对烧熔结合剂碳化硅磨具的探讨

通过对结合剂的分析和实验,利用烧熔结合剂代替烧结结合剂制造碳化硅磨具,减少结合剂的用量,降低烧成温度,获得良好的磨削性能。

Solid-phase sintering process and forced convective heat transfer performance of porous-structured micro-channels

A solid-phase sintering process for the low-cost fabrication of composite micro-channels was developed. Three kinds of composite micro-channels with metallic porous structures were designed. The sintering process was studied and optimized to obtain porous-structured micro-channels with high porosity. The flow resistance and heat transfer performance in the composite micro-channels were investigated. The composite micro-channels show acceptable flow resistance, significant enhancement of heat transfer and dramatic improvement of flow boiling stability, which indicates a promising prospect for the application in forced convective heat transfer.

Rapid pressure-assisted sinter bonding in air using 200 nm Cu particles and enhancement of bonding strength by successive pressureless annealing

To design an effective and realistically applicable sinter bonding process for power devices,we proposed a two-step process using a 200 nm Cu-particle-based paste to form a bondline having high-temperature sustainability and superior thermal conductance.This process involved rapid pressure-assisted sinter bonding in air followed by pressureless annealing in a nitrogen atmosphere.In the case of a paste prepared with a mixture of 20 wt.%malic acid and 80 wt.%ethylene glycol,sinter bonding at 300℃and 5 MPa for only 30 s resulted in a sufficient shear strength of 23.1 MPa.The shear strength was significantly enhanced to 69.6 MPa by the additional pressureless aging for 30 min.Therefore,the two-step sinter bonding process is expected to provide an outstanding production rate as a next-generation sinter bonding process.

Effect of Mg composition on sintering behaviors and mechanical properties of Al-Cu-Mg alloy

Al-3Cu-Mg alloy was fabricated by the powder metallurgy(P/M) processes. Air-atomized powders of each alloying element were blended with various Mg contents(0.5%, 1.5%, and 2.5%, mass fraction). The compaction pressure was selected to achieve the elastic deformation, local plastic deformation, and plastic deformation of powders, respectively, and the sintering temperatures for each composition were determined, where the liquid phase sintering of Cu is dominant. The microstructural analysis of sintered materials was performed using optical microscope(OM) and scanning electron microscope(SEM) to investigate the sintering behaviors and fracture characteristics. The transverse rupture strength(TRS) of sintered materials decreased with greater Mg content(Al-3Cu-2.5Mg). However, Al-3Cu-0.5Mg alloy exhibited moderate TRS but higher specific strength than Al-3Cu without Mg addition.

Design and characterization of Ti6Al4V/20CoCrMo−highly porous Ti6Al4V biomedical bilayer processed by powder metallurgy

The aim of this work was to develop a Ti6Al4V/20CoCrMo−highly porous Ti6Al4V bilayer for biomedical applications.Conventional powder metallurgy technique,with semi-solid state sintering as consolidation step,was employed to fabricate samples with a compact top layer and a porous bottom layer to better mimic natural bone.The densification behavior of the bilayer specimen was studied by dilatometry and the resulting microstructure was observed by scan electron microscopy(SEM)and computed microtomography(CMT),while the mechanical properties and corrosion resistance were evaluated by compression and potentiodynamic tests,respectively.The results indicate that bilayer samples without cracks were obtained at the interface which has no negative impact on the densification.Permeability values of the highly porous layer were in the lower range of those of human bones.The compression behavior is dictated by the highly porous Ti6Al4V layer.Additionally,the corrosion resistance of Ti6Al4V/20CoCrMo is better than that of Ti6Al4V,which improves the performance of the bilayer sample.This work provides an insight into the important aspects of a bilayer fabrication by powder metallurgy and properties of Ti6Al4V/20CoCrMo−highly porous Ti6Al4V structure,which can potentially benefit the production of customized implants with improved wear performance and increased in vivo lifetime.

Microstructure and properties of ultra-fine tungsten heavy alloys prepared by mechanical alloying and electric current activated sintering

The microstructure and properties of the 93W-4Ni-2Co-1Fe(mass fraction,%) tungsten heavy alloys prepared by mechanical alloying and electric current activated sintering from mixed elemental powders were investigated.After 15 h milling,the average W grain size in the powders is decreased to 120 nm.For the powders milled for 15 h,the density,hardness and transverse rupture strength of the alloys sintered only by an intensive pulse electric current are the maximum.When the total sintering time keeps constant,the properties of the sintered alloys can be obviously improved by optimizing the sintering time of pulse-and constant-currents.A bulk ultrafine alloy with an average W grain size of about 340 nm can be obtained by sintering 15 h-milled powders in a total sintering time of 6 min.The corresponding sintered density,hardness and transverse rupture strength reach 16.78 g /cm3,HRA84.3 and 968 MPa,respectively.

Microstructure and properties of alumina-silicon carbide nanocomposites fabricated by pressureless sintering and post hot-isostatic pressing

A1203/5%SIC nanocomposites were fabricated by pressureless sintering using MgO as a sintering aid and then post hot-isostatic pressed （HIP）, which can subsequently break through the disadvantage of hot-pressing process. The MgO additive was able to promote the densification of the composites, but could not induce the grain growth of A1203 matrix due to the grain growth inhibition by nano-sized SiC particles. After HIP treatment, A12OJSiC nanocomposites achieved full densification and homogeneous distribution of nano-sized SiC particles. Moreover, the fracture morphology of HIP treated specimens was identical with that of the hot-pressed A1203/SiC nanocomposites showing complete transgranular fracture. Consequently, high fracture strength of 1 GPa was achieved for the A1203/5%SIC nanocomposites by pressureless sintering and post HIP process.

Effect of annealing on microstructure and properties of Si_3N_4-AlN composite ceramics

Aiming at developing novel microwave-transparent ceramics with low dielectric loss, high thermal conductivity and high strength, Si3Na-AIN （30%, mass fraction） composite ceramics with La203 as sintering additive were prepared by hot-pressing at 1 800 ℃ and subsequently annealed at 1 450 ℃ and 1 850 ℃ for 2 h and 4 h, respectively. The materials were characterized by XRD and SEM. The effect of annealing process on the phase composition, sintering performance, microstructure, bending strength, dielectric loss and thermal conductivity of the materials was investigated. The results showed that both annealing at 1 850 ℃ and 1 450 ℃ promoted the phase transformation of α-Si3N4 to β-Si3N4. After annealing at 1 850 ℃, grain growth to a certain extent occurred in the materials. Especially, the elongated β-Si3N4 grains showed a slight increase in diameter from 0.2 μm to 0.6 μm approximately and a decrease in aspect ratio. As a result, as the annealing time increased to 4 h, the bending strength declined from 456 MPa to 390 MPa, whereas the dielectric loss decreased to 2.15× 10^-3 and the thermal conductivity increased to 16.3 W/（m.K） gradually. When annealed at 1 450 ℃, increasing the annealing time to 4 h significantly promoted the crystallization of glassy phase to La2Si6N803 phase in the materials, which led to the increase in bending strength to 619 MPa and thermal conductivity to 15.9 W/（m·K）, respectively, and simultaneously the decrease in dielectric loss to 1.53× 10^-3.

钠插层的层状锰氧化物的制备及其电化学性能

目的:制备不同钠含量层状锰氧化物应用于超级电容器的电极材料。方法:以高锰酸钾为氧化剂,葡萄糖为还原剂,采用水热法制备不同钠含量层状锰氧化物。经XRD显示在(100)晶面处呈现较好峰值,且在最佳钠加入量(65%)下材料(100)晶面的衍射峰向低角度偏移,说明适量的钠离子含量能够增加锰氧化物的层间距。SEM结果显示出最佳产品微观形貌呈现片层结构,团聚程度最小,结构更加蓬松,经EDX检测可知其钠相对于锰的原子含量为10.24%。TEM显示材料为规则的六角形片状结构且表层具有大量的微孔。通过对其EIS图谱的分析,最优样品电荷转移直线斜率较未掺杂时更接近90°,说明材料具有更优的比电容特性。结果:当钠离子加入量为65%时,1 A/g下首次放电比容量可达205.9 F/g,1000次循环后容量保持率为100%。结论:在钠掺杂为65%时钠掺杂具有较好的电容特性。

A simple approach to porous low-temperature-sintering BaTiO_3

Porous tetragonal BaTiO 3 ceramic was successfully prepared by a combination of hydrothermal and low-temperature-sintering method.The hollow TiO2@BaCO 3 as the sintering precursor was synthesized via a simple hydrothermal method,and then porous BaTiO 3 was generated by calcining the hollow TiO2@BaCO 3 precursor at 900 ℃ without additive.The hollow TiO2@BaCO 3 structure plays two important roles in the preparing of the porous BaTiO 3 ceramic.First,the TiO2@BaCO 3 hollow structure provides high surface areas and increases the contact points between BaCO 3 and TiO2,which can reduce the sintering temperature of the BaTiO 3 ceramic.Second,the cavity of the ordered arranged TiO2@BaCO 3 hollow sphere shows important influence on the porous structure,and the pore size of the as-prepared porous BaTiO 3 ceramic can be tuned from several nanometers to hundreds nanomters by changing the sintering temperature.The formation mechanism of the porous BaTiO 3 ceramic was proposed.