The vacuum-plasma-spraying technique presented in this article is suited to produce aluminum-matrix composites with a low coefficient of thermal expansion reinforced with fine ceramic particles, resulting in a uniform particle dispersion and bulk porosity of less than 1.5% in the as-sprayed condition. Plastic deformation of the plates followed by annealing resulted in significant increases in ultimate tensile strength, hardness, and elongation.
Composite materials based on aluminium are used in different ®elds where weight, thermal expansion, and thermal stability are key requirements. The aim of the present study was to develop a universal method and scienti®c approach for evaluating the design of lightweight, Al matrix composites with low coef®cients of thermal expansion (CTE) and high dimensional stability, and to produce such composites using the vacuum plasma spray (VPS) process. The methodology is general and could be applied to other composite systems. The VPS-produced Al and Al alloy 6061 based composites were reinforced with a variety of ceramic particles including Si 3 N 4 , B 4 C, TiB 2 , and 3Al 2 O 3 .2SiO 2 . These composites have low CTE values ((12 ± 13)610 26 K 21 ), similar to that of steel, and high dimensional stability (capable of keeping dimensions stable with changes in temperature). They have low porosity (98 ± 99% dense) and a uniform distribution of the strengthening particles. Hot rolling of the VPS-formed composites, followed by heat treatment, resulted in a signi®cant improvement in the mechanical properties. Deformed and heat treated 6061 based composites, containing 20 wt-%TiB 2 and 40 wt-%3Al 2 O 3 . 2SiO 2 , showed excellent mechanical properties (ultimate tensile strength 210 ± 250 MPa, elongation w4%).MST/4555
The development of nuclear fusion reactors is presently considered to be the only possible answer to the world's increasing demand for energy, while respecting the environment. Nuclear fusion devices may be broadly divided into two main groups with distinctively different characteristics: magnetic confinement fusion (MCF) and inertial confinement fusion (ICF) reactors. Although the two nuclear fusion technologies show similarities in energy levels (as high as 3 J/cm2) and type of environment (high temperature plasmas) to be contained, the materials of choice for the protective shields (first wall in the ICF and deflectors in the MCF) differ significantly. In ICF reactors, multiple laser beams are used to ignite the fuel in single pulses. This process exposes the first wall to microshrapnel, unconverted light, x-rays, and neutrons. B4C is a low Z material that offers high depth x-ray absorption to minimize surface heating, is not activated by neutrons (will not become radioactive), and offers high hardness and vapour temperature. The long term operation envisioned within MCF reactors, where a continuous nuclear fusion of the fuel is sustained within the confinement of a magnetic field, favours the use of high Z materials, such as W, to protect the plasma exposed deflectors. The reason is a lower erosion rate and a shorter ionization distance in the plasma, which favours the redeposition of the sputtered atoms, both resulting in a lower contamination of the plasma. The production of the first wall and the deflector shields using solid B,C and W materials respectively, is obviously unthinkable. However, ProTeC has developed high density coatings for both ICF and MCF nuclear fusion reactors. W coatings with less then 2% porosity have been produced for both, the Tokamac MCF reactor and its Toroid Fueler. The toroid fueler is a plasma generating device designed to accelerate particles and inject them into the centre of the operating fusion reactor in order to refuel. For the application in an ICF reactor, B4C coatings exhibiting porosity levels below 3% with a hardness above 2500 HV have been deposited directly onto Al substrate. Properties such as outgassing, resistance to erosion and shrapnel, and the influence of x-rays have been studied and showed exceptional results.
The growing need for new materials and material combinations with superior properties for severe service applications has led to the development of near net-shape forming techniques for certain materials, such as superalloys, refractory metals (Ta, W, and Mo) and highly reactive metals (Ti and its alloys). Vacuum plasma spray (VPS) was used to produce dense Ti-6Al-4V deposits for mechanical properties evaluation. Spherical Ti-6Al-4V powder, produced by Plasma Atomization (PA), a novel patented powder fabrication technique, was used as the starting powder. Plasma atomized Ti-6Al-4V powder characteristics include: high purity, tight particle size range, highly spherical with no attached satellites, and excellent flowability. The resulting as-sprayed Ti-6Al-4V deposits were dense and low in oxygen content. Thermal treatment was conducted after spraying in order to improve the structure and the properties of the spray formed material. The mechanical properties of the material, including tensile strength, elongation and hardness, in both the as-sprayed and the heat treated conditions were compared. The mechanical properties of these preliminary VPS Ti-6Al-4V specimens indicate that the combination of high purity starting powder and controlled environment deposition can be used to produce dense spray formed Ti-6Al-4V structures with properties comparable to those of cast or sintered powder metallurgy parts.
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