Design,fabrication of honeycomb-shaped 1–3 connectivity piezoelectric micropillar arrays for 2D ultrasound transducer application

As a core component of 2D ultrasound transducers, honeycomb-shaped 1–3 connectivity piezoelectric micropillar arrays have attracted enormous attention due to their unique performance and functionality. In this paper, honeycomb-shaped 1–3 connectivity piezoelectric micropillar arrays with a high aspect-ratio were designed and fabricated by means of deep X-ray lithography and powder injection molding in six steps: preparation of lost mold, powder-binder mixing, injection molding and demolding, removal of binders, and densification of powder. A polymer-based lost mold insert was generated by a synchrotron X-ray exposure and development process. The optimal volumetric ratio between the piezoelectric powder and binders was determined by torque rheology behavior, then they were homogeneously mixed with a twin extruder mixer. To fully fill in the micro-cavities of the lost mold, rheological properties of the mixture were analyzed with a capillary rheometer using different shear rates (50–5000 s⁻¹) and temperatures (140 °C, 150 °C, and 160 °C). After the mixture was completely injected, the lost mold was chemically dissolved in acetone and rinsed in methanol without bending or clustering of the micropillar arrays during evaporation. The binders in the injection molded portion were thermally decomposed using a continuous heating schedule of 200 °C, 390 °C, and 600 °C in argon gas under atmospheric conditions. Finally, the particles in the sample were densified into a coherent, solid mass by eliminating pores at 1300 °C. Based on the proposed micro-manufacturing process, defect-free honeycomb-shaped 1–3 connectivity piezoelectric micropillar arrays with a pattern dimension of 42 μm and aspect-ratio of 5 were successfully produced.     

Rapid fabrication of Al4SiC4 using a self-propagating high-temperature synthesis method

As a promising high-temperature ceramic, aluminum silicon carbide (Al₄SiC₄) has attracted much attention. Al₄SiC₄ is usually synthesized at high temperatures with a long reaction time in an electric furnace. Self-propagating high-temperature synthesis (SHS) is a promising technique for rapid synthesis. In this study, Al₄SiC₄ was prepared by the SHS method from a mixture of silicon, aluminum and carbon black with the addition of poly(tetrafluoroethylene) (PTFE) as an exothermic promoter. The experimental results showed that the use of a high-pressure Ar atmosphere could retain the gaseous materials in the pellet mixture, and the PTFE additive promoted the formation of silicon carbide. In addition, the oxide layer present on the surface of silicon particles inhibited the reaction between silicon and carbon. As a result, high-purity Al₄SiC₄ could be synthesized from aluminum, silicon, and carbon black with 15 wt% PTFE under 1.0 MPa Ar atmosphere in several seconds by the SHS method.     

Effect of residual excess carbon on the densification of ultra-fine HfC powder

The residual carbon content of ultra-fine hafnium carbide (HfC) powder was controlled by the optimization of the synthesis process, and the effect of residual carbon on the densification of HfC powder was analyzed. The amount of residual carbon in the HfC powder could be reduced by the de-agglomeration of HfO₂ powder before the carbo-thermal reduction (CTR) process. The average particle size of HfO₂ powder decreased from 230 to 130 nm after the de-agglomeration treatment. Ultra-fine (d₅₀: 110 nm) and highly pure (metal basis purity: >99.9 % except for Zr) HfC powder was obtained after the CTR at 1600 °C for 1 h using the C/Hf mixing ratio of 3.3. In contrast, the C/Hf ratio increased to 3.6 without the de-agglomeration treatment, indicating that a large amount of excess carbon was required for the complete reduction of the agglomerated HfO₂ particles. HfC ceramics with high relative density (>98 %) were obtained after spark plasma sintering at 2000 °C under 80 MPa pressure when using the HfC powder with low excess carbon content. In contrast, the densification did not complete at a higher temperature (2300 °C) and pressure (100 MPa) when the HfC powder contained a large amount of residual carbon. The results clearly indicated that residual carbon suppressed the densification of HfC powder in case the carbide powder had low oxygen content, and the residual carbon content could be controlled by the optimization of the synthesis process. The average grain size and Vickers hardness of the sintered specimen were 6.7(±0.7) μm and 19.6 GPa, respectively.     

Self-lubrication and wear-resistance mechanism of graphene-modified coatings

To reduce the friction coefficient of WC-17Co wear-resistant coatings, Graphene oxide were used to mix with WC-17Co powder. The SEM, EDS and Raman results were used to analyze the morphology and phase composition of graphene oxide in the powder and coating obtained by plasma spraying processes. The mechanical properties of the coatings were studied by using a microhardness tester and a universal testing machine. The friction and wear properties of the coatings were studied by using a UMT-2 friction and wear tester. The results show that among the pulverization processes, the spray granulation process can achieve a stronger and more uniform adhesion of graphene oxide on the surface of WC-17Co particles, and the graphene oxide content in the coating is higher. Graphene is still embedded in the coating as transparent, thin sheets. The bonding strength is approximately 63 MPa, the hardness is approximately 931 HV0.1, and the friction coefficient of the graphene oxide coating is reduced by approximately 22% compared to that of the coating without graphene. The formation of lubrication films in the micro-area improves the self-lubrication and antiwear effects.     

Experimental investigation on the mechanical,structural and thermal properties of Cu–ZrO2 nanocomposites hybridized by graphene nanoplatelets

Hybrid Cu–ZrO₂/GNPs nanocomposites were successfully produced using powder metallurgy technique. The effect of GNPs mass fraction, 0, 0.5, 1 and 1.5%, on the mechanical and electrical properties of the produced hybrid nanocomposite was investigated while maintaining ZrO₂ mass fraction constant at 5%. High-energy ball milling was applied for mixing powders followed by compaction and sintering. The morphological analysis of the produced powder showed acceleration of Cu particles fracture during ball milling with the addition of GNPs up to 0.5% with noticeable reduction of agglomeration size. Moreover, the crystallite size of Cu–5%ZrO₂/0.5%GNPs hybrid nanocomposites revealed smaller crystallite size, 142 nm, compared to 300 nm for Cu–5%ZrO₂ nanocomposite. Additionally, the hybrid nanocomposite with 0.5% GNPs shows homogeneous distribution of both reinforcement phases in the sintered samples. The compressive strength increased with the GNPs content and reached 504.6 MPa at 0.5%, 31% higher than the Cu-5%ZO₂. The thermal conductivity had the maximum value at 0.5 wt%GNPs and reached 345 W/m k. The results provide efficient manufacturing process for high strength and good conductivity hybrid nanocomposites, which is applicable in many structural applications such as heat exchange purposes.     

Investigation of advanced mica powder nanocomposite filler materials: Surface energy analysis,powder rheology and sound absorption performance

Two types of nano/micro sized mica powders for polymer composites, muscovite and phlogopite, were tested for their sound absorption capabilities. Acoustical performance was correlated to surface energy analysis and powder rheology testing. Inverse gas chromatography (iGC) was used to determine the surface energy, with the dominant component being the dispersive component. This reflected the non-polar, hydrophobic, character of the micas. The determined yield locus and Mohr's circles indicated that the material with the highest packing density exhibited more free flowing powder characteristics, compared with the lower packing density materials, which exhibited a greater cohesive powder flow behaviour. All tested mica powders were sensitive to aeration and become fluidised. Based on the acoustical measurements the worst sound absorption performance was found for the highest packing density material exhibiting the highest magnitude of the longitudinal elastic coefficient.     

Simplifying the powder metallurgy manufacturing process using soft computing tools

The tools of soft computing will aid the knowledge mining in predicting and classifying the properties of various parameters while designing the composite preforms in the manufacturing of Powder Metallurgy (P/M) Lab. In this paper, an integrated PRNET (PCA-Radial basis functional neural NET) model is proposed in different versions to select the relevant parameters for preparing composite preforms and to predict the deformation and strain hardening properties of Al–Fe composites. It reveals that the predictability of this model has been increased by 67.89% relatively from the conventional models. A new PR-filter is proposed by slightly modifying the conventional filters of RBFNN, which improves the power of PRNET even though raw data are highly non-linear, interrelated and noisy. Moreover, fixing the range of input parameters for classifying the properties of composite preforms can be automated by the Fuzzy logic. These types of models will avoid expensive experimentation and risky environment while preparing sintered composite preforms. Thus the manufacturing process of composites in P/M Lab will be simplified with minimum energy by the support of these soft-computing tools.     

化工冶金学家陈家镛

1958年中国科学院化工冶金研究所(现过程工程研究所)的创建,与建国初期的国家经济发展和国防建设的需求紧密相关。1956年陈家镛受到世界著名冶金学家叶渚沛的邀请,到正在筹建中的化工冶金研究所工作。作为国内该领域开拓者和学术带头人,陈家镛院士的学术经历是本文主线。以他带领同事们开展湿法冶金研究为案例,分析了国家重大战略需求与科学技术研究之间的关系。重点介绍了他在冶金、化工、材料等研究领域做出的重要学术贡献,以及将代表性科研成果经过中间试验应用于实际生产、解决企业所面临的技术难题的情况。藉此反映了以过程工程研究所为代表的国立科研机构,围绕国家重大战略需求开展科技攻坚的历程与成果。     

An effective approach to reinforced closed-cell Al-alloy foams with multiwalled carbon nanotubes

Exploring the reinforcing role of carbon nanotubes to obtain materials (polymers, metals, ceramics) with enhanced properties has been often attempted, but the success is strongly limited by the dispersing degree of carbon nanotubes. Here we report on an innovative colloidal approach to disperse the carbon nanotubes in the powders mixture of the precursor materials in order to profit from their reinforcing potential and obtain a new class of closed-cell metal foams. The feasibility of the proposed approach was demonstrated for aluminium foams reinforced with multi-walled carbon nanotubes. These nanocomposite metal foams synergistically combine the remarkable properties of both metal foams and carbon nanotubes. The results indicate that the tubular structure of carbon nanotubes is preserved throughout the entire the process. The carbon nanotubes are individually dispersed, stretched and randomly aligned in the aluminium-matrix of these closed-cell foams, thus potentiating their homogeneous 3D reinforcing role. Accordingly, the Vickers micro-hardness of the closed-cell foams was greatly enhanced.     

Microstructure evolution during fabrication and microstructure–property relationships in vapour-grown carbon nanofibre-reinforced aluminium matrix composites fabricated via powder metallurgy

Microstructure evolution of vapour-grown carbon nanofibre (VGCF)-reinforced aluminium matrix composites during fabrication and microstructure–property relationships of these materials were studied. Composites were fabricated using powder metallurgy, i.e. by mixing VGCFs and aluminium powder via ball-milling followed by sintering or hot extrusion. The mixing condition was selected to achieve small powder particle size and homogeneously dispersed VGCFs. Aluminium grains and VGCFs were elongated along the longitudinal direction of aluminium particles in the mixed powder. Detailed observation of the aluminium grains in the composites found grain size and morphology dominated by recrystallization. Apparently, grain growth was inhibited by VGCFs. Theoretical models considering strength increment due to grain refinement resulting from VGCF addition, load bearing of VGCFs, thermal mismatch of VGCFs and aluminium and Orowan effect were developed. Theoretical values coincided well with hardness, yield strength, and ultimate tensile strength of the composites, and thus the models could precisely explain the microstructure–property relationships.