Franciné Alves Costa

The influence of the dispersion technique on the characteristics of the W-Cu powders and on the sintering behavior

Abstract The influence of the dispersion technique on the sintering behavior of W–Cu composites is investigated. The dispersion of the copper phase and the fineness of the tungsten phase mostly influence the sinterability of W–Cu powders. By using high energy milling, particles containing very fine tungsten grains embedded in copper, called composite particles, can be produced. A powder consisting of composite particles has an optimal Cu dispersion and a very fine tungsten phase. This kind of powder improves significantly the sinterability of the W–Cu system in solid and in liquid states. Relative densities above 94% can be obtained easily for such powders at temperatures above the Cu melting point and for Cu contents as low as 19% in volume, even for short sintering times. A homogeneous fine structure is obtained. The sintering kinetics of such powders is described.

The Influence of the Milling Media Environment on the Characteristics of a W-Cu Composite Powder

W-Cu composite powders were prepared by high energy milling under two milling environments: cyclohexane and air. Composite particles are formed in both cases. The W particles are fragmented and embedded into the Cu particles. Both, W and Cu, are heavily strained, mainly in the first hours of milling. The composite powder has high homogeneity and is much finer than the original Cu powder. The mean particle size of the powders milled in both conditions is very close, but the wet milling was near 25% longer than dry milling and the size distribution is wider. This is consequence of the higher milling intensity of dry milling.

Effect of High Energy Milling on the Magnetic Properties of the WC-10wt.%Co Cemented Carbides

Cemented tungsten carbides were produced by liquid-phase sintering. In these work high energy milling (HEM) was used to produce homogeneous and finely grained powder mixtures. The milling effect on the magnetic properties of sintered samples is studied. Different mixtures in same composition (WC-10wt.%Co) were prepared by conventional mixture technique and wet HEM up to 300 hs in Planetary Mill. Magnetic hysteresis measurements on the sintered samples detected a significant increase in the coercitive field and a decrease on the saturation magnetization with milling time increasing. X-ray diffractogram show phase transformations with milling time. The Magnetic properties are correlated with phase relations and microstructural properties of the sintered samples.

Effect of Mechanical Alloying on Characteristic of Powders of Amnoia Hepatamolybdate, Copper and MoCu Sintered

The mechanical alloying of Mo-Cu powders allows the production of highly homogeneous sintered pieces, with very thin Mo particles and good dispersion of Mo particles in the ductile Cu phase, allowing the development of a route for the preparation of Mo-Cu simple composite powders, environmentally sustainable and able to increase the sinterability of the material without causing damage to their properties of thermal conductivity and electrical. Was used the precursor powders of molybdenum (Ammonium heptamolybdate) plus Cu, where two samples were prepared by mixing processes. For mechanical alloying, and by mixing manually, and both reduced and sintered in a resistive furnace with hydrogen gas. The materials were analyzed by optical microscopy, XRD and density measurements. The results confirm the effect of mechanical alloying on the increasing in high density of the sintered samples and thereby producing superior properties to those shown by the mixing manually sample.

The Influence of the Milling Environment on the Structure of a W-Cu Composite

This work reports an investigation about the influence of the environment of milling on the characteristics of the powders and on the structure and density of sintered samples made of these powders. Mixtures of composition W-30wt%Cu were milled for 51 hours in a high energy planetary mill in dry and wet (cyclohexane) conditions. The milled powders have composite particles. The powders were pressed and sintered at 1050º, 1150º and 1200°C under flowing hydrogen. The isothermal times were 0 minutes for the first two temperatures and 60 minutes for the latter. The samples reached around 95% of relative density. The powders were characterized by means of XRD and SEM. The sintered samples were characterized by means of SEM, optical microscopy and density measurement.

Mechanical Characterization of Alumina-Doped Tungsten Carbide

Cemented carbides have dominated the cutting tool market. Recent works have shown the development of new WC-materials in order to improve their mechanical properties and oxidation behavior. This work reports the first results produced by the addition of aluminum oxide in a tungsten carbide matrix. WC-material with 10 wt.% of cobalt was mixed with 5 and 10 wt.% of Al 2 O 3 in a planetary ball mill. Subsequently, samples with 10 mm in diameter were uniaxially hot-pressed. The composite material was characterized by X-ray diffraction, hardness and scanning electron microscopy. The results showed that the addition of 10 wt.% of Al 2 O 3 has improved the hardness value of the tungsten carbide matrix.