烧结温度和粉末预处理对SPS制备超细晶硬质合金的影响

采用亚微米WC粉和微米Co粉混合粉末作为原料,利用高能球磨与放电等离子烧结(SPS)技术制备超细晶WC-10Co硬质合金.研究表明,球磨后直接烧结时,当温度由1150℃增加到1200℃,试样的晶粒尺寸和硬度没有明显变化(平均晶粒尺寸约250nm),但致密度提高至98.6%,横向断裂强度由1045MPa提高到1819MPa.当对球磨后的混合粉末进行900℃真空处理后,在较低温度烧结的条件下试样的致密度则高达99%,且横向断裂强度与未处理粉末在相同工艺下烧结获得提高.     

碳化物抑制剂对WC-2.5TiC-10Co超细晶硬质合金微观组织及力学性能的影响

采用高能球磨和真空热压烧结相结合的方法制备了WC-2.5TiC-10Co超细晶硬质合金,并利用X射线衍射仪(XRD)、场发射扫描电镜(FESEM)等性能测试手段研究了Cr_3C_2、VC、TaC和NbC的添加对超细晶硬质合金微观组织和力学性能的影响。结果表明:经过球料比10∶1及转速为350r/min行星式高能球磨处理30h后,WC粉末的粒径由0.6mm减小到0.2mm以下;经过1410℃真空热压烧结1h后,XRD检测未发现新的反应物生成。添加0.45%Cr_3C_2、0.3%VC、0.5%TaC或NbC的硬质合金中有少量异常长大的WC晶粒,断口表面疏松且平坦,分析表明较大的WC晶粒在应力集中的作用下发生解理破坏,并成为材料断裂的裂纹源。当抑制剂Cr_3C_2和VC的含量再增加0.1%后,WC晶粒可以控制在0.5mm以下,断口表面致密成台阶状,抗弯强度可提高20%;TaC和NbC对抑制WC晶粒生长的作用并不显著,但添加NbC对提高硬质合金致密度的效果最显著。     

放电等离子烧结纳米晶ZrO2陶瓷研究

采用放电等离子烧结技术对纳米级ZrO2粉体进行致密化研究.运用XRD、SEM、TEM以及显微硬度仪对粉末及块体进行分析.实验结果表明运用放电等离子烧结技术对ZrO2(3Y)粉体进行致密化无法同时实现晶粒度与相对密度的最佳结合.目前,最佳晶粒尺寸100nm左右时相对密度95.8%,最大Kic=11.85MPa·m1/2.     

WC-20％Co复合粉的制备及其放电等离子烧结的研究

利用放电等离子烧结技术将WO3、Co3O4和碳黑的高能球磨混合粉经真空还原碳化后合成的WC-20％（质量分数）Co复合粉烧结为致密的高钴WC-Co硬质合金材料。研究了制备复合粉的工艺和放电等离子烧结过程以及制备合佥的相组成、显微组织、物理和力学性能。实验表明，高能球磨粉在真空条件下原位还原碳化反应得到物相纯净的超细复合粉，此后复合粉在1190～1210℃SPS烧结成致密块体材料。通过SEM观察发现，由于经1200℃液相烧结，溶解析出的WC相发生粗化，呈板状晶，平均宽度400nm，长度1μm；钴相均匀分布在WC相周围，无钴池形成。     

烧结保温时间对超粗晶WC-10Co硬质合金微观结构及性能的影响

超粗晶WC-Co硬质合金因耐磨性高和韧性好成为研究的一个热点,而致密度和晶粒的控制是获得优异性能的关键.采用轻度球磨法获得添加超细WC的复合粉末,通过真空烧结制备平均晶粒尺寸为8.3～8.8μm的超粗晶WC-10Co硬质合金,研究烧结保温时间对致密度、WC晶粒及力学性能的影响.结果表明:随着烧结保温时间从30 min增至120 min,致密度先增加后下降,Co在合金表面聚集氧化并使内部孔隙增多,部分WC晶粒聚集形成异常晶粒,这些缺陷结构阻碍了孔隙的消除;超细WC和球磨破碎细WC的先后溶解析出,使WC平均晶粒度先增加后减小,晶粒分布变宽.当烧结保温时间为60 min时,曲面类球状WC部分通过台阶生长机制转变为性能友好型的圆边六棱柱晶粒,抗弯强度和冲击韧性达到最高,分别为1733 MPa和28 kJ·m-2.此外,烧结过程中部分晶粒中原生缺陷难以完全消除,而较长的烧结保温时间下,多种缺陷的增多降低合金性能.     

TiAl纳米合金的机械活化-放电等离子原位烧结

（Ti-50％（原子分数）AD-10％Al2O3粉体经过球磨的机械活化（MA）后，用放电等离子烧结（SPS）工艺，在烧结的同时进行固化。采用机械活化-放电等离子烧结（MA—SPS）的方法原位烧结制备TiAl—Al2O3块体纳米材料。球磨前后，（Ti-50％（原子分数）AD-10％Al2O3粉体的衍射图（XRD）相似。MA后得到晶粒度〈25nm的纳米粉体，其中Al2O3起到机械活化和细化晶粒的作用，促使粉体快速纳米化。纳米粉体在温度低于800℃、烧结时间〈5min的烧结参数下，烧结成TiAl纳米合金。TiAl纳米合金的微观结构表明，合金有γ-TiAl和α2—Ti3Al双相组织。SPS原位烧结后，得到密度为3．73g／cm^3的（γ＋α2）双相组织，组成相的晶粒度〈130nm。     

机械合金化和放电等离子烧结制备Y3Al5O12陶瓷

采用机械合金化和放电等离子烧结制备YAG陶瓷,研究了球磨时间对原料颗粒大小和烧结合成YAG纯度的影响,并利用x射线衍射(XRD)、扫描电镜(SEM)等手段对反应过程及产物形貌和物相进行了分析.研究结果表明,机械合金化Y2O3和Al2O3粉体,可明显细化氧化物颗粒,球磨20h后,Y2O3和Al2O3晶粒大小约为34nm和32nm.球磨处理的Y2O3和Al2O3粉体具有很高的活性,促进放电等离子烧结低温反应合成和获得致密的YAG.对球磨20h的粉体在不同温度进行放电等离子烧结,在1200℃即可获得纯YAG陶瓷,在1500℃烧结,可得到相对密度为99.5%的YAG陶瓷.1500℃烧结的块体在可见光范围内透过率为13.8%.     

低温制备高致密度细晶W-10％TiC复合材料

采用高能球磨结合真空热压的手段制备了W-10％（质量分数）TiC复合材料。采用扫描电镜、透射电镜和x射线衍射等对复合粉体及复合材料进行表征。结果表明，通过高能球磨得到了粒径均匀，平均粒径约为100nm的纳米复合粉体，粉体经过1700℃真空热压烧结后致密度达到99．1％，并且保持细晶结构（平均晶粒尺寸为0．8gm）。热压和高能球磨导致的机械活化以及引入的Fe、Ni等杂质是复合材料低温烧结达到高致密度的重要原因。     

1400℃放电等离子烧结制备MgO-B_(2)O_(3)增韧无金属黏结相WC硬质合金EI北大核心CSCD

为了降低无金属黏结相碳化钨(WC)硬质合金的烧结温度并获得较高的断裂韧度,采用MgO和B_(2)O_(3)协同增韧WC硬质合金。通过放电等离子烧结技术(SPS)在1400℃的较低温度下制备出致密的WC-MgO-B_(2)O_(3)硬质合金块体材料,研究MgO-B_(2)O_(3)对无金属黏结相WC硬质合金的烧结机理、微观组织演变以及力学性能的影响规律。结果表明:MgO-B_(2)O_(3)的添加促进了WC的烧结致密化,显著降低了无金属黏结相WC硬质合金的烧结温度。随着MgO-B_(2)O_(3)添加量的提高,组织中的部分第二相形貌发生显著改变,逐渐由短杆状转变为长杆状,再转变为聚集时的块状。当MgO-B_(2)O_(3)添加量达到8%(质量分数)时,块体材料具有较好的断裂韧度,为(9.45±0.37)MPa·m^(1/2),同时其硬度为(18.16±0.17)GPa。     

高活性B_4C-SiC超细复合粉体的制备及烧结

以B4C、SiC粗粉为原料,采用机械合金化制备高活性的B4C-SiC超细复合粉体。通过XRD、SEM、LPSA和IR等测试技术研究球料比、过程控制剂及球磨时间对复合粉体性能的影响,确定机械合金化制备B4C-SiC超细复合粉体的最佳工艺条件,研究机械合金化过程中粉体有序-无序转变过程。随后,采用热压烧结工艺验证复合粉体的烧结活性。结果表明:球磨机转速是250 r/min的条件下,球料比为30:1,过程控制剂为2wt%,球磨时间为120 h时,可获得晶格无序的B4C-50wt%SiC超细复合粉体;该复合粉体在1900℃,30 MPa热压条件下烧结1 h,其体积密度为2.62 g/cm3,达到理论密度的93%,比普通混合粉体在相同热压条件下获得样品的致密度提高了8.1%;机械合金化工艺制备的B4C-SiC超细复合粉体具有极高的烧结活性。     

纳米氧化钛陶瓷的烧结

将醇盐水解制备的纳米氧化钛粉体（～13nm）在500～800℃下煅烧,用XRD研究氧化钛相变过程中粉体的热稳定性,发现在加入0．4wt％的金红石相作为晶种后;晶粒生长受到较好的控制,同时分别在30、57和200MPa下对纳米氧化钛样品进行热压烧结,用密度仪、压汞仪和SEM对烧结前后的样品进行表征后表明,700℃的热压烧结样品已开始致密化,200MPa、800℃热压烧结样品的相对密度为97．2％,此时3～15nm的小气孔仍难以消除,这些小气孔的存在是纳米氧化钛陶瓷在较高的压力下难以完全致密的主要原因．     

High Pressure Compaction and Sintering of Nano-Size γ- Al2O3 Powder

The effects of pressure on the compaction and subsequent sintering of nano-size Y- γ-Al₂O₃ powder were studied. Pressures up to 5 GPa were used to compact the powder in a WC piston/cylinder type die and also in a diamond anvil cell. The green body compacts obtained from both methods of compaction were pressureless sintered at temperatures between 1000°C to 1600°C. Results demonstrated that green body density was enhanced with increased compaction pressure. For compaction pressures less than 3 GPa, microstructures containing significant porosity developed at all sintering temperatures studied and is due to the development of a highly porous or vermicular structure during the y too phase transformation, occurring at temperatures between 1000°C and I I50°C. At compaction pressures greater than 3 GPa, however, the formation of the vermicular structure did not occur and near theoretical densities with grain size = 150 nm were obtained.     

超高压成型对碳化硅陶瓷微观结构的影响

以两面顶为成型设备,利用其超高压力(4.5GPa)来提高素坯的相对致密度,从而降低坯体的烧结温度、缩短烧结时间,并制备出高致密度的细晶碳化硅陶瓷。结果表明,经超高压成型后,碳化硅素坯的平均相对致密度为65.7%。与冷等静压成型后的坯体(45.5%)相比,提高了大约20%。在低压流动氮气保护下,超高压成型的坯体于1900℃下无压烧结30min,烧结体的致密度达到了98.3%,其晶粒尺寸在200nm左右。     

Processing of anatase prepared from hydrothermally treated alkoxy-derived hydrous titania

Spherical, submicrometre, amorphous hydrous titania powder synthesized by controlled hydrolysis and polymerization from titanium tetraethoxide solutions was hydrothermally converted to spherical polycrystalline anatase particles by autoclaving or refluxing. Green compacts produced with either autoclaved or refluxed powder via a colloid filtration route had a high density and were crack-free; processing with untreated hydrous titania resulted in cracked green compacts. Compacts of the hydrothermally treated powders could be sintered to 98% theoretical density at temperatures as low as 900° C. A compact of commercial powder produced in the same fashion was not observed to densify at such temperatures. Using various firing techniques, compacts of the hydrothermally treated powder could be sintered to 98% theoretical density or greater while controlling the titania phase assemblage as (1) anatase, (2) rutile, or (3) a mixture of anatase and rutile. By scaling the phase transformation and sintering kinetics, the grain size of the sintered microstructure can be controlled from a submicrometre to a micrometre scale.     

钼铜复合粉末的致密化及性能

对微波辅助法制备的钼铜复合粉末进行压制烧结,研究其致密化行为及复合材料性能。结果表明:烧结温度是控制钼铜复合材料成分、微观组织及综合性能的关键因素。1100℃下烧结的钼铜复合材料Cu含量最接近设计含量,过高的烧结温度将引起铜的损耗。在较低的烧结温度下(≤1100℃),复合材料的力学性能和物理性能随温度的升高而升高,但是过高的烧结温度(1200℃)会引起铜相的大量损失及颗粒异常长大,从而导致复合材料密度、硬度、导电率及导热率的降低。通过优化实验参数,1100℃下的复合材料具有理想的微观结构,铜相损失较少,复合材料成分接近设计成分,钼铜两相分散较为均匀,力学性能及物理性能优异,复合材料的密度、硬度、抗弯强度、电导率及热导率分别为9.79g/cm^3,229.1HV,837.76MPa,24.97×10~6S·m^-1和176.57W·m^-1·K^-1。     

Preparation of Gd_2O_2S:Pr Scintillation Ceramics by Pressureless Reaction Sintering Method

Fabrication of Gd2O2S:Pr scintillation ceramics by pressureless reaction sintering was investigated. The 2Gd2O3·(Gd,Pr)2(SO4)3·mH2O precursor was made by hydrothermal reaction using commercially available Gd2O3, Pr6O11 and H2SO4 as the starting materials. Then single phase Gd2O2SO4:Pr powder was obtained by calcining the precursor at 750°C for 2 h. The Gd2O2SO4:Pr powder compacts can be sintered to single phase Gd2O2S:Pr ceramics with a relative density of 99% and mean grain size of 30 μm at 1750°C for 2 h ...     

Nanostructured and near defect-free ceramics by low-temperature pressureless sintering of nanosized Y-TZP powders

Nanosized (∼6 nm) Y-TZP (3 mol% Y₂O₃) powders have been produced by chemical co-precipitation (Y-inorganic + Zr-organic precursors) and thorough isopropanol-washing step, after calcining in air at 450 °C. The nanocrystalline Y-TZP powders consisted of spherical soft agglomerates (∼100 nm in size) which were easily broken down during compaction resulting in a very uniform green microstructure with a narrow pore size distribution (average pore size less than 6.5 nm) and no detectable compacting defects. In spite of the relatively low green density (43% theoretical), Y-TZP powder compacts sintered to near theoretical density in the very low-temperature range of 1000 °C for 80–100 h to 1070 °C for 2 h, maintaining a grain size in the nanoscale (< 100 nm) and the sintered bodies were nearly defect-free. Hardly any grain growth took place up to 1000 °C; it was very rapid above this temperature. This revised version was published online in November 2006 with corrections to the Cover Date.     

橡胶等静压成型纳米ZrO2(3Y)粉素坯

对橡胶等静压成型(Rubber isostatic pressing,RIP)制备纳米Y-TZP陶瓷作了初步研究.研究结果表明,通过RIP成型,可以获得相对密度较高、体积较大的ZrO₂(3Y)素坯,并在较低温度下无压烧结得到纳米Y-TZP陶瓷.在1100℃下烧结2h所得的Y-TZP陶瓷的相对密度可达97％,晶粒仅为70nm左右.相对密度较高、平均孔径小是RIP成型素坯烧结温度低的主要原因.     

Transparent Polycrystalline Alumina Ceramic with Sub‐Micrometre Microstructure by Means of Electrophoretic Deposition

The optical quality attainable in coarse‐grained polycrystalline alumina is severely limited by grain‐boundary scattering, which is inherent to non‐cubic materials. The optical properties of sub‐micrometre polycrystalline alumina are of growing interest triggered by the fact that a decrease in the grain sizes of the final sintered material yields an improvement in the optical quality while the scattering mechanism changes as the grain size becomes comparable with the wavelength of light. To achieve transparent alumina ceramics with a fine‐grained microstructure, however, porosity and other defects must be avoided. This necessitates the optimization of processing and sintering procedures. Electrophoretic deposition (EPD) is a colloidal process in which ceramic bodies are directly shaped from a stable suspension by application of an electric field. Electrophoretic deposition enables the formation of homogeneous, uniform green microstructures with high density, which can be sintered to transparency. It is a simple and precise technique to synthesize not only monoliths, but also composites with complex geometries [1]. Alumina green bodies were deposited from stabilized aqueous suspensions with and without doping. Green alumina compacts were evaluated based on their pore size distribution and density. Densification behaviour was characterized by dilatometric studies conducted at constant heating rate. Samples were sintered at different temperatures with subsequent post‐densification by hot isostatic pressing. Transparency was evaluated by means of spectroscopic measurements. The measured in‐line transmission of the samples at 645 nm was more than 50 % and that is 58 % of the value of sapphire. The influence of dopings on transparency was investigated. The mechanical properties of the samples were tested.     

Densification and mechanical properties of mullite-SiC nanocomposites synthesized through sol-gel coated precursors

Mullite-SiC nanocomposites are synthesized by introducing surface modified sol-gel mullite coated SiC particles in the matrix and densification and associated microstructural features of such precursor are reported. Nanosize SiC (average size 180 nm) surface was first provided with a mullite precursor coating which was characterized by the X-ray analysis and TEM. An average coating thickness of 120 nm was obtained on the SiC particles. The green compacts obtained by cold isostatic pressing were sintered in the range 1500–1700°C under pressureless sintering in the N₂ atmosphere. The percentage of the theoretical sintered density decreases with increase in SiC content. A maximum sintered density of 97% was achieved for mullite-5 vol.% SiC. The fractograph of the sintered composite showed a highly dense, fine grained microstructure with the SiC particles uniformly distributed along the grains as well as at the grain boundaries inside the mullite. The Vicker’s microhardness of mullite-5 vol.% SiC composite was measured as 1320 kg/mm² under an applied indentation load of 500 g. This value gradually decreased with an increase in SiC content.