Oxidation of TiAl intermetallic

The oxidation kinetics of TiAl intermetallic at 500–900 °C in air is studied using a gravimetric method, and the phase composition of the scale is studied using an x-ray phase analysis. At t > 600 °C, the kinetics of oxidation is described by a parabolic equation. The oxides TiO₂ (rutile), γ-Al₂O₃, α-Al₂O₃, Ti₂O₃ are found in the scale. It is shown that at the first stage the γ-Al₂O₃ and low-titanium oxides form on the sample surface at t < 70 °C. At t ≥ 850 °C, the Ti₂O₃ forms on the external surface of the scale, TiAl₃ is found in the sublayer at the alloy/scale interface. It is shown that at t ≤ 800 °C the process is controlled by oxygen diffusion. At t > 800 °C, the oxidation mechanism changes: counterdiffusion of titanium ions through interstitial sites in TiO₂ lattice occurs.     

热浸镀锌钢板镀层织构与耐蚀性

用X射线衍射和动电位扫描方法研究了热浸镀锌钢板镀层织构、相分布和耐蚀性的关系.实验结果表明,镀锌层中纯锌相的主要织构组分为{0002}基面织构,当镀锌层厚度增加时,纯锌相中{0002}基面织构密度水平增加,纯锌相自腐蚀电位升高、腐蚀电流密度减小以及耐蚀性增加.X射线衍射分析电化学剥离后的铁锌相,结果表明,镀锌层由纯锌相和合金相组成;电化学实验表明,镀锌层各相耐蚀性不同,合金相的耐蚀性高于纯锌相的耐蚀性,且Fe-Zn合金相的耐蚀性随铁含量的增加而增加.     

脉冲电镀Ni镀层参数影响及耐腐蚀机理

用脉冲电流在钕铁硼磁体表面制备Ni镀层;并通过单因素试验依次对脉冲参数进行优化.实验发现当占空比为60％、频率为1000 Hz、电流密度为6 A/dm2时,Ni镀层的耐腐蚀倾向和腐蚀速率最小,Ni镀层耐电化学腐蚀性能较优.观察镀层表面的微观结构发现镀层表面Ni颗粒尺寸更加均匀,镀层表面平整度更高,因此镀层的综合质量更高...     

织构对纳米晶纯镍镀层耐蚀性能的影响

采用脉冲电镀法在黄铜表面制备出具有(111)、(200)和(220)晶面择优生长织构的纳米晶纯镍镀层.采用扫描电镜对镀层的显微形貌进行观察,采用X射线衍射对不同晶面织构的择优性进行表征,并对镀层在3.5%NaCl溶液中的动电位极化曲线和交流阻抗谱进行了测试,研究不同织构镀层的耐蚀性能.不同织构镀层的耐蚀性能存在显著差异:具有(220)强织构的镀层耐蚀性最差,其自腐蚀电流密度最大,为1.23μA·cm-²,镀层的电荷转移电阻为2.09kΩ·cm²;具有(200)强织构的镀层耐蚀性能最佳,镀层的电荷转移电阻为27.32kΩ·cm²,自腐蚀电流密度为0.15μA·cm^-2;具有(111)织构镀层的耐蚀性居中.认为织构引起的表面胞状物的差别是造成纯镍镀层耐蚀性能不同的原因.     

AZ31镁合金表面钼酸盐转化膜的制备与耐蚀性能

以Na2Mo O4为主盐,与氧化剂H2O2、成膜促进剂NaF和Na2Si O3一起组成化学转化液,在AZ31镁合金表面制备钼酸盐转化膜,利用扫描电镜和X线光电子能谱仪分析转化膜的形貌和组成,通过电化学阻抗测试研究转化膜在3.5%Na Cl溶液中的腐蚀行为,并讨论成膜机理,研究转化液中Na2Mo O4浓度与p H以及成膜温度和时间对薄膜结构与耐腐蚀性能的影响。结果表明:转化液的优化组成为0.2 mol/L Na2Mo O4+0.12 mol/L NaF+0.014mol/L Na2Si O3+0.012 mol/L H2O2;优化工艺条件为p H=5,温度60℃,转化时间30 min;转化膜为黄棕色,主要由Mg Mo O4,Mg F2,Mo O2,Mo O3和Mg Si O3组成,转化膜宏观上完整均匀,存在网状微裂纹;钼酸盐转化膜能有效提高AZ31镁合金的耐腐蚀性能,对基体合金有一定的保护作用。     

含氯离子环境下锌铝伪合金涂层的耐蚀性及电化学特性

采用盐雾试验和电化学阻抗谱测试技术研究了纯锌和锌铝伪合金涂层在含氯离子环境中的腐蚀行为和电化学特性,通过扫描电镜、X射线物相分析等手段研究了原始涂层及腐蚀后的表面形貌和腐蚀产物的相结构,并对两种涂层的腐蚀机理进行了初步的探讨.随着盐雾时间的增加,纯锌涂层表面逐渐生成疏松多孔的胞状腐蚀产物层,主要腐蚀产物为Zn₅(OH)₈Cl₂H₂O、ZnO和Zn₅(CO₃)₂(OH)₆,盐雾试验达到768 h后腐蚀产物层局部区域发生龟裂.锌铝伪合金涂层表面生成致密的腐蚀产物层,主要为Zn₅(OH)₈Cl₂H₂O、Zn_0.71Al_0.29(OH)₂(CO₃)_0.145·xH₂O及ZnAl₂O₄.电化学阻抗谱测试结果表明:随着盐雾时间的延长,两种涂层的电荷转移电阻均逐渐增大,但锌铝伪合金涂层的阻抗要明显大于纯锌涂层,表现出了更好的耐蚀性.     

Growth process and corrosion resistance of ceramic coatings of micro-arc oxidation on Mg-Gd-Y magnesium alloys

The regulation of ceramic coating formed by micro-arc oxidation on Mg-11Gd-1Y-0.5Zn (wt.%) magnesium alloys was investigated by scanning electron microscopy (SEM) and X-ray diffractometer (XRD). The relation of phase structure and corrosion resistance of MgO coating formed by micro-arc oxidation in different growth stages was analyzed. The results showed that the growth of coating accorded with linear regularity in the initial stage of micro-arc oxidation, which was the stage of anodic oxidation controlled ...     

NiCoCrAl-Y2O3涂层对TiAl金属间化合物高温抗氧化性的影响

分别用等离子喷涂和等离子-激光复合工艺,在TiAl金属间化合物表面制备NiCoCrAl-Y2O3涂层,对其进行高温氧化试验,并用XRD、SEM检测试样相组成及表面形貌,通过氧化动力学曲线、氧化物的组织结构形貌,分析两种不同工艺制备的NiCoCrAl-Y2O3涂层的高温氧化机理。     

Effect of Pb content on the surface topography and corrosion resistance of hot dip Zn-Al-Mg coatings

In this study,the effect of Pb content on the surface morphology and salt spray corrosion resistance of hot dip Zn-Al-Mg coatings was investigated.The results showed that the coating surface easily formed small grains of zinc spangle structures and that the salt spray corrosion resistance of the coating decreased when Pb content was greater than 0.01%.The microstructure and energy dispersive spectrum analysis of surface and cross-sectional areas was performed by scanning electron microscopy.Pb content present in the coating was analyzed by glow discharge spectrum.The results showed that the distribution of Pb in the coating was not uniform.The Pb content was segregated on the surface and at the cross-section of the Zn-Al-MgZn_2 ternary eutectic structure,especially,on the surface of the Zn-Al-MgZn_2 ternary eutectic structure.     

Oxidation of Cr-Ni coatings on diamond

The kinetics of the oxidation of chromium and chromium-nickel coated diamond powders in air at 750 and 850°C was studied by means of interrupted weighing. The coatings and metallized powders were subjected to x-ray phase analysis. Decrease of the powder mass confirms that permeation of the mass with volatile oxides predominates over the increment due to the weight of the absorbed oxygen in the oxides NiO and Cr₂O₃. The weight loss is caused by the burning away of both the coating (oxidation of chromium and its carbides to CrO with formation of CO and CO₂) and the diamond. Carbon from the diamond is also removed with CO and CO₂ as a result of successive reduction of chromium oxide by carbon, which diffuses to the oxidized layers, and further reduction of the carbides by the same mechanism. The higher the oxidation temperature and the thinner the coating, the greater the contribution of these reactions is to the processes responsible for the decrease in weight of the metallized diamonds. It is also encouraged by diffusion of carbon to the scale formed and by simultaneous diffusion of oxygen to the coating. The reactions of primary oxidation of chromium contained in the nickel solid solution, reduction of nickel by carbon and chromium, and dissolution of chromium in the reduced nickel contribute significantly to the oxidation of chromium-nickel coatings.Translated from Poroshkovaya Metallurgiya, No. 7(367), pp. 62–66, July, 1993.     

Oxidation of nickel-molybdenum coatings on diamond

Conclusions The main processes causing oxidation in air of pure and nickel-alloyed molybdenum coatings on diamond are: build up of oxides in the scale; removal of molybdenum and carbon in the composition of volatile oxides MoO₃ CO, and CO₂; renewal of the carbide layer on the boundary with the diamond as a result of the oxidation-reduction reactions taking place in this zone; enrichment of the scale with nickel as a result of selective oxidation of the molybdenum-nickel phases which reduces the rate of removal of molybdenum from MoO₃. The contribution of each component is determined by the oxidation conditions and the nickel content of the molybdenum coatings. The described mechanisms make it possible to predict the behavior of components made of molybdenum metallized diamond powders under specific service conditions.Translated from Poroshkovaya Metallurgiya, No. 4(340), pp. 53–58, April, 1991.     

HVAF喷涂La2O3改性WC-20Cr3C2-11NiMo涂层的耐磨耐蚀性能

为进一步提升高质量WC涂层的耐磨性、耐海水腐蚀性和耐海水气蚀性。采用大气超音速火焰喷涂(HVAF)在0Cr13Ni5Mo基体上制备稀土La₂O₃改性WC-20Cr₃C₂-11NiMo涂层。通过显微硬度测试、平面孔隙测试、摩擦磨损实验、电化学实验和模拟海水超声波气蚀实验,测试涂层的显微硬度、孔隙率、摩擦因数、摩擦磨损性能、耐海水腐蚀性能和耐海水气蚀性能,分析La₂O₃对WC-20Cr₃C₂-11NiMo涂层耐磨耐蚀性能的影响。结果表明,改性后的涂层显微硬度提升到1400 HV0.2左右,平均孔隙率降低约48.6%;涂层磨损质量降低约33%,摩擦因数降低约30%,摩擦磨损表面微凹坑和微裂纹明显减少;电化学自腐蚀电位明显右移,电化学自腐蚀电流密度明显减小;涂层的气蚀质量损失减少约20%,气蚀坑洞明显减少和变小。HVAF喷涂La₂O₃改性后的WC-20Cr₃C₂-11NiMo涂层硬度略微提升,致密性、耐磨性、耐海水腐蚀性和耐海水气蚀性得到明显提升,除表面疲劳磨损外,表面摩擦磨损机理从严重磨粒磨损转变为轻微磨粒磨损,气蚀机理主要为流体冲击波侵蚀。