以ABAQUS模拟软件为基础,创建管道环缝二维轴对称有限元模型,利用完全耦合方式计算了304不锈钢管焊接过程中的温度场和残余应力场,并在焊接完成后的残余应力场的基础上进行了焊后热处理工艺过程的有限元模拟.结果表明:二维轴对称模型能够有效地模拟304不锈钢管焊接热力耦合机制,相较于三维模型单元数目更少,节省大量计算时间;热处理后的残余应力场与热处理前相比,厚度方向残余应力降低,环向和纵向残余应力没有降低,但应力集中位置明显减少,应力分布较为平缓;焊后热处理过程中的塑性应变和高温蠕变是残余应力消除的力学机制,其中塑性应变起主要作用.

ZrC was produced by the combustion synthesis technology using Cu, Zr, and graphite as the starting element powders. The synthesis mechanism of ZrC was investigated by the combustion wave quenching experiment. Furthermore, the effects of sizes of C and Cu on the combustion synthesis behavior and products were also explored. Results revealed that ZrC was fabricated through the displacement reaction between C and Cu-Zr liquid. The Cu size hardly affected the combustion temperature and resultant products, indicating that the preparation cost of ZrC could be decreased by employing coarse Cu powders. With increasing C size, the burning temperature and ceramic particle size reduced. Graphite with size of 2.6 μm was used as the C source, and only ZrC nanoparticles and Cu were obtained. The products could be employed to prepare nano-sized ZrC/Cu composites without the elimination of by-products.

In the present study, the decoupling behavior of the arc coupling and rotating in the seven-wire rotating arc electrogas welding (EGW) is studied. It is found that the arc motion processes is composed of the arc axial motion process, arc coupled motion process, and arc circumferential rotation process. The arc is moving up and down along the axial direction. Moreover, it is observed that as the welding current increases, the arc axial motion frequency accelerates while the corresponding motion amplitude decreases. The arc coupled motion process does not always exist, and the arc coupled motion time and arc coupled forces increase as the welding current increases. Obtained results show that the arc axial motion hinders the arc coupled motion and the arc circumferential rotation. Meanwhile, the arc coupled motion and circumferential rotation are more obvious as the welding current increases.

The spiral structure of seven-wire is the fundamental cause of arc rotation. The arc rotation frequency decreases with the radius of twisting circle and the helix angle, and increases with the welding current. The arc presents the reciprocating rotating upward motion when welding torch oscillates along the thickness of the plate. The sidewall penetration along the thickness direction of plates is approximately the same. The rotating arc promotes the stirring of melting metal, and the stirring effect intensifies the flow of melting metal and accelerates the heat transfer from the molten pool to the sidewall, which has a positive effect on increasing the penetration of sidewall and refining the grains of weld seams.

The incorporation of WC promotes the sintering and grain refinement of Ti(C, N)-based cermets, leading to superior mechanical and functional properties. Herein, we present the reaction process of Co-Ti-C-BN-WC system and influence of WC content on microstructure and mechanical properties of Ti(C, N)-based cermets. The results reveal that Ti(C, N) is produced due to the combination of C/TiN or TiN/TiC, whereas TiB2 is formed due to the reaction between B/TiB or Ti/B. Moreover, (W, Ti)(C, N) solid-solution is synthesized due to the reaction of Wand C with TiN in the liquid state. In addition, XRD analysis indicates the presence of a small amount of CoW2B2 and Co3C phases with WC content of 15 and 20 mass%. Furthermore, the content of core-ring structure gradually increases with the increase of WC content from 5 to 20 mass%. Also, the grain size increases from 0.364 mu m to 0.484 mu m with increasing WC content from 5 to 20 mass%. On the other hand, the porosity initially decreases with increasing WC content, followed by a gradual increase. Consequently, the microhardness, fracture toughness and bending strength initially increase with increasing WC content, followed by a decrease. The maximum microhardness, fracture toughness and bending strength are found to be 2010HV10, 7.21 MPa.m(1/2), and 725 MPa, respectively.

This paper investigates the droplet formation and motion characteristics in seven-wire rotating arc electrogas welding. A high-speed video camera was used to observe the droplet formation and motion behaviors. The forces on the droplet in different welding parameters were analyzed to explain the droplet formation and motion processes. The results show that the small droplets at the end of six peripheral wires accumulate and grow toward the small droplet at the end of the center wire under the action of the electromagnetic force, and the coupled droplet forms under the action of electromagnetic force and surface tension at the end of the center wire. Gravity, plasma flow force, and rotating force affect the fall of the coupled droplet through the arc space and show non-axial motion and axial motion with different welding currents.

Ti(C,N)-TiB 2 -Co cermets were in situ synthesized, via reactive hot pressing from the Co-Ti-C-BN system, with a Co content ranging from 6 to 22 wt%. The microstructure, relative density, hardness, and fracture toughness of the sintered compacts was investigated by light microscopy, scanning electron microscopy, ceramic densitometry, and Vickers hardness test. The investigations indicate that during hot pressing (compacting pressure = 30 MPa), when the Co content is 14–22 wt%, the metal binder is extruded. Co and Ti are included in the extrudate, breaking the original ratio and deteriorating the properties of the sintered products. As the Co content increases from 6 wt% to 12 wt%, the porosity increases, and the relative density increases from 97.2% to 99.5%. The fracture toughness increases from 6.1 to 6.8 MPa m 1/2 . The Vickers hardness first increases from 1897 HV 10 to the maximum 1960 HV 10 and then decreases slightly to 1945 HV 10 . Keywords Ti(C,N)-TiB , -Co cermet , reactive hot pressing , low Co content , in situ synthesis

Ti(C,N)-TiB 2 -Co cermets were in situ synthesized, via reactive hot pressing from the Co-Ti-C-BN system, with a Co content ranging from 6 to 22 wt%. The microstructure, relative density, hardness, and fracture toughness of the sintered compacts was investigated by light microscopy, scanning electron microscopy, ceramic densitometry, and Vickers hardness test. The investigations indicate that during hot pressing (compacting pressure = 30 MPa), when the Co content is 14–22 wt%, the metal binder is extruded. Co and Ti are included in the extrudate, breaking the original ratio and deteriorating the properties of the sintered products. As the Co content increases from 6 wt% to 12 wt%, the porosity increases, and the relative density increases from 97.2% to 99.5%. The fracture toughness increases from 6.1 to 6.8 MPa m 1/2 . The Vickers hardness first increases from 1897 HV 10 to the maximum 1960 HV 10 and then decreases slightly to 1945 HV 10 .

Carbon nanotubes (CNTs) have attracted considerable attention due to their high aspect ratio, whisker-like form for best possible geometrical field enhancement, high electrical conductivity, and extraordinary thermal stability.Ion beam technology is a potential technique for controlled construction of CNTs.During collision with energetic ions, carbon atom of CNTs can get an adequate amount of energy to escape from the graphite lattice and produce a large number of defects.These defects are advantageous for adding some new functional groups and nanoparticles to modify CNTs.Meanwhile, the structure and atoms in the region of the defects can be rearranged and changed into amorphous structure, onion structure, and so on.These defects also can be used to form the junctions of CNTs and realize welding of CNTs and network formation of amorphous carbon nanowires.

Ultra-high-density silicon nanocone arrays with sharp tips have been fabricated by Ar+ sputtering at low temperatures. The investigation of SEM and AFM indicates that with an increasing substrate temperature from room temperature, 200 to 400°C, the density of silicon nanocone increases from 1–2 × 109, 3–4 × 109 to 1–2 × 1010 cm−2, respectively. The rooter diameter of the cones decreases from 120–150 to 40–50 nm and the tip angle of cones decreases from 32–36° to 20–26°. As predicted by the Bradley–Harper theory, the ripple wavelength decreases with substrate temperature during the carbon ripple formation process, which leads to an increase in the silicon nanocone density and a decrease in the silicon nanocone rooter diameter.

Silver nanowires are an ideal type of nano-electrode for electrochemical micromachining due to their large aspect ratio and good conductivity. In this paper, self-assembled silver nanowires electrode are used as the tool electrode for electrochemical micromachining. It shows that the silver nanowires fail in electrochemical micromachining. The failure mechanism is researched by computer simulation and experimentation. And the results show that the silver nanowires dissolve on account of the temperature rise when the temperature exceed the melting point of Ga. In addition, the chemical reaction of the silver nanowire in dilute sulfuric acid solution accelerates, intensifying the dissolution of the silver nanowire. Results indicate that the silver nanowire electrode is not suitable for electrochemical micromachining directly. Then, some protective measures should be taken for silver nanowire when it is used as tool electrode in electrochemical micromachining.

In situ Ti(C,N)-TiB2-Co cermets were produced by reactive hot-pressing from a Co-Ti-C-BN system. The reaction process and densification behavior were investigated through the comparative researches on the phase transition sequence, microstructure evolution pattern and shrinkage rate of powder compacts during sintering process. The results show that Ti(C,N) is synthesized via the dissolution of C into TiN unit cell, while TiB2 is formed through the combination of B and TiB as well as the reaction of Ti and B atoms in liquid. The viscose flow and dissolution precipitation mechanisms are responsible for the densification in the reaction stage, while the plastic flow method contribute to the elimination of closed micropores in the solid state sintering stage. An external pressure can promote the densification, and Ti(C,N)-based cermet sintered at 34 MPa pressure exhibits the maximum relative density and mechanical properties.

The CrN hard coatings with good surface roughness and good bonding strength were obtained on the M2 high speed steel substrate pretreated by polishing.The process parameters of high speed steel substrate pretreatment were studied by orthogonal design,such as different pressure,sand,dry or wet process parameters.The CrN hard coating was deposited on the pretreated substrate by multi-arc ion plating technique.The morphology,coating phase structure,coating roughness and coating adhesion of CrN coating were analyzed by scanning electron microscope (SEM),XRD,surface roughness measuring instrument and scratch tester.When the abrasive blasting pressure is higher and the sand hardness is higher,the coating roughness is larger,and the film base bonding strength is smaller.After the dry sand blasting pretreatment of glass bead sand material under 2bar pressure,the coating has the best comprehensive performance.The film-base adhesion of the coating is 78N,the surface roughness of the coating is 0.369 μ m,and the coating thickness is about 5 μm.The coating thickness is uniform,the coating surface is relatively smooth and dense,and there is no obvious hole structure.

The carbon nanotubes (CNTs) modified by the carbon particles with diameter of 120-180 nm are prepared by using hydrocarbon ion deposition techniques. Based on the investigation of scanning electron microscopy and transmission electron microscopy, the CNTs are decorated by some nanospheres with size of 120-180 nm randomly, and the full CNTs surface besides the area of nanosphere is coated by the graphene stacks with size of 10-15 nm. The nanospheres are composed of several nanoparticles of graphene stacks and are seamless connected with graphene stacks. The sparse distribution CNTs on Si substrate is crucial for the formation of carbon nanospheres. The formation of carbon nanospheres proceeds through the following three stages: the formation of graphene nanoparticle on CNTs surface and silicon substrate – the migration of active hydrocarbon groups towards the surface of the CNTs deposition zone at high temperature – the formation of carbon nanospheres by the aggregating hydrocarbon active groups.

Two-dimensional Zinc sulfide (ZnS) nanobowl arrays were synthesized via self-assembled monolayer polystyrene sphere template floating on precursor solution surface. A facile approach was proposed to investigate the morphology evolution of nanobowl arrays by post-annealing procedure. Photoluminescence (PL) measurement of as-grown nanoarrays shows that the spectrum mainly includes two parts: a purple emission peak at 382 nm and a broad blue emission band centering at 410 nm with a shoulder around 459 nm, and a blue emission band at 440 nm was obtained after the annealing procedure. ZnS nanoarrays with special morphologies and PL emission are benefits to their promising application in novel photoluminescence nanodevice.

Multi‐walled carbon nanotubes (MWCNTs) were irradiated by 1.2 keV Ar ion beams for 15–60 min at room temperature with current density of 60 µ A/cm 2 . The morphology and microstructure are investigated by scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. The results show that carbon nanofibers are achieved after 60 min ion irradiation and the formation of carbon nanofibers proceeds through four periods, carbon nanotubes—amorphous carbon nanowires—carbon nanoparticles along the tube axis—conical protrusions on the nanoparticles surface—carbon nanofibers from the conical protrusions.

以CaO-B2O3-SiO2 (CBS)玻璃粉体和Al2O3陶瓷粉体为原料,通过在CBS与Al2O3的质量比固定为50∶50的玻璃-陶瓷复合材料中添加适量的Bi2O3作为烧结助熔剂,探讨了Bi2O3助熔剂对CBS/Al2O3复合材料的烧结性能、介电性能、抗弯强度和热膨胀系数的影响规律.研究表明:Bi2O3助熔剂能通过降低CBS玻璃的转变温度和黏度促进CBS/Al2O3复合材料的致密化进程,于880℃下烧结即能获得结构较致密、气孔较少的CBS/Al2O3复合材料.然而,过量添加Bi2O3将使玻璃的黏度过低,从而恶化CBS/Al2O3复合材料的烧结性能、介电性能及抗弯强度.当Bi2O3的添加量为CBS/Al2O3复合材料的1.5wt％时,于880℃下烧结即能获得最为致密的CBS/Al2O3复合材料,密度为2.82 g· cm-3,这一材料具有良好的介电性能(介电常数为7.21,介电损耗为1.06×10-3),抗弯强度为190.34 MPa,0～300℃的热膨胀系数为3.52×10-6K-1.

A strategy is proposed for the synthesis of heterogeneous/homogeneous binary arrays via stepwise colloidal lithography, using ZnO and Ni as model materials. A series of controllable and specific binary arrays like pore/pillar, pore/pore, ring/triangle nanoparticle and ring/pore were designed and then fabricated. The periodicity of the binary array can be tuned by the size of the polystyrene spheres, the size and structure of each unit in the array can be selectively controlled by proper heat treatment, and the distance between the adjacent units of two arrays can be manipulated by the incidence angle of metal vapor flow. This study gives an effective guide to designing desired patterns of heterogeneous/homogeneous binary arrays and accurately determining their size and structure. Furthermore, this strategy allows two materials with different properties, such as magnetic, photonic, catalytic and semiconducting, to be assembled in one array with tunable arrangements, with potential applications in multi-function nanodevices.

The importance of failure analysis about high speed steel(HSS) cutting tools was expounded,and the main failure form was summarized.The failure mode such as brittle fracture,heat treatment cracking and insufficient hardness and so on was introduced.The failure reasons such as unqualified raw materials composition,overheating and decarburization and so on were studied.The methods and process of failure analysis from raw material composition and metallographic examination to heat treatment metallographic test were introduced.The inspection items,detection techniques and methods relating with the failure were summarized.