R. Angers

Mechanical properties and microstructure of new magnesium-lithium base alloys

Magnesium-lithium base alloys containing aluminum, silicon and rare-earth additions have been prepared by melting and solidification in a low-carbon steel crucible, homogenized at 350°C and extruded at the same temperature. The distribution of alloying elements in homogenized specimens was determined and the microstructure of these alloys characterized. The mechanical properties were measured and compared with those of similar alloys.

Characterization of SiCp/2024 aluminum alloy composites prepared by mechanical processing in a low energy ball mill

Abstract In the present work, SiC p /2024 composite powders were produced by low energy ball milling a mixture of centrifugally atomized 2024 particles and β -SiC reinforcements having a size range between 2 and 6 μm. The experimental parameters studied were the milling time (between 1 and 24 h) and the volume proportion of β -SiC in the starting powder mixture (between 5 and 35%). These SiC p /2024 composite powders were consolidated by hot extrusion using optimized processing parameters. The microstructure of the extruded composites showed a uniform distribution of β -SiC particles in the 2024 aluminum matrix. Moreover, the mechanical properties (yield strength and Young’s modulus) improved with the SiC content although some reduction in ductility was observed.

SiCp/Mg composites made by low-energy mechanical processing

AbstractComposite powders containing 10, 20 and 30 vol% SiCp particulates in a Mg matrix were produced using mechanical processing. A small laboratory ball mill was used to achieve a uniform distribution of the reinforcements in the Mg matrix. The particle size distribution and the microstructure of the composite powders were studied as a function of processing time. Based on these observations, four successive stages of processing were identified. It was shown that a homogeneous distribution of SiC in a Mg matrix may be obtained under low-energy milling conditions. The influence of milling time and concentration of SiCp on tensile strength, stiffness, elongation and impact properties of rods extruded from the resulting composite powders were investigated. The hardness of SiCp/Mg composites was also evaluated to determine the influence of SiCp content.

Formation of irregular particles during centrifugal atomization of AZ91 alloy

Centrifugal atomization by the rotating disk process is usually used to produce spherical powders. However a significant proportion of irregular particles is frequently found in these powders. Irregular particles do not form by an atomization mechanism but by fragmentation of a layer of the atomized metal which solidifies at the surface of the rotating disk. In this paper, the shape and microstructure of irregular particles produced during rotating disk atomization of AZ91 magnesium alloy are described. Their size distributions are discussed as a function of the shape and angular velocity of the rotating disk. Solutions are proposed to reduce the formation of these particles.

Inverted Disk Centrifugal Atomization of AZ91 Magnesium Alloy

Abstract Magnesium AZ91 alloy powder was produced by centrifugal atomization under various conditions using an inverted disk atomizer. The particle size distribution was obtained as a function of the disk shape and rotation speed. The microstructure of particles and their shape were examined and characterized. Their cooling rates were obtained from theoretical relations and related to the secondary dendrite arm spacing.

Microstructural and mechanical properties of rapidly solidified CuNiSn alloys

Abstract Rapid solidification (RS) by melt spinning of CuNiSn alloys rendered more chemically homogeneous materials beneficial to mechanical strengthening. The structure was microcrystalline and manifested none of the tin segregation evident in conventionally cast alloys. Although there was microsegregation of tin in the form of γ precipitates at the grain boundaries of rapidly solidified ribbons, their degree of segregation was significantly reduced. Age hardening increased with tin (by spinodal decomposition) and nickel (by alloy hardening) content of the alloy. Solid solubility of tin in a high tin content alloy otherwise unattainable by conventional methods was achieved by RS.

Preparation of high purity SiB4 by solid-state reaction between Si and B

Abstract Silicon tetraboride (SiB 4 ) was synthesized by solid-state reaction between Si and B crystalline powders. Excess silicon was used and later removed from the resulting product by reaction with clorine vapors in a fixed-bed reactor at 430°C. The purity of SiB 4 (97·5 wt%) and the chemical composition (B/Si = 4·04) were determined by atomic absorption and X-ray diffraction analyses. The crystal structure was investigatedby X-ray diffraction. From this work, it is possible to confirm the existence of SiB 4 and reject that of the so-called compound SiB 3 .

The alpha ⇆ gamma transformation in iron powders

The alpha ⇆ gamma transformation in various size fractions of three different types of iron powder was studied by differential thermal analysis. The alpha-to-gamma transformation temperature increases considerably with decreasing particle size and with the number of thermal cycles through the transformation for a given particle size. The gamma-to-alpha transformation temperature decreases with decreasing particle size and remains about constant during thermal cycling through the transformation.

Fabrication and tensile properties of rapidly solidified Cu-10wt.%Ni alloy

Abstract Cu-10wt.%Ni ribbons were produced by melt spinning and cut into small particles with a blade cutter mill. The powders were then hot consolidated to full density by hot pressing followed by hot extrusion. Tensile properties of the resulting pieces were measured. Cu-10wt.%Ni cast ingots were also hot extruded and mechanically tested to compare with the rapidly solidified alloy and to evaluate the possible benefits brought by the rapid solidification process.

Mechanical characterization of Dense silicon tetraboride (SiB4)

High purity (>97·5% wt) silicon tetraboride (SiB4) powder was consolidated in solid polycrystalline shapes for physical and mechanical evaluation. Green compacts were obtained by cold isostatic compaction and then isostatically hot-pressed up to 99·4% of theoretical density. Elastic modulus, flexural strength, microhardness, specific density, porosity and microstructural aspects of dense specimens were investigated.