Microstructure and Mechanical Properties of ZrC_(x)-NbC_(y)-Cu Composites by Reactive Infiltration at 1300℃

ZrC_(x)-NbC_(y)-Cu composites were fabricated by pressure-less reactive infiltration of Zr-Cu binary melts into porous NbC preforms at 1300℃.The effect of Zr content in the infiltrator on microstructure of the as-synthesized composites was studied.Mechanical properties of the composites were reported.A partial displacement of Nb atoms in NbC by Zr atoms from Zr-Cu melt occurs during the reaction between Zr-Cu melt and porous NbC preform.The formation of a core-shell structure suggests the reaction is mainly a dissolutionprecipitation type.NbC dissolves into Zr-Cu melt,from which the(Nb,Zr)C_(z)phase precipitates and grows.With increasing Zr content in the Zr-Cu infiltrator,the reaction is enhanced and the infiltration is easily chocked.ZrC_(x)-NbC_(y)-Cu composite is synthesized using Zr_(14)Cu_(51)infiltrator.The flexural strength and fracture toughness of ZrC_(x)-NbC_(y)-Cu composite reach 637 MPa and 12.7 MPa·m^(1/2),respectively.And the improved toughness is probably attributed to residual Cu phase and plate-like Nb_(x)C_(y)phases.

Synthesis and catalytic performance of bimetallic NiMo-and NiW-ZSM-5/MCM-41 composites for production of liquid biofuels

This work presents a synthesis of bimetallic NiMo and NiW modified ZSM-5/MCM-41 composites and their heterogeneous catalytic conversion of crude palm oil( CPO) to biofuels. The ZSM-5/MCM-41 composites were synthesized through a self-assembly of cetyltrimethylammonium bromide( CTAB) surfactant with silica-alumina from ZSM-5 zeolite,prepared from natural kaolin by the hydrothermal technique. Subsequently,the synthesized composites were deposited with bimetallic NiMo and NiW by impregnation method. The obtained catalysts presented a micro-mesoporous structure,confirmed by XRD,SEM,TEM,EDX,NH_3-TPD,XRF and N_2 adsorption-desorption measurements. The results of CPO conversion demonstrate that the catalytic activity of the synthesized catalysts decreases in the series of NiMo-ZSM-5/MCM-41 > NiW-ZSM-5/MCM-41 > Ni-ZSM-5/MCM-41 > Mo-ZSM-5/MCM-41 > W-ZSM-5/MCM-41 > NiMo-ZSM-5 > NiW-ZSM-5 > ZSM-5/MCM-41 > ZSM-5 > MCM-41. It was found that the bimetallic NiMo-and NiW-ZSM-5/MCM-41 catalysts give higher yields of liquid hydrocarbons than other catalysts at a given conversion. Types of hydrocarbon in liquid products,identified by simulated distillation gas chromatography-flame ionization detector( SimDis GC-FID),are gasoline( 150-200 ℃; C5-12),kerosene( 250-300 ℃; C5-20) and diesel( 350 ℃; C7-20).Moreover,the conversion of CPO to biofuel products using the NiMo-and NiW-ZSM-5/MCM-41 catalysts offers no statistically significant difference( P> 0.05) at 95% confidence level,evaluated by SPSS analysis.

Synthesis of Y_2O_3 particle enhanced Ni/TiC composite on TC4 Ti alloy by laser cladding

A Y2O3 particle enhanced Ni/TiC composite coating was fabricated in-situ on a TC4 Ti alloy by laser surface cladding. The phase component, microstructure, composition distribution and properties of the composite layer were investigated. The composite layer has graded microstructures and compositions, due to the fast melting followed by rapid solidification and cooling during laser cladding. The TiC powders are completely dissolved into the melted layer during melting and segregated as fine dendrites when solidified. The size of TiC dendrites decreases with increasing depth. Y2O3 fine particles distribute in the whole clad layer. The Y2O3 particle enhanced Ni/TiC composite layer has a quite uniform hardness along depth with a maximum value of HV1380, which is 4 times higher than the initial hardness. The wear resistance of the Ti alloy is significantly improved after laser cladding due to the high hardness of the composite coating.

Tribological behavior and mechanism of NiCrBSi-Y_2O_3 composite coatings

The NiCrBSi-Y2O3 composite coatings were prepared on the surface of 45 carbon steel by plasma spray, the microstructure and tribological properties of the coatings were investigated. The results show that the NiCrBSi-Y2O3 composite coatings are mainly composed of γ-Ni, CrB, Cr7C3 and Y2O3. With addition of Y2O3, hard phases such as CrB, Cr7C3 emerge in composite coating, and the density of the composite coatings also increases. The NiCrBSi-0.5Y2O3 composite coating presents excellent tribological properties. Its friction coefficient is 0.175, which is about 37% of that of the pure NiCrBSi coating. The mass wear loss is 1.2 mg, which is reduced by 43% compared with the pure NiCrBSi coating. When the loads are 6-10 N, the NiCrBSi-0.5Y2O3 composite coating suffers from slight wear and the wear mechanisms are mainly adhesive wear accompany with slight micro-cutting wear and micro-fracture wear. As the load increases to 12 N, the wear mechanisms are adhesive wear and severe micro-cutting wear.

Y/Al-5Ti-1B复合变质对Al-7Si合金微观组织和力学性能的影响

在传统铸造Al-Si合金中存在的粗大树枝晶α-Al相以及针状共晶Si严重割裂基体,显著降低合金的力学性能。为细化Al-Si合金的组织,提升其力学性能,本文使用扫描电镜(SEM)、电子探针(EPMA)、X射线衍射仪(XRD)以及万能材料试验机,研究了不同添加量Y/Al-5Ti-1B变质剂(Al-5Ti-1B均为2%,稀土Y分别为0.05%、0.1%、0.2%、0.3%、0.4%、0.5%,质量分数)对Al-7Si合金微观组织和力学性能的影响,并探究了其对Al-7Si合金的变质机理。实验结果表明,当Al-5Ti-1B含量为2%、稀土Y含量为0.4%时,变质效果最佳,共晶Si由粗大针状变为细小颗粒状,长和宽分别减小至2.7和0.8μm,相较于未经变质处理的Al-7Si合金,减小了90.6%和4.7%。合金抗拉强度由原来的168.1 MPa提升至209.1 MPa,增加了24.4%。同时伸长率从6.23%提升至9.62%,增长了54.4%。此外,合金的断裂方式也从脆性断裂转变为韧-脆混合断裂。

Mg-Gd-Y-Zn-Zr合金碎屑固相再生工艺研究

通过热压烧结以及挤剪复合成形工艺对Mg-7Gd-4Y-2Zn-0.4Zr合金碎屑进行固相再生。在碎屑中添加体积分数5%、7%和9%的SiC颗粒,研究了SiC颗粒含量对固相再生坯料微观组织和力学性能的影响。结果表明,热压烧结后坯料中的界面明显,O元素在烧结界面富集。此外,微观组织中存在大块SiC颗粒,不同试样的塑性均较差。相比于其它试样,SiC体积分数7%的热烧结试样的综合性能最优,其抗拉强度为232 MPa,伸长率为1.76%。挤剪复合成形后,微观组织中的烧结界面消失,平均晶粒尺寸细化至10μm。此外,原本团聚分布的SiC颗粒均匀、弥散地分布在合金内部。SiC体积分数5%的固相再生坯料具有较优的综合力学性能,其抗拉强度为269 MPa,伸长率为12.2%,相比于固溶态合金分别提升了24.5%和62.7%。

Microstructure and mechanical properties of WC-20wt% Co/ZrO_2(3Y)cermet composites

The cermet composites WC-20wt%Co/ZrO2（E6）with four different comtents of ZrO2（3Y）were prepared by normal vacuum sinter processing;the optical microscope and SEMwere used to characterize their microstructures.The hardness.bending strength and impact toughness of the specimens were determined.The experimental results show that ZrO2（3Y） particles in WC-20wt%Co matrix are sphcrical particles in different sizes which are distributed uniformly in Co phases and WC phases,the bending strength and impact toughness of the WC-20wt%Co cermet composites added ZrO2（3Y）improve remarkably.but the hardness values have little change.

Ni-Mo-Y-Gr复合材料的制备及其在宽温域条件下的摩擦学性能

采用放电等离子烧结技术制备了Ni-Mo-Y-Gr(石墨烯)自润滑复合材料,通过光学显微镜、扫描电镜、X射线衍射、拉曼及高温摩擦实验机对复合材料的微观组织、成分、力学性能及摩擦磨损性能进行了研究。结果表明:Ni-Mo-Y-Gr复合材料的组织均匀致密,随着石墨烯含量的增加,复合材料的密度、硬度及屈服强度呈下降趋势,实际密度大于计算理论密度,即复合材料制备过程中发生了冶金熔合与固溶;Ni-Mo-Y-Gr复合材料在室温至600℃范围内具有较低的摩擦系数及磨损率,表明其具有较好的摩擦学性能;在室温、200和400℃时石墨烯起到了良好的润滑作用,在600℃时的主要润滑相为石墨烯、NiO、MoO2、MoO3和NiMoO_(4);在800℃时形成NiMoO_(4)及镍钼的氧化物,难以形成完整、有效的润滑层,从而使复合材料的摩擦学性能有所下降。

Investigation of ZSM-5/MCM-41 Composite Molecular Sieve for Reducing Olefin Content of FCC Gasoline

ZSM-5/MCM-41 composite molecular sieve was prepared by the nano-assembling method.The ZSM-5 molecular sieve,the MCM-41 molecular sieve,the ZSM-5/MCM-41 mechanical mixture and the ZSM-5/MCM-41 composite molecular sieve were characterized by X-ray powder diffractometry,N_2 adsorption isotherms,temperature programmed desorption of ammonia and scanning electron microscopy and their properties were analyzed.Using FCC gasoline as the feed,activities of different molecular sieves for reducing olefin content were investigated in a continuous high-pressure micro-reactor unit under the following conditions:a reaction temperature of 400℃,a reaction time of 2 h,a weight hourly space velocity of 3h^(-1),and a reaction pressure of 2.0 MPa.The results showed that the HMCM-41 molecular sieve had low reaction performance,and the HZSM-5 molecular sieve demonstrated high aromatization activity,while the ZSM-5/MCM- 41 composite molecular sieve exhibited a best olefin-reducing performance because of its high isomerization activity and moderate aromatization activity.With a largest olefin-reducmg capability and a reasonable distribution of products,the composite molecular sieve was more suitable for FCC gasoline upgrading compared to other three catalysts.

Synthesis of Al_2O_3/TiCN-0.2%Y_2O_3 Composite by Hot Pressing

Al2O3/TiCN composites were synthesized by hot pressing.The influences of components and HP temperature on mechanical properties,such as bending strength,breaking tenacity and Vickers hardness were investigated.The results showed that the mechanical properties of Al2O3/TiCN composite increased with temperature when hot pressing temperature is below 1650 ℃.The mechanical properties reached their maximums when the composites were sintered at 1650 ℃ for 30 min under hot pressing pressure of 35 MPa,the value of bending strength,breaking tenacity and Vickers hardness was 1015 MPa,6.89 MPa·m1/2,and 20.82 MPa,respectively.When hot pressing temperature was above 1650 ℃,density decreased because of decomposition with increased temperature,and mechanical properties dropped because of rapid growth of grains in size at high temperature.Microstructure analysis showed that the addition of Y2O3 led to the formation of YAG phase so as to inhibit the growth of crystals.This helped to improve breaking tenacity of the composites.TiCN particles with diameters of 1 μm dispersed at Al2O3 grain boundaries,inhibited grain growth and enhanced mechanical properties of the composites.SEM study of the propagation of indentation cracks showed that the bridge linking behavior between matrix and strengthening phase might lead to the formation of the coexisted field of crack deflection,branching and bridge linking.The mechanism of this phenomenon was that the addition of Y2O3 improved the dispersion of TiCN particles so as to enhance the tenacity of the composites.The breaking tenacity was changed from 5.94 to 6.89 MPa·m1/2.

连梁可更换的Y型偏心支撑组合框架力学性能试验研究

为研究连梁可更换的Y型偏心支撑组合框架(简称“Y型V-EBCF”)的力学性能,设计制作了一榀Y型V-EBCF试件,其中可更换式连梁由低屈服点钢加工并通过高强螺栓与周边构件相连。对Y型V-ECBF试件和拆卸了连梁后的试件分别进行了拟静力试验,分析了试件的失效模式、荷载-位移曲线和残余位移角,试验结果表明:在连梁失效前,结构具有稳定的滞回性能和良好的耗能能力;当拆卸失效连梁后,结构在组合框架的不平衡内力下恢复至原位,残余变形角为0.002 rad,小于规范限值(0.005 rad)及最大可更换残余位移角限值(0.0023 rad),且余下试件再加载时的滞回曲线依旧饱满稳定,表明Y型V-ECBF体系具有良好的震后恢复能力;采用现行AISC360-16规范相关公式可以准确计算低屈服点钢连梁的承载力,但超强系数建议取3.0以防止周边构件的破坏;Y型V-ECBF体系的刚度和承载力等于偏心支撑中连梁和组合框架的刚度与承载力之和。此外,Y型V-EBCF中的连梁会引起框架梁跨中承担额外的弯矩,导致跨中混凝土板的开裂,该文给出了计算跨中混凝土板裂缝宽度的公式。

Y型蜂窝等效模型及蜂窝夹芯结构车体的仿真分析

复合材料夹芯结构在轨道车辆车体轻量化中应用广泛,但在大型夹芯结构车体仿真计算时,存在结构层次复杂且分析经验较为缺乏等问题。本文提出考虑蜂窝双壁影响的Y型蜂窝等效模型,然后基于Y型蜂窝等效构建碳纤维铝蜂窝夹芯板和格栅增强碳纤维铝蜂窝夹芯板仿真分析模型,并将其分别与三点弯曲试验进行验证。根据传统列车车体的蒙皮骨架形式,构建碳纤维铝蜂窝车体和格栅增强碳纤维铝蜂窝车体,并运用BSEN12663:2010标准和《复合材料设计手册》中的设计标准分析其刚度、强度、应变等力学性能。研究结果表明:碳纤维铝蜂窝夹芯板和格栅增强碳纤维铝蜂窝夹芯板三点弯曲仿真结果与试验值误差分别为2.8%和0.1%,验证了Y型蜂窝等效模型具有较高的精度;碳纤维铝蜂窝车体的比刚度最低提升了49.4%,强度最高提升了64.5%;格栅增强碳纤维铝蜂窝车体的比刚度最低提升了67.6%,强度最高提升了66.2%。对于2种蜂窝夹芯结构车体的蒙皮来说,格栅增强碳纤维铝蜂窝车体应变最低下降了36.9%,失效因子最低下降了61.1%,相比碳纤维铝蜂窝车体有较充足的安全余量;相比原不锈钢车体,2种蜂窝夹芯结构车体具有较好的减重效果,碳纤维铝蜂窝车体减重33.4%,格栅增强碳纤维铝蜂窝车体减重13.1%。基于Y型蜂窝等效模型的碳纤维夹芯结构仿真分析,为先进复合材料轨道车辆车体结构轻量化设计提供了参考。

Pore Structure and Catalytic Performance of Steam-Dealuminated ZSM-5/Y Composite Zeolites

For investigating the effect of dealumination on the pore structure and catalytic performance, ZSM-5/Y composite zeolites synthesized in situ from NaY gel were dealuminated by steaming at different temperatures. XRD (X-ray diffraction) characterization indicates that the relative crystallinity of the composite zeolites decreases with the increase in Si/Al ratio after steaming. N2 adsorption-desorption suggests that more mesopores are formed while the BET (Brunauer, Emmett and Teller) specific surface area and the micropore specific surface area decrease as the temperature of steaming rises. Daqing heavy oil was used as feedstock to test the catalytic cracking activity of ZSM-5/Y composite zeolites. The experimental results of the catalytic cracking performance reveal that the distribution of products differs due to the different conditions of hydrothermal treatment. Further hydrothermal treatment leads to an increase in the yield of light oil, and a decrease in the yield of gas products and coke.

Fracture Mechanism of 3D, Five-directional Braided (SiO_2)_f /SiO_2 Composites Prepared by Silicasol-infiltration-sintering Method

Three-dimensional （3D） five-directional braided （SiO2）/SiO2 composites were prepared by silicasol-infiltration-sintering （SIS） method. The flexural properties and microstructures were studied. The flexural strength and flexural elastic modulus were found to be 73 MPa and 12 GPa, respectively. The results of stress vs deflection curve and SEM examinations revealed that the fracture mechanism of 3D, five-directional braided （SiO2）/SiO2 composite was a mixture mode of ductile and brittle. The ductile mode was attributed to the weak bonding strength of fiber/matrix at low temperature. The brittle fracture might be caused by the propagation of micro defect or crack, which existed in the as-prepared composites for the ten-cycle process.

Mg-Gd-Y-Zn-Zr系高强稀土镁合金研究现状及发展趋势

由于镁合金室温下塑性差,高温下强度较低,限制了它在诸多领域的应用发展。近年来国内外学者陆续开发出了含长周期堆垛有序结构相的Mg-Gd-Y-Zn-Zr系高强稀土镁合金,并对该合金系制备加工时组织性能的变化及机理进行深入研究。文章综述了近年来Mg-Gd-Y-Zn-Zr系高强稀土镁合金的研究现状及进展,分析了合金成分、常规塑性加工技术及热处理等对合金组织性能的影响,并展望该合金的研究方向。

Fabrication and fracture analysis of MoSi_2 matrix composites by mechanical alloying

Four composites, MoSi 2+ZrO 2, MoSi 2+ZrO 2(Y 2O 3), MoSi 2+ZrO 2+SiC and MoSi 2+ZrO 2(Y 2O 3)+SiC are fabricated by mechanical alloying. It is clear that cracks produced on the MoSi 2 matrix composites during hardness testing belong to the Palmquist crack system. The value of highest fracture toughness of MoSi 2+ZrO 2+SiC composite is 7.58?MPa·m 1/2 , which is nearly three times that of monolithic MoSi 2. This can be attributed to well distributed ZrO 2 and SiC particles along the boundaries of very fine MoSi 2 grains.

BaZr_(0.9)Y_(0.1)O_(2.95)/Na_2SO_4 Composite with Enhanced Protonic Conductivity

Heterogeneous composite BaZr0.9Y0.1O2.95/Na2SO4 was designed and fabricated with Y-doped BaZrO3 as matrix and Na2SO4 as dispersant by conventional powder processing to improve the total conductivity of barium zirconate. The electrical conduction of the composite was studied by electrical and electrochemical methods. Microstructure of the heterogeneous composite was examined by SEM. The experimewtal results show that the protonic conductivity of Y-doped BaZrO3 is greatly improved upon incorporating Na2SO4 in the material. Microstructure observation indicates that a multiphase structure with Na2SO4 disperses at the grain boundaries of BaZr0.1Y0.9O2.95. Electromotive force （EMF） measurements under fuel cell conditions reveal that the total ionic transport number of the composite is more than 0.9 at 750 ℃.

Anaortic Off-Pump Complete Arterial Revascularization Using Composite LIMA RIMA Y Sequential 5 Grafts in a Patient with Triple Vessel Disease Performed in a Low Resource Country: A Case Report

The use of bilateral internal thoracic arteries to treat coronary artery disease is very less despite of improved long-term survival. In this case report, a patient presented with TVD has been managed with anaortic off-pump complete arterial revascularization (OPCABG) by using composite LIMA RIMA Y Sequential 5 grafts to achieve complete arterial revascularization successfully. This type of operative procedure is technically difficult in a resource poor country like Bangladesh. However, this has been done by a group of young cardiac surgeon. During follow up, the patient is in a good condition.

Microstructure and Fracture Toughness of Al_2O_3/3Y-TZP Composites

The composites were prepared by ball-milling ZrO_2(3%Y_2O_3) and γ-Al_2O_3 nanoparticles, pressing unidirectionally, cold-pressing isostatically and pressurelessly sintering in air. The phases of ZrO_2 in composites were examined by X-ray diffraction. The microstructure of Al_2O_3/3Y-TZP composites was observed by scanning electron microscope (SEM) and transmission electron microscopy (TEM) respectively. The X-ray analysis reveals that ZrO_2 of both surface and fracture surface is mainly t-ZrO_2. The SEM image shows that there are some intragranular particles in large granulars. The fracture toughness K_ 1c of Al_2O_3/70%ZrO_2(3%Y_2O_3(mole fraction)) composite tested by single-edge notched bending is 13.5 MPa·m 1/2. Being toughened by the ferroelastic domain switching and the intragranular microstructure explains high toughness of the composite.

黄晶梨Y形篱壁树形早期产量调查与栽培技术要点

黄晶梨在山东地区表现优良,结果早,能自花授粉结实,丰产。采用Y形树形的黄晶梨幼树调查分析表明,苗木栽植第4年进入盛果期,666.7 m^(2)枝量87293条,其中,长枝、中枝、短枝,分别占总枝量的12.02%、7.74%、80.24%,产量达到3330 kg。介绍了其栽培技术要点。