Order–disorder transition in nanocrystalline Ni3Al prepared by a chemical route

Ni₃Al alloys of nanometer dimensions in the range 10–38 nm could be synthesized by reaction sintering of sol–gel-derived Ni/SiO₂ nanocomposite and commercially available micrometer-sized aluminum powder. The sintering was carried out at a temperature of 923 K and a pressure of 2.4 MPa. By a suitable choice of sintering conditions a disordered phase of Ni₃Al was stabilized. The disordered phase could be converted to an ordered one by an increase of heat treatment temperature.     

Li掺杂对ZnO陶瓷结构与电学性能的影响

研究了用传统方法在1200～1400℃烧结的ZnO陶瓷，以及用放电等离子体烧结(SPS)方法烧结的ZnO陶瓷的结构特征与电学性能。以ZnO为基添加了不同浓度的LiOH，制备了不同Li掺杂浓度的ZnO陶瓷。研究了掺杂、烧结温度，以及烧结方法等因素对ZnO基陶瓷的微观结构、电学性能的影响。实验表明，用传统方法烧结时，ZnO在烧结温度低于1400℃的情况下难以成瓷，而放电等离子体烧结(SPS)方法可以显著降低烧结温度。ZnO陶瓷的晶粒大小。密度随着烧结温度的增大而增大。在同样的烧结温度下，LiOH含量越大，ZnO基陶瓷的电阻率越大。     

Microprobe analysis of low alloyed sintered steels

Homogenization of Mo, W and Cr in alloyed P/M carbon steels during sintering with a transient liquid phase has been investigated by microscopic and microanalytical means. The reaction was found to start with carburization of the VIa metal, continues with the formation of different carbides, and generation of a liquid phase between the carbide and -Fe. The steady state equilibrium remains stable until all VIa metal has been consumed. Microprobe analysis was found to yield optimum results if selected model samples, in which homogenization should not proceed too fast, are investigated.Dedicated to Professor Günther Tölg on the occasion of his 60th birthday     

High coercivity FePt-C bulk magnet processed by spark plasma sintering and hot deformation

A high coercivity of 11 kOe has been obtained in spark plasma sintered and hot-deformed Fe₅₃Pt₄₄C₃ bulk magnets. The origin for the high coercivity has been investigated using X-ray diffraction and transmission electron microscopy. The average grain size of the ordered phase was ∼100 nm, which is less than the single domain size of the L1₀-FePt phase. Fe₃C particles were found surrounding the L1₀-FePt grains, which suppress the grain growth. The L1₀ ordering is also found to increase in hot-deformed sample by annealing in a magnetic field of 10 T at 600 °C.     

氧离子导体La1.9Y0.1Mo2O9细晶粒陶瓷的制备和电学性质研究

采用溶胶凝胶法合成的La_1.9Y_0.1Mo₂O₉纳米晶粉体, 结合微波烧结技术制备出不同晶粒度的La_1.9Y_0.1Mo₂O₉块体样品. 利用X射线衍射仪(XRD)、高分辨透射显微镜(HRTEM)、场扫描显微镜(SEM)对粉体及陶瓷块体的物相、 形貌进行了表征, 利用交流阻抗谱仪测试了样品不同温度下的电导率. 实验结果表明, 掺Y的La_1.9Y_0.1Mo₂O₉能将高温立方β 相稳定到室温; 块体样品致密均匀, 平均晶粒度范围在60 nm–4 μm之间; 致密度高的样品表现出高的电导率, 其中900 ℃烧结样品的电导率600 ℃时高达0.026 S/cm, 比固相反应法制备的La_1.9Y_0.1Mo₂O₉样品高出约1倍. 总结认为样品的致密性对电导率影响较大, 是通过影响晶界电导率来影响总电导率的, 样品的晶粒度(在60 nm–4 μm范围内)对电导率的影响还不能确定. 关键词： 氧离子导体 1.9Y_0.1Mo₂O₉')" href="#">La_1.9Y_0.1Mo₂O₉ 细晶粒陶瓷 微波烧结     

人造金刚石与硬质合金复合材料的研制

 本实验选用TiH₂及其它微量元素做粘结剂，在DS-029B型六面顶压机上烧结人造金刚石与硬质合金复合材料。实验中，采取TiH₂脱氢与金刚石净化同时进行的工艺，在高真空和一定温度下脱氢，得到高活性的新鲜钛，使其具有更强的粘结作用，以获得高磨耗比的金刚石复合材料。实验中比较了不同净化温度对磨耗比的影响；同一种粘结剂不同含量与磨耗比之间的关系；同时还测试了其耐热性及时间极限。结果表明，这种复合材料在850 ℃下，加热3 min，磨耗比没有明显改变。     

Microstructure and mechanical properties of nano-Y2O3 dispersed ferritic steel synthesized by mechanical alloying and consolidated by pulse plasma sintering

Ferritic steel with compositions 83.0Fe–13.5Cr–2.0Al–0.5Ti (alloy A), 79.0Fe–17.5Cr–2.0Al–0.5Ti (alloy B), 75.0Fe–21.5Cr–2.0Al–0.5Ti (alloy C) and 71.0Fe–25.5Cr–2.0Al–0.5Ti (alloy D) (all in wt%) each with a 1.0?wt% nano-Y₂O₃ dispersion were synthesized by mechanical alloying and consolidated by pulse plasma sintering at 600, 800 and 1000°C using a 75-MPa uniaxial pressure applied for 5?min and a 70-kA pulse current at 3?Hz pulse frequency. X-ray diffraction, scanning and transmission electron microscopy and energy disperse spectroscopy techniques have been used to characterize the microstructural and phase evolution of all the alloys at different stages of mechano-chemical synthesis and consolidation. Mechanical properties in terms of hardness, compressive strength, yield strength and Young's modulus were determined using a micro/nano-indenter and universal testing machine. All ferritic alloys recorded very high levels of compressive strength (850–2850?MPa), yield strength (500–1556?MPa), Young's modulus (175–250?GPa) and nanoindentation hardness (9.5–15.5?GPa), with up to 1–1.5 times greater strength than other oxide dispersion-strengthened ferritic steels (<1200?MPa). These extraordinary levels of mechanical properties can be attributed to the typical microstructure of uniform dispersion of 10–20-nm Y₂Ti₂O₇ or Y₂O₃ particles in a high-alloy ferritic matrix.     

Analysing the sintering of heterogeneous powder structures by in situ microtomography

This work analyses the microstructure changes of various copper-based powder systems during sintering from 3D images provided by in situ synchrotron microtomography. The investigated systems include a copper powder with a wide particle size distribution of 0–63 µm poured into a quartz capillary, a pre-sintered copper compact with artificially created large pores and a mixture of copper and alumina particles. The experiments were carried out at the European Synchrotron in Grenoble, France. Powders were sintered up to 1060°C under reducing atmosphere in a furnace located between the X-ray source and the detector. During each experiment, 3D images were taken at various times of the thermal cycle. We have obtained images with a resolution of 1.5 µm and the time of acquisition of every image was ～1 min. Quantitative analysis of these images allowed the changes of various important parameters to be followed. Such parameters characterise the sintering process at the particle length scale: interparticle coordination, pore size distribution and particle centre-to-centre distance. Moreover, by tracking the displacement of each particle centre and comparing it to the displacement predicted by classical mean field assumption, we have been able to assess the magnitude of particle rearrangement occurring during sintering. From these data, the sintering behaviour of heterogeneous powder systems is discussed with particular emphasis of collective particle phenomena.     

Capillary-driven interdiffusion along interphase boundaries in solids

We consider chemical interdiffusion along interphase boundary (IB) between two immiscible solid phases. We derive explicit expressions for capillary-related excess chemical potentials of the atoms diffusing along the IB. The obtained expressions contain both a local term which depends on local curvature of the IB, and a non-local one which depends on overall system geometry and on energy of all surfaces and interfaces in the system. The obtained expressions are employed for describing the sintering of two immiscible two-dimensional solid particles controlled by surface and IB diffusion processes. We demonstrate that the sintering of particles is accompanied by relative rigid-body rotation of the particles even for fully isotropic surfaces and interphase boundaries.     

Influence of sintering temperature and pH on the phase transformation,particle size and anti-reflective properties of RHA nano silica powders

Nano silica powders were synthesized from rice husk ash, the most silica-rich raw material, using alkaline extraction followed by acid precipitation. The phase transformation during sintering, the influence of sintering temperature and pH on the particle size and anti-reflective properties of nano silica were investigated. The results showed that the amorphous SiO₂ sintered at 600°C were transformed to a cristobalite structures completely during the sintering process at 800°C and 1100°C. With the increasing sintering temperature and pH, the particle size distributions (d₅₀) were increased respectively in the range of 62–84, 192–240, and 283–329?nm at sintering temperatures of 600°C, 800°C, and 1100°C. When the sintering temperatures were increased at 1100°C, 98.15% and 96.84% of transmittances were obtained respectively at the highest and lowest points of the anti-reflection band and could be used for anti-reflective applications.