Anodization mechanism on SiC nanoparticle reinforced al matrix composites produced by power metallurgy

Specimens of aluminum-based composites reinforced by silicon carbide nanoparticles (Al/SiCnp) produced by powder metallurgy (PM) were anodized under voltage control in tartaric-sulfuric acid (TSA). In this work, the influence of the amount of SiCnp on the film growth during anodizing was investigated. The current density versus time response and the morphology of the porous alumina film formed at the composite surface are compared to those concerning a commercial aluminum alloy (AA1050) anodized under the same conditions. The processing method of the aluminum alloys influences the efficiency of the anodizing process, leading to a lower thicknesses for the unreinforced Al-PM alloy regarding the AA1050. The current density versus time response is strongly dependent on the amount of SiCnp. The current peaks and the steady-state current density recorded at each voltage step increases with the SiCnp volume fraction due to the oxidation of the SiCnp. The formation mechanism of the anodic film on Al/SiCnp composites is different from that occurring in AA1050, partly due the heterogeneous distribution of the reinforcement particles in the metallic matrix, but also to the entrapment of SiCnp in the anodic film.

On Ti-18Si-6B and Ti-7.5Si-22.5B powder alloys prepared by high-energy ball milling and sintering

Recently, a new ternary phase was discovered in the Ti-Si-B system, located near the Ti6Si2B composition. The present study concerns the preparation of titanium alloys that contain such phase mixed with α-titanium and other intermetallic phases. High-purity powders were initially processed in a planetary ball-mill under argon atmosphere with Ti-18Si-6B and Ti-7.5Si-22.5B at. (%) initial compositions. Variation of parameters such as rotary speed, time, and ball diameters were adopted. The as-milled powders were pressureless sintered and hot pressed. Both the as-milled and sintered materials were characterized by X-ray diffraction, scanning electron microscopy and energy-dispersive spectrometry. Sintered samples have presented equilibrium structures formed mainly by the α-Ti+Ti6Si2B+Ti5Si3+TiB phases. Silicon and boron peaks disappear throughout the milling processes, as observed in the powder diffraction data. Furthermore, an iron contamination of up to 10 at. (%) is measured by X-ray spectroscopy analysis on some regions of the sintered samples. Density, hardness and tribological results for these two compositions are also presented here.

Hardness and Electrical Resistivity of Copper-Iron Powder Metal Compacts

Although powder metallurgical methods have been used for years to fabricate tungsten and platinum, very little scientific data have been recorded until the beginning of this century. A large percentage of all commercial production at present is based upon past practice rather than upon scientific knowledge.

Evaluation of Horizons, Inc. Th metal powder : progress report no. 1 for February 18, 1954-March 4, 1954 /

Three samples of thorium powder as supplied by Horizons, Inc. of Cleveland, Ohio were compared. The powder was processed entirely without the use of protective atmospheres with the exception of the sintering which was performed in a tank argon atmosphere with a dew point of approximately -80°C and the hot-pressing which was carried out in vacuum. The equipment and procedures used for cold-pressing and sintering were identical to those used in the evaluation of Sylvania produced thorium powders. The hot-pressing was done with standard uranium hot-pressing equipment.

An investigation of the slip-casting mechanism as applied to stainless steel powder /

The slip-casting technique, which is successfully employed in the ceramic industry, was utilized to produce sintered stainless steel components experimentally. The procedure used is described, along with an evaluation of the physical and mechanical properties of the samples produced. Specimens were made with properties comparable to those of wrought stainless steel and of cold pressed and sintered steel powder.

Consumable electrode arc-melting of cold-compacted thorium powder /

The consumable electrode arc melting of cold-compacted thorium powder has been developed to produce dense, clean and soft ingots which can be hot rolled without cracking. By using a water-cooled copper crucible, contamination has been prevented and resultant ingots cleaner than the original powder have been produced.

Interfacial microstructure in Y1Ba2Cu3O7-δ high Tc superconductors

The microstructures of YBa2Cu3O7-δ ceramics prepared from freeze dried powders and containing an excess of CuO have been studied by analytical electron microscopy. Special attention has been paid to the interfacial microstructure. It was found that a liquid phase formed during sintering between 890°C and 920°C and this promoted grain growth and densification. Both clean grain boundaries and boundaries containing an amorphous intergranular film, which was rich in Cu, have been observed. Both CuO and BaCuO2 were present as secondary phases.

Sintering and densification mechanisms of Y2BaCuO5 pellets

The sintering and densification of Y2BaCuO5 (Y-211) pellets made from powders with different characteristics have been investigated in the temperature range 1000-1140°C. A pellet made from powder containing Ba-rich secondary phases shows very early liquid-assisted sintering and densification and clear evidence of exaggerated grain growth. The melting of BaCuO2 and YBa2Cu3O7-δ (Y-123) secondary phases increases the rate of densification of Y-211 pellets made from other powders at temperatures above 1025-1030°C. All the liquid produced by the melting of the latter phases recrystallizes as intergranular layers of Y-123. These intergranular layers account for the darker appearance and for measurable electrical conductivities at room temperature of the pellets sintered at the higher temperatures. The development of exaggerated grain growth within a uniform fine-grained matrix opens the possibility of using controlled secondary recrystallization to obtain large single domains of Y-211, provided that the trapping of porosity can be avoided or minimized. © 1999 Elsevier Science S.A.

Study on Young's modulus and microhardness of carbon nanotubes reinforced copper nanocomposite

Carbon nanotubes (CNTs) were discovered by Iijima in 1991 as the fourth form of carbon. Carbon nanotubes are the ultimate form of the carbon fibre because of its high Young's modulus in the order of 1 TPa, which is very useful for load transfer in nanocomposites. In the present work, CNT/Cu nanocomposites were fabricated by the powder metallurgy technique, and after extrusion of the nanocomposites, bright field transmission electron microscopic studies were carried out. From the transmission electron microscopic images obtained, a novel method of ascertaining the Young's modulus of multiwalled CNTs is worked out in the present paper, which turns out to be 0.94 TPa, which is consistent with experimental results. Furthermore, an attempt is made to investigate the microhardness of copper by reinforcing it with multiwalled CNTs. There is an increase in hardness by twofold in CNT/Cu nanocomposites as compared to pure Cu matrix. This is due to high relative density, even distribution of CNTs and proper bonding at CNT/Cu interfaces.

Sintering of beta titanium: Role of dislocation pipe diffusion

Sintering of titanium in its high temperature beta phase was studied by isothermal dilatometry. The sintering shrinkage y did not follow the normal time exponent type of behaviour, instead being described by the equation y = Kt(m)/[1-(A+Bt)(2)], where m = 1.93 +/- 0.07, with an activation energy of 62-90 kJ mol(-1). A detailed analysis of these results, based on the 'anomalous' diffusion behaviour reported for beta titanium, is carried out. It is shown that the generation of a high density of dislocations during the alpha --> beta phase transformation, coupled with sluggish recovery at the sintering necks, enables sintering mass transport by pipe diffusion through dislocation cores from sources of matter within the particles to become dominant.

快速凝固/粉末冶金高阻尼铝合金挤压成形过程的数值模拟

采用有限元分析软件ANSYS,分析了快速凝固/粉末冶金(Rapidly Solidified/Powder Metallurgy,RS/PM)高阻尼铝合金FMS0714/10(Zn-30Al)的挤压成形过程,研究了模具与坯料间的摩擦条件和挤压比对阻尼铝合金成形过程的影响,探讨了挤压过程材料表面产生裂纹的机理,进行了成形工艺优化.研究结果表明:挤压过程中FMS0714/10(Zn-30Al)阻尼铝合金材料的流动与变形不均匀,导致了应力应变分布的不均匀:材料表面应力应变较大,芯部应力应变较小;表面过大的应变和轴向拉应力是表面裂纹的诱因;减小模具和坯料间的摩擦,增大挤压比,可以减小材料表面应力,使应变分布趋于均匀,从而减少材料表面损伤,优化材料表面质量,提高成品合格率.数值模拟的研究结果将为FMS0714/10(Zn-30Al)阻尼铝合金材料挤压工艺的制订以及新材料的设计和研制提供有益的参考.