Metal alloy honeycomb structures were fabricated using a paste extrusion technique and characterized for potential application as interconnects in solid oxide fuel cells. Thermal expansion characteristics of Fe-Cr, Fe-Ni, Ni-Cr, Fe-Ni-Cr, and similar alloys containing an oxide dispersion were determined and compared with the thermal expansion behavior of yttria-stabilized zirconia (YSZ). A method was developed to calculate thermal expansion mismatch between two materials under a variety of heating and cooling conditions. It was shown that Fe 20 wt% Cr and Fe 47.5 wt% Ni alloys have low expansion mismatch with YSZ under a wide range of heating and cooling conditions. Oxidation experiments showed that Fe-Cr alloys have superior oxidation resistance in air at 700℃compared with Fe-Ni-Cr alloys with similar chromium contents. The inclusion of oxide dispersions (Y₂O₃ and CaO) into an alloy honeycomb was shown to improve oxidation resistance without affecting thermal expansion behavior. The honeycomb extrusion process provides a method by which experimental alloys can be produced and characterized rapidly to develop an alloy suitable for use as an interconnect in a solid oxide fuel cell.

Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

This work details an investigation into the production of porous shape memory alloys (SMAs) via hot isostatic press (HIP) from prealloyed powders. HIPing is one of three main methods for producing porous SMAs, the other two are conventional sintering and selfpropagating hightemperature synthesis (SHS). Conventional sintering is characterized by its long processing time at near atmospheric pressure and samples made this way are limited in porosity range. The SHS method consists of preloading a chamber with elemental powders and then initiating an explosion at one end, which then propagates through the material in a very short time. HIPing provides a compromise between the two methods, requiring approximately 5 hours per cycle while operating in a very controlled environment. The HIPing method gives fine control of both temperature and pressure during the run which allows for the production of samples with varying porosity as well as for finetuning of the process for other characteristics. By starting with prealloyed powder, this study seeks to avoid the drawbacks while retaining the benefits of HIPing with elemental powders. In an extension of previous work with elemental powders, this study will apply the HIP method to a compact of prealloyed powders. It is hoped that the use of these powders will limit the formation of alternate phases as well as reducing oxidation formed during preparation. In addition, the nearspherical shape of the powders will encourage an even pore distribution. Processing techniques will be presented as well as a detailed investigation of the thermal and mechanical properties of the resulting material.

The implementation of technologies such as aluminum powder metallurgy (P/M) can be used in the automobile industry to have potential economic and environmental advantages. This technology to produce vehicle components can offer the combination of weight savings due to the low density of aluminum and material and machining savings via near net shape processing attributes. In an effort to expand the scope of application for aluminum P/M, considerable research has emphasized the development of new alloys and composites. One such alloy is P/M 2324, an aluminum-copper-magnesium alloy developed to have increased mechanical properties over the standard aluminum P/M alloys of the AC2014 type. The objective of this work was to undertake a comprehensive study on the effects of hot deformation on the emerging alloy P/M 2324 as well as the alloy with a SiC addition. Here, a forgeability study of these alloys and its wrought counterpart AA2024 was completed. To

Magnesium and its alloys are attractive for use in automotive and aerospace applications because of their low density and good mechanical properties. However, difficulty in forming magnesium and the limited number of available commercial alloys limit their use. Powder metallurgy (P/M) can be used to alleviate the formability problem through near-net-shape processing. The surface layer on Mg powders acts as a barrier to diffusion and sintering is problematic. X-ray photoelectron spectroscopy (XPS) was used to identify the composition of the layer, as well as a focused ion beam (FIB) process for obtaining thin films was utilized to prepare samples for analysis with transmission electron microscopy (TEM). Sintering of pure magnesium compacts has been studied by differential scanning calorimetry (DSC), which identified several decomposition reactions during heating. It was also found that alloying additions of calcium and yttrium promote surface layer disruption during sintering by DSC measurements and testing indicates improved mechanical properties.

Aluminum powder metallurgy (PM) parts have found applications in automotive, aerospace and transportation. Sintered aluminum parts have been developed and compete with traditionally fabricated ingot metallurgy (IM) products for specific applications. To extend the range of application of (PM) alloys which offer the advantage of net and near net shape production, processing parameters and corrosion behaviour of the aluminum alloys need to be improved. In this research, processing parameters and corrosion behaviour of a commercial Al-Mg-Si aluminum alloy (Alumix 321) were investigated. This alloy is the PM equivalent of wrought AA6061. Four sintering temperatures (610 °C, 620 °C, 630 °C, 640 °C) and two pressing pressures (200 MPa, 400 MPa) were used and the optimum pressing and sintering procedure was selected. In addition to different processing routes of aluminum powder metallurgy alloys, a series of electrochemical experiments on both (IM) and (PM) aluminum alloy was performed with the aim of correlating corrosion behaviour with production techniques. As a modification step, post sintering treatments and surface alteration techniques were applied. Hot rolling, hot swaging, repressing, resin impregnation and shot peening were performed and their effect on corrosion behaviour was investigated; their effect on density, hardness, and microstructure was also studied. Hardness after hot swaging and hot rolling increases and near full density was achieved (? 99%), while for resin impregnation and shot peening surface nature and roughness were affected, respectively. Electrochemical techniques such as open circuit potential (OCP), Tafel extrapolation (TE), cyclic polarization (CP) and stair step polarization (SP) were performed on the ingot, wrought, and post sintered alloys immersed in a 3.5 wt% NaCl solution. Electrochemical experiments show that corrosion current decreases as a result of post sintering treatments. The electrochemical experiments also show different corrosion mechanisms that were later confirmed by the metallographic analysis. The corrosion product and corroded surfaces of the alloys were characterized by optical microscopy, scanning microscopy (SEM), energy dispersive spectroscopy (EDS), wavelength dispersive spectroscopy (WDS), and X-ray diffraction (XRD). Results show that pitting is the main corrosion mechanism of the wrought alloy. However, powder metallurgy alloys show pitting, crevice, and intergranular corrosion. / Effect of processing parameters on corrosion behaviour of Alumix 321 PM alloy

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Dissertation (Ph.D.)--Worcester Polytechnic Institute. / Keywords: Heat Treatment; Powder Metallurgy; Phase Transformations; Finite Element Modeling Includes bibliographical references.

No description available.