送粉激光熔敷耐磨涂层制备工艺与组织结构

采用20%WC作为镍基自熔合金的掺杂增强相，研究了该复合材料在送粉激光熔敷工艺条件下的熔敷层显微组织、显微硬度与熔敷工艺规范间关系，得出了在实验条件下的优化工艺参数：激光功率为2．5kW(光斑离焦量60mm)；扫描速度为2．4mm／s；送粉量为3．0g／min．     

激光熔覆Al2O3陶瓷涂层组织结构

研究了45钢表面激光熔覆等离子Al2O3陶瓷喷涂层的组织结构、硬度及滑动磨损特性。结果表明，等离子喷涂Al2O3陶瓷涂层呈层片状，涂层疏松，由α－Al2O3,ZrO2和γ－Al2O3组成。激光熔覆Al2O3陶瓷涂层致密，由α－Al2O3及ZrO2组成。激光熔覆Al2O3涂层硬度较高，滑动磨损时其耐磨性也明显优于等离子喷涂Al2O3陶瓷涂层。     

激光熔覆Ni+Cr_2O_3复合涂层的耐蚀性

研究了激光搭接熔覆Ni+Cr2 O3复合涂层在 0 .5mol/LH2 SO4 +0 .5mol/LNaCl水溶液中的电化学行为 .试验表明Cr2 O3粒子在激光熔池中发生了完全溶解 ,涂层具有胞状枝晶组织特征 .激光熔覆Ni+Cr2 O3复合涂层比单一熔覆Ni合金涂层和 2Cr13马氏体不锈钢基材具有更低的维钝电流密度和更宽的钝化区范围 ,明显改善了在该腐蚀介质中的抗点蚀能力 .     

不同Ca/P比粉末对宽带激光熔覆梯度生物陶瓷涂层组织结构的影响

采用梯度设计思想,利用宽带激光熔覆技术,在TC4合金表面分别熔覆Ca/P为1.4和1.5的CaH-PO4.2H2O+CaCO3混合粉末制备含羟基磷灰石[Ca10(PO4)6(OH2),简称HA]、β-磷酸三钙[β-Ca3(PO42),简称β-TCP]的度生物陶瓷涂层.采用XRD、SEM等表征手段,研究不同Ca/P粉末配比对生物陶瓷涂层组织结构的影响.研究表明:由于P在激光条件下存在烧损现象,当Ca/P为1.5的粉末经激光熔覆后所生成的陶瓷组织较Ca/P较1.4结晶状态更好.不同Ca/P粉末以及CeO2的添加量对催化合成HA+β-TCP有着深刻的影响.当Ca/P=1.4,CeO2的添加量为0.4wt%时,催化合成HA+β-TCP的数量最多;而当Ca/P=1.5,CeO2的添加量在0.2～0.4wt%范围内,催化合成HA+β-TCP的量最多.     

Low-temperature sintering and microwave dielectric properties of Ba<Subscript>2</Subscript>Ti<Subscript>3</Subscript>Nb<Subscript>4</Subscript>O<Subscript>18</Subscript> ceramics

The effects of CuO and H3BO3 additions on the low-temperature sintering,microstructure,and microwave dielectric properties of Ba2Ti3Nb4O18 ceramics were investigated.The addition of less amount of CuO (< 1 wt%) considerably facilitated the densification of Ba2Ti3Nb4O18 ceramics.Appropriate addition of H3BO3 (< 3.5 wt%) remarkably improved the microwave dielectric properties of ceramics.The addition of H3BO3 and CuO successfully reduced the sintering temperature of Ba2Ti3Nb4O18 ceramics from 1300 to 1050 ℃.B...     

Fabrication of High-purity Ternary Carbide Ti3AlC2 by Spark Plasma Sintering （SPS） Technique

The effect of silicon on synthesis of Ti3AlC2 by spark plasma sintering （SPS） from TiC/Ti/Al powders was investigated. X-ray diffraction （XRD） and scanning electron microscope （SEM） were used for phase identification and microstructure evaluation. The results show that addition of silicon can considerably accelerate the synthesis reaction of Ti3AlC2 and fully dense, essentially single-phase （purity 〉98%） polycrystalline Ti3AlC2 could be successfully obtained by sintering 2TiC/lTi/lAl/0.2Si powders at 1 200- 1 250 ℃ under a pressure of 30 MPa. SEM photographs show that the obtained Ti3AlC2 samples from mixtures powders are in plane-shape with a size of about 2-5 μm and 10-25 μm in the thickness dimension and elongated dimension, respectively.     

Ferroelectric properties of Bi<Subscript>4</Subscript>Zr<Subscript>0.5</Subscript>Ti<Subscript>2.5</Subscript>O<Subscript>12</Subscript> thin films prepared on LaNiO<Subscript>3</Subscript> bottom electrode by sol-gel method

The Bi4Zr0.5Ti2.5O12 (BZT) thin films were fabricated on the LaNiO3 bottom electrode using sol-gel method. The structure and morphology of the films were characterized using X-ray diffraction, AFM and SEM. The results show that the films have a perovskite phase and dense microstructure. The 2Pr and 2Vc of the Pt/BZT/LaNiO3 capacitor are 28.2 μC/cm2 and 14.7 V respectively at an applied voltage of 25 V. After the switching of 1×1010 cycles, the Pr value decreases to 87% of its pre-fatigue values. The dielectric constant (ε) and the dissipation factor (tanδ) of the BZT thin films are about 204 and 0.029 at 1 kHz, respectively. The films show good insulating behavior according to the test of leakage current. The clockwise C-V hysteresis curve observed shows that the Pt/BZT/LaNiO3 structure has a memory effect because of the BZT film's ferroelectric polarization.     

Eleetronie Structures and Bonding Properties of Ti2AlC and Ti3AlC2

The relation among electronic structure, chemical bond and property of Ti2AlC, Ti3AlC2 and doping Si into Ti2AlC was studied by density function and the discrete variation （DFT-DVM） method. After adding Si into Ti2AlC, the interaction between Si and Ti is weaker than that between Al and Ti, and the strengths of ionic and covalent bonds decrease both. The ionic and covalent bonds in Ti3AlC2, especially in Ti-Al, are stronger than those in Ti2AlC. Therefore, in synthesis of Ti2AlC, the addition of Si enhances the Ti3AlC2 content instead of Ti2AlC. The density of state （DOS） shows that there is mixed conductor characteristic in Ti2AlC and Ti3AlC2. The DOS of Ti3AlC2 is much like that of Ti2AlC. Ti2SiAl1-xC has more obvious tendency to form a semiconductor than Ti2AlC, which is seen from the obvious difference of partial DOS between Si and Al 3/7.     

Crystallization and Electrical Properties of （Ba0.4Pb0.3）Sr0.3TiO3 Thin Film by Pulsed Laser Deposition

（Ba0.4Pb0.3）Sr0.3TiO3 thin films were fabricated via pulsed laser deposition （PLD） technique on Pt/TiO2/SiO2/Si substrate. The crystallization of the films was characterized by XRD and FSEM, and the experimental results suggested deposition parameters, especially the deposition temperature was the key factor in forming the perovskite structure. The dielectric properties of the film deposited with optimized parameters were studied by an Agilent 4294A impedance analyzer at 1 MHz. The dielectric constant was 772, and the loss tangent was 0.006. In addition, the well-shaped hysteresis loop also showed that the film had a well performance in ferroelectric. The saturated polarization P, remnant polarization Pr and coercive field E were about 4.6 μC/cm2, 2.5 μC/cm2 and 23 kV/cm （the coercive voltage is 0.7 V）, respectively. It is suggested the film should be a promising candidate for microwave applications and nonvolatile ferroelectric random access memories （NvFeRAMs）.     

Influences of dopants on microstructure and magnetic properties of (Mg<Subscript>0.476</Subscript>Mn<Subscript>0.448</Subscript>Zn<Subscript>0.007</Subscript>)(Fe<Subscript>1.997</Subscript>Ti<Subscript>0.002</Subscript>)O<Subscript>4</Subscript> ferrites

Influences of addition of CaO, CoO and V2O5 on the microstructure and magnetic properties of (Mg0.476Mn0.448Zn0.007)(Fe1.997Ti0.002)O4 ferrites were investigated. The powders of (Mg0.476Mn0.448Zn0.007) (Fe1.997Ti0.002)O4 composition were prepared by using a conventional ceramic powder processing technique. The experimental results showed that the average grain size of the sintered ferrites codoped with 0.03wt% CaO, 0.04wt% CoO and 0.06wt% V2O5 was about 15 μm; the saturation magnetization of ferrites was 68.78 emu/g. The addition of V2O5 in the ferrites can not only increase value of the saturation magnetization, but also decrease the average grain size of (Mg0.476Mn0.448Zn0.007)(Fe1.997Ti0.002)O4 ferrites. Simultaneous incorporation of CoO, CaO and V2O5 dopants into (Mg0.476Mn0.448Zn0.007)(Fe1.997Ti0.002)O4 ferrites can not only improve the saturation magnetization of the materials, but also inhibit abnormal grain growth.     

The Preparation of CoWO4／WO3 Nanocomposite Powder

Ammoniwn metatungstate and cobalt nitrate were mixed at the molecular level in distilled water and then spruy-decomposed to CoWO4/WO3 nanoconposite powder. The particle morphology, crystalline size,forming course, chemical composition ant phase structure of the powder were studied by SEM , TEM , DTA- TG , IR and XRD , respectively. Reshlts show that the powder is homogeneous, spherical and nano-aggregated.     

Microstructure and wear behaviour of laser-induced thermite reaction Al<Subscript>2</Subscript>O<Subscript>3</Subscript> ceramic coatings on pure aluminum and AA7075 aluminum alloy

Wear-resistant laser-induced thermite reaction Al2O3 ceramic coatings can be fabricated on pure Al and AA7075 aluminum alloy by laser cladding （one-step method） and laser cladding followed by laser re-melting （two-step method） using mixed powders CuO-Al-SiO2 in order to improve the wear properties of aluminum and aluminum alloy, respectively. The microstructure of the coatings was characterized by scanning electron microscopy （SEM） and X-ray diffraction （XRD）. The wear resistance of the coatings was evaluated under dry sliding wear test condition at room temperature. Owing to the presence of hard α-Al2O3 and γ-Al2O3 phases, the coatings exhibited excellent wear resistance. In addition, the wear resistance of the coatings fabricated by two-step method is superior to that of the coatings fabricated by one-step method.     

Effect of Grain Size of CaCO3 and SiO2 on the Formation of C3S Under Different Conditions

The effect of grain size of CaCO3 and SiO2 on the formation of C3S under various conditions, such as rapid heating rate（800 ℃/min）, normal heating rate（30 ℃/min） and in the presence or absence of ZnO, was studied. The results show that the decomposition temperature of CaCO3, the temperature of appearance of liquid phase and the f-CaO content descend when the grain size of CaCO3 and SiO2 becomes smaller, which attributes to the reactive activity enhancement of powders due to the decrease of the particle size. When the grain size of CaCO3 and SiO2 is below 1 μm, the rate of the formation of C3S is greatly raised. A rapid sintering rate and the presence of ZnO have an important effect on the formation of C3S and can lower the temperature of the formation of C3S by about 50 ℃.     

Fabrication of homogenous dispersion TiB<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composites

In order to get a homogenous mixture and compact of TiB2-Al2O3, hybridization as a surface modification method was used to prepare nano-scale Al2O3 coated TiB2 particles. PE-wax particles were first coated onto TiB2 particles by hybridization, and then the nano-scale Al2O3 particles were coated onto the surface of TiB2 coated by PE-wax particles again. SEM, TEM and EDS were used to characterize the microstructure of as-received core/shell particles and its compacts. The experimental results show that a particle-scale homogenous dispersion of TiB2 and Al2O3 can be formed not only in mixed powder but also in dewaxed compacts. The compacts then were sintered by gas-pressing sintering (GPS). Finial products show improved mechanic properties comparing with reference samples fabricated by normal ways.     

WC/Ni60激光熔覆复合涂层的强碱腐蚀磨损行为

利用激光熔覆制备WC增强涂层,通过光学显微镜(OM)、电子扫描显微镜(SEM)和EDS对试样观察和分析,并依据颗粒相分布均匀性,获得推荐优化工艺参数是送粉量为7.8g/min、扫描速度为4mm/s、激光功率为2.0kW和离焦量为50mm。在此基础上,应用M-200摩擦磨损试验机考察了WC/Ni60涂层在40% NaOH强碱溶液作用下的摩擦磨损行为,结果表明,涂层的摩擦磨损机制随工况的变化而变化,钝化膜的生成和溶解成为一个动态过程,且所制备的涂层在中速中载时较干摩擦能够显著降低摩擦因数和磨损量。     

Microstructure and mechanical properties of CaCO<Subscript>3</Subscript> whisker-reinforced cement

Composite Portland cement (PC) played an important role in various kinds of construction engineering owing to low hydration heat, low-cost, and application of solid industrial waste, but its brittleness and low strength limited its use in stress-bearing locations. The aim of this study is to improve the toughness and fracture resistance by incorporating CaCO₃ whisker in cement matrix. Effect of different content of calcium carbonate whiskers on the mechanical properties of PC was investigated. The results showed that the flexural strength, impact strength and split tensile strength were increased by 39.7%, 39.25% and 36.34% at maximum, respectively. Microstructure and elements of the whiskers in hardened cement were observed and analyzed by SEM/EDS. The mechanisms of the reinforcement of CaCO₃ whisker on cement were also discussed, and the conclusion was that the improvement could be correlated to energy-dissipating processes owing to crack bridging, crack deflection, and whisker pull-out at the crack tips.     

The influence of mo additive on the microstructure and property of Ti/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite

The influence of Mo on the microstructure, bending strength and HV of Ti/Al₂O₃ composite was studied, and the influence mechanism was analyzed. The results indicate that after the addition of Mo, the composite organization is finer and phases distribution is better-proportioned which make the microstructure denser, the bending strength and HV of composite are also increased to a degree. But the bending strength increases first then decreases with the increasing of Mo content, so the appropriate Mo content for the Ti/Al₂O₃ composite is to be further confirmed. WANG Zhi: Born in 1962 Funded by Natural Science Foundation of China (No. 50232020) and Natural Science Foundation of Shandong Province (No. 2002F21)     

Photocatalytic degradation of rhodamine B dye with MWCNT/TiO<Subscript>2</Subscript>/C<Subscript>60</Subscript> composites by a hydrothermal method

Multi-walled carbon nanotube (MWCNT)/TiO2/C60 composite catalysts were prepared by hydrothermal method. TiO2 was deposited on the MWCNT surface. Their photocatalytic activities for degradation of Rhodamine B dye were studied. X-ray diffraction, field emission transmission electron microscopy, ultraviolet-visible light absorption spectrum and photoluminescence spectrum were carried out to characterize the composite catalysts. The results indicated that MWCNTs and C60 could greatly enhance the photocatalytic activity of TiO2.     

2738模具钢表面激光熔覆Ni基WC复合涂层的摩擦磨损性能

在2738模具钢表面通过CO2激光熔覆制备Ni基WC复合涂层。分别对2738钢基体和Ni-WC激光熔覆层进行干摩擦试验。用三维表面形貌仪测量磨损体积,用扫描电镜观察磨痕的表面形貌。试验结果表明,Ni-WC复合涂层试样的硬度显著提高,表面硬度超过1200HV,保证了Ni-WC熔覆层的耐磨性。熔覆层的平均摩擦因数约为0.24,与2738钢基体的摩擦因数0.43相比,降低了约44%。熔覆试样的比磨损率比基体试样的比磨损率下降了96.7%,WC硬质相提高了摩擦副表面的承载能力。磨粒磨损为Ni-WC复合涂层的主要磨损机理。     

Effect of Pb substitution on the microstructure and ferroelectric properties of Ba<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>TiO<Subscript>3</Subscript> ceramic

Ferroelectric Ba0.7Sr0.3TiO3（BST） and partially Pb^2＋ substituted for Ba^2＋ ceramics （Ba0.7-xPbx）Sr0.3TiO3 （x=0.1-0.4, BPST） were prepared by using conventional solid-reaction method. XRD analysis shows that the samples microstructure changes from cubic phase to tetragonal one with the Pb^2＋ content increasing. ESEM analysis shows that the Pb^2＋ substituted samples have a denser and more uniform surface morphology than that of pure BST. Measured electrical properties suggest that the Pb^2＋ substitution for Ba^2＋ in the BST system enhances the ferroelectric performance obviously when x=0.2. In addition, the substitution increases the samples Curie temperature （To） r （Ba0.5Pb0.2）Sr0.3TiO3 ceramic has good ferroelectric properties measured at a maximal electric field of 30 kV/cm under the condition of room temperature. The corresponding saturated polarization （Ps）, remnant polarization （Pr） and coercive field （Ec） is respectively 15.687 μC/cm^2, 8.100 μ C/cm^2 and 6.611 kV/cm. The measured Tc of （Ba0.5Pb0.2）Sr0.3TiO3 is 117 ℃.