Sialon结合刚玉材料凝胶注模成型及其性能

研究了Sialon结合刚玉耐火材料浓悬浮体的流变性能和稳定性能.固相体积分数79%的悬浮体,在中等剪切速率时表现剪切变稀特征,剪切速率10～100 s-1范围表现出突出的"切稀"行为,符合凝胶注模成型的要求.计算了在剪切速率10～20s-1范围内的Bingham值为22960Pa,建立的流变模型为:σ=22960 391 γ.凝胶注模成型后的坯体具有3.11g/cm3的体积密度和14MPa的抗折强度.烧结材料的物相组成为刚玉和Sialon,六方柱状Sialon晶体发育完整,具有均匀一致的显微结构,性能达到了使用机械成型产品的性能,高温抗折强度提高3.8倍.     

结合相对SiC基复相材料高温氧化行为的影响

利用X-射线衍射仪、扫描电镜和热重分析仪等手段,在1100～1500℃研究了Sialon结合SiC复相材料的高温抗氧化行为。结果表明:随氧化温度升高,由于氧化致密层的形成,试样氧化增重速率降低,出现氧化钝化现象;Sialon结合SiC复相材料高温抗氧化性能优于Si3N4结合SiC复相材料;高温氧化使得SiC质复相材料常温抗压强度比氧化前提高;随氧化温度升高,Sialon结合SiC复相材料的氧化膜表面形成较多气泡和开口空洞,使耐压强度呈下降趋势;Si3N4结合SiC复相材料随氧化温度升高,耐压强度降低,这是由于冷却过程方石英化伴生的网状裂纹密度增大。     

放电加工用金属结合剂碳化硅工具的研究

本文利用热压烧结工艺制备了含有20vol％～50vol％SiC的放电加工用金属结合剂工具电极。采用非均相沉淀包裹法制得Cu包SiC复合粉体。并对试样的气孔率、电阻率、抗弯强度进行了研究，结果表明，随着SiC含量的增加，试样气孔率和电阻率提高，而抗弯强度下降；在20vol％-50vol％SiC含量范围内，采用直接混合法和包裹法制备的试样具有大致相同的气孔率、电阻率，但包裹法的强度却大大提高。用X—ray衍射、扫描电镜（SEM）、能谱分析（EDAX）等测试手段对试样进行了成分和微观形貌分析。研究结果表明，包裹法制得的Cu结合SiC试样，SiC分散更均匀，并通过形成Cu2O—SiO2共熔物（玻璃相）来提高SiC和Cu的界面结合强度。     

碳化钛悬浮体分散特性和流变性能的研究

通过对碳化钛粉体在去离子水介质中的Zeta电位和浓悬浮体的粘度等测试，详细研究了碳化钛浓悬浮体的分散特性以及流变行为。实验结果表明，碳化钛粉体的等电点在pH=2，添加分散剂可以使碳化钛的Zeta电位绝对值增大。调整分散剂用量可制备出固相体积含量高达52％的碳化钛浓悬浮体，该悬浮体能够达到均一稳定的分散，其流变行为在低剪切速率下符合Power-law模型、高剪切速率下符合Quemada模型。     

金属核心--高聚物膜复合悬浮相电流流变体材料的研究

电流变流体(简称ERF)是一种具有广泛应用前景的功能材料.一般认为电流变流体中的悬浮相对电流变效应起着决定作用,因此悬浮相材料的研究与开发有着重大的理论意义和工程应用价值.本文针对电流变流体悬浮相材料的开发与研究,应用乳液聚合一相分离法制备了金属核心一高聚物膜电流变流体复合悬浮相材料,并对其电流变流体性能进行测定,结果表明乳液聚合一相分离法是实验室条件下制备金属核心一高聚物膜电流变流体复合悬浮相的有效方法,乳液聚合可以有效地控制高聚物的结构,高整其粘度,获得合适的复合悬浮相的颗粒粒径.包覆的效果主要由高聚物膜与金属核心的酸碱性决定,因此"酸碱匹配”是选择包覆材料的的重要依据.如Lewis酸选择金属.Al、Zn、Ni或其氧化物,则Lewis碱应选择高聚物;乳液聚合一相分离法中凝聚剂也影响着包覆效果,强亲水性强电解质NaCl作为乳液聚合一相分离法中凝聚剂能实现最佳包覆.金属核心一高聚物膜复合悬浮相电流变流体的电流变效应的强弱,取决于金属核心和包覆膜的共同作用.金属核心激发产生空间电荷极化,增强电流变效应,金属越活泼,金属核心在复合悬浮相中所占比例越高,电流变效应越强;包覆膜则主要防止漏电,保证极化效果的实现与发挥.聚苯乙烯一丙烯酸丁酯(比例101)与Zn形成的复合悬浮相其电流变流体的电流变效应较强,又无漏电电流,是综合性能较好的悬浮相材料,是今后可以进一步改进与提高的悬浮相材料.     

SiC颗粒对轧辊表面镀层应力影响的有限元分析*

目前针对多颗粒复合镀层有限元模型的建立尚不准确。以轧辊的服役工况为背景,利用Python语言和ABAQUS软件建立试块底面带有SiC颗粒增强Ni基复合镀层的环-块滑动摩擦有限元模型,系统研究SiC颗粒含量和尺寸对涂层表面及涂层-基体界面峰值等效应力的影响规律。结果表明：当SiC颗粒含量为3 vol.%～9 vol.%时,涂层表面和涂层-基体界面峰值应力随颗粒含量的增大而增大,分别增大了78.01%和32.06%;当SiC颗粒含量为9 vol.%～15 vol.%时,随着颗粒含量的增大,涂层表面峰值应力呈下降趋势,降低了13.02%,而涂层-基体界面峰值应力基本保持不变;当SiC颗粒直径为0.8～1μm时,涂层表面及涂层-基体界面峰值应力随颗粒尺寸的减小而增大,分别增大了51.5%和32.6%;当SiC颗粒直径为0.3～0.8μm时,涂层表面及涂层-基体界面峰值应力基本保持不变。综合考虑轧辊表面镀层的性能需求以及实际复合电镀工艺,依据界面应力与镀层结合状态之间的关系,SiC颗粒含量以9 vol.%左右为宜,SiC颗粒直径以0.8μm左右为宜。所建立的多颗粒随机分布涂层基体的有限元模型更接...     

SiC／CoSb3复合热电材料的制备及热电传输特性

以Co、Sb粉体为原料，利用机械合金化（MA）和放电等离子烧结（SPS）法制备SiC／CoSb3复合热电材料。采用X-射线衍射法确定机械合金化粉末和SPS烧结块体的相组成，用透射电子显微镜（TEM）观察粉体形貌和块体的显微结构。在300～800K范围内测量了复合热电材料的电阻率、塞贝克系数和功率因子，研究了纳米SiC颗粒的添加对复合材料热电性能的影响。研究结果表明，SiC颗粒的引入使复合材料的电阻率降低，功率因子提高。在680K时0．1vol％SiC／CoSb3复合材料的功率因子比单相CoSb3热电材料提高了约100μW／m·K^2。     

C／C-SiC材料的快速制备及显微结构研究

分别以碳毡和二维碳纤维为预制体，采用化学液相气化渗入法结合熔融渗硅反应法快速制备了C／C-SiC陶瓷复合材料。对这种材料的密度和气孔率进行了表征，并通过XRD，OM和SEM等方法对其相组成、显微结构和反应机理进行了研究。结果表明：不同预制体制备的C／C—SiC材料密度和气孔率分别为～2．0g／cm^3和～1．0％。其相组成包括反应生成β-SiC以及未反应的游离Si和C。C／C—SiC中纤维被环状的沉积碳包裹，生成SiC的反应只发生在Si与沉积碳之间，纤维没有损伤。Si，C和SiC各相分布和含量因预制体的不同而有明显差异。     

原位合成SiC/MoSi2复合材料的研究

以Mo、Si、C原始粉末为原料,进行机械球磨混合制备混合粉,然后进行原位反应热压烧结制备SiC/MoSi2复合材料.利用X射线衍射仪、扫描电镜对试样进行物相和显微组织观察,并对原位反应机制进行了探讨.结果表明,在选定的球磨条件下,Mo、Si、C混合粉没有发生机械合金化;Mo-Si-C三元系混合粉在原位反应条件下可消除Mo5Si3C等中间相,得到的颗粒细小、相分布均匀以及相组成为SiC与MoSi2的SiC-40vol％/MoSi2复合材料.     

工艺参数对Mo/Cu粉末凝胶注模成形的影响

本文采用甲基丙烯酸羟乙酯（HEMA）-1,6-己二醇二丙烯酸酯非水基凝胶注模体系制备了浓Mo/Cu粉末浆料。研究了分散剂用量、单体含量和固相体积分数对浆料流变行为的影响。并研究了单体含量、单体/交联剂比例、引发剂用量、温度等工艺参数对固化行为和坯体抗弯强度的影响。结果表明,固相体积分数对浆料就变行为的影响最大,其次是引发剂用量和单体含量。随着单体含量的增加和单体/交联剂比例的减小,坯体抗弯强度增加;引发剂用量对坯体抗弯强度的影响较小。根据上述结果,Mo/Cu粉末非水基凝胶注模的合理工艺参数如下：HEMA含量为25 vol.% ~ 30 vol.%, 单体/交联剂比例为10：1 ～ 15：1,引发剂用量为1.5 vol.% ~ 2.5 vol.%,固化温度在60℃与80℃之间。     

Near-net shaped Al/SiCP composites via vacuum-pressure infiltration combined with gelcasting

To solve the problem of difficult machining, the near-net shaped Al/SiC_P composites with high volume fraction of SiC particles were fabricated by vacuum-pressure infiltration. The SiC_P preform with a complex shape was prepared by gelcasting. Pure Al, Al4Mg, and Al4Mg2Si were used as the matrices, respectively. The results indicate that the optimal parameters of SiC_P suspension in gelcasting process are pH value of 10, TMAH content of 0.5 wt.%, and solid loading of 52 vol.%. The Al matrix alloyed with Mg contributes to improving the interfacial wettability of the matrix and SiC particles, which increases the relative density of the composite. The Al matrix alloyed with Si is beneficial to inhibiting the formation of the detrimental Al₄C₃ phases. The Al4Mg2Si/SiC_P composite exhibits high relative density of 99.2%, good thermal conductivity of 150 W·m⁻¹·K⁻¹, low coefficient of thermal expansion of 10.1×10⁻⁶ K⁻¹, and excellent bending strength of 489 MPa.     

Gelcasting of titanium hydride to fabricate low-cost titanium

In this work, low-cost titanium was fabricated by gelcasting of titanium hydride powder. The effects of morphology and grain composition of powder raw material and solid loading on the rheological behavior of gelcasting slurry were studied. The degreasing, dehydriding and sintering behaviors of gelcasted green body were investigated by differential thermal analysis(DTA) and dilatometer.The results show that the solid loading of titanium hydride slurry reaches 50 vol%. Combination of dehydriding and sintering in one process accelerates the densification, and the relative sintered density of the final part achieves96.5 %. In order to test the ability of gelcasting process for fabricating structural materials, a resin handle produced by3 D printing technology was used as a model and a titanium handle was successfully fabricated. Higher solid loading and better sinterability of titanium hydride powder promote manufacture of bulk titanium with high relative density,complex shape and well-defined microstructure.     

Porosity and mechanical properties of porous titanium fabricated by gelcasting

Porous Ti compacts with large size and complex shape for biomedical applications were fabricated in the porosity range from 40.5% to 53.8% by controlling gelcasting parameters and sintering conditions. The experimental results show that the total porosity and open porosity of porous titanium compacts gelcast from the Ti slurry with 34 vol.% solid loading and sintered at 1100℃ for 1.5 h are 46.5% and 40.7%, respectively, and the mechanical properties are as follows： compressive strength 158.6 MPa and Young＇s modulus 8.5 GPa, which are similar to those of human cortical bone and appropriate for implanting purpose.     

Titanium with controllable pore fractions by thermoreversible gelcasting of TiH2

Thermoreversible gelcasting, a near-net-shape processing technique, is demonstrated here for titanium. The gelcasting system is composed of TiH₂ particles suspended in a triblock copolymer gel that behaves as a viscous liquid above 56 °C and an elastic solid at room temperature, a temperature-dependent transition that is fully reversible when solvent is present. Organic pyrolysis to remove the gel followed by vacuum sintering to densify the Ti powders (produced by decomposition of the hydride) results in titanium with near full density and low contamination. Incorporation of polypropylene and poly(methyl methacrylate) space-holder particles into the gel results in titanium with controlled porosities up to 44 vol.% and with low contamination. These foams exhibit tailorable stiffness and strength, together with excellent compressive ductility and energy absorption.     

Dispersion of concentrated aqueous neodymia-yttria-alumina mixture with ammonium poly(acrylic acid) as dispersant

A stable aqueous slurry using ammonium polyacrylic acid polyelectrolyte as dispersant and a neodymia-yttria-alumina mixture was prepared as the starting powder. The effect of the polyelectrolyte concentration and the pH of the slurry on the stability of the suspension is studied, and the optimal pH value and the amount of dispersant needed to obtain a stable slurry were determined. Highly consistent slurries with optimal pH and dispersant concentration were prepared by ball milling. The rheological behavior of the slip with different solid loading (48-58 wt.%) has been studied by measuring the viscosity and shear stress as a function of shear rate. Slip with solid loadings of 53 wt.% shows near-Newtonian behavior but becomes non-Newtonian with typical shear-thinning behavior above this solid loading value. The density and microstructure of the cast product bears a direct relationship to the state of the slip induced by variation of the pH and the concentration of the dispersant as well as by solid loading. Transparent Nd:YAG ceramics were obtained by sintering of compacts prepared from optimized slurries at 1750 °C in vacuum.     

Tensile creep of Mo–Si–B alloys

Multiphase Mo–Si–B alloys containing a Mo solid solution matrix and brittle Mo₃Si and Mo₅SiB₂ (T2) intermetallic phases are candidates for ultra-high-temperature applications_. The elevated temperature uniaxial tensile response at a nominal strain rate of 10^?4 s^–1 and the tensile creep response at constant load between 1000 °C and 1300 °C of a (i) single phase solid solution (Mo–3.0Si–1.3B in at.%), (ii) two-phase alloy containing ～35 vol.% T2 phase (Mo–6Si–8B in at.%) and (iii) three-phase alloy with ～50 vol.% T2 + Mo₃Si phases (Mo–8.6Si–8.7B in at.%) were evaluated. The results confirm that Si in solid solution significantly enhances both the yield strength and the creep resistance of these materials. A Larson–Miller plot of the creep data showed improved creep resistance of the two- and three-phase alloys in comparison with Ni-based superalloys. The extent of Si dissolved in the solid solution phase varied in these three alloys and Si appeared to segregate to dislocations and grain boundaries. A stress exponent of ～5 for the solid solution alloy and ～7 at 1200 °C for the two multiphase alloys suggested dislocation climb to be the controlling mechanism. Grain boundary precipitation of the T2 phase during creep deformation was observed and the precipitation kinetics appear to be affected by the test temperature and applied stress.     

Oxidation resistant Mo-Mo<Subscript>2</Subscript>B-silica and Mo-Mo<Subscript>2</Subscript>B-silicate composites for high temperature applications

Development of Mo composites based on the Mo-Si-B system has been demonstrated as a possible new route to achieving a high temperature Mobased material. In this new system, the silicide phases are replaced directly with silica or other silicate materials. These composites avoid the high ductile to brittle transition temperature observed for Mo-Si-B alloys by removing the Si that exists in solid solution in Mo at equilibrium with its silicides. A variety of compositions is tested for room temperature ductility and oxidation resistance. A system based upon Mo, Mo₂B, and SrO·Al₂O₃·(SiO₂)₂ is shown to possess both ductility at 80 vol.% Mo and oxidation resistance at 60 vol.%. These composites can be produced using a powder processing approach and fired to greater than 95% theoretical density with a desirable microstructure of isolated boride and silicate phases within a ductile Mo matrix.     

GELCASTING OF NANO-SIZE Y-TZP

ＧＥＬＣＡＳＴＩＮＧＯＦＮＡＮＯ－ＳＩＺＥＹ－ＴＺＰＪ．Ｓｕｎ;Ｌ．Ｇａｏ;Ｊ．Ｋ．ＧｕｏａｎｄＤ．Ｓ．Ｙａｎ（ＳｔａｔｅＫｅｙＬａｂ．ｏｆＨｉｇｈＰｅｒｆｏｒｍａｎｃｅＣｅｒａｍｉｃｓａｎｄＳｕｐｅｒｆｉｎｅＭｉｃｒｏｓｔｒｕｃｔｕｒｅ,Ｓｈａｎｇ...     

High temperature corrosion of metallic materials in simulated waste incineration environments at 300–600 °C

The durability of the materials employed in waste incineration plants is affected by different factors that together result in severe degradation of the materials. The effects of alloying elements, as well as deposit composition and temperature range are investigated in this work. Different alloys were exposed in laboratory experiments to a specifically simulated waste incineration atmosphere N₂ – 8 vol.% O₂ – 2000 vppm HCl – 15 vol.% H₂O – 200 vppm SO₂ at 300–600 °C. The samples are covered with different salt mixtures especially chlorides and sulphates. Experiments with PbCl₂‐KCl‐ZnCl₂ at 450 °C, which is molten, showed catastrophic corrosion, but this was not observed in the case with KCl, which is solid. Mixtures of five different sulphates did not cause significant mass losses at 600 °C, but sulphate‐chlorided mixtures caused bigger mass losses. The presence of Al and Si in the alloys decreased mass change effects, the presence of Mo in alloys tested showed a negative effect.     

Simultaneous synthesis and densification of WSi2 and WSi2-20vol.%Nb composite by field-activated and pressure-assisted combustion

A method to simultaneously synthesize and consolidate the silicide WSi₂ and the composite WSi₂-20 vol.%Nb from W, Si, and Nb powders was investigated. Combustion synthesis was carried out under the combined effect of an electric field and mechanical pressure. The final density of the products increased nearly linearly with the applied pressure. Highly dense WSi₂ and WSi₂-20 vol.%Nb with relative densities of up to 97% were produced under the simultaneous application of a 60 MPa pressure and a 3000A current on the reactant powders. The percentages of the total shrinkage occurring before and during the synthesis reaction were 17 and 83% for the WSi₂, and 22 and 78% for the WSi₂-20 vol.% Nb. The respective Vickers microhardness values for these materials were 8.2 and 5.8 GPa. From indentation crack measurements, the fracture toughness values for WSi₂ and WSi₂-20 vol.%Nb were calculated to be 3.2 and 9.1 MPa m¹², respectively.