C3H8O3含量对AZ91D镁合金微弧氧化过程及膜层特性的影响

在含有不同C₃H₈O₃含量的硅铝复合电解液中,利用交流脉冲电源在AZ91D镁合金基体上制备了一系列微弧氧化膜。利用SEM和膜层测厚仪分别研究了陶瓷膜层的微观形貌特征及厚度,采用全浸泡实验和电化学阻抗谱测试了膜层在3.5%NaCl中性溶液中的耐蚀性能。结果表明,微弧氧化过程中的起弧电压和终止电压均随C₃H₈O₃含量的增加而呈上升的变化趋势。随着C₃H₈O₃含量的增加,膜层耐蚀性先提高后降低,而膜厚变化幅度不大。膜层的耐蚀性主要取决于内部致密层,当C₃H₈O₃含量为5 mL/L时,膜层相对较致密,因而表现出良好的耐蚀性能。     

表面微弧氧化处理对不锈钢与环氧树脂粘接性能的影响

采用热浸镀铝工艺在不锈钢表面镀铝,分析了浸镀时间与浸镀温度对合金层及纯铝层厚度的影响并获得最佳镀铝工艺参数,在此基础上再进行微弧氧化试验。用剪切法测试了氧化膜与环氧树脂之间的结合强度,采用SEM、XRD和激光共聚焦显微镜对微弧氧化膜的微观成分与结构进行了表征,进而探讨分析了不锈钢微弧氧化处理对其与环氧树脂粘接性能的影响。结果表明:适宜的浸镀温度为710 ℃,浸镀时间为11 min;微弧氧化膜主要由α-Al₂O₃和γ-Al₂O₃组成,不同微弧氧化时间下氧化膜产物基本相同;随着氧化时间增加,陶瓷膜表面粗糙度增大,微弧氧化膜-环氧树脂的结合强度增大,当时间增至30 min时,膜层表面粗糙度最大值为1.265 μm,结合强度增加到最高值33.20 MPa,比未处理过的试样结合强度提高了2.8倍。     

硅酸盐体系电解液中添加Na2WO4对LY12铝合金陶瓷膜性能的影响

通过SEM、XRD、硬度试验、电化学腐蚀试验研究了在硅酸盐体系电解液中加入不同浓度的Na₂WO₄对LY12铝合金微弧氧化陶瓷膜表面形貌及性能的影响。结果表明,添加Na₂WO₄改变了膜层的微观结构,使微弧氧化膜层硬度增加,表面平滑,呈现出小而少的孔洞结构,且表面堆积少量形状不规则的白色质点;随着Na₂WO₄添加量的增加,膜层的硬度值呈现先增加后降低的趋势,当Na₂WO₄含量为4 g/L时,膜层达到最高硬度440.3 HV0.3,较基体(硬度值约168 HV0.3)提升了272.3 HV0.3;XRD分析证明W元素参与了微弧氧化过程,并生成W的氧化物WO₃,陶瓷层物相主要由α-Al₂O₃和γ-Al₂O₃以及WO₃组成;电化学极化曲线分析结果表明添加剂Na₂WO₄有效地提高了膜层的耐腐蚀性能,耐腐蚀性能最好的添加量为 1 g/L,此时自腐蚀电位为-532.0 mV,腐蚀电流为0.011 μA。Na₂WO₄的添加可有效改善陶瓷膜层的表面形貌及性能。综合考虑膜层的性能,添加剂Na₂WO₄的最佳添加量为 4 g/L。     

激光重熔处理对铝合金微弧氧化层组织及性能的影响

采用激光重熔处理改善6061铝合金微弧氧化层的耐蚀性,采用光学显微镜、共聚焦显微镜、扫描电镜、X射线衍射仪、电化学工作站等研究了500～1000 W激光功率下微弧氧化层孔隙率、粗糙度、表面形貌、物相组成及耐蚀性能。结果表明,经过激光重熔处理后微弧氧化层主要由α-Al₂O₃和γ-Al₂O₃两相组成,随着激光功率的增加,γ-Al₂O₃向α-Al₂O₃转化的程度增加。激光功率为500～900 W时微弧氧化层孔隙率先增加后减小,但粗糙度变化不明显;1000 W时微弧氧化层鼓起、开裂,粗糙度、孔隙率增加。激光功率为900 W时微弧氧化层表面微孔孔径减小甚至闭合、裂纹数量减少,孔隙率降至最低,耐蚀性能最好。     

Nb2O5/TiO2微弧氧化复合膜层微观组织和高温性能的研究

为了研究Ti6Al4V钛合金微弧氧化膜层的抗高温氧化性能,在硅酸钠电解液中添加纳米铌(Nb)颗粒制备了Nb₂O₅/TiO₂复合膜层。采用扫描电子显微镜(SEM)和X射线衍射仪(XRD)分析膜层的微观结构和相组成。结果表明：随着纳米Nb浓度增加,膜层表面微孔直径增大、数量减小,膜层中Nb元素含量逐渐增加至5at%,膜层厚度由42.28μm增加至55.48μm;膜层由锐钛矿型TiO₂、金红石型TiO₂、Al₂TiO₅、Nb₂O₅及Nb-Ti化合物组成,金红石型TiO₂峰值和Nb₂O₅峰值逐渐上升;试样增重由基体10.25 mg/cm²降低至Nb浓度为6 g/L制备膜层的2.281 mg/cm²,平均氧化速率由2.8472×10^-5 mg·cm^-2     

马氏体时效钢蒸汽氧化膜的组织与性能

马氏体时效钢的热处理是实现其优异综合力学性能的关键工序，将时效工艺中的空气替换为水蒸气，有助于形成保护性氧化膜提高其耐蚀性。对T-250(00Ni18Mo3Ti1Al)和00Ni12Cr5Mo3TiAlV两种马氏体时效钢进行高温蒸汽氧化试验，采用X射线衍射仪、扫描电子显微镜及能谱仪对氧化膜进行表征，使用拉伸法测试膜层与基体的结合性能。结果表明：两种钢的蒸汽氧化膜外层均由Fe₃O₄和少量Fe₂O₃组成。T-250钢的内氧化层为连续的Fe₃O₄层和少量楔入基体的非连续层，Ti和Mo元素富集；00Ni12Cr5Mo3TiAlV钢的内氧化层为楔入基体的(Fe, Cr)₃O₄非连续层，不含连续层，这种结构特征使其蒸汽氧化膜与基体的结合性能优于T-250钢。     

添加剂C6H12N4对6063铝合金微弧氧化黑色陶瓷膜结构与性能的影响

用硅酸盐-磷酸盐的复合溶液体系对6063铝合金进行微弧氧化,获得颜色均匀的黑色陶瓷膜。研究了添加剂(C₆H₁₂N₄)对膜层的表面形貌、成分、组织结构、黑度、附着力、粗糙度和耐蚀性的影响。结果表明,添加剂使微弧氧化膜层黑度增加,膜层均匀性和附着力显著提高,粗糙度降低,但膜层的相组成不变,均为γ-Al₂O₃和Al₈₆V₁₄。含添加剂的体系获得的微弧氧化膜层在3.5% NaCl溶液中的腐蚀电流密度相比无添加剂的体系获得的黑色膜层有很大程度的降低。     

6061-7075异种铝合金搅拌摩擦焊接件表面整体陶瓷防护膜的制备

通过微弧氧化处理,使6061与7075铝合金的搅拌摩擦焊接件(连接件)被一层陶瓷膜整体包裹,通过扫描电镜(SEM)、能谱(EDS)、X射线衍射(XRD)和电化学工作站等分析了母材和焊缝区表面膜层的形貌和成分,并基于检测结果推导了整体陶瓷膜的生长机制。结果表明：整体微弧氧化后,连接件表面的膜层是致密的;6061和7075表面膜主要成分为α-Al₂O₃、γ-Al₂O₃和少量的Al₂SiO₅,而焊缝区则主要由α-Al₂O₃和γ-Al₂O₃组成;微弧氧化降低了连接件不同区域间的腐蚀电位差,显著提高了连接件整体的耐蚀性。     

电解液浓度对镁合金微弧氧化层耐蚀性与溶血率的影响

在电解液中加入 (NaPO₃)₆并在镁合金表面制备微弧氧化层,研究 (NaPO₃)₆浓度对镁合金微弧氧化层的影响.结果显示,微弧氧化层中含有MgO,Mg₂SiO₄,Mg₃(PO₄)₂等物质;随 (NaPO₃)₆浓度增加,微弧氧化层厚度增加,表面微孔孔径变大,当 (NaPO₃)₆浓度达到7 g/L时,微弧氧化层截面出现较明显的微裂纹;微弧氧化处理后的镁合金的耐蚀性明显高于基体的.当 (NaPO₃)₆浓度为5 g/L时其耐蚀性最佳;镁合金基体溶血率为72.3%,在不同浓度 (NaPO₃)₆下微弧氧化处理的镁合金溶血率均在1%~2.5%之间,溶血作用消除.     

NaOH对铝合金微弧氧化膜特性的影响

在Na₂SiO₃电解液体系下,对ZAlSi12Cu2Mg1微弧氧化膜的形成进行研究,通过改变NaOH的含量,研究了其对电解液的电导率、微弧氧化的临界起弧电压、膜层特性及微观形貌的影响。并测定了氧化膜的相组成。结果表明：NaOH含量从1.0 g/L到3.0 g/L变化时,电解液的电导率由14.00 ms/cm几乎呈线性增大到26.28 ms/cm,正向临界起弧电压由360 V呈线性降低下降到290 V;含量从1.0 g/L增大到2.5 g/L时,膜厚从92 μm迅速增加到125 μm。含量超过2.5 g/L,膜厚减小,致密层所占比例下降。XRD分析表明：氧化膜层中主要由莫来石、SiO₂和α-Al₂O₃、γ-Al₂O₃和WO₃相。     

Devitrification of Al-Ce Amorphous Ribbon Investigated Using In situ High Energy X-ray Diffraction

Metastable phases formed during vitrification or devitrification open an avenue to study the intrinsic structural hierarchy in amorphous materials. The phase transformation sequence of Al89Ce11 amorphous ribbon was investigated using differential scanning calorimetry, in situ high energy X-ray diffraction (HEXRD) and ex situ high-resolution scanning transmission electron microscope. The results reveal the devitrification pathway following the reaction: amorphous → ε-Al₆₀Ce₁₁ +  fcc-Al → η-Al₄₁Ce₅ +  fcc-Al → Al₁₁Ce₃ +  fcc-Al. It has been found that both ε-Al₆₀Ce₁₁ and η-Al₄₁Ce₅ metastable phases have same Ce-centered 1-6-6-6-1 motif, suggesting that the structural motif can be inherited. Formation of metastable phase with large unit cell is related to the short-range orders developed during solidification. Structural heredity provides a new method to tailor the microstructure and properties of Al-based alloys based on genetic mechanism.     

Influence of Pre-strain on the Mechanical Properties of A6111-T4P Sheet with Bake Hardening

A6111 is an aluminum alloy, which exhibits good formability and excellent bake hardening property. This study aimed to reveal the influence of strain path, pre-strain orientation(α) as well as pre-strain level on the mechanical properties of A6111-T4 P sheet under bake treatment through uniaxial tension test.(0–5)% pre-strain, 150–170 °C bake temperature and 20–30 min bake time were considered in the study by referring to the actual production process. The results show that both pre-strain level and strain path play significant roles in improving the material properties. In the condition that tensile orientation(β) parallel with pre-strain orientation(β = α), the yield strength can be remarkably improved, and much higher parameter of n in Hockett–Sherby model can be obtained than those when tensile orientation non-parallel with pre-strain orientation(α≠β). In addition, when the pre-strain level, paint bake process were settled and β = α, the curves obtained in five tension orientations are similar in the plastic deformation stage.     

Enhancing High-Temperature Strength and Thermal Stability of Al_2O_3/Al Composites by High-Temperature Pre-treatment of Ultrafine Al Powders

Amorphous Al_2 O_3-reinforced Al composite(am-Al_2 O_3/Al) compacted from ultrafine Al powders for high-temperature usages confronts with drawbacks because crystallization of am-Al_2 O_3 at high temperatures will result in serious strength loss.Aiming at this unsolved problem,in this study,high-temperature Al materials with enhanced thermal stability were developed through introducing more thermally stable nano-sized particles via high-temperature pre-treatment of ultrafine A1 powders.It was found that the pre-treatment at ≤550℃ could introduce a few Al_2 O_3 in the Al matrix and increase the strength of the composites,but the strength was still below that of am-Al_2 O_3/Al because without being pinned firmly,grain boundaries(GBs) were softened at high temperature and intergranular fracture happened.When the pre-treatment was carried out at 600℃,nitridation and oxidation processes happened simultaneously,producing large numbers of intergranular(AlN+γ-Al_2 O_3) particles.GB sliding and intergranular fracture were suppressed;therefore,higher strength than that of am-Al_2 O_3/Al was realized.Furthermore,the(AIN+γ-Al_2 O_3)/Al exhibited more superior thermal stability compared to amAl_2 O_3/Al for annealing treatment at 580℃ for 8 h.Therefore,an effective way to fabricate high-temperature Al composite with enhanced thermal stability was developed in this study.     

低合金钢在模拟酸性土壤中的耐蚀性研究

用硅藻土模拟酸性土壤,对两种接地网材料用的实验钢进行室内加速腐蚀实验。通过实验室埋片腐蚀实验、激光拉曼光谱和电化学方法研究其在模拟酸性土壤中的耐蚀性。结果表明,两者的腐蚀速率呈现先升后降的趋势;Q235钢的腐蚀失重明显大于低合金A钢的,且两者的腐蚀速率相差近一倍,腐蚀形貌由局部腐蚀逐渐发展为全面腐蚀;腐蚀产物均出现分层结构,外锈层成分大致相同,主要为α-FeOOH,Fe₃O₄,Fe₂O₃和γ-FeOOH,内锈层成分差别较大,低合金A钢中保护性锈层α-FeOOH所占比例大。Tafel极化曲线测试表明,低合金A钢的自腐蚀电位更正,腐蚀电流密度更小。     

Temperature Effect on Early Oxidation Behavior of NiCoCrAlY Coatings: Microstructure and Phase Transformation

Initial oxidation behavior of NiCoCrAlY coating prepared by arc-ion plating has been studied in air at 900, 1000 and 1100 °C. The results showed that phase transformation from transient θ-Al₂O₃ to α-Al₂O₃ was highly related to the temperature and oxidation time. The oxide scale in the initial stage was mainly composed of θ-Al₂O₃ at 900 °C. Instead, more amount of α-Al₂O₃ emerged out with increasing oxidation temperature. The elemental distribution after oxidation confirmed that faster chromium diffusion to the oxide scale played an important role in the speedy transformation from θ-Al₂O₃ to α-Al₂O₃. Y segregation at scale/coating interface resulted in less cavity formation and hence improved the oxide scale adherence.     

The Minor Precipitation at the Final Stage of U720Li Solidification

The minor precipitations caused by B and Zr which are the normal constituents of U720 Li alloy have been studied by analyzing the solidification process and the composition evolution. The present study aims to supply the elementary information about the existing form of B and Zr in the as-cast microstructure, which is helpful for the subsequent processing, such as homogenization treatment. The M_3B_2 and Ni_5Zr phases were observed in the U720 Li alloy in as-cast state, which were usually accompanying with each other together with g-Ni_3 Ti phase at the edge of eutectic(γ+γ'). Combining the DTA analysis and heating and quenching tests, the solidification sequence was determined to be the following: c matrix, eutectic(γ+γ'), g-Ni_3Ti, M_3B_2 and Ni_5Zr. The in situ composition analysis by EDS and EPMA revealed that the precipitation and microstructure were governed by the composition evolution in the liquids. The solidification of c matrix increased the Ti concentration in the residual liquids and resulted in the eutectic(γ+γ') formation; the(γ+γ') formation increased the Ti/Al radio in the liquids and the g-Ni_3Ti was formed in front of the eutectic(γ+γ'); the g-Ni_3Ti precipitation consumed up Al and Ti and increased the concentration of B, Mo and Cr, and M_3B_2 boride is formed;the previous precipitation of the phases consumed up most of the elements other than Ni and Zr, and Ni_5Zr is formed finally. The melting points are in the ranges of 1130–1140 °C for Ni_5Zr phase, 1180–1190 °C for M_3B_2 boride and1190–1200 °C for g-Ni_3Ti phase.     

Synthesis and properties of Ba3NaRu2O9−δ and Ba3(Na, R)Ru2O9−δ (R=rare earth) crystals

Crystals of Ba₃NaRu₂O_9−δ (δ≈0.5) and Ba₃(Na, R)Ru₂O_9−δ (R=Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb) were grown by an electrochemical method, and their crystallographic, magnetic, and electric properties were studied. All crystals have a hexagonal structure of space group P6₃mmc. Ba₃NaRu₂O_9−δ and Ba₃(Na, R)Ru₂O_9−δ (except Ce) have a negative asymptotic Curie temperature suggesting the existence of an antiferromagnetic order; however, they are paramagnetic at temperatures above 1.7 K. Ba₃NaRu₂O_9−δ has an effective magnetic moment P_eff of 0.91 μ_B, while P_eff of Ba₃(Na, R)Ru₂O_9−δ (except Ce) reflects the large free-ion moment of the rare earth ions. Ba₃(Na, Ce)Ru₂O_9−δ shows peculiar magnetic behavior that differs from the magnetism of other Ba₃(Na, R)Ru₂O_9−δ crystals. The resistivity of all crystals exhibits an activation-type temperature dependence with an activation energy in the range of 0.10.2 eV.     

Friction characteristic of micro-arc oxidative Al2O3 coatings sliding against Si3N4 balls in various environments

The alumina ceramic coatings were prepared on 2024Al alloy by micro-arc oxidation (MAO) technique. The phase structure of the MAO Al₂O₃ coating was determined using X-ray diffraction. The thickness and micro-hardness of the MAO Al₂O₃ coatings was measured using eddy current thickness equipment and micro-hardness tester. The friction property of MAO Al₂O₃ coatings sliding against Si₃N₄ ceramic balls were investigated in air, water and oil by a ball-on-disk tribo-meter, and the worn surfaces of the MAO Al₂O₃ coatings were observed using scanning electron microscope (SEM). The results showed that the MAO Al₂O₃ coatings mainly contained -Al₂O₃ and γ-Al₂O₃ phase. The micro-hardness of the polished MAO coatings was HV1740 ± 87. With an increase in normal load and sliding speed, the friction coefficient in air increased from 0.74 to 0.87, while decreased from 0.72 to 0.57 in water and 0.24 to 0.11 in oil. This indicates that the fluid lubrication could improve the friction behavior of the MAO Al₂O₃ coatings. The worn surfaces' observation indicated that the wear mechanism of the MAO Al₂O₃ coatings changed from abrasive wear in air to mix wear in water, and became microploughing wear in oil.     

Fe-EBT Chelate Complex: A Novel Mean for Growth of α-FeOOH and γ-Fe2O3 Nanostructures

Acicular goethite (α-FeOOH) and worm-like maghamite (γ-Fe₂O₃) nanostructures have been prepared adopting a novel route, using Na₂[Fe(HL)₂(H₂O)₂] chelate complex in alkaline medium. It is found that concentration of hydrated Fe(III) ions increased with increasing temperature, which later play a key role in generation of different phases of iron oxide. Phase and morphology of the products are investigated using XRD, FTIR, SEM, and TEM analysis. Using UV-Vis spectra, various electronic transitions of goethite and maghamite particles are examined. Maghamite nanostructures exhibit superparamagnetic property at room temperature. On the basis of experimental observations and analytical data, growth mechanism of the nanostructures is discussed.     

Effects of plasma-sprayed NiCrAl/ZrO2 intermediate on the combination ability of coatings

A NiCrAl/ZrO₂ composite coating was deposited on the surface of metal carrier FeCrAl alloy by a plasma-spray technique. After static-state oxidation at 800°C, the transitions in structure and composition of the coating was analyzed by XRD, SEM and EDX. The results showed that the surface phases of the as-sprayed coating were mainly composed of Ni and ZrO₂. When the oxidation time was extended from 8 to 50 h, NiO crystallites were formed and these grew coarse on the coating surface, and alloy elements were diffused between the NiCrAl/ZrO₂ coating and the FeCrAl substrate. With the pretreatment, an intermediate coating was prepared with a coarse and porous structure, high cohesive strength and high heat resistance. These developed properties could provide high geometric surface area for a catalytic γ-Al₂O₃ washcoat, and enhance the adhesive strength between ceramic washcoat and metal substrate so as to extend the lifetime of the washcoat.