Oxidation of the three-phase Cu-20Ni-30Cr and Cu-20Ni-40Cr alloys at 700-800 °C in 1 atm O2

The oxidation of two ternary Cu-Ni-Cr alloys containing approximately 30 and 40 at.% Cr, but with a similar Ni content, was studied at 700-800 °C in 1 atm of pure oxygen. Both alloys contain a mixture of three phases, where the phase with the largest copper and lowest chromium content (α) forms the matrix, while the phase with an intermediate content of Ni and Cr (β) and that richest in chromium (γ) are present in the form of particles dispersed in the α matrix. The kinetics of oxidation were rather irregular and presented two approximately parabolic stages which for the alloy with 40 at.% Cr were followed by a final nearly linear stage. Generally, the corrosion rates decreased by increasing the chromium content in the alloy under constant temperature and increased with temperature for a constant alloy composition. The scales formed on the two alloys were rather complex and consisted in most cases of an outermost copper oxide layer followed by a layer containing a mixture of oxides of nickel and copper as well as Cu-Cr and Ni-Cr spinel and finally by an innermost very irregular and convoluted but continuous Cr₂O₃ layer which protruded into the alloy and contained a number of Cu-rich metal islands.     

不同晶粒尺寸的Cu-40Ni合金在酸性介质中的耐蚀性能

采用电弧熔炼(CA)和机械合金化(MA)通过热压烧结工艺制备了晶粒尺寸差别较大的Cu-40Ni合金,借助于PARM273A和M5210电化学综合测量仪,利用动电位扫描法和交流阻抗技术对比研究了上述合金在酸性介质中的腐蚀电化学性能以及腐蚀机理。结果表明:随着H 浓度的增加,CA Cu-40Ni合金的自腐蚀电位负移,而MA Cu-40Ni合金则正移,两种合金的动电位扫描极化曲线均未出现钝化现象;随着H 浓度的增加,CA Cu-40Ni合金的极化电阻增大,腐蚀电流减小,合金的耐蚀性能增加,而MA Cu-40Ni合金的极化电阻减小,腐蚀电流增加,合金的耐蚀性能降低。两种合金的交流阻抗谱均由双容抗弧组成,腐蚀过程受电化学反应控制。晶粒细化后,合金中存在大量晶界,参与腐蚀反应的活性原子数增加,促使MA Cu-40Ni合金的腐蚀速度高于CA Cu-40Ni合金。     

不同晶粒尺寸5083铝合金晶间腐蚀和应力腐蚀开裂的差异性

通过冷轧和退火获得具有不同晶粒尺寸(8.7～79.2μm)的5083铝合金板.研究其微观结构、晶间腐蚀(IGC)、应力腐蚀开裂(SCC)和裂纹扩展行为.结果表明,粗晶粒样品表现出更好的抗IGC性能,其腐蚀深度为15μm.慢应变速率测试结果表明,细晶粒样品表现出更好的抗SCC性能,敏感性指数ISSRT为11.2％.此外,...     

Ti35合金在含氟离子硝酸中电化学腐蚀行为

Ti35合金具有优良的耐腐蚀性能,可在沸腾状态下高浓度的氧化性酸介质中进行长期工作,是商业后处理较为理想的候选材料。本文采用电化学测试系统测试了Ti35合金在含有不同氟离子浓度的6M硝酸溶液中的开路电位(OCP)、极化曲线、电化学阻抗谱(EIS),探讨了氟离子对Ti35合金耐蚀性能的影响。结果表明：随着氟离子浓度的增加,合金耐蚀性下降,但总体而言合金仍具有良好的耐蚀性。影响合金耐蚀性转变的氟离子浓度临界值约为50ppm,进一步应用混合电位理论,解释合金耐蚀性转变的原因。     

Oxidation behavior of three-phase Cu-25Ni-30Cr alloy at 700- 800℃ under high oxygen pressures

The thermogravimetric analysis of a ternary Cu-25Ni-30Cr alloy prepared by conventional casting was performed in 0.1 MPa pure O2 at 700 - 800 ℃. The results show that the alloy is composed of three phases,where the phase with the largest copper and lowest chromium content forms the matrix, while the other two,much richer in chromium, form a dispersion of isolated particles. At variance with another three-phase Cu-20Ni-20Cr alloy, which forms complex scales containing the oxides of the various components and double oxides plus an irregular region composed of alloy and oxides, the present alloy can form a very irregular but continuous chromia layer at the base of the mixed internal region, producing a gradual decrease of the oxidation rate down to very low values. A larger chromium content needed to form chromia layer for a ternary three-phase alloy is attributed to the limitations to the diffusion of the alloy components in the metal substrate imposed by their multiphase nature.     

晶粒细化对Cu—20Ni—20Cr合金氧化行为的影响

为探讨晶粒尺寸变化对三元复相合金氧化行为的影响，采用机械合金化制备了纳米晶三元Cu-20Ni-20Cr合金，并对比研究了该合金与同成分的铸态合金在700℃～800℃，0．1MPa纯氧气中的氧化行为。结果表明，铸态合金表面没有形成连续的Cr2O，保护膜，而是形成了含有所有组元氧化物及它们复合氧化物的复杂氧化膜结构。纳米晶Cu—20Ni—20Cr合金在700℃时合金表面形成了连续的Cr2O3氧化膜，而800℃时虽没有形成Cr2O3外氧化膜，但氧化膜规则平坦，外层是CuO，中间层是Cu2O，NiO和Cr2O3组成的混合氧化物区，内层则形成了一薄但不连续的Cr2O3层。晶粒细化降低了合金表面形成Cr2O3氧化膜所需活泼组元Cr的临界浓度。     

Electrochemical techniques for monitoring stress corrosion cracking of Type 40Cr steel in acidified chloride solution

Electrochemical impedance spectroscopy （EIS） and electrochemical noise （EN） techniques were used to detect stress corrosion cracking （SCC） on 40Cr steel specimens exposed to the acidified chloride solution at ambient. To test these two techniques, slow strain rate tensile （SSRT） tests were performed with 40Cr specimen in the identical corrosive solution at room temperature. In impedance measurements, phase shifts in frequency range from 1 to 1 000 Hz show a clear difference between the stressed and non-stressed specimens, suggesting that stress corrosion cracks are detected by the impedance measurements. EN signals in the process of SCC were recorded and then analyzed by standard deviation （STD）. On the other hand, the mechanical properties, such as maximum tensile strength （MTS） and fracture strain （FS） measured by the SSRT, decrease significantly when the specimens are exposed to the corrosive solution relative to that in an inert medium. The SSRT results are consistent with fractography of the tested specimens by scanning electron microscopy （SEM）. Analysis of the fracture surface clearly shows intergranular attack, suggesting that stress corrosion cracks are formed.     

不同晶粒度硬质合金的磨削性能研究

本文通过磨削试验,从磨削功率、磨削比、磨削表面光洁度等方面研究了粗晶、细晶、超细晶粒三种含Co量相同的K类硬质合金的磨削性能。研究结果表明,上述三种硬质合金在各磨削参数相同的情况下,所消耗的磨削力、磨削能随硬质合金晶粒尺寸的增加而增大。同一砂轮对上述硬质合金的磨削比随晶粒尺寸的增加而增大。在磨料粒度与硬质合金粒度相当时,所加工表面的月。值随WC晶粒度的变粗而变差．     

Electrochemical behavior of copper-nickel alloys in acidic chloride solutions

The electrochemical behavior of Cu-Ni alloys in acidic chloride medium was investigated. Commercial Cu-Ni alloys were investigated using potentiodynamic techniques, complemented by electrochemical impedance spectroscopy. The influence of alloy composition, chloride ion concentration and immersion time on the electrochemical response of the alloys was analyzed. Results of present investigations with pure metals (Cu and Ni) are also considered in this paper for the sake of comparison. Potentiodynamic measurements reveal that the increase in nickel content decreases the corrosion rate of the alloy and when the nickel content exceeds 30%, an increase in the corrosion rate was recorded. Also, the corrosion current density increases with increasing the concentration of chloride ions up to 0.6 M.The experimental impedance data were fitted to an equivalent circuit model representing the electrode/electrolyte interface. The relevance of the proposed model to the corrosion/passivation phenomena occurring at the electrode/solution interface was discussed.     

三元Cu60Ni20Cr20合金的制备及其显微组织

采用机械合金化,随后在750℃、58 MPa 下热压制备了致密的块体纳米晶Cu60Ni20Cr20合金,用x射线衍射仪、扫描电子显微镜等分析手段对比研究了不同晶粒尺寸的Cu60Ni20Cr20合金的显微组织.结果表明:随着球磨时间的延长,由于晶粒的细化和应变的结果,衍射峰偏移并有明显的宽化产生,Cr在Cu中的固溶度明显增加,在球磨40 h后,合金已由双相变成亚稳态的单相.由于机械合金化的粉末处于非平衡态,其过饱和固溶体随热压和真空退火过程的进行会慢慢分解,合金由单相变成两相,a-Cu和γ-Cr两相颗粒均成倍长大,但仍保持纳米级尺度.扫描电子显微镜(SEM/EDX)观察表明,合金致密度很高且显微组织均匀.讨论了晶粒细化对合金显微组织的影响.     

Electrochemical behavior of titanium‐tantalum alloys in sulfuric acid solutions

Titanium exhibits a good corrosion resistance in oxidizing acids and neutral media but it is severely attacked in reducing acids. On the contrary, tantalum presents an excellent resistance in both oxidizing and reducing acids, but its high cost limits its use to very aggressive conditions. The titanium‐tantalum alloys are promising materials for use in reducing acids, due to their lower cost and density when compared to tantalum, and their higher corrosion resistance when compared to titanium. Titanium‐20, 40, 60 and 80 wt% tantalum alloys were prepared by arc‐melting and their microstructures were characterized by scanning electron microscopy and X‐ray diffractometry. Their electrochemical behaviors were studied in 20 to 80 wt% sulfuric acid solutions at room temperature, using open‐circuit potential measurements, potentiodynamic polarization and electrochemical impedance spectroscopy. Different behaviors were observed depending on the tantalum content and acid concentration. A clear tendency of increase in corrosion resistance with the increase of tantalum content is observed, especially in 80 wt% sulfuric acid solutions.     

Corrosion behavior of two heat treatment Al-Zn-Mg-Cu alloys in different intergranular corrosion solution

The electrochemical behavior of two kinds of artificial aged Al-Zn-Mg-Cu alloys in two intergranular cor-rosion (IGC) solutions were studied using electrochemical impedance spectroscopy (EIS) and open circuit potential (OCP) at steady-state. EDAX result indicates that different artificial ageing methods change the composition and content of Cu and Zn in different zones. Zn/Cu depleted precipitation-free zone that plays a very important role in IGC is formed by heating the solubilized Al alloy for 135℃ at 16 h. All impedance spectra of the two alloys in two IGC solutions can be divided into three types. The two different states A1 alloys takes on one time constant and two capacitive arcs at high-mediate frequency and low frequency in the NaCl (NH4 )2SO4 solution respectively; but in the NaCl HCl solution, impedance displays one capacitive arc at the high-mediate frequency and an inductive loop at low frequency. OCP results show that more micro-galvanic cells in the NaCl (NH4)2SO4 solution than that in the NaCl HCl solution results in more potential fluctuation amplitude, and long-term drift of OCP is due to the long-term variation of the cathodic and anodic corrosion processes.     

Electrochemical behavior of Co-Cr and Ni-Cr dental cast alloys

The cast structures influencing the electrochemical corrosion behavior of Co-Cr and Ni-Cr dental alloys were studied using potentiodynamic polarization and AC impedance in 0.9% (mass fraction) NaCl solution at (37±1) °C. The phase and microstructure of the alloys that were fabricated using two different casting methods viz. centrifugal casting and high frequency induction casting, were examined using X-ray diffraction analysis, scanning electron microscopy and energy dispersive spectroscopy. The roles of alloying elements and the passive film homogeneity on the corrosion resistance of Co-Cr-Mo and Ni-Cr-Mo dental cast alloys were reviewed. The results of electrochemical study show that the dependence of corrosion resistance on the microstructure associated with the casting methods is marginal. The Co-Cr alloy exhibits more desirable corrosion resistance properties than the Ni-Cr alloy. There is severe preferential dissolution of Ni-rich, Cr and Mo depleted zones in the Ni-Cr alloy.     

Effect of grain size on corrosion behavior of electrodeposited bulk nanocrystalline Ni

Nanocrystalline (NC) and coarse-grained Ni with different grain sizes (from 16 nm to 2 μm) were fabricated by direct current electrodeposition. Effect of grain size on the electrochemical corrosion behavior of these Ni deposits in different corrosion media was characterized by using potentiodynamic polarization test, electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and immersion corrosion test. Results show that in the NaOH or NaCl solution, the NC Ni exhibits improved corrosion resistance with the decrease of grain size. But in H2SO4 solution, the higher grain boundary density accelerates corrosion due to no passive process and the corrosion resistance of NC Ni decreases with refining grain size. The distinct experimental results of NC Ni in corrosion behavior can be reasonably explained by the positive or negative effect of high-density grain boundaries in different corrosion media.     

6082铝合金搅拌摩擦焊焊缝的电化学腐蚀行为

通过室温静态挂片试验以及动电位极化曲线测试,在室温0．2mol／LNaHSO3＋0．6mol／L NaCl溶液中,对6082铝合金搅拌摩擦焊（FSW）焊缝以及6082铝合金母材的电化学腐蚀行为进行了研究。结果表明,主轴转速为1200r／min,焊接速度为200mm／min,搅拌头倾角为3°时的焊缝与母材相比,平均腐蚀速率较小,腐蚀电位Ecorr正向移动,腐蚀电流密度J变小。同时使用扫描电子显微镜（SEM）对室温静态挂片试验试样的表面形貌进行了观察,发现焊缝表面上只出现少量较浅的点蚀坑,而母材表面的点蚀现象较为严重。     

Corrosion behavior of hafnium in anhydrous isopropanol and acetonitrile solutions containing bromide ions

The corrosion behaviors of hafnium in Et₄NBr isopropanol and acetonitrile(ACN) solutions were investigated using electrochemical measurements, ICP-AES and SEM techniques. Results revealed that the open circuit potential gets more positive due to the increased passivity of the surface oxide film with increasing immersion time until it reaches a steady state value. The potentiodynamic anodic polarization curves did not exhibit an active dissolution region near corrosion potential due to the presence of an oxide film on the electrode surface, which was followed by pitting corrosion. SEM images confirmed the existence of pits on the electrode surface. Cyclic voltammetry and galvanostatic measurements allowed the pitting potential (?_pit) and the repassivation potential (?_p) to be determined. ?_pit increased with increasing potential scanning rate but decreased with increasing temperature, Br^? concentration and ACN concentration. The impedance spectra showed that the resistances of the solution and charge transfer decreased with the increase of ACN concentration.     

Cu-17Ni-3Al-X合金在中性盐雾中的腐蚀行为

采用中性盐雾加速试验、扫描电镜、X射线衍射仪、光电子能谱仪等研究了Cu-17Ni-3Al-X合金在中性盐雾中的腐蚀行为。结果表明:在中性盐雾腐蚀过程中,该合金具有良好的耐盐雾腐蚀性能,合金的腐蚀速率随腐蚀时间的延长而迅速降低,腐蚀480 h后平均腐蚀速率仅为0.010 mm/a。这是因为腐蚀后合金表面生成一层致密的Cu2O膜,随着腐蚀的进行,Cu2O膜增厚,同时外层的Cu2O膜被进一步氧化生成疏松的Cu2(OH)3Cl颗粒。合金在中性盐雾中腐蚀后,主要是α(Cu)固溶体被腐蚀,合金中的第二相仍残留在晶界处。     

Electrochemical corrosion behavior of 300M ultra high strength steel in chloride containing environment

The electrochemical corrosion behavior of 300M ultra high strength steel in chloride containing environment was investigated by potentiodynamic polarization technique, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). The results show that uniform corrosion occurs on 300M steel during the electrochemical measurements because no anodic passivation phenomenon is observed on polarization curves within the measurement range. The tests also show that 300M steel is highly susceptible to chloride containing solution, which is characterized by corrosion current density increasing with the addition of chlorides, and corrosion potential shifting towards positive direction and corrosion resistance decreasing, positively suggesting that chloride ions speed up the corrosion rate of 300M steel. Meanwhile corrosion products on the 300M steel surface formed during the salt spray test are too loose and porous to effectively slow down the corrosion rate. Additionally, a schematic structure of uniform corrosion mechanism can explain that 300M steel has better property of stress corrosion cracking (SCC) resistance than stainless steels.     

Hg和Ga元素对Mg阳极材料组织和电化学腐蚀性能的影响(英文)

采用动电位极化、恒电流和交流阻抗测试方法研究了Hg和Ga元素对Mg2%Hg,Mg2%Ga和Mg2%Hg2%Ga合金电化学腐蚀性能的影响,并用扫描电镜、X射线衍射和能谱分析了上述合金的显微组织和腐蚀表面形貌。结果表明:Mg2%Ga合金是固溶体,Mg-2%Hg和Mg-2%Hg2%Ga合金的晶界有白色第二相。Mg-2%Ga合金的平均电位为1.48V,腐蚀电流密度为0.15mA/cm2,电化学活性差,耐腐蚀性能好。Mg-2%Hg-2%Ga合金的平均电位1.848V,腐蚀电流密度为2.136mA/cm2,电化学活性好,耐腐蚀性能差。MgHgGa合金的活化机制是Hg和Ga原子的溶解沉积。     

Analysis of corrosion behavior of LY12 in sodium chloride solution with wavelet transform technique

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