Dispersion Of Al2O3 Particles Research Articles

コンポキャスティング法による粒子分散型アルミニウム合金基複合材料の製造および諸特性

An attempt to fabricate particle dispersed Al-4mass% Cu alloy composites was made by compocasting. The recovery of particles introduced in the molten metal is governed by the particle size, fraction solid of the metal and Mg concentration in the metal. Mg 0.5mass% is required in the metal to ensure homogeneous dispersion of SiC particles 40μm in size in the molten metal. A spinel product MgAl2O4 is observed at the Al2O3 particle-Al interface, but no reaction product is found at the SiC-Al interface. The wear loss of the composites decreases with increases in size and content of dispersed Al2O3 particles so significantly that 2017 alloy containing 2.5mass% of Al2O3 particles is equivalent to FC25 cast iron in wear loss. Rolling of Al2O3 particle dispersed 2017 alloy composites results in a decrease in tensile elongation with increases of size and content of particles. The strength of the alloy containing dispersed Al2O3 20μm in size from 0 to 7.5mass% decreases only slightly by rolling.

Enhancement of ionic conduction in CaF2 and BaF2 by dispersion of Al2O3

Ionic conductivity measurements were performed on polycrystalline CaF2, BaF2 and those dispersed with Al2O3 particles. The ionic conductivity of both CaF2 and BaF2 increased by about 1 to 2 orders of magnitude by dispersion of Al2O3 particles, while X-ray diffraction measurements showed there were no other phases present other than fluoride and Al2O3. The conductivity of the dispersed system strongly depended on the particle size and the concentration of Al2O3, which suggested the high ionic-conductivity layers were formed at the interface between the ionic conductor matrix and the Al2O3 particles. The effective thickness and electrical conductivity of the interface layer at 500° C were calculated, using a simple mixing model, to be 0.3 to ~ 0.6μm and ~ 10−3 S cm−1, respectively.

Creep of polycrystalline sodium chloride containing a dispersion of alumina

The creep of polycrystalline NaCl contaning a fine dispersion of Al2O3 particles is analysed in terms of dependence on stress, temperature, volume fraction and size of dispersion, and grain size of samples. Compressive creep experiments around 0.8 Tm show that the dispersion inhibits diffusive creep. The creep is characterized by a threshold stress above which the creep rate increased linearly with applied stress. The threshold stress decreases with increasing temperature and is proportional to the volume fraction of the dispersion in agreement with a model proposed by Burton. The activation energy corrected for the temperature dependence of the threshold stress falls within a narrow range consistent with grain-boundary diffusion of chlorine in sodium chloride. The grain-size dependence is not consistent with a modified diffusive creep model but it is suggested that it may be controlled by inhibited grain-boundary sliding according to a new model.

Electrical Resistivity of Internally Oxidized Cu–Al Alloys

The electrical resistivities at room temperature have been investigated precisely after partial and complete internal oxidation. The internal oxidation rates obtained through electrical resistivity measurements are always smaller than the real rates which are obtained metallo-graphically. This suggests that the resistivities of subscales after partial internal oxidation are greater than those after complete internal oxidation, and that it is wrong to estimate internal oxidation rates through resistivity measurements. After complete internal oxidation, deviations from Matthiessen's rule (DMR) are observed in the internally oxidized Cu–Al alloys. The DMR's at 20°C have the same magnitudes as those of the residual resistivities and are nearly proportional to the volume fraction of dispersed Al2O3 particles. The DMR at 20°C in the Cu–1.0 vol%Al2O3, alloy is 0.037 µΩ-cm. The origin of the DMR is attributed to dispersed oxide particles.

The fatigue deformation of dispersion hardened copper single crystals

Abstract Constant strain amplitude fatigue deformation at room temperature has been studied in single crystals of copper with and without a dispersion of Al2O3 particles. The size, shape and distribution of the alumina particles were varied by internally oxidizing copper—aluminium single crystals by two different methods. Although the saturation stress level does not seem to be affected by the presence of the dispersed phase, the fatigue hardening and the resulting dislocation structure are significantly different.

On the behaviour of vacancies in quenched AlAl 2O 3 alloys

Thin foils of SAP, an alloy of Al with dispersed Al 2O 3-particles, were quenched from temperatures above 500°C into brine at −20°C and subsequently examined by transmission electron microscopy. It was found that vacancy loops can be obtained by quenching SAP if the alloy is quenched from high temperatures with a high quenching rate and if the interparticle spacing is not too small. The “interstitial strain” field normally formed around the particles by differential thermal contraction effects during cooling was not observed after quenching from temperatures close to the melting point. It is suggested that the strain field around the particles acts as a sink for vacancies and the strain is relieved by the high excess vacancy concentration. During quenching from lower temperatures, on the other hand, the concentra tion and the mobility of the excess vacancies appear not to be sufficiently high to prevent the rapid set-up of the strain field which becomes large enough around the bigger particles to generate dislocations.