机械合金化制备钙钛矿结构铁电陶瓷粉末的研究进展

作为一种高性能的新型陶瓷材料,铁电陶瓷已经成为国内外研究的一个热点.本文主要从机械合金化制备高性能铁电材料的相形成机理以及采用机械合金化制备各种钙钛矿结构的铁电陶瓷(钛酸钡、钛酸铅、锆钛酸铅、铌镁酸铅)粉末方面,介绍了采用机械合金化方法制备这种高性能铁电陶瓷材料的国内外有关研究进展.     

机械合金化在金属陶瓷制备领域的应用

指出了机械合金化的主要原理为高效球磨作用,并概述了机械合金化的主要应用领域,总结了该方法的主要特点,以及在制备复相陶瓷材料中的发展方向和应解决的问题。     

机械合金化对制备SiO_2-Al复合粉的影响

本文研究了过程控制剂的添加量对SiO_2-Al复合粉出粉率的影响及球磨时间对粉末的细化和固相反应温度的影响.应用激光粒度仪、扫描电镜、X射线衍射仪和差热分析仪对球磨后的复合粉进行分析.研究表明,经20 h球磨时,过程控制剂的添加量为4%时,出粉率高达85%;随着球磨时间的延长,SiO_2-Al复合粉被逐渐细化,20 h球磨后,其中位径降至4.35 μm,但是并没有发生固相反应;随着球磨时间的延长,降低了SiO_2和Al的固相反应温度.     

机械合金化——新型固态非平衡加工技术

机械合金化是一种新型固态非平衡加工技术。本文回顾了机械合金化过程的唯象学描述 ,并阐述了机械合金化形成非晶、纳米晶、超饱和固溶体等亚稳组织的机理及其应用     

机械合金化制备的TiB_2的提纯

利用化学方法对机械合金化制备的TiB2 和MgO粉末进行分离 ,以便得到高纯TiB2 。结果表明可以利用盐酸对TiB2 和MgO粉末进行分离 ,分离后仅含有微量MgO杂质     

机械合金化在镍氢电池中的应用

概述了机械合金化及镍氢电池相关的基本概念,总结了机械合金化在镍氢电池中的应用,并对机械合金化与镍氢电池的应用与发展进行了展望。     

机械合金化在金属陶瓷制备领域的应用

指出了机械合金化的主要原理为高效球磨作用 ,并概述了机械合金化的主要应用领域 ,总结了该方法的主要特点 ,以及在制备复相陶瓷材料中的发展方向和应解决的问题     

机械合金化法制备铜复合材料工艺研究

通过研究机械合金化的原理,并将球磨时间、压制压强、烧结温度和烧结时间四个因素作为变量,来探究这些因素对铜复合材料本身特性的影响,试图探索用机械合金化法制备铜复合材料的最佳工艺。     

机械合金化Ni-20Cr合金电化学腐蚀行为研究

利用电化学方法以及化学浸泡法,结合XRD、TEM等表面分析技术,研究了机械合金化Ni-20Cr及粗晶Ni-20Cr合金在质量分数为3.5%NaCl溶液中的电化学腐蚀性能。结果表明机械合金化方法制备的Ni-20Cr合金的电化学腐蚀性能要低于粗晶Ni-20Cr合金。相对于粗晶合金,晶粒细化是合金机械合金化后耐蚀性能降低的主要原因。     

钛和沥青机械合金化合成纳米级碳化钛

Abstract TiC powder was synthesized by mechanical alloying of titanium and asphalt in this paper. Deoiled asphalt as a carbon source not only provided element C in the fabrication of TiC but also cracked itself by the mechanical alloying process. The results of X-ray diffraction demonstrated the synthesis of cubic TiC. Gas phase chromatography showed that the discharged gas was composed of low molecular weight hydrocarbons, including H2, CH4 and C2H6. The formation mechanism of titanium carbide by mechanical alloying, and the thermodynamic and kinetics were discussed. These results showed that mechanical alloying is a promising method to prepare TiC and to crack asphalt with some light fraction byproducts.     

Nanostructured titanium aluminides prepared by mechanical alloying and subsequent thermal treatment

Ternary Ti-Al-Nb elemental powder blends with minor addition of SiC were synthesized in a high energy ball mill in order to understand the structural evolution during mechanical alloying (MA) and subsequent thermal treatment. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) techniques were employed to study the structural development during MA. Ti-48%Al-4%Nb-3%SiC and Ti-48%Al-8%Nb-3%SiC blends milled to 20 h were subjected to thermal treatment at 750 °C for 1 h in vacuum. Repeated cold welding and fracturing events of MA resulted in nanocrystalline structure with supersaturated solid solution and amorphous phase. The powder particles were also refined to submicron size due to high energy collision. The nanocrystalline supersaturated solid solution evolved by MA was sustained for prolonged milling time. There was no evidence of intermetallics formation even after early solid solubility extension and formation of nanocrystalline structure. However, nanostructured TiAl and Ti₃Al intermetallic compounds were observed after giving thermal treatment to MA powder blend. Since their surface area and energy were enhanced to a great extent, the dispersed ceramic particles reacted with titanium and formed nanosilicide particles.     

High-energy mechanical alloying of thermoplastic polymers in carbon dioxide

High-energy ball milling was performed on low density polyethylene (LDPE) and isotactic polypropylene (iPP) as well as on 20/80 binary mixture of both polymers. Mechanical alloying was carried out at high pressure with carbon dioxide for a short period. The presence of CO₂ avoids oxidative mechano-chemical degradation of polymers and enhances the effectiveness of the milling. The effects of the mechano-chemical treatment on the molecular and physical properties of both single polymers and blends of intrinsically incompatible polymers were explored by FTIR spectroscopy, thermal analysis, intrinsic viscosity determination and solvent fractionation. Structural changes on PP and PP/LDPE blend were observed and have a strong dependence on the milling time. Mechanical tests confirm an overall improvement in blend properties by mechanical alloying. Experimental evidences are presented to suggest that CO₂ high-energy ball milling causes a self-compatibilization of the blend LDPE-iPP by breaking iPP polymer chains and allowing them to recombine with the neighboring LDPE chains.     

Improvement of wetability,sinterability, mechanical and electrical properties of Al2O3-Ni nanocomposites prepared by mechanical alloying

The wetability improvement and particle size reduction of alumina/Ni composites through mechanical alloying were addressed. Their effect on the sinterability (at high temperature), mechanical and electrical properties were studied. Al₂O₃ matrix nanocomposites reinforced with different volume fractions of Ni up to 10 vol% were prepared by mechanical alloying. The milled powders were cold pressed and sintered at different firing temperatures up to 1600 °C. The morphology of powders and the microstructure of sintered bodies were investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS), respectively. Furthermore, relative density, apparent porosity, mechanical properties and electrical resistivity of the sintered composites were investigated. The results revealed that Al₂O₃ matrix was successfully coated with Ni thin film through mechanical alloying; the thickness of coat was increased with increasing the Ni content. Moreover, the increasing of both Ni content and sintering temperature up 1600 °C, led to a remarkable increase in the relative density and facture toughness of the sintered specimen. On the other hand, microhardness and elastic modulus were decreased with increasing of Ni content, while they increased significantly with the increase of sintering temperature. The electrical resistivity was decreased with increasing Ni content and sintering temperature.     

Effect of milling variables on the synthesis of NiAl intermetallic compound by mechanical alloying

NiAl intermetallic compound was synthesized by mechanical alloying of elemental mixtures of Ni and Al powders in a Spex mill. The compound formation took place according to a mechanically induced self-propagating reaction (MSR), and the influence of milling variables on its ignition time was determined using a factorial design. Results indicated ignition time as a function of initial particle size of Ni, process control agent, and ball-to-powder ratio. Also, an interaction between ball-to-powder ratio, process control agent, and a set of balls was found to control the average particle size of as-milled powders.     

Characterization of Al2024-CNTs composites produced by mechanical alloying

In the present work, the 2024 aluminum alloy (Al₂₀₂₄) alloy has been produced by mechanical alloying (MA). The alloy was then strengthened by dispersion of carbon nanotubes (CNTs) during different times. Thus, the effect of CNTs concentration and milling time on the microstructure of the Al₂₀₂₄-CNTs composites was studied. The results show a homogeneous dispersion of CNTs into the Al-matrix phase by mechanical milling (MM). It was observed that the increment in the milling time, for a fixed amount of CNTs, causes a reduction of the particle size of powders resulting from MA. The finest particle size was obtained at 20 h of milling. These observations were confirmed by scanning and transmission electron microscopy. After 10 h of milling, Cu, Mg and other alloying elements constituting the Al₂₀₂₄ alloy, form a solid solution and only some remnant Mn particles were observed but not detected by X-ray diffraction.     

Influence of B4C nanoparticles on mechanical behaviour of Silicon brass nanocomposite through mechanical alloying and hot pressing

This research article has concentrated to develop a novel silicon brass of [82Cu4Si14Zn]_100-x – x wt.% B₄C (x = 0, 3, 6, 9, and 12) nanocomposites which were synthesized by mechanical alloying followed by vacuum hot pressing for consolidation of powders into bulk samples. Single vial planetary ball mill was used to synthesize the nanocomposite powders in which the ball-to-powder ratio of 10:1 with the milling time of 20 h was used. The milled powders were compacted and sintered simultaneously using vacuum hot pressing equipment for 1 h at 900 °C. The structural, mechanical and tribological properties were characterized and investigated by x-ray line profile analysis (XRD), scanning electron microscopy (SEM), electron backscattered diffraction images (EBSD), energy dispersive x-ray spectroscopy (EDS), Vickers microhardness, compression test, and dry sliding wear behaviour analysis. It has been found that B₄C nanoparticles had homogeneously distributed and embedded in the nanocrystallite matrix. As a result, the fabricated nanocomposites were exhibited superior properties than the conventional alloy. Here, 12 wt% B₄C reinforced silicon brass of bulk nanocomposite was produced higher hardness and compressive strength than the unreinforcement matrix. Further, the worn morphologies were evidenced the mild wear occurred at higher reinforced nanocomposites owing to decohesion and lower wear rate with considerable wear resistance.     

Microstructures and mechanical properties of B4C-TiB2-SiC composites fabricated by ball milling and hot pressing

B₄C-TiB₂-SiC composites were fabricated via hot pressing using ball milled B₄C, TiB₂, and SiC powder mixtures as the starting materials. The impact of ball milling on the densification behaviors, mechanical properties, and microstructures of the ceramic composites were investigated. The results showed that the refinement of the powder mixtures and the removal of the oxide impurities played an important role in the improvement of densification and properties. Moreover, the formation of the liquid phases during the sintering was deemed beneficial for densification. The typical values of relative density, hardness, bending strength, and fracture toughness of the composites reached 99.20%, 32.84?GPa, 858?MPa and 8.21?MPa?m^1/2, respectively. Crack deflection, crack bridging, crack branching, and microcracking were considered to be the potential toughening mechanisms in the composites. Furthermore, numerous nano-sized intergranular/intragranular phases and twin structures were observed in the B₄C-TiB₂-SiC composite.     

Direct preparation of La-doped SrTiO3 thermoelectric materials by mechanical alloying with carbon burial sintering

Thermoelectric Sr_1-xLa_xTiO₃ (x = 0, 0.02, 0.05, 0.08) nanoparticles were directly prepared by mechanical alloying, followed by carbon burial sintering to produce the bulk counterparts, for the purpose of obtaining pure phase and fine microstructures in a facile process. Electrical and thermal transport properties have been measured over the temperature range from 300 K to 1100 K. La was successfully doped into the SrTiO₃ during the milling process and acted as an n-type dopant. Core structure and superstructure in bulk samples, leads to a relatively high absolute Seebeck coefficient. The dimensionless figure-of-merit ZT changes with the increasing of La content and temperature, and the maximum ZT value can reach 0.06 at 300 K for x = 0.02 and 0.20 at 1000 K for x = 0.08. This strategy for bulk thermoelectric materials is simple, cost-effective and has great potential in large-scale industrial applications.     

Carbon content-dependent microstructures,surface characteristics and thermal stability of mechanical alloying derived SiBCN powders

Three types of SiBCN: carbon-lean, -moderate and -rich powders with the same Si/B/N mole ratio were subjected to high-energy ball milling to yield an amorphous structure. The effects of carbon content on microstructures, solid-state amorphization, surface characteristics and thermal stability of the as-milled powders were studied in detail. Results showed that the increases in carbon content can drive solid-state amorphization accompanied by strain-induced, crystallite refinement-induced and/or chemical composition-induced nucleation of nano-SiC from an amorphous body. The specific surface area increases as carbon content increases. The amorphous networks of Si–C, C–B/C–C, C–N, B–N and C–B–N bonds that compose the amorphous nature, but the species and contents of the chemical bonds are carbon content-dependent. Carbon-moderate powders possess satisfying thermal stability while carbon-rich ones perform the worst. Mechanical alloying derived SiBCN powders have outstanding oxidation resistance below 800 °C; however only carbon-moderate powders show desirable anti-oxidation ability at higher temperatures. Thus, mechanical alloying of SiBCN appears a suitable technique for developing amorphous matrix materials for practical applications.