Preparation of Mg-Ti System Alloy and FGM with Density Gradient by Spark Plasma Sintering Technique

A new kind of functionally graded materials (FGM) with density gradient has come to show great potentials as flier-plates for creating quasi- isotropic compression waves. In order to meet the demand of lower density in the front face for such flier-plate, Mg with a low density of 1.74g/cm^3 is selected to make a Mg-Ti FGM. Mg- Ti alloys with various weight ratios were siatered by spark plasma sintering ( SPS ) technique at relative low temperatures, and the processing of densification is mainly investigated. It is found that, up to 75wt% Ti , the Mg- Ti alloys can be fully densified at 560℃ due to the conglutinnation of Mg and the formation of a small amount of Mg- Ti solid solution. Finally, the Mg- Ti FGM with a density gradient from 1.74g/cm^3 to 3.23 g/cm^3 is successfully fabricated.     

Fabrication of Fe-6 .Swt%Si Bulk by Spark Plasma Sintering

Fe-6.5 wt % Si composite compact was fobricated by spark plasma sintering (SPS) . Mechanical alloying( MA )was used to prepare Fe-Si composite powders. The composite powders were sintered by SPS at elevsated temperature from 500℃ to 700℃ . The experimental results indicate that the non-equilibrium state of composite Fe-Si is preserved in the compact. The density of the bulk rises with the increasing temperature and there is no diffusion of silicon and iron in the interface.     

Spark plasma sintering of undoped SnO<Subscript>2</Subscript> ceramics

Various parameters in spark plasma sintering(SPS),such as sintering temperature,holding time,heating rate,and pressure,were adopted to investigate their effects on the densification of pure SnO2 power.The obtained experimental data show that the SPS process enhances densification.The high-density undoped SnO2 ceramics (96.6% of theoretical) was obtained at much lower temperature (1000℃),within a much shorter time,compared to the conventional sintering process.The high-density undoped SnO2 ceramics (96.6% of theoretical) were obtained by SPS,under the condition of temperature:1000℃,pressure:40MPa,heating-rate:200℃/min,and holding time:3min     

Influence of plasma on the densification mechanism of SPS under multi-field effect

The densification mechanism of an Fe-based alloy powder containing tiny oxide particles under the synergic multi-field effect of spark plasma sintering （SPS） was investigated. Metallographic microscopy and scanning electron microscopy were used to observe the morphology of samples sintered at different temperatures, and the temperature dislribution in an individual spherical powder particle during sintering was calculated in consideration of the influence of plasma, which was qualified and quantified through the analysis of the U-Icurve. The plasma was observed to play a substantial role in activating and heating the samples at the very early stage of sintering, whereas the joule-heat effect played a dominant role during sintering. Moreover, the plasma also facilitated the diffusion and migration of materials for neck formation.     

Sintering behaviors of porous 316L stainless steel fiber felt

Isothermal sintering experiments were performed on the 316 L stainless steel fiber felts with fiber diameters of 8 μm and20 μm. Surface morphologies of the sintered specimens were investigated by using scanning electron microscopy(SEM) and optical microscopy. The results show that the amount of the sintering necks and the relative densities of the fiber felt increase with the increasing of both the sintering temperature and the sintering time. And the activation energies estimated present a decline at high relative densities for both 8 μm and 20 μm fiber felts. Moreover, the sintering densification of the fiber felts is dominated by volume diffusion mechanism at low temperature and relative densities. As more grain boundaries are formed at higher temperature and relative density, grain boundary diffusion will also contribute to the densification of the specimen.     

Preparation and properties of crystallizable Glass/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composites for LTCC material

The investigated low temperature Co fired ceramics(LTCC) composite of 60wt% CaO-Al2O3-B2O3-SiO2 glass and 40wt% α-Al2O3 as a filler is a non-reactive system, which is a critical part of the low temperature Co fired ceramics process. Through a study on densification process, the phase transformation and microstructure can be revealed. Its composites typically consist of CaO-Al2O3-B2O3-SiO2 glass and α-Al2O3 powders of average particle size (D50=3.49 mm). The sintering behavior, phase evaluation, sintered morphology, and microwave dielectric properties were investigated. In the fire range of 800 to 900 ℃, the composites were crystallized after completion of densification. It is found that the composites start to densify at 825 ℃, simultaneously, the dielectric constant (εr) reaches its maximum. With increasing heat-treatment temperatures, due to the loose microstructure of the material, tanδ increases slightly. The last of the sintered samples were identified as partly Anorthite at 850 ℃. At that temperature it has εr of 7.9 and tanδ less than 1×10-3, and can be used as a promising LTCC material.     

Electrical property of 8-mol% yttria-stabilized zirconia electrolyte by spark-plasma sintering

The 8-mol% yttria-stabilized zirconia (8YSZ) is widely chosen as electrolytes in solid oxide fuel cells (SOFC) and oxygen sensors because of its excellent high- temperature ionic conductivity[1—4]. The ionic conductivity of the electrolyte is strongly related to the microstructure of the electrolyte. Gibson et al. [5] investigated the relation-ship between the density of YSZ and its corresponding ionic conductivity. Spark-plasma sintering (SPS) is a relatively new sintering method fo…     

Synthesis and spark plasma sintering of Al-Mg-Zr alloys

Although casting is commonly used to process aluminum alloys, powder metallurgy remains a promising technique to develop aluminum based materials for structural and functional applications. The possibility to synthesize Al-Mg-Zr alloys through mechanical alloying and spark plasma sintering techniques was explored. Al-10Mg-5Zr and Al-5Mg-1Zr alloyed powders were synthesized through wet ball milling the appropriate amount of elemental powders. The dried milled powders were spark plasma sintered through passing constant pulsed electric current with fixed pulse duration at a pressure of 35 MPa. The samples were vacuum sintered at 450, 500, 550, 600 and 620℃ for 10, 15 and 20 min. The Al-10Mg-5Zr alloy displays poor densification at lower sintering temperatures of 450, 500, 550 and 600℃. Its sinterability is improved at a temperature of 620℃ whereas sintering temperatures higher than 620℃ leads to partial melting of the alloy. It is possible to sinter the Al-5Mg-1Zr alloy at 450, 500 and 550℃. The increase of sintering temperature improves its densification and increases its hardness. The Al-5Mg-1Zr alloy displays better densification and hardness compared to Al-10Mg-5Zr alloys.     

High-pressure Sintering of Boron Carbide-Titanium Diboride Composites and Its Densification Mechanism

A high-pressure hot-pressing process was applied to densify a commercial boron carbide-titanium diboride (B_4C-TiB_2) powder mixture.Nearly fully dense (98.6%) materials were obtained at 1700℃ under a pressure of 100MPa.Compared to the sintering temperature required to achieve similar results when a pressure of only 30MPa was applied,the sintering temperature was found to decrease by about 200℃ under pressure of 100 MPa.Analysis of the thermodynamics and microstructure showed that the plastic deformation of the B_4C grains induced by high pressure dominated the densification mechanism when high pressure was applied.Furthermore,higher pressure resulted in remarkably improved mechanical properties of the composites,which could be traced back to the generation of stacking faults in the B_4C grains and aggregation of TiB_2.     

THE CHARACTERISTICS OF THE PRESSURELESS SINTERED Si_3N_4-MgO-Ce0_2 CERAMICS

An investigation of the pressureless sintering of Si3N4 with MgO-CeO2 revealed that MgO-CeO2 is a most effective sintering aid for silicon nitride. The amount of MgO-CeO2 and sintering conditions have a strong influence on the densification behaviour and mechanical properties of the sintered materials. The effect of the additive and sintering conditions are discussed. The silicon nitride pressureless sintered with MgO-CeO2 retained a relative density of 98. 5% and a bending strength of 950 MPa. The Si Mg-Ce-O-N system is of great value for application and theoretical study.     

放电等离子烧结制备碳化钛块材研究

利用放电等离子烧结（SPS）对碳化钛（TiC）/氢化钛（TiH2）混合粉末进行烧结以制备块材。利用X射线衍射（XRD）并结合Rietveld精修法对块材进行定性与结构分析;借助扫描电子显微镜（SEM）对块材断面微观形貌进行观察;测试了块材硬度并探讨SPS技术制备TiC块材的致密化过程与反应机理。结果表明：混合粉末经SPS烧结,获得了高度致密的TiC块材;与传统烧结方法比较,SPS技术更具低温快速性。     

Comparative study of β-Si3N4 powders prepared by SHS sintered by spark plasma sintering and hot pressing

β-Si3N4 powders prepared by self-propagating high-temperature synthesis (SHS) with additions of Y2O3 and Al2O3 were sintered by spark plasma sintering (SPS). The densification, microstructure, and mechanical properties of Si3N4 ceramics prepared using this method were compared with those obtained by hot pressing process. Well densified Si3N4 ceramics with finer and homogeneous microstructure and better mechanical properties were obtained in the case of the SPS technique at 200℃ lower than that of hot pressing. The microhardness is 15.72 GPa, the bending strength is 716.46 MPa, and the fracture toughness is 7.03 MPa.m1/2.     

Consolidation and microstructures of microwave sintered W-25Cu alloys with Fe addition

W-25Cu alloys were microwave sintered in a 2.45 GHz multimode applicator. The densification, microstructure and their dependence on sintering mode and Fe addition were investigated in detail. Owing to the volumetric heating intrinsic in microwave processing, a microstructure with larger W grain size in center regions was observed as against larger grain size in edge regions for conventional sintering. Microwave sintering demonstrates its intrinsic advantages such as rapid heating rate, densification enhancement and microstructural homogeneity; but it undesirably promotes W grain growth. Under microwave sintering, the role of Fe addition on compact consolidation is not so substantial as under conventional sintering. Moreover Fe degrades the microstructural quality, generating worse uniformity and coarser W grains.     

Atomic force microscope study of WC-10Co cemented carbide sintered from nanocrystalline composite powders

In order to compare the spark plasma sintedng （SPS） process plus hot isostatic press （HIP） with vacuum sintedng plus HIP, an investigation was carried out on the topography, microstructure and gain size distribution of nanocrystalline WC-10Co composite powder and the sintered specimens prepared by SPS plus HIP and by vacuum sintering plus HIP by means of atomic force microscopy （AFM）. The mechanical properties of the sintered specimens were also investigated. It is very easy to find cobalt lakes in the specimen prepared by vacuum sintering plus HIP process. But the microstructure of the specimen prepared by SPS plus HIP is more homogeneous, and the grain size is smaller than that prepared by vacuum sintering plus HIP. The WC-10Co ultrafine cemented carbide consolidated by SPS plus HIP can reach a relative density of 99.4%, and the transverse rupture strength （TRS） is higher than 3540 MPa, the Rockwell A hardness （HRA） is higher than 92.8, the average grain size is smaller than 300 nm, and the WC-10Co ultrafine cemented carbide with excellent properties is achieved. The specimen prepared by SPS with HIP has better properties and microstructure than that prepared by vacuum sintering with HIP.     

Synthesis and Sintering of Mg2Si Thermoelectric Generator by Spark Plasma Sintering

Raw Mg,Si powder were used to fabricate Mg2Si bulk thermoelectric generator by spark plasma sintering (SPS).The optimum parameters to synthesize pure Mg2Si powder were found to be 823 K,0 MPa,10 min with excessive content of 10wt% Mg from the stoichiometric Mg2Si.Mg2Si bulk was synthesized and densified simultaneously at low temperature (823 K) and high pressure (higher than 100 MPa) from the raw powder,but Mg,Si could not react completely,and the sample was not very dense with some microcracks on the surface.Then,Mg,Si powder reacted at 823 K,0 MPa,10 min in SPS chamber to form Mg2Si green compact,again sintered by SPS at 1023 K,20 MPa,5 min.The fabricated sample only contained MgESi phase with fully relative density.     

Mechanism of conductive powder microstructure evolution in the process of SPS

Spark plasma sintering (SPS) is an advanced sintering technology that has been re-cently developed mainly in Japan. It has the advantages of the rapid heating rate (1000℃/min), short holding time (3―5 min), rapid cooling, controllable pressure and sintering atmosphere, as well as the special feature of the environment compatibility[1]. Up to now it has been used to fabricate various materials such as pure metal, alloys, ceramics, composites and polymer materials, especially, some new-type m…     

图像分析技术分析晶粒对Ti_3AlC_2/TiB_2材料性能的影响

采用DS-5M图像分析仪分析了不同TiB2含量的Ti3AlC2/TiB2复合材料微观晶粒大小和分布情况,分析结果表明,TiB2体积含量为10%的烧结样品晶粒发育较完善,分布也较均匀,随着TiB2含量的增加,层状晶粒的生长受到进一步的抑制,晶粒尺寸明显变小。采用阿基米德常数法测定烧结试样的密度,发现TiB2体积含量为10%的烧结样品相对密度最大,达到99.07%,TiB2体积比含量超过10%,相对密度逐渐减小;SPS烧结过程中TiB2体积含量少于10%时,样品呈现一个很窄的快速致密化阶段,随着TiB2含量的增加,原料发生反应所需温度升高和反应过程所需时间增加,降低了材料的致密化程度。可见图像分析复合材料微观晶粒的情况能很好地呼应材料宏观性能测试结果,提供了一种有效的测试分析手段。     

Preparation of Superfine-Cemented Carbide by Spark Plasma Sintering

92WC-8Co puwder mixture with superfine-tungsten carbide was respectively sintered by spark plasma sintering（ SPS ） and sintering isostutic pressure （SIP）. Complete dense samples with 200 nm WC grains and 94.2HRA hardness were prepared by spark plasma sintering at 1 150 ℃ and under 4.5 kN for 5 minutes. SIP was carried out at 1 400 ℃ for 30 minutes with a result of 300-400 nm WC grains and 93 HRA hardness. The results show that sintering temperature is greatly decreased by SPS, sintering time is largely shortened and WC grain growth is effectively retarded. Micropores and drawb（wks in superfine-cemented carbide made by SPS are greatly declined, which is very useful to improving nwehanical properties.