坯料温度对AZ31镁合金反挤成形的影响

在300～400℃温度范围内,挤压比λ=5的条件下,对铸造态AZ31镁合金的反挤压成形进行了实验研究,分析了挤压变形力、挤压成形性以及组织性能的变化规律.实验结果表明:AZ31镁合金在300～400℃范围内反挤成形,随变形温度的升高,挤压变形力呈现下降的趋势;而△T(坯料温度的不均匀度)的增大,使得挤压件表面质量变差,外表面出现垂直于挤压方向的横向裂纹;随变形温度的降低,挤压件晶粒逐步细化,硬度上升.为AZ31镁合金反挤压变形温度的优化提供了基础.     

AZ31和稀土镁合金微弧氧化膜的对比研究

在相同的工艺参数下制备了AZ31和Mg 10Gd 2Y-0.4Zr稀土镁合金微弧氧化膜层.利用SEM、XRD和EDS对两种陶瓷膜层的组成、微观形貌和元素组成进行了表征;通过电化学测试和盐雾试验评价了两种陶瓷膜层的耐蚀性能;利用显微硬度仪研究了两种陶瓷膜的显微硬度.结果表明:两种陶瓷层的厚度、表面形貌和致密性相似;陶瓷膜由MgO和Mg2SiO4组成,其中MgO为主晶相;与AZ31镁合金陶瓷膜相比,稀土镁合金陶瓷膜中的MgO含量增多,Mg2SiO4含量减少;两种镁合金表面陶瓷化后的耐蚀性和硬度大大提高,AZ31镁合金陶瓷膜耐蚀性优于稀土镁合金陶瓷膜,稀土镁合金陶瓷膜的硬度高于AZ31镁合金陶瓷膜.     

磷酸盐对钛合金微等离子体氧化陶瓷膜结构和耐蚀性的影响

研究了3种磷酸盐分别作为电解质交流微等离子体氧化TC4钛合金所制得的陶瓷膜的耐蚀性,其中3号磷酸盐的效果最好.并在铝酸钠体系和硅酸钠体系下,进一步研究了3号磷酸盐对微等离子体氧化陶瓷膜的结构、形貌、成分和耐蚀性能的影响:磷在陶瓷膜中不形成晶相,而是以非晶相物质沉积在膜层中;铝酸钠体系,磷元素由膜内层向外层逐渐减少;硅酸钠体系,磷元素在膜内、外两层含量高,中间处含量低;两体系下,3号磷酸盐的用量适当增加,陶瓷膜耐点蚀性提高.     

Structure,optical properties and thermal stability of Al2O3-WC nanocomposite ceramic spectrally selective solar absorbers

Traditional metal-dielectric composite coating has found important application in spectrally selective solar absorbers. However, fine metal particles can easily diffuse, congregate, or be oxidized at high temperature, which causes deterioration in the optical properties. In this work, we report a new spectrally selective solar absorber coating, composed of low Al₂O₃ ceramic volume fraction (Al₂O₃(L)-WC) layer, high Al₂O₃ ceramic volume fraction (Al₂O₃(H)-WC layer) and Al₂O₃ antireflection layer. The features of our work are: 1) compared with the metal-dielectric composites concept, Al₂O₃-WC nanocomposite ceramic successfully achieves the all-ceramic concept, which exhibits a high solar absorptance of 0.94 and a low thermal emittance of 0.08, 2) Al₂O₃ and WC act as filler material and host material, respectively, which are different from traditional concept, 3) Al₂O₃-WC nanocomposite ceramic solar absorber coating exhibits good thermal stability at 600 °C. In addition, the solar absorber coating is successfully modelled by a commercial optical simulation programme, the result of which agrees with the experimental results.     

Effect of Ni on the structural, optical, thermal and dielectric properties of ADP single crystals

The effects of the addition of Ni²⁺ on the growth and various properties of ammonium dihydrogen phosphate single crystals grown from aqueous solution by the slow evaporation method have been studied. The grown crystals were subjected to HRXRD, UV-Vis, TG/DTA and dielectric studies. The structural perfection of the grown crystal has been analyzed by high resolution X-ray diffraction rocking curve measurements. UV-Vis studies show that the grown crystal has good transparency in the entire visible region which is an essential requirement for a nonlinear crystal. Higher decomposition temperature was observed from TG/DTA. Dielectric constant and dielectric loss were measured for the grown crystal for different frequencies and temperatures.     

AZ31镁合金环境友好阳极氧化处理研究

通过正交试验得到AZ31镁合金无铬、无强氧化物的阳极氧化处理配方及工艺,运用扫描电子显微镜、X射线衍射分析及电化学测试系统对阳极氧化膜的组织结构与耐蚀性进行了表征。结果表明,该环境友好阳极氧化工艺可在AZ31镁合金表面形成具有一定耐蚀性的阳极氧化膜;所得阳极氧化膜表面质量好,是一种多孔的陶瓷膜,膜的物相主要是晶态的MgO、ZnO、Mg以及非晶态的MgAl2O4、Mg18Al23等;阳极氧化处理试样的自腐蚀电流密度减小,而腐蚀电位有所提高,说明镁合金表面形成的阳极氧化膜提高了镁合金表面的耐腐蚀性能。     

电解液组成对AZ91D镁合金微弧氧化的影响

在含有NaAlO2、KF的电解质溶液中,采用恒电流方式对AZ91D镁合金进行微弧氧化获得陶瓷膜.研究了电解液组分及浓度对陶瓷氧化膜厚度及表面形貌的影响,同时,采用动电位极化曲线及电化学交流阻抗评价了陶瓷氧化膜的耐蚀性.研究发现:NaAlO2单独存在时即可产生火花放电现象,但得到的氧化膜较薄;氟化钾的加入可以显著增加氧化膜厚度,膜厚的增长速度与氟化钾的加入量呈线性关系.SEM表面形貌分析表明:电解质浓度较低时产生的氧化膜宏观上较粗糙、微观上颗粒结合紧密;高浓度时得到的氧化膜宏观上细致光滑,微观上存在明显的孔洞和放电隧道,呈熔融状态结合在一起.动电位极化曲线及电化学交流阻抗的测试一致表明,经微弧氧化处理后的镁合金耐蚀性显著提高.     

Electrical and optical properties of copper-complexes thin films grown by the vacuum thermal evaporation technique

In this work, the synthesis and characterization of molecular materials formed from K₂[Cu(C₂O₄)₂], 1,8-dihydroxyanthraquinone and its potassium salt are reported. These complexes have been used to prepare thin films by vacuum thermal evaporation. The synthesized materials were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), fast atomic bombardment (FAB+) mass and ultraviolet–visible (UV–vis) spectroscopy. Electrical transport properties were studied by dc conductivity measurements. The electrical activation energies of the complexes, which were in the range of 0.36–0.65 eV, were calculated from their Arrhenius plots. Optical absorption studies in the 100–1100 nm wavelength range at room temperature showed thin films' optical band gaps in the 2.3–3.9 eV range for direct transitions. On the other hand, strong visible photoluminescence (PL) at room temperature was noticed from the thermally-evaporated thin solid films. The PL of all investigated samples were observed with the naked eye in a bright background. The PL and absorption spectra of the investigated compounds are strongly influenced by the molecular structure and nature of the organic ligand.     

热处理对AZ31B镁合金轧板组织和性能的影响

研究了AZ31B镁合金轧板经不同温度、时间退火后的组织和性能及其再结晶行为。结果表明,热轧板材在退火过程中主要发生再结晶;退火后,强度略有下降,但伸长率明显提高;在523K下退火,保温60min,可获得平均晶粒直径为10μm的细晶组织,其抗拉强度为258MPa,断裂伸长率为22.3%,综合性能较好。热轧态板材呈脆性准解理断裂,退火后转变为韧性断裂。     

表面粗糙度对PS-PVD YSZ陶瓷层性能的影响EI北大核心CSCD

采用PS-PVD工艺在预制有NiCoCrAlYTa黏结层的K417G高温合金上制备YSZ陶瓷层;采用万能拉伸试验机、粒子冲刷仪、静态氧化炉等设备测试PS-PVD YSZ陶瓷涂层的结合强度、抗粒子冲刷和抗高温氧化性能;采用SEM和EDS分析涂层表面、截面形貌和元素分布等。结果表明:表面粗糙度对YSZ陶瓷层拉伸结合强度、抗粒子冲刷和抗高温氧化性能的影响很大。随着粗糙度的增大,结合强度先增大而后减小。Ra=0.40μm表面上沉积的YSZ涂层,其结合强度最高,达到23.5 MPa。拉伸断裂发生在涂层内部,并距离黏结层40~70μm的位置。随着表面粗糙度的增大,冲刷速率先减小而后增大,Ra=0.40μm涂层的抗粒子冲刷性能最好,冲刷速率仅为2.8×10^-3 g/g,表面起伏小和孔隙率低是涂层具有良好抗粒子冲刷性能的重要原因。不同表面粗糙度制备的YSZ涂层均能生成致密连续的热生长氧化物(TGO)层。粗糙度大则生长的TGO起伏大,更容易导致局部增厚和应力集中而失效。     

添加剂对镁合金微弧氧化膜性能的影响

在偏铝酸盐一六偏磷酸盐体系中对镁合金进行微弧氧化处理,研究了金属盐缓蚀剂钨酸盐、多元醇或酸等添加剂对氧化膜性能的影响.通过正交实验优化和对微弧氧化膜结构,成分及性能的测试评价,得到了性能较好的微弧氧化电解液配方.SEM检测发现,复合添加剂(NaaEDTAlg/L,CH3(CH2)11SO3Na0.5g/L)通过抑制破坏性的微弧,能促进成膜、降低起弧电压,得到结构更加均匀和完整的陶瓷涂层;XRD检测表明,膜层的主要成分是MgO、Mg3(PO4)2,MgAl2O4和AlPO4等化合物;中性盐水腐蚀测试表明,陶瓷膜在48 h内具有较平缓的腐蚀速度;EIS和动电位极化曲线表明,在电解液中加入复合添加剂使镁合金试样微弧氧化膜的耐腐蚀性能得到了很大的提高.     

微弧氧化时间对AZ61镁合金陶瓷膜形貌及性能的影响

用现有的微弧氧化方法制备的镁合金陶瓷膜厚度有限,且属于多孔结构。采用电流密度0.4 A/dm2,在AZ61镁合金表面制备了陶瓷膜;研究了不同微弧氧化时间(30,50,70,90,120,160 m in)对陶瓷膜微观性能的影响。结果表明:在电流密度一定的条件下,处理时间对陶瓷膜微观组织和性能有着较大的影响,随氧化时间延长,阳极电压、陶瓷膜厚度和粗糙度增大;孔隙率先增大后减小,最大值出现在70 m in时,陶瓷膜表面熔融物颗粒和孔隙尺寸增大且分布不均;50 m in时陶瓷膜耐蚀性最好。     

Effects of tool rotational and welding speed on microstructure and mechanical properties of bobbin-tool friction-stir welded Mg AZ31

The effects of rotational and welding speeds on the microstructure and mechanical properties of bobbin-tool friction stir welded (BT-FSW) Mg AZ31 were investigated. The results indicated that the thermo-mechanically affected zone (TMAZ) consisted of equiaxed grains, which were inconsistent with the deformed, rotated and elongated grains found in the TMAZs of bobbin-tool friction stir welded Al alloys and friction stir welded Al and Mg alloys. The average grain size increased as the ratio of the rotational speed to welding speed increased. Excellent welds with no degradation in hardness were produced using a low heat input. Mechanical tests revealed that the ultimate tensile strengths gradually increased with increasing welding speed while keeping the rotational speed constant. The rotational and welding speeds had only slight influences on the yield stress and fracture elongation.     

高温氧化对钛合金微弧氧化陶瓷膜组成与结构的影响

针对钛合金不耐高温氧化的问题,在铝酸钠电解液体系中,利用双相脉冲直流微弧氧化技术,在TC4钛合金表面原位生长以Al2TiO5为主晶相的复合氧化物陶瓷膜,研究了1000℃高温氧化对陶瓷膜试样的相组成、结构的影响及膜层增重特点.研究表明,陶瓷膜层试样的高温氧化过程包括Al2TiO5分解、基体氧化和膜层表面形貌变化3个方面.高温氧化后,膜层的主晶相由Al2TiO5变为α-Al2O3和金红石型TiO2,同时,膜层的表面形貌发生显著的变化;由于膜层和基体的热膨胀系数不同和基体钛的氧化,使得高温氧化后膜层在冷却过程中表面出现裂纹和脱壳.陶瓷膜层极大地减少了TC4钛合金在1000℃高温氧化时的增重,因此,陶瓷膜层可用于TC4钛合金的恒温氧化防护.     

Effect of Deformation Temperature on Microstructure and Mechanical Properties of AZ31 Mg Alloy Processed by Differential-Speed Rolling

A differential-speed rolling(DSR) was applied to AZ31 magnesium alloy sample at different rolling temperatures of 473,523,573,and 623 K with 1-pass and 2-pass operations.The microstructural evolution and mechanical properties of the deformed samples were investigated.The rolling temperature was found to be an important parameter affecting the microstructural development.After DSR at 473 K,the microstructure was more homogeneous than that obtained after deformation by equal-speed rolling(ESR).The fully recrystallized microstructures were generated after DSR at 573 and 623 K.As to mechanical properties,the yield strength(YS) and ultimate tensile strength(UTS) decreased monotonously with increasing rolling temperature.In contrast,the elongation of the DSR-deformed samples was improved as the rolling temperature increased.The strain hardening exponent(n) calculated by Hollomon equation increased with increasing the rolling temperature,which would explain an increase in the uniform elongation.     

AZ31镁合金微弧氧化陶瓷层表面Mg(OH)2膜层的制备及耐蚀性

采用不同浓度的NaOH溶液对AZ31镁合金微弧氧化(Micro-arc oxidation, MAO)陶瓷层进行水热处理, 研究了水热溶液浓度对MAO陶瓷层组织结构及耐蚀性能的影响, 探讨了水热成膜及膜层的腐蚀机理。研究结果表明：水热处理过程中MAO陶瓷层表面的MgO部分溶解, 释放出的Mg ²⁺与水热溶液中的OH ^-结合形成Mg(OH)₂纳米片沉淀在陶瓷层表面及孔洞内。随着水热溶液中NaOH浓度的增加, 水热处理过程中形成的Mg(OH)₂将MAO陶瓷层表面的孔洞及裂纹等固有缺陷闭合, 提高了膜层的致密性。电化学实验结果表明, MAO及水热复合处理所制备的Mg(OH)₂/MAO复合膜层比单一MAO陶瓷层具有更好的耐蚀性, 而且随着NaOH浓度的提高, Mg(OH)₂/MAO复合膜层的耐蚀性增强; 浸泡实验结果表明Mg(OH)₂/MAO复合膜层能为镁合金基体提供长久的腐蚀防护保护能力。     

等径角挤压对AZ31镁合金组织及力学性能的影响

研究了电磁连铸AZ31镁合金沿A路径经常规等径角挤压(ECAE)和两步ECAE变形后的微观组织与力学性能.结果表明:与预挤压态相比,常规ECAE态合金随着挤压道次的增加,晶粒不断细化,伸长率不断提高,但屈服强度与抗拉强度逐渐降低;两步ECAE可以使晶粒进一步细化,伸长率、屈服强度与抗拉强度均提高.伸长率、屈服强度与抗拉...     

Influence of thermal annealing on electrical and optical properties of Ga-doped ZnO thin films

Influence of thermal annealing on electrical properties of GZO films has been studied by means of Hall effect measurements and optical characterization based on Drude model analysis for transmission and reflection spectra. Electrical resistivity increased with increasing annealing temperature. Changes of electrical properties were compared between air and N₂ gas atmosphere. Thermal stability in the air was worse compared to the N₂ gas atmosphere. Annealing at rather high temperature caused decrease in the Hall mobility and increase in optical mobility. The difference between the Hall mobility and the optical mobility was attributed to carrier scattering at grain boundaries. Three kinds of deposition method, ion plating using DC arc discharge, DC magnetron sputtering, and RF power superimposed DC magnetron sputtering were compared in terms of the thermal stability.     

Effects of heat treatment on adhesion strength of thermal barrier coating systems

Thermal barrier coatings (TBCs) are widely used as protective and insulative coatings on hot section components of gas turbines and their applications, like blades and combustion chambers. The quality and performance properties of TBCs are of great importance in terms of their resistance to service conditions. In a TBC system, there is a close relationship between the adhesion properties of coating layers. The adhesion strength of TBCs varies depending on the coating technique used and the surface treatments. In this study, CoNiCrAlY and YSZ (ZrO₂ + Y₂O₃) powders were deposited on stainless steel substrate. High Velocity Oxy-Fuel (HVOF) and Atmospheric Plasma Spraying (APS) techniques were used to produce the bond coats. The ceramic top layers on CoNiCrAlY bond coats were produced by the APS technique. The TBC specimens were subjected to heat-treatment tests. Adhesion strength for top coat/bond coat interface of as-sprayed and heat-treated samples was investigated. The results showed that the heat treatment of the coatings in different temperatures led to an increase in the adhesion strength of TBCs.