Synthesis, characterization and physical properties of Al-Cu-Fe quasicrystalline plasma sprayed coatings

The phases and microstructures of Al-Cu-Fe powders and coatings were investigated in this study. Powders were prepared by grinding a chill cast ingot and by high pressure gas atomization. The contrasting solidification rates of these two processes yielded very different solidification structures. The cast ingot was very inhomogeneous and contained icosahedral ([psi]), cubic ([beta]), monoclinic ([lambda]) and tetragonal ([theta]) phases. The gas atomized powder had a finer scale of phase segregation and consisted primarily of the [psi] and [beta] phase; a small fraction of the [lambda] phase was present as well;Plasma arc sprayed (PAS) coatings were formed using the above powders. The chemical uniformity of the starting powder was carried over into the PAS coatings. Evaluation of starting powder size during PAS revealed that small powder particles (e.g., \u3c45[mu]m) tended to lose Al by vaporization. This mass loss brought the composition of the coating into a two-phase region of the Al-Cu-Fe phase diagram and produced less of the desired [psi] phase;Substitution of 1 at. pct. B for Al was done to study the effect on altering the solidification microstructure of Al63 Cu25Fe12 chill cast ingots, gas atomized powder and PAS coatings. Boron significantly altered the structure of the chill cast ingot, but had less impact on the solidification of the atomized powders or PAS coatings. Differential thermal analysis and electron microscopy indicated that B was modifying solidification by a solute-drag mechanism;Oxidation and tribological behaviors of PAS Al63 Cu25Fe12 coatings were examined. The coatings were resistant to catastrophic oxidation at 500∘ and 700∘C in flowing O2 for up to 250 hours. The weight gain of oxidized samples followed parabolic kinetics. Pin-on-disc wear tests with a Al2 O3 pm against PAS Al63 Cu25Fe12 coatings showed brittle behavior at room temperature and increasing plastic behavior at temperatures up to 600∘C. Initial coefficients of friction between the ceramic pin and the quasicrystal coatings ranged from 0.4 to 0.6 at 25∘C and 600∘C, respectively. These values increased with sliding distance. The increase in frictional force was attributed to increased contact area between the pin and coating as sliding progressed

The effects of the middle school advisory program on the self concept of sixth grade students

Thesis (M.S.E.)--University of Kansas, Counseling, 1984

Design and optimization of a multi-particle accelerator beam transport and delivery system for material irradiation in nuclear and fusion science

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, February 2012."December 2011." Cataloged from PDF version of thesis.Includes bibliographical references (p. 129-131).A beam delivery and transport system were designed for the use in MIT Materials Test Facility (M2TF). The purpose of this beam delivery system was to design a 36 MeV Proton Cyclotron for DPA accumulation and a 100 MeV Helium Cyclotron for irradiation failure and volumetric helium accumulation simulation. The purpose of the beam transport system was to incorporate the two cyclotrons into the beam transport system and transport their beams to the target chamber, the location of the target sample. The cyclotrons were designed using Opera-3D and Acfields. The beam transport system was designed using TRANSPORT. The shielding analysis for the entire facility was designed using SolidWorks and calculated with MCNP/X The design specification of M2TF with respect to beam energy, current density, and control were achieved based on these design tools and previously developed analytic methods. The design process for the cyclotrons resulted in a 4.3T lsochronous Proton Cyclotron and 3.9T Isochronous Helium Cyclotron. A beam transport system connected the cyclotrons to the target chamber with three doublet quadrupoles and one dipole bending magnet The shielding calculation proved the total effect dose rate in rem/year for the final design facility was safe for operational workers.by Tyler Christopher Sordelet.S.M

Electrochemical Pitting And Repassivation On Icosahedral AL-CU-FE, And A Comparison With Crystalline Phases

We report the electrochemical potentials at which localized pitting and repassivation occur on icosahedral Al-Cu-Fe, and on a series of related alloys and elemental metals. The electrochemistry occurs in a buffered NaCI solution, pH 8.4. Under these conditions, pitting and repassivation appear to be controlled mainly by the chemical composition of the alloy, although the quasicrystalline phase displays an anomalous resistance to repassivation. Corrosion of this phase proceeds by dissolution of Al and Fe, leaving behind pits which are Cu-enriched

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

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

Room Temperature Oxidation of Al-Cu-Fe and Al-Cu-Fe-Cr Quasicrystals

We have investigated formation of oxides on quasicrystalline and crystalline alloy surfaces of similar composition, in different oxidizing environments. This includes a comparison between a quaternary orthorhombic approximate of Al-Cu-Fe-Cr quasicrystal and the ternary Al-Cu-Fe quasicrystalline and crystalline phases. We noted that each sample showed the following common trends: preferential oxidation of the Al, enrichment in the concentration of Al present at the surface upon oxidation, water concentration is directly related to oxide thickness, and the oxide thickness displays a strong correlation with the bulk concentration of Al in the sample

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

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

METHOD OF MAKING QUASICRYSTAL ALLOY POWDER, PROTECTIVECOATINGS AND ARTICLES

A method of making quasicrystalline alloy particulates wherein an alloy is superheated and the meltis atomized to form generally spherical alloy particulates free of mechanical fracture and exhibiting a predominantly quasicrystalline in the atomized condition structure. The particulates can be plasma sprayed to form a coating or consolidated to form an article of manufacture