A comparative study of four modified Al coatings on Ni3Al-based single crystal superalloy

Four modified Al diffusion coatings (Al, Cr–Al, Al–Si and Cr–Al–Si coatings) were prepared on Ni₃Al based single crystal superalloy IC20. The oxidation tests were carried out at 1 150 °C for up to 100 h. Cyclic hot corrosion tests were carried out at 950 °C for 50 h. The results indicate that the oxidation and corrosion resistances of IC20 alloy are improved significantly by the coatings, and both oxidation and hot corrosion resistances of the four coatings are rated in the order (from worst to best) of Cr–Al, Al, Cr–Al–Si, Al–Si coatings. It is found that the degradations of Al and Cr–Al coatings are very quick due to the serious inter-diffusion between the coatings and substrates. The inter-diffusion between Si-containing coatings and substrates is reduced since Si effectively retards the outward diffusion of Mo. The weak effects of Cr and benefit effects of Si to the oxidation and hot corrosion resistance were discussed. The hot corrosion degradation mechanism of superalloy IC20 was analyzed.     

Studies on thermally grown oxide as an interface between plasma-sprayed coatings and a nickel-based superalloy substrate

A thermally grown oxide layer formed by hot corrosion was investigated as an interface between plasma-sprayed coatings and a nickel-based superalloy substrate. The hot corrosion mechanism of NiCr-Cr₂O₃ and Al₂O₃-40wt% TiO₂ (A40T) plasma coated Inconel 617 was evaluated. The experiments were carried out at 1000℃ using a combination of Na₂SO₄, NaCl, and ₂O₅ salts to simulate the conditions of a gas turbine in a marine environment. The hot corrosion results revealed the spallation and dissolution of oxides upon prolonged exposure. Optical images and scanning electron micrographs of the exposed samples revealed the formation of oxide scale and provided details of its morphology in NiCr-Cr₂O₃ coated samples. Microstructure characterization of A40T coatings demonstrated a thermally grown oxide (TGO) layer at 1000℃. Increasing the thickness of the TGO layer decreased the corrosion resistance. The elemental analysis and image mapping revealed the migration of active elements from the substrate and coatings toward the corrosive environment.     

新型定向凝固高温合金750℃抗热腐蚀性能

研究了涂有75%Na2SO4+25%NaCl盐膜的新型定向凝固镍基高温合金在750℃的热腐蚀行为,采用X射线衍射仪和带能谱的扫描电镜分析腐蚀产物相组成以及微观结构.结果表明:该合金在开始阶段腐蚀速率较大,随着腐蚀时间的延长以及合金腐蚀层厚度的增加,腐蚀速率降低.腐蚀层可分为3个区域:外层是以TiO2和Cr2O3为主相对疏松的氧化层,中间层具有保护性的是富Cr层,内层是以Al,Ti为主的氧化物以及点状分布的硫化物.合金的热腐蚀主要由氧化-硫化共存伴随着表面腐蚀物挥发形成,在此过程中腐蚀持续向合金基体推进,使得腐蚀层不断增厚.     

CrN/Cr涂层对Ti22Al26Nb合金的高温防护研究

采用电弧离子镀技术在O相Ti22Al26Nb合金表面镀覆CrN以及CrN/Cr涂层并研究了其在800和900℃空气中的等温氧化行为,结果显示O相钛合金表面施加单一的CrN涂层后,涂层表面在氧化时形成了保护性的氧化膜Cr2O3层,因此合金受到了良好的高温防护,但是涂层和基体合金之间发生了明显的互扩散;在CrN涂层和钛合金基体之间施加纯Cr扩散障层后形成的CrN/Cr涂层,其表面除了象单一CrN涂层那样氧化后形成了一层连续、致密、结合良好的保护性氧化膜Cr2O3层外,还能有效的抑制涂层与基体合金之间的互扩散,此外扩散障Cr层的存在使得靠近其基体的晶粒也出现了长大现象。     

55%铝—锌—1.6%硅合金镀层的耐蚀性能

在盐雾试验（ＮＳＳ、ＡＳＳ）、曝气试验、浸泡试验和缝隙腐蚀试验的基础上,通过与锌镀层和铝镀层的对比,研究了５５％Ａｌ－Ｚｎ－１．６％Ｓｉ合金镀层的耐蚀性能．镀层中富锌相的存在,导致缝隙腐蚀中的自催化酸化闭塞电池难以形成,因而该镀层的耐缝隙腐蚀性能优于铝镀层;在其他试验条件下,由于镀层表面富铝相占较大面积,使得镀层的耐蚀性高于锌镀层,接近于铝镀层．钝化处理后各镀层耐蚀性均有显著提高．     

Isothermal oxidation behavior and mechanism of a nickel-based superalloy at 1000℃

The oxidation behavior of a nickel-based superalloy at 1000°C in air was investigated through X-ray diffraction, scanning electron microscopy, andenergy-dispersive spectroscopy analysis. A series of oxides, including external oxide scales (Cr2O3, (TiO2 + MnCr2O4)) and internal oxides (Al2O3,TiN), were formed on the surface or sub-surface of the substrate at 1000°C in experimental still air. The oxidation re-sistance of the alloy was dependent on the stability of the surface oxide layer. The continuity and density of the protective Cr2O3 scale were affected by minor alloying elements such as Ti and Mn. The outermost oxide scale was composed of TiO2 rutile and MnCr2O4 spinel, and the growth of TiO2particles was controlled by the outer diffusion of Ti ions through the pre-existing oxide layer. Severe internal oxidation oc-curred beneath the external oxide scale, consuming Al and Ti of the strength phaseγ′ (Ni3(Al,Ti)) and thereby severely deteriorating the sur-face mechanical properties. The depth of the internal oxidation region was approximately 35μm after exposure to experimental air at 1000°C for 80 h.     

氧化铈对NiCoCrAlY涂层抗热腐蚀性能的影响

为了研究纳米氧化铈对NiCoCrAlY涂层抗热腐蚀性能的影响,考察了添加3种不同含量纳米氧化铈的NiCoCrAlY熔覆涂层在1 050℃混合硫酸盐(质量分数为75％ Na2SO4-+25％ K2SO4)作用下的热腐蚀行为,并与未加纳米颗粒的涂层进行了比较.结果表明:添加纳米氧化铈后,涂层的抗热腐蚀性能得到了较大提高,其...     

The effect of Al and Cr elements on the oxidation resistance of MoSi_2 via first-principles calculation

The properties of structure, energy and oxidation resistance of interstitial and substitutable MoSi_2 systems have been investigated using the density functional theory. The calculated lattice constants for pristine MoSi_2 confirm the early experimental results. In the interstitial MoSi_2, the impurity energy of O atom was computed for the stable interstitial site in the systems. The results reveal that the O atom prefers to occupy the Oct2 site with the lowest impurity energy. In the substitution MoSi_2, the Si sites tend to be substituted with Al and Cr atoms,whereas, Mo sites do not behave like the Si sites. The co-substitution of Al/Cr atoms and the direction of the O diffusion in MoSi_2 have been analyzed as well. The results from electronic structural analysis indicate that the SiO bond is the main factor to inhibit the diffusion of O, and the alloying elements of Al and Cr contribute to the oxidation resistance of MoSi_2.     

电解铝硅合金耐蚀性研究

对比了电解铝硅合金和常规铝硅合金的耐蚀性.电化学试验和湿热试验结果表明电解铝硅合金具有良好的耐蚀性.讨论了电解铝硅合金耐蚀机理,含有较多的微量元素及合金组织均匀细小是其腐蚀性能良好的原因.     

Wear and corrosion resistance of laser-cladded Fe-based composite coatings on AISI 4130 steel

The wear and corrosion resistance of Fe_72.2Cr_16.8Ni_7.3Mo_1.6Mn_0.7C_0.2Si_1.2 and Fe_77.3Cr_15.8Ni_3.9Mo_1.1Mn_0.5C_0.2Si_1.2 coatings laser-cladded on AISI 4130 steel were studied. The coatings possess excellent wear and corrosion resistance despite the absence of expensive yttrium, tungsten, and cobalt and very little molybdenum. The microstructure mainly consists of dendrites and eutectic phases, such as duplex (γ+α)-Fe and the Fe–Cr (Ni) solid solution, confirmed via energy dispersive spectrometry and X-ray diffraction. The cladded Fe-based coatings have lower coefficients of friction, and narrower and shallower wear tracks than the substrate without the cladding, and the main wear mechanism is mild abrasive wear. Electrochemical test results suggest that the soft Fe_72.2Cr_16.8Ni_7.3Mo_1.6Mn_0.7C_0.2Si_1.2 coating with high Cr and Ni concentrations has high passivation resistance, low corrosion current, and positive corrosion potential, providing a better protective barrier layer to the AISI 4130 steel against corrosion.     

Improvement of oxidation resistance of Nb–Ti–Si based alloys with additions of Al,Cr and B at different temperatures

The effects of Cr, Al and B addition on the microstructure and high-temperature oxidation behaviors (at 1200, 1250 and 1300 ?°C) of Nb–Ti–Si based alloys were investigated. The results showed that the addition of Cr stabilized α-Nb₅Si₃, while Al promoted the formation of β-Nb₅Si₃ and adding B promoted the formation of γ-Nb₅Si₃. Among the three elements, Al and Cr were beneficial to oxidation resistance at 1200 ?°C, and B was favorable to the oxidation resistance at 1300 ?°C. At 1250 ?°C, Al and B had the same effects on the improvement of oxidation resistance. The ratio of these alloying elements might play an important role in enhancing oxidation resistance. The oxidation resistance of the three kinds of silicides was compared, and the sequence was: γ-Nb₅Si₃> β-Nb₅Si₃> α-Nb₅Si₃. To predict the effects of the investigated alloying elements on the oxidation resistance of Nb–Ti–Si based alloys in a wider range of concentration, an artificial neural network (ANN) model was established, showing excellent accuracy and generalization ability. With the instructions of the ANN model, the oxidation resistance can be optimized with less additions of alloying elements.     

Oxidation and interdiffusion behavior of a germanium-modified silicide coating on an Nb-Si-based alloy

To investigate the interdiffusion behavior of Ge-modified silicide coatings on an Nb-Si-based alloy substrate, the coating was oxidized at 1250℃ for 5, 10, 20, 50, or 100 h. The interfacial diffusion between the (Nb,X)(Si,Ge)₂ (X=Ti, Cr, Hf) coating and the Nb-Si based alloy was also examined. The transitional layer is composed of (Ti,Nb)₅(Si,Ge)₄ and a small amount of (Nb,X)₅(Si,Ge)₃. With increasing oxidation time, the thickness of the transitional layer increases because of the diffusion of Si from the outer layer to the substrate, which obeys a parabolic rate law. The parabolic growth rate constant of the transitional layer under oxidation conditions is 2.018 μm·h-1/2. Moreover, the interdiffusion coefficients of Si in the transitional layer were determined from the interdiffusion fluxes calculated directly from experimental concentration profiles.     

High-temperature oxidation resistance of ceramic coatings on titanium alloy by micro-arc oxidation in aluminate solution

Ceramic coatings with aluminum titanuate (Al₂TiO₅) were prepared on Ti–6Al–4V alloy using pulsed bi-polar Micro-arc Oxidation (MAO). The micromorphology and phase composition of the micro-arc-oxidition ceramic coatings on the titanium alloy were characterized by X-ray powder diffraction (XRD), and scanning electron microscopy (SEM) respectively. The results revealed that the distinct discharge channels and pores on the surface of the micro-arc-oxidition coatings appeared, and these channels were connected in the molten state. The electrolyte concentration was inversely proportional to the coating hardness; additionally, the coating prepared with sodium aluminate and sodium hypophosphite concentrations of 4 ?g/L and 0.5 ?g/L, respectively, was the most refined after high-temperature sintering, and it was demonstrated to better prevent oxidation. Increasing the electrolyte concentration coincided with fluctuating coating thermal shock resistance. The thermal shock resistance of the coating respectively prepared with sodium aluminate, and the sodium hypophosphite concentrations of 4 ?g/L and 0.5 ?g/L was the highest. Additionally, the high-concentration coatings performed significantly better than the low-concentration coatings. The oxidation resistance of the coating samples was also significantly higher than that of the TC4 titanium alloy substrate. The adhesion strength between the coatings and the substrate with and without the sealing treatment was measured by tensile tests. Then, the high-temperature oxidation performance of the coating samples with and without the sealing treatment was investigated by conducting a high-temperature oxidation experiment at a calcinating temperature of 500 ?°C. The results indicate that the adhesion strength between the coatings and substrate was high for the as-prepared and sealed micro-arc oxidation samples regardless of whether they were calcined. The high-temperature oxidation mass increase curves for the sealed and unsealed coating samples calcined at 500 ?°C for 500 ?h revealed that the high-temperature-oxidation-induced mass increase of the coating samples sealed with a sodium silicate solution was much lower than that of the titanium alloy substrate. Thus, the sealing treatment significantly improved the high-temperature oxidation resistance of the TC4 titanium alloy. Lastly, the high-temperature oxidation behavior at 500 ?°C was analyzed and discussed.     

铝合金微弧氧化陶瓷膜的微观结构和耐蚀性

采用非对称方波输出模式的恒流交流电源,利用微弧氧化方法在铝合金表面沉积Al2O3陶瓷膜,考察了微弧氧化工艺参数(电流密度、处理时间)对膜层微观结构和耐蚀性的影响.结果表明:工艺参数对膜层组织结构和性能的影响存在较佳的范围,即氧化时间为15-20min,电流密度在20A/dm2左右;氧化时间过短时,试样表面存在陶瓷膜未完全覆盖的区域,而当电流密度过大时,膜层表面将会出现大量的显微裂纹,导致膜层性能大幅度降低;在恒流非对称方波输出模式下,工艺参数对膜层的相组成影响不大,微弧氧化膜层由晶态Al2O3和非晶态Al2O3组成.     

Cr3 C2含量对Cr3 C2/Ni3 Al复合材料摩擦磨损性能的影响

采用热等静压法制备Ni3 Al合金和Cr3 C2含量不同的Ni3 Al基复合耐磨材料,利用扫描电镜、能谱仪、X射线衍射仪及摩擦磨损试验机,系统地研究Cr3 C2含量对材料组织特征、硬度及摩擦磨损性能的影响。结果表明：Cr3 C2/Ni3 Al复合材料中,Cr3 C2颗粒与Ni3 Al颗粒之间发生互扩散作用,使部分Cr3 C2颗粒转变为M7 C3( M=Cr, Fe, Ni)结构;在特定的摩擦磨损条件下,随着Ni3 Al基体中Cr3 C2比例增大,Cr3 C2/Ni3 Al复合材料的耐磨性能显著提高,达到了Ni3 Al合金耐磨性能的4~10倍。此外,随着Ni3 Al基体中Cr3 C2比例的增大,Cr3 C2/Ni3 Al复合材料对对磨盘的切削、刮擦作用减弱,对磨盘的磨损量减少。     

铝合金镁合金微弧氧化陶瓷层的形成机理及性能

利用扫描电镜(SEM)、盐雾腐蚀试验及对比磨损试验等分析手段研究了铝合金、镁合金微弧氧化陶瓷层的形成机理、镁合金微弧氧化陶瓷层耐蚀性及铝合金微弧氧化陶瓷层耐磨性。研究结果表明,镁合金微弧氧化陶瓷层的耐蚀性优于铬化处理,铝合金微弧氧化陶瓷层的耐磨性优于电镀硬铬涂层。     

Cr/WC激光表面改性梯度层组织及磨损行为

用5kWCO2激光器对先后预置不同成分合金粉末的铸造铝硅合金表面进行2次激光扫描，制备了Cr/WC激光表面改性梯度层，并对其显微组织进行了分析，结果表明，在梯度层表面产生了大量的Al9Cr4化合物，且有更多的硅元素固溶在α-Al中，增加了固溶强化的作用，自表面至基体激光改性梯度层的显微硬度呈现明显的连续变化趋势，而单次激光表面改性层与基体之间的显微硬度值则有一突变，微动磨损实验表明，激光改性后的表面抗微动磨损的能力增强，磨损机制不同于铝硅合金基体，而表现出较好的抗粘着损伤性能。     

Effect of Al2O3 and Y2O3 on the corrosion behavior of ZrO2-benzotriazole nanostructured coatings applied on AA2024 via a sol-gel method

zirconia-based nanostructured coatings were deposited on AA2024 to improve the corrosion resistance properties. Three different nanostructured coatings, namely, zirconia-benzotriazole, zirconia-alumina-benzotriazole, and zirconia-yttria-benzotriazole, were applied on AA2024 via a sol-gel method using the dip-coating technique. Next, the coatings were annealed at 150℃ after each dipping period. The phases and morphologies of the coatings were investigated using grazing incidence X-ray diffraction (GIXRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), and atomic force microscopy (AFM). The corrosion properties were evaluated using electrochemical methods, including polarization and electrochemical impedance techniques in 3.5wt% NaCl solution. The obtained results confirm the formation of homogeneous and crack free zirconia-benzotriazole-based nanostructured coatings. The average roughness values for zirconia-benzotriazole, zirconia-alumina-benzotriazole, and zirconia-yttria-benzotriazole nanostructured coatings were 30, 8, and 6 nm, respectively. The presence of alumina as a stabilizer on zirconia coating was found to have a beneficial impact on the stability of the corrosion resistance for different immersion times. In fact, the addition of alumina resulted in the dominance of the healing behavior in competition with the corrosion process of zirconia-benzotriazole nanostructured coating.     

长城1号防护涂层抗热腐蚀的性能

用等离子喷涂方法将长城1号及X－40涂层镀复在GH864高温合金试样上，然后进行了热腐蚀试验，并用OM，SEM，EMPA进行性能分析，结果表明，长城1号涂层显示出比X－40涂层更优越的腐蚀抗力，提出了长城1号，X－40涂层GH864基体合金可能的腐蚀机制。     

Mg对Galvalume镀层微观结构、耐蚀性和成形性的影响

利用扫描电镜、X射线衍射仪、电化学测试和杯突试验研究了Mg(质量分数15%)对Galvalume(Zn-55Al-16Si)镀层微观结构、耐蚀性和成形性的影响.扫描电镜和X射线衍射仪检测结果显示,添加Mg后在Zn-55Al-16Si-15Mg镀层的枝晶间区出现了MgZn2相;腐蚀产物的微观形貌显示Mg能减少镀层腐蚀产物中的裂纹,并提高其致密性.电化学检测结果显示,Zn-55Al-16Si-15Mg镀层的腐蚀速度仅为Galvalume的341%,因此Mg能显著地提高Galvalume镀层的耐蚀性;MgZn2作为强化相,强化了镀层的枝晶间区,减少了成形杯弯曲外表面的微裂纹,显著地提高了Galvalume镀层的成形性.