细晶粒Ti（C，N）基金属陶瓷的研究进展

综述了细晶粒Ti（C,N）基金属陶瓷的研究现状,简要分析了原始粉末粒径、烧结工艺、烧结方法对其性能的影响,介绍了几种新的制备方法,指出必须发展新的制备技术,以充分发挥细晶粒金属陶瓷的优越性。     

纳米Ti(C,N)增强Ti(C,N)基金属陶瓷的制备研究

采用Ti(C,N)纳米粉末制备Ti(C,N)基金属陶瓷.研究了烧结温度、保温时间和升温速度等工艺参数对含10wt％纳米粉末的Ti(C,N)基金属陶瓷性能的影响,得到优化烧结工艺为1450℃,保温75min,升温速度3℃/min.用优化工艺制备的Ti(C,N)基金属陶瓷抗弯强度提高了约36.7％,增强机理主要表现为细晶强化、弥散强化和固溶强化.     

双A层MAX相Mo2Ga2C的热压烧结研究

本工作采用真空热压烧结的方法, 研究Mo₂Ga₂C粉体的烧结性能, 制备致密的Mo₂Ga₂C块体材料, 并且表征所制备材料的微观结构。实验发现750 ℃是合适的烧结温度, 过高的烧结温度(850 ℃)会导致样品分解, 主要产物为Mo₂C。在750 ℃烧结过程中, 随着烧结时间的延长, 样品的晶粒没有明显长大, 但是样品内部空隙显著变小, 内部织构增强, 相对密度明显提高。因为Mo₂Ga₂C晶体的片状结构, 热压烧结过程中, 部分片状晶粒会偏转, 导致烧结样品的多数晶粒的(00l)晶面会倾向垂直于热压方向。在750 ℃烧结8 h, 可以得到几乎完全致密(相对密度98.8%)的Mo₂Ga₂C块体材料。     

Effects of binder system and processing parameters on formability of porous Ti/HA composite through powder injection molding

Porous titanium-hydroxyapatite (Ti/HA) composite is a developed composite material suitable for bio-medical applications. Powder injection molding (PIM) with space holder method is used to produce porous Ti/HA with mechanical properties, similar to human bone, and pores helps to initiate tissue growth. However, the differences in physical and mechanical properties of these composites are the main challenges during debinding and sintering. Therefore, the main objective is to determine effects of binder systems and processing parameters on formability of Ti/HA composite. In PIM, a binder system is necessary to produce green and ultimately sintered part. There are two binder systems and variation of sintering temperature has been used. Results revealed that Polyethylene glycol (PEG)-based binder system is applicable with NaCl space holder and optimum sintering parameters, including temperature, heating rate, and holding time of 1300 °C, 10 °C/min, and 5 h, respectively. The fabricated porous Ti/HA exhibits average porosity, pore size distribution, compressive strength, and roughness values of 55%, 60 μm to 170 μm, 370 MPa, and 0.323 μm, respectively. FESEM results showed that the pores are interconnected. It may be an appropriate material for future bio-medical applications.     

Synthesis of Aluminium-Cementite Metal Matrix Composite by Mechanical Alloying

Cementite powder was prepared from elemental iron and graphite powder by mechanical alloying (MA) in a specially built dual-drive planetary mill. The phase evolution, particle-size distribution, and morphology of particles were studied during 40 hours grinding period. X-ray diffraction (XRD) shows formation of cementite and other iron carbides along with elemental iron after milling, whereas after annealing only cementite is present. Initially particle size increases with milling due to ductility of iron powder and then reduces with further milling.

Al-cementite composite was synthesized by mixing cementite with Al powders, and then by hot pressing or cold compaction and sintering. XRD analysis of Al-Fe₃C composite shows Fe₃C, FeAl, Al, and other iron carbides along with Al₄C₃ after sintering. Scanning electron microscope (SEM) micrograph of hot-pressed samples shows excellent compatibilility between Al matrix and cementite particles.     

双屏蔽(B4C-W)/6061Al层状复合板设计与性能

基于B₄C和W良好的屏蔽中子和γ射线性能,采用6061铝合金作为基体,设计了一种新型双屏蔽(B₄C-W)/6061Al层状复合材料,通过放电等离子烧结后加热轧制成板材,对制备的复合材料微观组织和力学性能进行了研究。结果表明,屏蔽组元B₄C和W颗粒均匀地分布在6061Al基体中,层界面、B₄C/Al、W/Al异质界面之间结合良好,无空隙和裂纹。在颗粒与基体界面处形成扩散层,扩散层的厚度约为6 μm (W/Al)和4 μm (W/Al)。轧制态的(B₄C-W)/6061Al层状复合板的屈服强度(109 MPa)和极限抗拉强度(245 MPa)明显优于烧结态的复合材料,但断裂韧性降低。强度提高的原因主要是轧制后颗粒的二次分布、均匀性及界面结合强度提高,基体合金的晶粒尺寸减小,位错密度增加。层状复合板的断裂方式为基体合金的韧性断裂和颗粒的脆性断裂。      

超细/纳米粉末改进Ti(C,N)基金属陶瓷性能研究进展

综述了近几年超细或纳米粉末改进Ti(C,N)基金属陶瓷性能的方法,简要分析了含超细或纳米粉末Ti(C,N)基金属陶瓷的致密化问题.总结了真空烧结 热等静压处理和放电等离子烧结的特点,并分析了微波烧结和等离子活化烧结制备Ti(C,N)基金属陶瓷的可能性.     

Nb掺杂TiO2压敏陶瓷的施主掺杂固溶度

研究了不同烧结温度TiO2压敏陶瓷的显微结构、施主掺杂固溶度和电学性能。采用SEM和EDS测试了其显微结构和晶粒化学组成。随烧结温度增加,TiO2晶粒迅速长大,显微结构均匀致密,但过高的烧结温度将导致较多气孔。1350℃为比较合适的烧结温度,其晶粒大小为15μm左右。在施主掺杂浓度一定的条件下,施主掺杂离子Nb5+在TiO2晶粒中的固溶度、晶粒电子浓度和电导率随烧结温度上升而增加,晶粒电阻率随烧结温度上升而下降。以能谱中O为参考确定TiO2晶格数量计算得到的固溶度及其电学性能更符合实验测试结果。     

Effect of processing conditions on the characteristics of pores in hot isostatically pressed alumina

Effect of processing conditions on the characteristics of residual pores was studied with an optical microscope in hot isostatically pressed translucent alumina ceramics. Green bodies formed by isostatic pressing were sintered at 1300, 1400 and 1600°C and then hot isostatically pressed at a temperature 50°C below the respective sintering temperature for 1 h at 100 MPa. All specimens were fully dense within experimental accuracy (±0.1%), and the grain size increased with increasing sintering/hot isostatic pressing temperatures. A variety of pores were found in all specimens. The distribution of pores was uniform at various locations within the specimen. The pore population decreased with increasing pore size, but was finite in the size range exceeding 84 m. The pores in this range increased with increasing sintering/hot isostatic pressing temperature. Except for these large pores, the pore population was similar under all processing conditions.     

Sintering of Mo2FeB2 layered cermet containing SiC fibers

In the present investigation Mo₂FeB₂ based cermet (KH-C50) and its composites containing SiC fibers were sintered in two different atmospheres namely hydrogen and vacuum. It was observed that vacuum sintered samples have remarkably lower porosities than the hydrogen sintered ones. Two different sintering cycles were employed for each of the atmosphere and properties of the material were studied. Introduction of fibers in the composite imparts shrinkage anisotropy during sintering. The 2 vol.% SiC fiber-containing vacuum sintered cermets have transverse rupture strength (TRS) similar to straight cermet, but sintered at faster heating rate accompanied with a reduction stage.     

功能梯度Ti(C, N)基金属陶瓷制备技术

通过真空液相烧结制备出Ti(C,N)基金属陶瓷基体,并对基体表面进行双辉等离子渗碳处理。运用扫描电子显微镜(SEM) 、电子探针(EPMA)、X射线衍射(XRD)等分析手段对渗碳前后材料的显微组织形貌、成分分布以及物相组成进行分析。结果表明,双辉等离子渗碳后金属陶瓷表面富Ti、Mo、W、C、N元素,贫Ni。渗碳过程中表层高的碳活度驱使内部的Ti、Mo、W元素向外迁移,从而迫使Ni向内迁移。渗碳后,材料表层富硬质相,近表层富粘结相。渗碳处理使试样表层硬度得到提高,对横向断裂强度影响不大。     

Pore size distribution,grain growth,and the sintering stress

The effects of a pore size distribution and of the pore separation on the sintering stress is examined using a simple model. The sintering stress is found to be proportional to the mean of the pore sizes weighted according to the Voronoi cell pertaining to each pore, rather than to the simple pore size average. Large heteropores are shown to have little effect on the mean effective sintering stress. Decreases in pore coordination number of such pores, resulting from grain growth can significantly increase the stress intensification factor. The near-constancy of the sintering stress, observed experimentally for many powders over a wide range of sintered densities, does not directly follow from the simple model. It is argued that this constancy results from pore shrinkage, due to densification, which is compensated by pore growth due to coarsening.     

Porous ceramic bone scaffolds for vascularized bone tissue regeneration

Hydroxyapatite scaffolds with a multi modal porosity designed for use in tissue engineering of vascularized bone graft substitutes were prepared by three dimensional printing. Depending on the ratio of coarse (mean particle size 50 microm) to fine powder (mean particle size 4 microm) in the powder granulate and the sintering temperature total porosity was varied from 30% to 64%. While macroscopic pore channels with a diameter of 1 mm were created by CAD design, porosity structure in the sintered solid phase was governed by the granulate structure of the printing powder. Scaffolds sintered at 1,250 degrees C were characterized by a bimodal pore structure with intragranular pores of 0.3-0.4 microm and intergranular pores of 20 microm whereas scaffolds sintered at 1,400 degrees C exhibit a monomodal porosity with a maximum of pore size distribution at 10-20 microm. For in-vivo testing, matrices were implanted subcutaneously in four male Lewis rats. Scaffolds with 50% porosity and an average pore size of approximately 18 microm were successfully transferred to rats and vascularized within 4 weeks.     

Denitrification of Ti(C,N) based cermet during powder mixing process

Changes in the nitrogen content of Ti(C,N)-based cermets during powder mixing and sintering processes were investigated and the denitrification mechanism was re-evaluated. The denitrification of N-containing cermets occurrs mainly during the powder mixing process, and is relatively small during sintering periods. Denitrification during powder mixing is caused by oxidation of the Ti(C,N) powders in contrast to denitrification during sintering, which is caused by the decomposition of the nitrides due to the high nitrogen partial pressure. It was concluded that the main source of oxygen for the powder oxidation was the water present in the ethanol solvent.     

Effect of nanocrystalline binder on the microstructure and mechanical properties of ultrafine Ti(CN) cermets

The influence of highly deformed nanocrystalline binder ingredient on the overall microstructure and mechanical properties of ultrafine grade Ti(C_0.5N_0.5) cermet was investigated. Nanocrystalline Ni and Ni-aluminides viz. NiAl and Ni₃Al, synthesized by mechanical milling/alloying, were blended to the cermet powder prior to sintering. The mechanically milled nano-Ni contained a mixture of f.c.c. and hexagonal Ni phases. The cermet with nanocrystalline Ni showed a considerably improved microstructure over cermets with commercial coarse grade Ni and exhibits a high Vickers hardness of 16.1 GPa, along with a good fracture toughness value of 9 MPa m^1/2. However, no significant change in the mechanical properties could be detected in the case of nanocrystalline NiAl and Ni₃Al binder addition. The enhanced properties of the cermets containing nano-Ni were attributed to the finer particle size of the hard phase after sintering along with improved particle size distribution caused by rapid dissolution, which prevents excessive coalescence of the hard particles. On the other hand, the presence of high porosity in the cermets containing nano-NiAl and -Ni₃Al apparently nullified any such enhancement.     

Characterization of the Pore Structure of Ceramics via Propagation of Light and Infrared Radiation

The pore size distributions of alumina and magnesia ceramics were determined by measuring the directional-hemispherical transmittance and reflectance. These values are highly sensitive to changes of the pore structure. The partially sintered alumina samples were measured at room temperature in a wavelength range from 0.5 to 6 m. The equation of radiative transfer can be solved for absorbing and scattering media by a three-flux solution. With this three-flux solution the scattering coefficients were derived from the measured directional-hemispherical transmittance and reflectance. The scattering coefficients can also be calculated theoretically by the Mie theory, if the pore size distribution is known. Finally, the quantitative pore size distribution was determined by fitting the theoretical scattering coefficients to the experimental scattering coefficients. To check the correctness of the derived pore-size distribution, scanning electron microscopy (SEM) and atomic force microscopy (AFM) pictures of the alumina samples were taken. The pore-size distribution was then derived by counting the pores and determining the diameters D of the spherical pores. Both results agree well and show that the new procedure is a valuable tool to extract structural information during the final sintering state.Paper presented at the Sixteenth European Conference on Thermophysical Properties, September 1–4, 2002, London, United Kingdom.     

表面多孔NiTi-羟基磷灰石/NiTi生物复合材料的制备与性能

利用放电等离子烧结技术制备了表面多孔NiTi-羟基磷灰石(HA)/NiTi生物复合材料,研究了烧结温度对复合材料宏观形貌、微观结构、表面孔隙特征、力学性能及体外生物活性的影响。结果表明:随着烧结温度从800℃提高到950℃,NiTi-HA/NiTi复合材料由复杂的Ti、Ni、Ti_2Ni、Ni_3Ti、HA混合相逐渐转变为单一的NiTi+HA相,内外层界面形成稳定的冶金结合且表面孔隙率与平均孔径呈缓慢减小趋势;同时抗压强度显著提高而弹性模量变化不明显。与传统NiTi、多孔NiTi及多孔NiTi-HA材料相比,950℃温度下制备的NiTi-HA/NiTi复合材料不仅具有良好的界面结合和表面孔隙特征(孔隙率45.6%、平均孔径393μm)、较高的抗压强度(1 301MPa)、较低的弹性模量(10.2GPa)以及优异的超弹性行为(超弹性恢复应变4%)的最佳匹配,而且还具有良好的体外生物活性。     

Ti(C,N)基金属陶瓷烧结过程的冶金基础及其显微组织特征Ⅱ芯-环结构的形成机理及烧结过程中的脱气演化

综述了Ti(C,N)基金属陶瓷烧结过程中的冶金反应规律.介绍和分析了Ti(C,N)基金属陶瓷典型芯-环结构组织的形成过程和机理,以及烧结过程的脱气现象和规律.     

Freeze casting of porous Ni-YSZ cermets

Dual-phase porous Ni-YSZ cermets were fabricated via the freeze casting of a ceramic/camphene slurry. After removing the frozen camphene via sublimation at room temperature, the green samples were sintered for 3 h in air at various temperatures, ranging from 1100 to 1350 °C, and then reduced in an Ar-5% H₂ atmosphere at 700 °C for 3 h. The fabricated Ni-YSZ cermets showed 3-D pore channels formed by the replication of the entangled camphene dendrite network and small pores in the Ni-YSZ walls produced by partial sintering of the NiO-YSZ composite. Furthermore, the fabricated samples were found to possess reasonable electrical conductivities, thus rendering them suitable for use as the basic components of planar solid oxide fuel cells (SOFCs).     

多孔α-Al2O3基陶瓷片状载体的制备与性能

采用干压成型法制备了多孔α-Al₂O₃基陶瓷片, 研究了烧结温度和掺杂SiO₂对其结构、形貌和性能的影响. 提高烧结温度能增加α-Al₂O₃基陶瓷片的抗压强度, 但收缩率也会随之增大。最佳烧结温度为1180℃, 收缩率小于0.5%, 抗压强度大于80 MPa。当掺杂SiO₂粉体后, 陶瓷片中的无定形SiO₂在烧结过程中晶化形成方石英, 能够促进α-Al₂O₃陶瓷片的烧结。当SiO₂含量为12wt%, 并在1180℃下烧结时, 陶瓷片的收缩率仅为1.2%, 抗压强度大于110 MPa。与α-Al₂O₃陶瓷片相比, 其孔径更小但孔径分布更宽。研究表明, α-Al₂O₃和SiO₂/Al₂O₃陶瓷片均具有良好的分子筛膜生长活性。但由于载体具有不同的物化性质, 所制备的ZSM-5分子筛膜具有不同的形貌和尺寸。