泡沫钛制备及力学性能评价研究

利用占位体烧结法在不同的占位体粒径、体积分数以及不同的烧结温度、时间条件下制备出泡沫钛。采用光学金相、扫描电镜等对泡沫钛的孔隙结构进行分析;通过室温压缩实验对泡沫钛的力学性能进行评价。结果表明,泡沫钛孔隙横截面呈圆形,纵截面呈椭圆形,其孔隙率与占位体体积分数的差值随占位体粒径、体积分数的增加、烧结温度的升高、时间的延长呈升高的变化趋势。同时,烧结温度越高,所制备的泡沫钛孔壁越致密。与传统的泡沫材料不同,泡沫钛应力-应变关系曲线并没有出现明显的应力平台,抗压缩强度和弹性模量随孔隙率的增加呈下降的变化趋势,当孔隙率为67.6%时,抗压缩强度和弹性模量分别达到14.4 MPa和1.17 GPa。抗压缩强度随孔径的增大呈先升高再降低的变化趋势,而弹性模量随孔径的增加基本不变,当孔径达到1.15～1.53 mm时,其抗压缩强度和弹性模量分别达到48.9 MPa和1.72 GPa。     

碳化硅晶须制备微孔陶瓷

介绍一种制备碳化硅微孔陶瓷的新方法。以碳化硅晶须为主要原料,不添加任何造孔剂,采用传统的烧结工艺,在1700℃下制备出孔隙率高于56%、平均孔径为3.8?m、弯曲强度为158 MPa的碳化硅微孔陶瓷,并研究了制备工艺对制品性能的影响。研究结果表明微孔的形成机理主要是晶须之间的架桥作用;通过调节碳化硅晶须的长径比、烧结助剂用量、烧结温度等条件,可以有效地控制微孔陶瓷孔隙率的高低、孔径的大小及其力学性能。     

十六烷基硫酸钠制备Al_2O_3泡沫陶瓷及性能研究

首次以长链表面活性剂十六烷基硫酸钠对氧化铝陶瓷粉体进行修饰,用固相含量(质量分数)为8%~40%的浆料经搅拌发泡制备了颗粒稳定泡沫,常温常压干燥后在1550℃下烧结2 h,得到容重76~355 kg/m~3(气孔率91.1%~98.1%)的轻质氧化铝泡沫陶瓷。研究了p H、十六烷基硫酸钠浓度及浆料固相含量对氧化铝泡沫浆料稳定性以及泡沫陶瓷性能的影响。通过加入质量分数0.2%~1.0%PVA制备稳定泡沫浆料同时有效地提高了干燥泡沫坯体的强度。     

泡沫铝的新型渗流法制备及其压缩性能

在热传计算的基础上,采用锌粒子为前驱体、铝熔体为渗流体,通过氩气渗流制备通孔泡沫铝;对泡沫铝的制备、压缩性能及锌残余量进行研究。结果表明:滑石粉隔热层厚度与渗流时间之间的关系为x2=7.35×10-8τ;优化的渗流工艺如下:渗流温度740℃、锌粒子预热温度220℃、锌粒子直径3 mm;平均孔径为3 mm的泡沫铝的屈服强度随孔隙率的增加而减小;孔隙率为63%和67%的泡沫铝的屈服强度都随孔径的增大而提高;泡沫铝孔隙率从60%提高到71%,锌残余量从11.3%降低到4.5%。     

植物种子模板法制备Al_2O_3泡沫陶瓷的研究

将小米种子排列成模板,通过在模板内对Al2O3浆料进行离心成形来制备孔径均匀的Al2O3泡沫陶瓷。观察了浆料固相含量对Al2O3生坯密度均匀性的影响,研究了植物种子特性对Al2O3生坯干燥和焙烧行为的影响,测量烧结产物的密度、收缩率、孔隙率和压缩强度,并通过体式显微镜和扫描电镜观察Al2O3泡沫陶瓷的宏观结构和显微组织。研究结果表明,小米和Al2O3生坯具有较好的收缩匹配性,干燥后可以保持生坯形状完整。在较高的固相含量(50%,体积分数)下,离心时的物质分离现象被抑制,孔壁具有较高的生坯相对密度(63.8%)。1500℃烧结2h后,Al2O3泡沫陶瓷具有致密的孔壁和较高的烧结相对密度(98.9%),其孔隙度为66.5%,抗压强度为5.26MPa。     

盐球渗透铸造法制备开孔泡沫铝的孔结构及压缩性能

使用圆盘造粒机制备近球形的NaCl颗粒,并将其用于渗透铸造制备开孔泡沫铝。盐球的平均抗压缩强度为3.9 MPa,在超声波清洗机中可在5 min内完全塌陷。通过控制热压烧结时间为0.5～2 h,热压温度700℃,可制备堆积密度在0.66～0.83 g/cm³的预制体。延长热压烧结时间会使开孔泡沫铝的孔径从0.48 mm增加到1.16 mm,孔隙率从64%增加到82%。压缩实验结果表明,不同孔隙结构下泡沫体的宏观变形特征基本相同,均表现出逐层塌陷的变形特征。此外,泡沫铝的致密化应变值、弹性模量、平台屈服应力和能量吸收能力均随着孔隙率的增加而降低。当孔隙率为64%时,能量吸收能力最大(15.0 MJ·m^-3)。     

浆料固含量和颗粒配比对重结晶烧结SiC的影响

重结晶烧结Si C(RSi C)晶界纯净,无第二相,气孔大多为开孔,是理想双连续相复合材料的陶瓷相,获得不同孔隙率性能优良的Si C陶瓷是制备双连续相复合材料的关键。以粒径为140和5μm的Si C为原料,调节粗细颗粒质量比和浆料固含量制备浆料并进行注浆成型,在2350℃条件下烧结后获得RSi C陶瓷材料。研究粗细颗粒质量比和浆料固含量对RSi C陶瓷材料孔隙率以及力学性能的影响。研究发现,随着粗颗粒的增多,孔隙率增加,压缩强度和抗弯强度下降;随着浆料固含量的增大,RSi C陶瓷材料的孔隙率下降,压缩强度和抗弯强度提高。通过调节工艺参数,可获得孔隙率不同的RSi C陶瓷材料,孔隙率最低为16%,最高为37.5%。     

造孔剂添加量对凝胶注模成型工艺制备8YSZ多孔陶瓷性能的影响

采用叔丁醇基凝胶注模成型工艺结合添加造孔剂法制备了高固相含量的YSZ多孔陶瓷。研究了固相含量为50%(体积分数)时,不同造孔剂添加量对烧结8YSZ多孔陶瓷的孔径及其分布、气孔率、抗弯强度以及热导率的影响。研究结果显示:8YSZ多孔陶瓷的气孔分布均匀,孔径在10μm左右,孔壁致密;气孔率在22.9%～39.8%之间,且随着造孔剂添加量的增加而增加;抗弯强度随着造孔剂添加量的增加而减小,最高可达(85.24±2.31)MPa;热导率在0.735～1.108W/m·K之间,且随着造孔剂添加量的增加而降低。上述结果表明,凝胶注模工艺中同时添加造孔剂不仅可以实现高固相含量多孔陶瓷的制备,而且可以同时实现孔结构可控,最终得到兼具有高强度、高气孔率和低热导率的8YSZ多孔陶瓷。     

凝胶-发泡法制备多孔氧化铝隔热材料的研究

结合凝胶注模和发泡法制备了多孔氧化铝隔热材料,研究了发泡剂用量、固相含量和烧结温度等对氧化铝陶瓷气孔率的影响.结果表明,当发泡剂用量为1 wt％、固相含量为45vol％、烧结温度为1500℃时,可制备出总气孔率和闭气孔率高、孔径较小且分布均匀、强度高和热导率低的多孔氧化铝陶瓷.     

离心法制备氧化铝-氧化锆泡沫陶瓷过滤器

通过在发泡聚苯乙烯模板内的离心成型方法来制备Al2O3-ZrO2泡沫陶瓷过滤器,测量了浆料在不同pH值下的Zeta电位,分析了浆料的固相含量对离心时间的影响。观察了不同离心加速度和浆料固相含量下产物生坯密度的变化,测量了最终产物的烧结密度、收缩率、孔隙率和压缩强度,并通过扫描电镜观察了烧结试样的显微结构。试验结果表明,在pH=10时,浆料具有较好的分散性。在较低的固相含量和较高的离心加速度下,浆料的分离现象明显,生坯中出现密度梯度。但在高的固相含量(50%,体积分数)下,分离现象被抑制,孔筋具有较高的生坯密度(61.5%)和烧结密度(91.1%),最终产物的孔隙率在75.3%～83.1%,压缩强度为2.07～3.82 MPa。     

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.     

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.     

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.