闭孔泡沫铝的导热性能

研究了孔隙率、孔径对闭孔泡沫铝合金导热系数的影响，结果表明，由于大量孔洞的存在，泡沫铝的导热系数较同样成分的实体材料显著下降，孔隙率在0．80—0.93范围内，约为实体材料的1／30—1／80，随着孔隙率的增加，导热系数迅速下降，而孔径对泡沫铝的导热系数影响不大．从串-并联和并-串联模型出发，分析了孔隙率对泡沫铝材料导热系数的影响，发现串-并联模型更能反映泡沫铝的结构特征，与实测值吻合更好。     

原料和制备工艺对闭孔石英泡沫陶瓷性能的影响

以石英为主要原料,钠长石或钾长石作熔剂,CacO3或CasO4为成孔剂,PVA为粘结剂,干压成型后于1600℃左右烧结成闭孔泡沫陶瓷.运用SEM对泡沫陶瓷的显微结构进行了表征.结果表明,以高温粘度较小的钠长石作熔剂的泡沫陶瓷其气孔封闭性优于以钾长石作熔剂的泡沫陶瓷;采用CaSo4作成孔剂的泡沫陶瓷具有较高的气孔率;烧成温度提高和保温时间延长,可提高泡沫陶瓷的气孔率;烧成速度越快,气孔数量越多,气孔越不规整;而成型压力增加,泡沫陶瓷强度降低.     

高强度碳化硅泡沫陶瓷的制备及其抗压强度研究

选用Al2O3、Y2O3作为烧结助剂,通过有机模板复制法及多次浸渍涂覆工艺制备出高强度碳化硅泡沫陶瓷材料。系统地研究了原料组成、烧结温度等工艺参数对制得的碳化硅泡沫陶瓷物相组成、宏观结构、微观结构的影响,同时对陶瓷的气孔率、力学性能等进行了测试。结果表明:通过选取不同PPI值的有机泡沫模板,泡沫陶瓷宏观孔径可控;随着涂覆次数的增加,陶瓷体孔径减小、孔棱直径增加;随着烧结温度的提高,孔棱致密度增加,抗压强度显著提高;在1700℃下获得了20PPI值,气孔率为77%,抗压强度达2.48MPa的碳化硅泡沫陶瓷。     

纳米SiC填料对SiOC泡沫陶瓷性能的影响

以聚硅氧烷为先驱体,采用先驱体转化法及有机泡沫浸渍法相结合制备了SiOC泡沫陶瓷。研究了纳米SiC填料含量对SiOC泡沫陶瓷的抗压强度、孔隙率的影响,并对泡沫陶瓷的微观形貌进行了分析。结果表明：随着纳米SiC填料含量的增加,Si0C泡沫陶瓷抗压强度先升高后降低;在相同的裂解温度下,添加纳米SiC填料可提高泡沫陶瓷的孔隙率。当SiC填料含量达5％时泡沫陶瓷抗压强度达最大值17．8MPa,其孔隙率为88％。微观结构分析显示,SiOC泡沫陶瓷呈三维网状结构,孔径为100～500μm,具有良好的贯通性,且孔筋处结构较为均匀致密。     

采用聚硅氮烷制备SiCN泡沫陶瓷

采用含乙烯基聚硅氮烷为原料，利用先驱体转化法与有机泡沫浸渍法相结合制备SiCN泡沫陶瓷。通过聚氨酯泡沫及聚硅氮烷的热分析制定温度曲线，研究了裂解温度、浸渍／裂解增强处理次数等工艺参数对泡沫陶瓷抗压强度的影响，采用XRD、SEM及EDS对SiCN泡沫陶瓷进行了物相、微观结构及成分分析。结果表明，在1000～1400℃温度范围内，随着温度的升高，泡沫陶瓷的抗压强度先升高后降低，增强处理对提高抗压强度有明显效果，当裂解温度为1300℃，经二次增强处理后，试样的抗压强度达11．5MPa。XRD研究表明，随着温度的逐步升高，聚硅氮烷的裂解产物发生了由非晶态向晶态的转变。微观结构分析显示，SiCN泡沫陶瓷呈三维网状结构，具有良好的贯通性，开孔气孔率达到85％。     

热处理保温时间对高钛高炉渣制备泡沫微晶玻璃的影响北大核心CSCD

以高钛高炉渣和废玻璃粉为主要原料,采用发泡和析晶同步进行的＂一步法＂制备泡沫微晶玻璃,研究热处理保温时间对泡沫微晶玻璃的组织与性能影响。结果表明：在1000℃下,随保温时间从30 min延长至60 min,泡沫微晶玻璃中主晶相由斜辉石Ca（Ti,Mg,Al）（Si,Al）2O6转变为钙铁辉石Ca Fe（Si2O6）和普通辉石Ca（Mg,Fe,Al）（Si,Al）2O6,其晶相含量增加且由粒状结构向棒状结构过渡,材料孔径增大,体积密度、导热系数与吸水率逐渐降低,抗压强度升高;保温时间在60~120 min时晶相不发生明显变化,其含量缓慢增加且逐渐融合呈球状结构,材料出现连通孔,体积密度、导热系数与吸水率逐渐升高,抗压强度下降。综合而言,当保温时间为60 min时,所制得的泡沫微晶玻璃具备最优综合性能。     

闭孔泡沫铝吸声性能的影响因素

利用熔体转移发泡法制备闭孔泡沫铝,从孔径大小、打孔率、背后空腔以及背后贴膜方面对其吸声性能进行研究.结果表明:孔径大的闭孔泡沫铝吸声系数要远好于孔径小的闭孔泡沫铝的吸声系数;打孔后闭孔泡沫铝吸声系数有了明显的提高,当分别打孔0.5%、1%和2%N,闭孔泡沫铝最高吸声系数从0.42分别增加到了0.53、0.75和0.96;打孔闭孔泡沫铝背后加空腔吸声曲线都表现出明显的亥姆霍兹共振器吸声特性,且随空腔厚度的不断增加,低频吸声系数逐渐增加,高频吸声系数逐渐降低,最高吸声系数向低频迁移;背后贴膜闭孔泡沫铝吸声特性曲线出现峰值吸声特征消失的现象,表现出吸声系数随频率增加而增加的特性.     

成孔剂和硅粉粒度对反应烧结氮化硅性能的影响

以硅粉为原料，通过添加不同含量的成孔剂，反应烧结制备出具有不同气孔率的低密度多孔氮化硅陶瓷，研究了成孔剂含量和硅粉粒度对反应烧结氮化硅性能的影响。结果表明，随着成孔剂含量的增加，试样气孔率变大，强度随之减小，烧结后试样中的α-Si3N4相增多，介电常数实部和介电损耗降低，最低介电常数实部可达到2．4左右；不同粒度硅粉中添加30％（质量分数，下同）成孔剂的坯体烧结，在气孔率保持不变的条件下，初始硅粉粒度越小，烧结后试样强度越大，介电常数实部和介电损耗明显减小。     

添加CeO2对BZN和BMZN微波陶瓷介电性能的影响

添加CeO2对BZN和BMZN微波陶瓷介电性能的影响表明，引入CeO2对BZN和BMZN陶瓷密度和微观形貌没有明显的影响，也不易造成第二相的形成；添加适量的CeO2能调节BZN和BMZN陶瓷的谐振频率温度系数在-10^-5／℃～＋10^-5／℃之间；CeO2对BZN陶瓷Qf值的影响不大，但会使BMZN陶瓷的Qf值明显降低；考虑电容率、Qf值和谐振频率温度系数三方面因素，获得较好性能的BZN和BMZN陶瓷性能如下：BZN＋0．75％CeO2，εr=39．45，Qf=51201GHz，τf=8．20×10^-6／℃：BMZN＋0．50％CeO2，εr=40．48，Qf=51381GHz，τf=12．7×10^-6／℃。     

发泡剂浓度对钙长石多孔陶瓷结构与性能的影响

以α-Al_2O_3、Si O_2和Ca CO_3为主要原料,采用泡沫注凝法+无压烧结法制备了钙长石多孔陶瓷。通过调控发泡剂浓度获得不同气孔结构的多孔陶瓷样品。采用XRD,SEM分析了样品的物相组成和显微结构,测试了制备材料的气孔率、体积密度、抗压强度等性能。探究了发泡剂浓度对制备材料的显微结构与性能的影响。结果表明,在相同烧结温度下,发泡剂浓度对制备材料的物相组成影响不大。随着发泡剂浓度的增大,气孔率先增加后缓慢下降,中位孔径先增大再减小后再增大,而抗压强度呈先下降后增加趋势;在发泡剂浓度为0.5~32 g/L的范围内,制备材料的气孔率为82.14%~90.61%,中位孔径为70~130μm,抗压强度为0.14~3.84 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.