Surface oxidation of a quasicrystalline Al–Cu–Fe alloy: No effect of surface orientation and grain boundaries on the final state

We have used x-ray photoelectron spectroscopy and Auger electron spectroscopy to examine the characteristics of oxides on two types of quasicrystalline Al–Cu–Fe samples. One type was formed by consolidation of powders, resulting in multiple grains with random surface orientations. The other was a single grain, oriented to expose a fivefold surface. Both were oxidized to saturation in a variety of environments at room temperature. We measured the elemental constituents that oxidized, the extent of oxygen-induced Al segregation, and the depth of the oxide. Under the conditions of our experiments, there was little, if any, significant difference between the two types of samples. Hence, surface orientation and bulk microstructure played little or no role on the final state of the oxide under these conditions

Analysis of Gas-Phase Clusters Made from Laser-Vaporized Icosahedral Al−Pd−Mn

An icosahedral Al−Pd−Mn quasicrystal sample is laser vaporized to form metal clusters by gas aggregation. The clusters are subsequently laser ionized and mass analyzed in a time-of-flight mass spectrometer. The mass spectra show cluster compositions which are qualitatively similar to that of the sample. This is consistent with a kinetically controlled cluster growth process. Cluster thermodynamic stability is probed by multiphoton ionization/fragmentation, which induces primarily Al and Mn loss. The resulting spectra are composed of a series of Pd-rich Al−Pd clusters. The average cluster composition is 60 (±1)% Pd. This composition is close to a known eutectic in the Al−Pd system. When manganese is seen on these clusters, it is always in units of Mn3. These results are discussed in terms of relative binding strengths in the Al−Pd−Mn alloy system

Reactive plasma atomization of aluminum nitride powder

Experiments were performed to synthesize AlN powders by reacting Al with N using a conventional dc arc plasma as heat source. Feeding Al powder into Ar/N plasma open to atmosphere produced mainly Al oxide. Experiments using a chamber backfilled with nitrogen suppressed the Al oxide, but little AlN was formed. A furnace and crucible assembly was designed to feed molten Al directly into a DeLaval nozzle attached to the face of the dc arc plasma gun. Resulting submicron powders show a significant increase in AlN formation. This was dependent on chamber pressure, plasma velocity, and molten liquid feed rate. Experimental parameters, equipment design, effects of atomization/vaporization/condensation are discussed

Inference of hidden structures in complex physical systems by multi-scale clustering

We survey the application of a relatively new branch of statistical physics--"community detection"-- to data mining. In particular, we focus on the diagnosis of materials and automated image segmentation. Community detection describes the quest of partitioning a complex system involving many elements into optimally decoupled subsets or communities of such elements. We review a multiresolution variant which is used to ascertain structures at different spatial and temporal scales. Significant patterns are obtained by examining the correlations between different independent solvers. Similar to other combinatorial optimization problems in the NP complexity class, community detection exhibits several phases. Typically, illuminating orders are revealed by choosing parameters that lead to extremal information theory correlations.Comment: 25 pages, 16 Figures; a review of earlier work

Characterization of Gas Atomized Cu48Ti34Zr10Ni8 Amorphous Alloy

The advent of multi-component metallic alloys, which exhibit relatively good glass forming ability, has opened opportunities for processing metallic glasses into thick cross section components. The relatively good glass forming ability is important because conventional processing techniques (e.g., casting, extrusion and rolling) may be used to fabricate useful shapes while retaining the excellent engineering properties of an amorphous structure. In particular, the favorable processing characteristics of bulk amorphous alloys are the low cooling rates which can be exercised to yield an amorphous structure and the operating temperature range between the glass transition temperature (Tg) and the crystallization temperature (Tx). Current work is focused on developing a processing strategy that will allow us to fabricate even larger cross section amorphous alloys than are currently achievable by casting methods. The technique involves producing high pressure gas atomized (HPGA) Cu48Ti34Zr10Ni8powders and consolidating them at temperatures above Tg, but below Tx. Thermal analysis of atomized powders by DSC provides details of the influence of powder particle size, which is related to cooling rate during atomization. The results of experiments characterizing the thermal and kinetic behavior of Cu48Ti34Zr10Ni8powders indicate that short processing times are required to retain the amorphous structure during consolidation in the temperature regime between Tg and Tx

Computer Simulation of Final-Stage Sintering: II, Influence of Initial Pore Size

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65612/1/j.1151-2916.1990.tb06687.x.pd

One-piece, composite crucible with integral withdrawal/discharge section

A one-piece, composite open-bottom casting mold with integral withdrawal section is fabricated by thermal spraying of materials compatible with and used for the continuous casting of shaped products of reactive metals and alloys such as, for example, titanium and its alloys or for the gas atomization thereof

Enhancement of Mechanical Properties of Aluminum and 2124 Aluminum Alloy by the Addition of Quasicrystalline Phases

A structural and mechanical characterization of pure aluminum and 2124 T6 aluminum alloy reinforced with quasicrystalline phases of composition Al65Cu20Fe15 and Al70.5Pd21Mn8.5 (%at.) were performed. The quasicrystalline phases were synthesized by arc melting and then milled to produce powder of the alloys, which were then mechanical mixed with the starting powders of aluminum and 2124 aluminum alloy. The composites were produced by hot extrusion of a mechanical mixture containing 20% (%wt.) of the reinforcing phases on the metallic matrix. The structural characterization of the composites was carried out by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Mechanical characterization was carried out by Vickers hardness measurements and torsion tests at room temperature. The pure aluminum/quasicrystal composite showed the presence of the same phases from the starting powder mixture while for the 2124 aluminum alloy/Al65Cu20Fe15 the quasicrystalline phase transformed to the tetragonal ω-Al7Cu2Fe during the solution heat treatment. Mechanical strength of the composites presented a substantial increase in comparison to the original matrix metal. While the equivalent ultimate tensile strength of the Al/quasicrystal composites reached values up to 215MPa and Vickers hardness up to 60HV, the 2124/quasicrystal composites reached values up to 670MPa and Vickers hardness up to 190HV