高温气冷堆燃料元件基体石墨的SiC/SiO2抗氧化涂层研究

提高高温气冷堆用石墨的抗氧化性能对改进高温气冷堆的安全性具有重要意义.通过热力学分析确认了SiC/SiO2,复合涂层在高温气冷堆正常服役条件和事故条件下均能保证其长期热稳定性.结合气相反应扩散法、泥浆浸渗法和高温氧化法,在高温气冷堆燃料元件基体石墨表面制备出SiC/SiO2复合涂层;对涂覆SiC/SiO2复合涂层的高温气冷堆燃料元件基体石墨在各种氧化条件下的氧化行为进行了分析.结果表明在高温气冷堆用石墨可能遇到的多种氧化条件下,SiC/SiO2复合涂层均能够保持长期稳定并显著改善基体石墨的抗氧化性能.     

炭材料高温抗氧化莫来石/SiC复合涂层的制备及其1150℃高温抗氧化性能(英文)

采用化学气相反应及料浆刷涂烧结复合工艺在石墨表面制备高温抗氧化莫来石/SiC复合涂层。XRD物相分析结果显示涂层外层由莫来石及微量SiO2相组成,涂层内层主要由β-SiC相组成。通过高温抗氧化试验研究涂层的高温抗氧化行为并测试涂层氧化后的洛氏硬度。结果表明:所制备的莫来石/SiC复合涂层具有良好的高温抗氧化及热震性能,经过1150℃、109h的高温氧化及12次1150℃→室温的循环热震试验后,涂层试样的质量增加率为0.085%。硬度测试结果表明:所制备的莫来石/SiC复合涂层各层之间具有良好的结合性能。     

Cf/SiC复合材料SiC/Yb2SiO5抗氧化复合涂层研究

硅酸镱(Yb2SiO5)是Cf/SiC复合材料非常理想的抗氧化涂层材料.用脉冲CVD法在Cf/SiC复合材料上先制备SiC粘附层.用溶胶凝胶法制备粒径为200~300 nm的单相Yb2SiO5粉体,然后用PCS-SiC-Yb2SiO5浆料浸涂法制备SiC-Yb2SiO5过渡层,因PCS粘结强度大,且热解后能在原位生成SiC,故能大大增加涂层的结合力.配备低粘度、高固含量的Yb2SiO5浆料,并用浆料浸涂烧结法制备致密、细晶粒的Yb2SiO5涂层.1500 ℃静态空气中氧化实验表明:SiC/Yb2SiO5复合涂层具备优异的抗氧化性能.     

SiC涂层对高温气冷堆用石墨摩擦磨损性能的影响

利用MM-200磨损试验机对高温气冷堆反射层用石墨（IG11）及HTR-10高温气冷堆燃料元件基体石墨（MG）的摩擦磨损性能进行了研究。结果发现,摩擦系数随载荷增加而逐渐减小,两种石墨的摩擦系数基本相同。石墨的磨损速率随载荷增加而增大,石墨IG11的耐磨性优于MG的。利用气相反应扩散法在石墨基体上涂覆SiC涂层后可以明显改善其耐磨性,且随着涂覆温度的升高改善效果更为明显;低温涂覆SiC涂层后IG11的耐磨性优于MG的,高温涂覆SiC涂层后MG的耐磨性优于IG11的。     

SiC 涂层对不同碳基体氧化防护行为的研究

为了提高碳材料的抗氧化性能,采用料浆烧结法在石墨和C/C复合材料上制备了SiC 抗氧化涂层.测试了SiC涂层在1200℃的高温下对不同碳基体的氧化防护能力,利用扫描电子显微镜 (SEM)、X-射线衍射仪(XRD)对涂层结构进行分析.结果表明:SiC涂层对不同碳材料的抗氧化防护行为有很大差异,在1200℃的高温下SiC涂层对石墨具有较好的抗氧化性能,而对C/C复合材料的氧化防护性能较差.     

高温气冷堆包覆燃料颗粒ZrC涂层的研究进展

高温气冷堆包覆燃料颗粒关键涂层为SiC涂层,随着高温气冷堆提升功率和向超高温气冷堆发展的趋势,SiC涂层已不能满足包覆燃料颗粒性能要求.ZrC材料具有优良的组织和性能,作为一种最具潜力的包覆颗粒涂层材料,其研究和应用逐渐得到重视和发展.本文介绍了高温气冷堆包覆燃料颗粒ZrC涂层的研究背景、晶体性质、制备方法、组织结构和性能特征.指出了ZrC涂层研究中的现存问题,并预言了进一步的发展趋势.     

SiC/Si-MoSi2/MoSi2涂层的抗氧化性能

用液硅渗透和料浆烧结法在石墨基体上制备了SiC/Si-MoSi2/MoSi2抗氧化涂层,并研究了涂层的组织结构以及抗氧化性能.结果表明涂层结构由内到外依次为SiC内层、Si和MoSi2组成的中间过渡层、MoSi2外层,呈现出良好的梯度分布特征.涂层在1700℃的高温下具有极好的抗氧化性能和抗热震性能.     

炭/炭复合材料表面SiC/ZrSiO4-SiO2复合涂层的抗氧化性能与红外发射特性研究

为提高炭/炭(C/C)复合材料的高温抗氧化性能并降低其红外发射率,采用包埋–刷涂法在其表面制备了SiC/ZrSiO_4-SiO_2复合涂层。借助XRD、SEM等表征分析了涂层的成分与微观结构,并研究了SiC/ZrSiO_4-SiO_2复合涂层包覆C/C复合材料在1500℃动态空气条件下的抗氧化性能,以及在90和500℃下的红外发射率。结果表明:由疏松结构SiC内涂层和镶嵌结构ZrSiO_4-SiO_2外涂层组成的SiC/ZrSiO_4-SiO_2复合涂层具有优异的抗氧化性能,在1500℃流动空气(0.6 L/min)等温氧化条件下氧化50 h后试样的氧化失重率仅为0.03%。在C/C复合材料表面制备SiC/ZrSiO_4-SiO_2复合涂层后其红外发射率明显降低,并随温度升高而越低。复合涂层包覆试样在90℃时3~5μm和8~14μm波段的平均红外发射率分别为0.55和0.66;在500℃时3~5μm和8~14μm波段的平均红外发射率分别为0.48和0.62。SiC/ZrSiO_4-SiO_2复合涂层包覆C/C复合材料可作为优良的低红外发射率高温热结构材料应用于航空航天领域。     

C／C复合材料防氧化涂层SiC／SiC—MoSi2的制备与抗氧化性能

采用包埋法和涂刷法在C/C复合材料表面依次制备了SiC内涂层和SiC-MoSi2外涂层,借助XRD与SEM对涂层的微观结构进行了分析,研究了涂覆后的C/C复合材料在高温静态空气中的防氧化性能.结果表明:SiC/SiC-MoSi2复合涂层有效缓解了MoSi2与C/C热膨胀不匹配问题,涂层无裂纹;复合涂层在900和1500℃静态空气环境下均可对C/C复合材料有效保护100 h以上;涂层的多层、多相结构以及在高温氧化后表面生成的SiO2薄膜是其具有优异防氧化性能的原因.     

镍基合金表面二硅化钼复合涂层的制备和性能

为了改善K403镍基高温合金的高温抗氧化性能,采用大气等离子喷涂在镍基合金表面制备了4种不同结构的MoSi2复合涂层。结果表明:4种结构涂层中K403/NiCoCrAlY/ZrO2/30%(体积分数)ZrO2-MoSi2/MoSi2复合涂层的抗热震性能最好,且该涂层的界面结合强度最高(22.5 MPa)。MoSi2涂层的自身结合强度大于涂层界面结合强度,结合机理以机械咬合式为主。该复合涂层在1 200℃氧化120 h后的质量增加仅为3.42 mg/cm2,提高K403合金和传统氧化锆涂层的抗氧化性能。MoSi2复合涂层表面在高温时生成了一层致密的SiO2保护膜,阻碍了氧的扩散,减轻了过渡层NiCoCrAlY/ZrO2界面处的氧化。     

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).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

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.