β-SiC晶须的孪晶构型观察SCIEI

利用透射电子显微镜研究了气—液—固(VLS)法生长的β—SiC晶须中的孪晶构型。在竹节状的SiC晶须中,β—SiC节与含高密度堆垛层错(或一维无序)的节之间孪生相连,其李晶界为{111}_β;同时还观察到有的β-SiC节被{111}_β孪晶界分为两节。此外,在晶须的头部及分叉处还观察到了孪晶界平行晶须轴向的孪晶结构。利用选区电子衍射和像衍衬分析发现,这种双晶SiC晶须的孪晶面平行于基体的{001}_M。     

OBSERVATION OF TWIN CONFIGURATIONIN β-SiC WHISKERS

利用透射电子显微镜研究了气—液—固(VLS)法生长的β—SiC晶须中的孪晶构型。在竹节状的SiC晶须中,β—SiC节与含高密度堆垛层错(或一维无序)的节之间孪生相连,其李晶界为{111}_β;同时还观察到有的β-SiC节被{111}_β孪晶界分为两节。此外,在晶须的头部及分叉处还观察到了孪晶界平行晶须轴向的孪晶结构。利用选区电子衍射和像衍衬分析发现,这种双晶SiC晶须的孪晶面平行于基体的{001}_M。     

多节状SiC晶须的特性及其增强Si3N4陶瓷复合材料的性能研究

以稻壳为原料,在非金属催化剂作用下合成了SiC晶须(简称SiCw),运用TEM、XRD研究了晶须的形貌特征及晶体结构,并对其应用于Si3N4陶瓷复合材料的力学性能进行了检测.结果表明SiCw的产率可达30%以上,晶须外观挺直、表面粗糙呈多节状,节间距为0.5μm～1.5μm,直径分布为0.53±0.28μm,长度分布为10.3±6.1μm,长径比分布为23.1±18.3,晶型以β-SiC为主,并有少量的α-SiC变体,两节之间具有孪晶关系;粗糙多节的晶须增加了与基体材料的接触面及摩擦效应,增强了"桥联"强度,其补强、增韧的Si3N4陶瓷复合材料室温强度为856±22 MPa,高温(1 300℃)强度为418.5±14.2 MPa,断裂韧性为11.3±1.0 MPa·m1/2.     

用稻草和硅粉合成碳化硅晶须

采用碳热还原法用废弃稻草和硅粉合成碳化硅晶须。通过扫描电镜、透射电镜观察晶须形貌,采用X射线衍射(XRD)仪对物相进行分析。结果表明:由稻草和适量硅粉合成的碳化硅晶须多为直晶、较光滑,晶须直径为20~100nm;晶体中含有孪晶等面缺陷。直接加热至1350℃和先升至1600℃再迅速降至1350℃的加热方式均能得到碳化硅晶须。先升至较高温度再降到较低温度有利于碳化硅晶须的生长。保温时间延长,晶须产量增大,晶须直径略有增大。晶须生长机理为气-液-固(VLS)机理。     

Si/C/N纳米微波吸收剂的制备

采用化学气相沉积方法,在1200℃～1600℃温度范围内,于不同的NH3流量条件下,合成了Si/C/N纳米粉体,研究了粉体的制备工艺、成分、相组成与其微波介电性能之间的关系.结果表明：NH3流量增加,粉体中N含量升高,随着合成温度的提高,粉体的晶化程度增强,主要为β-SiC相.在SiC晶格中固溶有N原子,且N原子的固溶量随合成温度升高而减少.Si/C/N纳米粉体中SiC微晶含量,以及SiC微晶中固溶的N原子浓度对粉体的ε＇,ε（＂）和损耗因子tgδ（ε＂/ε＇）起着重要作用.N原子固溶所导致的极化驰豫损耗和漏导损耗是Si/C/N纳米粉体具有吸波性能的主要机理.     

涂覆预处理对SiC增强铁基堆焊层组织的影响

采用PIRAC技术处理后SiC表面的涂覆层由Cr3 Si,Cr7C3,Cr23C6等组成.通过等离子堆焊_后送粉技术制备SiC增强铁基合金复合涂层.结果表明,未预涂覆SiC颗粒在涂层表层完全分解,由于分解产物碳、硅扩散不均匀,影响了各区域的成分.上部出现大量初生多边形状碳化物,中部为树枝晶,底部为不规则胞状晶.预涂覆SiC颗粒分布在涂层表面上,没有发生明显溶解,原始形态保持完好.SiC颗粒与基体之间包括界面反应区和过渡区,界面反应区由(Fe,Cr)7C3,(Fe,Cr) 23 C6碳化物和α-(Fe,Cr)固溶体组成;过渡区为固溶较多Cr元素的α-(Fe,Cr)固溶体,耐蚀性较好,形貌难以显示.     

C/C复合材料表面原位生长SiC_w的工艺

以三氯甲基硅烷(CH3SiCl3,MTS)为先驱体原料,采用化学气相沉积法在C/C复合材料基体上原位生长碳化硅晶须,研究稀释气体流量、催化剂以及沉积温度对碳化硅晶须生长的影响。结果表明:有催化剂存在时可以制备具有较高长径比的SiCw,无催化剂制备的SiC主要以短棒状或球状SiC为主;随着稀释气体流量或者沉积温度的增加,SiCw的产率是先增加、后减少,在1 100℃、载气和稀释气体流量均为100 mL/min时,制备的碳化硅晶须的产率最高,晶须质量最好。     

热处理在金刚石表面热蒸镀覆SiO_2/SiC晶体复合涂层

采用高温热蒸镀方法处理在金刚石表面镀覆上了SiO_2/SiC晶粒复合涂层,同时研究了热处理温度和Al助剂对金刚石表面形成SiO_2/SiC晶粒复合涂层的影响。研究结果表明,在较低温度(1400℃),金刚石表面形成许多SiC和SiO_2和SiC颗粒。当温度升高到1450℃时,金刚石表面镀覆了良好的SiO_2/SiC复合涂层,形成了许多SiO_2和SiC颗粒、微米棒与晶须。Si粉中添加适量的Al(5 mass%)就会促进Si的蒸发,在1400℃时金刚石表面就会形成大量的SiO_2和SiC颗粒、微米棒与晶须。     

碳热还原合成Ti(C,N)晶须的相转变行为及生长机理

以TiO2和碳黑为主要原料,NaCl为卤化剂,NiCl2作为晶须生长的添加剂,在N2气氛下采用碳热还原法,在不同温度下合成Ti（C,N）晶须。采用X射线衍射研究合成样品的相组成及合成过程中原料的相转变行为,采用扫描电镜观察合成样品的形貌,探讨晶须的生长机理并建立生长模型。结果表明：在1 200℃合成时,主要发生TiO2与碳黑、氮气之间的直接还原反应,形成TiN;在温度为1 250-1 400℃时,NaCl分解产生的Cl原子起卤化作用,从NiCl2中分解出的Ni起催化作用,合成出Ti（C,N）晶须,晶须长度在10-30μm之间,直径大约1μm;合成的晶须表面光滑,顶端残留有催化剂颗粒,具有典型的气-液-固晶须生长机制特征。     

Si_3N_4复合陶瓷材料的微观组织和断裂机制

使用AEM和HREM研究了添加纳米SiC颗粒和同时添加纳米SiC颗粒及SiC晶须的两种Si3N4 复合陶瓷材料的微观组织和断裂机制。结果表明 ,部分SiC颗粒分布在Si3N4 晶内 ,SiC晶须分布在Si3N4 晶粒之间 ,SiC颗粒和晶须与Si3N4 界面之间不存在第二相组织 ,非晶组织大多分布在Si3N4 三叉晶界。断裂裂纹主要沿晶界和相界面扩展 ,也可能穿过少数Si3N4 晶粒。当裂纹扩展遇到SiC颗粒和 /或SiC晶须时 ,会发生转弯 ,产生分枝裂纹或微裂纹并在Si3N4 晶内和Si3N4 晶粒的断裂表面引起晶格畸变 ,这降低了裂纹扩展能量 ,从而改善复合陶瓷材料的断裂强度和断裂韧性     

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.