidizer such as Fe³⁺ ions, or (c) substituting external anodic polarization for dissolved oxidizers.The overall potential, E_corr acquired by a specimen undergoing pitting or crevice corrosion is demonstrated to be near the protection potential, E_p below which pitting corrosion cannot propagate. Any potential active to E_corr and E_p results in cathodic polarization and suppression of the anode reaction in a crevice or pit. Since both E_corr and E_p vary with the extent of previous localized attack, E_p is not a unique property of the alloy as has been sometimes suggested and is of limited value in classifying alloy resistance to localized corrosion.     

核电汽轮机转子堆焊焊接接头的电偶腐蚀行为及有限元仿真

采用宏观电化学试验和浸泡试验研究25Cr2Ni2MoV汽轮机转子堆焊焊接接头在80 ℃,3.5% Cl?环境下的电偶腐蚀行为. 电化学试验结果表明,焊缝为腐蚀薄弱区,腐蚀电位从高到低依次为热影响区、母材、焊缝. 浸泡试验结果表明,随着母材面积的增大,焊缝平均腐蚀厚度逐渐加深. 进一步利用宏观电化学测试所获的电化学参量建立焊接接头电偶腐蚀有限元模型对比浸泡试验结果. 结果表明,有限元仿真结果能有效模拟堆焊焊接接头的电偶腐蚀行为,为实际生产提供电偶腐蚀速率预测.     

TiB2/Al 复合材料摩擦行为研究

采用挤压铸造法制备TiB_2/Al复合材料并发现其在低载高速下具有自润滑特性,因此借助于摩擦试验研究了载荷、滑动速度、摩擦副对该材料摩擦行为的影响。结果表明,低载高速条件下TiB_2/Al复合材料与GCr15轴承钢室温干摩擦时,随着滑动时间的延长,平均摩擦系数未出现明显的上升或下降过渡现象,仅瞬时摩擦系数呈现出不同程度的湍流波动状态。滑动速度为0.8 m/s时,随着载荷的增大,TiB_2/Al复合材料与GCr15干摩擦的平均摩擦系数基本不变,但瞬时摩擦系数的波动幅度减小,摩擦系数的标准偏差减小。载荷为0.49 N时,随着滑动速度的增大,平均摩擦系数没有明显的变化,在0.165～0.255之间波动。与等速度变载荷时相比,等载荷变速度条件下TiB_2/Al复合材料的摩擦系数分散性比较大。采用GCr15为摩擦副时,TiB_2/Al复合材料的瞬时摩擦系数湍流波动较复合材料自摩擦时要大些。自磨时复合材料的平均摩擦系数为0.08左右,与GCr15对磨时平均摩擦系数为0.18左右。     

Ni-xCr-6.8Al基合金热腐蚀行为

研究铸态和预氧化态Ni-xCr-6.8Al基合金在Na2SO4＋25%NaCl混合盐中873K时的热腐蚀行为。结果表明：NixCr6.8Al基合金的质量损失随着Cr元素含量的增加而减少,预氧化可以明显改善材料的抗热腐蚀性能,并且与Cr含量无关。Ni12Cr6.8Al基和Ni16Cr6.8Al基合金的热腐蚀动力学遵循抛物线规律,Ni-20Cr-6.8Al基合金遵循指数规律,所有的预氧化试样的热腐蚀动力学都符合对数规律。铸态合金热腐蚀的机理可以用酸碱熔融模型解释,而预氧化合金的热腐蚀机理在很大程度上由预氧化过程中形成的氧化层的性质决定。     

T2/TC4在静态人造海水中的电偶腐蚀行为研究

进行T2/TC4电偶对在静态人造海水中的电偶腐蚀实验,通过电化学工作站、原子发射光谱分析仪、扫描电子显微镜(SEM)、能谱仪(EDS)、X射线衍射仪(XRD)研究T2/TC4在静态人造海水中电偶腐蚀时的铜离子释放速率与腐蚀行为。结果表明：当T2/TC4发生电偶腐蚀时反应强烈,T2为电偶对阳极发生加速腐蚀,TC4为电偶对阴极;与T2自腐蚀相比,T2/TC4电偶腐蚀的铜离子释放速率提高了数十倍,可以维持在160μg/(cm2.d)左右,能达到抑制大多数海洋生物附着的海洋防污要求;T2自腐蚀的腐蚀产物以Cu2O为主,与TC4电偶腐蚀后的T2试样表面无腐蚀产物覆盖。     

Fabrication and wear behavior of CNT/Al composites

Aluminum matrix composites reinforced with carbon nanotube were fabricated by a powder metallurgy method. The effects of carbon nanotube content on the relative density, the hardness, and the friction and wear behavior of the composites under dry sliding condition were investigated using the ball （pin）-on-block tester. By scanning electron microscopy （SEM）, the worn surfaces and worn chips were observed, and the wear mechanism of composites was analyzed and discussed. The results indicate that the addition to the aluminum matrix of 2.0%（mass fraction） carbon nanotube causes the increase in the Vickers hardness of about 80%. Within the range of carbon nanotubes content from 1.0% to 2.0%, both the friction coefficient and wear rate of composites decrease with the increase of carbon nanotube content. The delamination wear is the main wear mechanism for the composites.     

The oxidation and hot corrosion behavior of tungsten-fiber reinforced composites

The oxidation and hot corrosion behavior of a tungsten-fiber, reinforced Ni~ 20Cr alloy has been examined under the following exposure conditions: (a) pure oxygen at 1 atm pressure; (b) sulfidation in H₂–10 %H₂S; (c) presulfidation in H₂–10 %H₂S followed by oxidation in oxygen; and (d) oxidation in 1 atm oxygen after precoating with approximately 1 mg/cm² of Na₂SO₄. Rapid oxidation of the tungsten fibers causes considerable distortion of the matrix and catastrophic degradation of the matrix follows. Inter diffusion between the matrix and the fibers is also important. During sulfidation, only the matrix forms sulfides, the fibers remaining unaffected. Consequently, presulfidation, although having a dramatic effect on the oxidation of the matrix does not have a damaging effect on the fibres. Equally, the presence of sodium sulfate is not critical, although severe oxidation of the exposed tungsten fibers is still observed.     

Galvanic corrosion of carbon steel coupled to antimony

Galvanic corrosion of carbon steel coupled to antimony was studied in aerated and N₂-purged electrolytes at ambient and 60 °C temperatures. Free corrosion potential of antimony and carbon steel shifts to more active values with increasing temperature and N₂ purging of the electrolyte. Under all experimental conditions, antimony remains less electronegative than carbon steels. Aeration and temperature affect potentiodynamic behaviour of both materials. As a consequence, the corrosion current for the antimony–carbon steel couple increases with increasing temperature and with aeration. There was a good agreement between the corrosion currents obtained through the Evans’ experiment and super-imposed potentiodynamic scans.     

Electrochemical behavior of microbiologically influenced corrosion on Fe_3Al in marine environment

In this article,microbiologically influenced corrosion behavior of Fe3Al intermetal-lic compound in microorganism culture medium has been investigated by using weight loss methods,electrochemical techniques,and electron microscopy.Polar-ization curves showed that a sharp electrical current peak caused by surface pitting could be observed after Fe3Al electrodes were immersed in culture medium for 15 days when the polarization potential was about-790 mV vs SCE.Based on the electrochemical impedance spectrosco...     

原电池效应对混合硫化矿细菌浸出的影响

研究了黄铜矿与黄铁矿混合矿细菌浸出过程的原电池效应，提出了原电池效应模型。研究结果表明：当黄铜矿细菌浸出过程中加入黄铁矿及C时，浸出率大大提高，黄铜矿浸出30d，Cu浸出率可达40％；单一黄铁矿细菌浸出时，黄铁矿会被大量氧化分解，而当与黄铜矿混合浸出时，黄铜矿氧化加快，黄铁矿氧化速率降低；加入C及黄铁矿与黄铜矿混合时，由于接触电位的影响，黄铜矿氧化反应电流增大、反应起始电位负移，反应加尉，而黄铁矿的氧化反应受到抑制；混合矿浸出过程中，黄铜矿表面Cu含量较单一矿浸出时低得多，说明混合效应对浸出具有强化作用；黄铜矿中Cu浸出愈多，表面生成的元素硫愈多，黄铁矿细菌浸出时，表面不会有元素硫产生。     

Effect of calcium addition on the corrosion behavior of Mg–5Al alloy

The corrosion behavior of four Mg–5Al–xCa alloys (x = 0.0 to 2.0 wt.%) was evaluated in an alkaline NaCl solution. Surface analyses indicated that the benefits of Ca addition are the refinement of the precipitates and a decrease in grain size. Furthermore, the refinement of the precipitates (Mg₂Ca, Al₂Ca) became more complete with increasing of Ca content. The electrochemical tests revealed that the pitting resistance was improved in Ca-containing specimens. In addition, the polarization resistance of the Mg–5Al specimens increased with increasing Ca content. This is due to the fact that precipitation which is expected to act as a barrier is more continuous over the Mg matrix with a smaller grain size and higher precipitation density.     

Galvanic corrosion of polyacrylnitrile (PAN) and pitch based short carbon fibres in polyetheretherketone (PEEK) composites

When an electric current is conducted through a short fibre reinforced polyetheretherketone composite, being in contact with a stainless steel electrode, carbon fibre corrosion occurs. Surface analysis shows that structural defects range from debonding events and fibre cracking in the early stage of the corrosion process to the final disintegration of the fibre. The extent of fibre corrosion is quantified by atomic force microscopy, and the influence of fibre type, fibre volume content and the aqueous medium on the fibre corrosion is reported. Overall, polyacrylnitrile based fibres have a higher corrosion resistance than pitch based ones.