火电机组过/再热器锅炉管内壁铝化物涂层研究(Ⅱ):蒸汽氧化、强度及组织演化

目的 分析表征锅炉管内壁铝化物涂层的综合性能。方法 通过动态高温蒸汽氧化实验、高温拉伸试验、高温持久试验和650 ℃/10 000 h热暴露实验,分别评价Super304H锅炉管内壁铝化物涂层的抗蒸汽氧化性能、高温强度、高温持久性能和涂层组织时效稳定性,并通过X射线仪、电子显微镜和能谱技术分析涂层结构与物相、氧化产物和断口特征。结果 采用料浆法可在Super304H锅炉管内壁制备厚度约40 μm的铝化物涂层,涂层以FeAl相为主,且与母材呈冶金结合。在650 ℃、1000 h饱和蒸汽氧化过程中,涂层表面生长极薄的α-Al2O3,氧化膜厚度小于1 μm,抗氧化能力优于表面喷丸Super304H及更高Cr含量的HR3C合金。在650 ℃高温,涂层Super304H合金的强度与断裂韧性与母材相当,持久寿命与母材持平,蠕变断裂位置未发生在涂层一侧。650 ℃长时热暴露过程中,涂层由FeAl相向Fe3Al相退化。结论 涂层制备过程未对合金母材组织有显著影响,铝化物涂层显著提高了Super304H合金650 ℃饱和蒸汽氧化性能,对合金的高温力学性能无显著影响。长时热暴露后,涂层与基体互扩散造成组织退化。     

Super304H钢表面铝扩散涂层的组织结构和抗蒸汽氧化性能

目的以Super304H钢为基体制备铝扩散涂层,提高其抗蒸汽氧化性能。方法通过料浆渗铝的方法在Super304H表面制备铝扩散涂层,采用不连续称重法对渗铝Super304H在650℃纯水蒸气中的氧化动力学进行研究,并使用X射线衍射仪、扫描电子显微镜和透射电子显微镜对铝扩散涂层以及氧化膜的物相组成和微观组织结构进行表征和分析。结果渗铝过程中,料浆层中的Al向Super304H基体内扩散,而基体中的Fe向外扩散,形成接近化学平衡配比的FeAl外层和贫Al的FeAl中间层。Al不断通过FeAl层向奥氏体(γ)基体中扩散,使得基体中Al的浓度升高,当Al的浓度增加至临界值时,导致局部区域析出NiAl,后者的形核和长大进一步加剧其周围基体中Ni的贫化。随着γ基体中Ni元素含量的持续降低及Al含量持续升高,γ基体将变得不稳定,并逐步转变为铁素体(α-Fe),最终形成由α-Fe和弥散分布其中的NiAl相组成的互扩散层。在FeAl中Cr元素和水蒸气分子的共同作用下,铝扩散涂层在650℃纯水蒸气中形成连续致密且与基体结合紧密的α-Al_2O_3膜,显著地降低了Super304H的氧化速率。结论采用料浆渗铝法,可在Super304H钢表面制备出三层结构的铝扩散涂层,由外到内依次为FeAl外层、贫Al的FeAl中间层、由α-Fe和弥散分布其中的NiAl组成的互扩散层。这种结构的铝扩散涂层在650℃纯水蒸气中可形成α-Al_2O_3膜,降低Super304H的氧化速率,提高其抗蒸汽氧化性能。     

CVD法制备铝化物涂层组织结构的温度依赖效应

铝化物涂层制备技术由于非视线性沉积优势广泛应用于燃气轮机关键热端部件上,可在部件外表面以及内腔表面制备抗氧化耐腐蚀铝化物涂层。涂层的组织结构是影响其服役性能的关键,然而如何调控铝化物涂层的组织结构从而获得理想性能的涂层是目前研究的难点问题。针对这一问题,研究了关键制备参数温度对铝化物涂层组织结构的影响作用。首先,采用化学气相沉积方法(CVD)在Mar-M247镍基高温合金表面制备了不同沉积温度下的铝化物涂层。然后,采用扫描电子显微镜(SEM)、X射线衍射仪(XRD)以及能谱分析仪(EDS)分析了铝化物涂层的显微组织结构、物相组成以及合金元素在涂层中的分布情况。结果表明,不同沉积温度下所得到的铝化物涂层均为双层结构,外层是富含Al元素的β-NiAl层,内层为富含拓扑密排相(TCP)的互扩散层;随着沉积温度的升高,β-NiAl层与互扩散层的厚度逐渐增加,两者与温度之间具有正相关关系。本研究揭示的温度参数对铝化物涂层组织结构的作用规律可为高性能CVD法铝化物涂层的制备提供参考。     

T92钢表面铝化物涂层的组织演化

在高温下长时间暴露,钢材表面的渗铝层与母材之间容易发生元素互扩散,对母材组织产生影响,影响母材的力学性能。为研究超超临界机组用T92钢表面铝化物涂层的抗蒸汽氧化性能及组织演化特性,采用低温粉末包埋渗铝法在T92钢锅炉管内壁制备铝化物涂层,并在650℃饱和蒸汽环境中进行热暴露试验,结合扫描电镜（SEM）、透射电镜（TEM）观察及X射线衍射分析,研究铝化物涂层的氧化行为以及T92基体与铝化物涂层之间的扩散退化行为。研究结果表明：低温粉末包埋渗铝可在T92锅炉管内壁制备厚度约30.4μm的双层结构铝化物涂层,各层结构连续均匀且组织稳定,与母材呈冶金结合。在650℃、3 000 h饱和蒸汽氧化过程中,涂层表面生长厚度约0.3μm的α-Al2O3氧化膜。650℃长时热暴露过程中,Fe-Al金属间化合物始终是涂层的主要物相,但涂层由FeAl相向FeAl2相退化。铝化物涂层经长时间热暴露后组织退化,但仍具有优异的抗氧化性能,能够对T92钢提供很好的保护。     

模拟高温海洋环境中铝化物/搪瓷复合涂层腐蚀行为研究

对镍基高温合金GH4169基体先采用包埋渗铝工艺制备铝化物涂层,随后在渗铝涂层表面喷烧搪瓷涂层,得到了渗铝+搪瓷复合涂层.该涂层外层由搪瓷涂层组成,厚度约为40 μm;中间层为渗铝涂层,厚度约20μm,主要为Ni2Al3相,搪瓷涂层和渗铝涂层结合良好;内层为互扩散区,厚度约为3μm.分别考察了搪瓷+渗铝复合涂层、渗铝涂...     

镍基高温合金上Co改性铝化物涂层的组织结构与耐蚀性能

为研究Co改性铝化物涂层在室温环境中的耐蚀性,利用包埋法渗Co和气相沉积渗Al(两步法)制备出两种不同Co含量的Co改性铝化物涂层,采用XRD、SEM、EDS分析涂层的组织结构。结果表明:850℃和1 000℃渗Co涂层外层和内层均为γ-(Ni,Co)相,内层有氮化物/碳化物相析出。Co改性铝化物涂层与简单NiAl涂层结构一致,外层为β-(Co,Ni)Al相,内层为互扩散区含有大量的富Cr(W)相。简单NiAl涂层的自腐蚀电流为0.04μA/cm2,约为Co改性铝化物涂层的十分之一。这说明在涂层中添加Co降低涂层的耐蚀性,一方面因为Co的腐蚀电位(-0.28V)低于Ni的腐蚀电位(-0.25V),另一方面因为渗Co过程中产生的夹杂物与涂层电位不一致,容易成为微阴极区,加速涂层的腐蚀。     

K465高温合金铝化物涂层Ni/Al互扩散系数计算

根据铝化物涂层形成过程中Al原子浓度分布，采用有限差分法反求铝化物外层Ni／Al互扩散系数．结果表明：相同温度下，铝化物外层Ni／Al互扩散系数随Al原子浓度增加而增大，表现出与Al浓度相关性；合金表面渗铝外层Ni／Al互扩散系数明显小于纯Ni表面渗铝外层Ni／Al互扩散系数．     

双丝电弧喷涂Ni-Al复合涂层热处理组织及性能

采用双丝电弧喷涂在6061-T6铝合金基体上制备Ni-5Al（质量分数,%）为底层,Ni-20Al（质量分数,%）为面层的Ni-Al复合涂层。Ni-Al涂层经400-550℃/4-48 h热处理后,采用SEM,XRD,EDS和TEM对涂层的显微结构进行了表征,并分析了不同热处理工艺对Ni-Al涂层显微组织和相结构的影响,讨论了涂层与铝合金基体界面反应机理,以及基体和涂层之间的界面元素扩散行为。结果表明,热处理后的涂层相组成变化较小,涂层/基体界面发生扩散,形成金属间化合物NiAl3。随着热处理温度升高和时间的延长,在NiAl3相和涂层之间形成Ni2Al3相,同时界面扩散区逐渐增厚,该过程由铝原子的扩散所控制。热处理后的TEM分析表明,涂层中存在NiAl3、Ni2Al3及Ni的退火孪晶相。Ni-Al涂层随着热处理温度升高和时间的延长,涂层与基体的结合强度略有升高,同时涂层具有较强的抗氧化性能。     

镍基高温合金Al-Cr涂层的恒温氧化行为

采用电弧离子镀沉积Cr和粉末包埋法渗Al的联合工艺制备了Al-Cr涂层,并利用粉末包埋法制备了渗Al涂层,分析了2种涂层的组织结构和成分,研究了镍基高温合金DSM11基体、渗Al涂层和Al-Cr涂层在1000和1100℃下的恒温氧化行为.结果表明:渗Al涂层和Al-Cr涂层组织致密,与基体结合良好且成分分布均匀.2种涂层都明显分为2个区域:外层和互扩散区.渗Al涂层外层由b-NiAl相和Ni2Al3相组成,Al-Cr涂层外层由b-NiAl相、Ni2Al3相、a-Cr相和AlCr2相组成.AlCr涂层可以显著改善基体合金的抗氧化性能,且明显优于渗Al涂层.Al-Cr涂层优良的抗氧化性能源于在氧化过程中出现了Cr(W)析出带,能够一定程度阻碍涂层中的Al元素向基体扩散,降低了涂层退化速度,而Cr的存在可以促进Al的选择性氧化,提高涂层的自修复能力.     

硅改性铝化物涂层的CVD制备工艺

研究了CVD法制备硅改性铝化物涂层工艺。结果表明,采用先渗硅后渗铝的两步法工艺可在Inconel 718表面获得铝-硅涂层。铝-硅涂层分为明显的两层结构,内层富硅,外层富铝。硅的加入阻碍高温条件下Al原子的内扩散,并促进了试样表面Al2O3膜的生成。铝-硅涂层具有比单一的铝化物涂层更为优秀的耐高温氧化性能。     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.     

Theoretical Analysis for the Motion and Temperature of Melt Droplets in Spray Degassing Process

The motion of melt droplets in spray degassing process was analyzed theoretically. The height of the treatment tank in spray degassing process could be determined by the results of theoretical calculation of motion of melt droplets. To know whether the melt droplets would solidify during spraying process, the balance temperature of melt droplets was also theoretically analyzed. Then proof experiments for theoretical results about temperature of melt droplets were carried. In comparison, the experimental results were nearly similar to the calculation results.