混料时间对航空刹车摩擦材料性能的影响

研究了航空刹车摩擦材料混合料的混料时间对烧结后摩擦材料性能的影响。通过检测混合料不同部位的含碳量和烧结材料的硬度及摩擦磨损性能 ,结果发现 ,混合料的均匀度与混料时间关系不大 ,而烧结摩擦材料的硬度随混料时间的增加而降低。混料 16h比混料 8h的烧结材料硬度下降了 10HRF。随混料时间增加 ,摩擦系数增加 ,材料的磨损增加 ,而对偶的磨损下降。通过 5 0次刹车试验的平均总磨损 (材料磨损加对偶磨损 )、平均摩擦系数和摩擦材料崩块情况对比 ,表明混料 6～ 1 0h的烧结材料具有良好的摩擦磨损性能 ,其摩擦系数为 0 .1 92～ 0 .2 0 5 ,总磨损为 3 .78～ 3 .90 μm/次 ,无崩块 ,材料的烧结硬度为 6 2 .5～ 6 6 .8HRF。

用陶瓷金刚石砂轮加工CVD滚轮的试验研究

本试验利用自主研发编号为DG型的多元氧化物陶瓷结合剂,此结合剂具有高强度、低膨胀系数、烧成温度低的性能。采用特殊炼制工艺,利用热压烧结成型法制作成修整CVD滚轮用的陶瓷结合剂金刚石砂轮。通过在外圆磨床M1420上现场修整,对用于齿轮加工的CVD金刚石滚轮进行磨削试验,最终达到CVD滚轮鼓型精度的提高,极大的解决了CVD滚轮的崩边问题,修整效果及磨削性能指标较原来有很大提高。砂轮选用的金刚石粒度为140/170,以不同磨块成型密度,不同烧结硬度,根据不同的磨削参数,进行对比磨削试验,测定最佳试验效果来最终确定最佳砂轮制作工艺参数。

Microstructure evolution and mechanical properties of spark plasma sintered W-Ni-Mn alloy

Tungsten heavy alloys(90W-6Ni-4Mn)were prepared through spark plasma sintering(SPS)using micron-sized W,Ni,and Mn powders without ball milling as raw materials.The effects of sintering temperature on the microstructure and mechanicalproperties of the90W-6Ni-4Mn alloys were investigated.SPS technology was used to prepare90W-6Ni-4Mn alloys withrelatively high density and excellent comprehensive performance at1150-1250°C for3min.The90W-6Ni-4Mn alloys consistedof the W phase and theγ-(Ni,Mn,and W)binding phase,and the average grain size was less than10μm.The Rockwell hardness andbending strength of alloys first increased and then decreased with increasing sintering temperature.The best comprehensiveperformance was obtained at1200°C,its hardness and bending strength were HRA68.7and1162.72MPa,respectively.

Sintering kinetics of Ni_2FeSb powder alloys produced by mechanical milling

A ternary Ni2FeSb shape memory alloy was fabricated by powder metallurgy route. Sintering kinetics was estimated from dilatometry tests; whereas the microstructure and morphology of the powder and consolidated bulk samples were evaluated by XRD and SEM, respectively. Microhardness tests were performed on the surface of sintered samples. The results indicated that milling time has an effect on the shape and particle size as well as the homogeneity of the crystalline structures of the powders. Samples with longer milling time presented higher relative densities, better distribution of the elements on the alloy as well as the L21 and martensite phases, which will give the shape memory effect. The estimated activation energy values ranged from 109 to 282 kJ/mol at temperatures between 750 and 1273 K, indicating that sintering is controlled mainly by volume diffusion. Microhardness was improved by increasing the milling time and the heating rate.

Constrained sintering and wear properties of Cu-WC composite coatings

Coatings of metal matrix composites(Cu?WC)were fabricated by solid-state sintering.WC reinforcing particles indifferent quantities from5%up to30%(volume fraction)were mixed with Cu particles.After mixing,the powders were poured ontothe surface of copper substrates.Sintering was carried out at1000°C under a reducing atmosphere in a vertical dilatometer.Sinteringkinetics was affected by both rigid substrates and WC particles which retarded the radial and axial densification of powders.However,the coatings were strongly attached to the substrate,and WC particles were randomly distributed within the matrix.The addition ofthe reinforcing particles enhanced the microhardness and reduced the volume loss in wear tests to1/17compared to the unreinforcedsample.The predominant wear mechanism was identified as abrasion at a load of5N.20%WC(volume fraction)reinforcingparticles led to the maximum values of properties for the composite coating.

Preparation,characterization and densification studies of W-Ag nanocomposites produced by chemical route

W-Ag has applications in a wide range of cutting-edge fields,counting heat sinks and microwave absorbers for micro—electronic components,electric arc ends,and filaments for welding processes,electrical contacts,and durable electronic connections.Chemical methods provide a number of benefits,including improved purity,and controlled particle size.The present study focused on the fabrication of W-Ag nano composites using chemical synthesis.W-Ag nanocomposites with average size less than 50 nm were synthesized using Tungsten hexacarbonyl(W(CO)_(6),and silver acetate(CH_(3)-COOAg)as metal precursors in the present study.The W-Ag composites were sintered using conventional sintering.X-ray diffraction studies of as-prepared powders showed amorphous W-phase and FCC Ag,while sintered W-Ag composites exhibited crystalline BCC W and FCC Ag phase.The effect of sintering temperature on relative density and mechanical properties of W-Ag sintered compacts was investigated.Relative density in excess of 97.6%,98.2%and 98.8%was achieved for W-20.3 wt.%Ag,W-30.1 wt.%Ag and W-39.8 wt.%Ag composites on conventional sintering at 1000℃ for 1 h.Vickers hardness of 364±10 and 320±8 Hv and 279±6 were achieved for W-20.3 wt.%Ag,W-30.1 wt.%Ag and W-39.8 wt.%Ag composite compacts respectively.The hardness value of W-Ag composites decreased with an increase in Ag content.The combination of properties realized in this study renders the composites suitable for automotive and heat sink applications.

日本出土的唐三彩

本文从日本奈良县、京都府等48个遗址中出土的唐三彩中，有选择地介绍了三彩碗、三彩陶枕、三彩瓶等12种器形的唐三彩，并分析了在日本出土的唐三彩的性质。文章以日本出土的唐三彩残片的数量及出土唐三彩遗址的性质为根据，指出日本出土的唐三彩，并不是作为贸易品而传入日本的，而是作为寺院的祭北用器由遣唐僧带回日本的。由遣唐使带回日本供达官贵人作为奢侈品消费的唐三彩，仅占其中的极少一部分。