Richard A. Waldo

Microstructure and creep behavior in AE42 magnesium die-casting alloy

The micro structural analysis of die-cast AE42 reveals a correlation between micro structure and creep strength. A lamellar-phase Al11RE3, which dominates the interdendritic microstructure of the alloy, partly decomposes above 150‡C into Al2RE and Al (forming Mg17Al12). The increased solubility of aluminum in magnesium at higher temperatures may also promote the decomposition of Al11RE3. The creep strength decreases sharply with these phase changes. A mechanism for the decrease in creep strength of AE42 is proposed whereby the reduced presence of lamellar Al111RE3 and/or the presence of Mg17Al12 contribute to the observed poor creep strength at higher temperatures.

Vapor deposited thin gold coatings for high temperature electrical contacts

Using electron beam evaporation, thin films of Au over Ni and Au over Pd/sub 80/Ni/sub 20/ have been deposited on stainless steel and copper alloy substrates for high temperature electrical contact studies. The structure and composition of the films were studied in detail using electron probe microanalysis (EPMA) and X-ray photoelectron spectroscopy (XPS) with sputter depth profiling. The contact properties, such as contact resistance, fretting wear resistance, and thermal stability have been measured. The Ni and Pd/sub 80/Ni/sub 20/ layers of about 200 to 300 nm thickness have been shown to be effective in maintaining high temperature stability up to 340/spl deg/C in air by blocking the diffusion of elements in the substrates to the Au surface. These coatings also show good fretting wear resistance. These desired properties have been achieved with the thickness of the Au, Ni, and Pd/sub 80/Ni/sub 20/ layers substantially less than that of the conventional electroplated coatings.

Liquid Chromatographic Determination of Azide as the 3,5-Dinitrobenzoyl Derivative

Abstract A method for the determination of azide after conversion to 3,5-dinitrobenzoyl azide has been developed. The derivatization reaction is fast (3 min.), quantitative, and yields a product with strong ultraviolet absorption. The derivatization reaction mixture is separated by high performance liquid chromatography so that the azide derivative can be easily quantitated. The detection limit of the method is 10 ng NaN3/mL. The total analysis time is 20 minutes per sample.

Characterization of potassium tantalum niobate films formed by metalorganic deposition

Thin films of potassium tantalum niobate, KTa0.6Nb0.4O3, with a Curie temperature of 20 °C were deposited on a variety of substrates by metalorganic deposition. These films had peak relative permittivities of 16 000 at 20 °C. Hysteresis plots of electric displacement as a function of electric field, taken at 0 °C, revealed a coercive field of 800 V/cm, a spontaneous polarization of 3.9 μC/cm2, and a remnant polarization of 0.5 μC/cm2. The hysteresis loops did not change significantly as the temperature was varied down to −100 °C.

Directional Solidification and Microsegregation in a Magnesium-Aluminum-Calcium Alloy

Creep-resistant Mg-4Al-4Ca (AX44) alloy was solidified under different growth/cooling rates using a directional solidification (DS) technique. The solidification behavior and microsegregation of the alloying elements in the castings was investigated. Computational thermodynamics calculations of phase equilibria and experimental observations confirm that the solidification microstructure in this alloy consists of α-Mg, C36-(Mg,Al)2Ca, and C14-Mg2Ca phases. A relationship was established between the primary dendrite arm spacing and the cooling rate, which can be used to predict mechanical properties such as yield strength and creep. The microsegregation of alloying elements (Al and Ca) predicted by the Scheil model in AX44 agrees well with the electron probe microanalysis (EPMA) measurements, suggesting that the Scheil model can be used in microstructure simulation of magnesium castings.

Thermoelectric performance of p-type skutterudites YbxFe4−yPtySb12 (0.8 ≤ x ≤ 1, y = 1 and 0.5)

Thermoelectric performance of p-type skutterudites currently lags that of the corresponding n-type materials, and improvement of this important class of materials has become the focus of considerable research effort world-wide. Recent calculations find promising band structure features in p-type skutterudite materials of the type AFe3NiSb12 (A = Ca, Sr, or Ba), which could potentially lead to excellent thermoelectric properties. Recent work on the Yb-filled analogs of these formulations (YbFe3NiSb12) however, finds that the onset of intrinsic conduction at lower than expected temperatures deteriorates the performance above 500 K. This leads to performance in the temperature range of interest for automotive waste heat recovery applications. We, therefore, seek a way to increase the band gap in order to find a way to minimize the deleterious effects of intrinsic conduction on thermoelectric performance. Here, we present ab initio band structure calculations, the synthesis and thermoelectric properties of Yb...

Characterization of surface modified α-iron by nitrogen plasma immersion ion implantation: a microstructural study

Abstract This paper discusses the morphology of pure iron surfaces modified by nitrogen plasma immersion ion implantation and compares them to similar surfaces treated with conventional plasma nitriding. Analysis of the samples was performed with glancing angle X-ray diffraction and traditional Bragg–Brentano geometry X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and depth profiling using X-ray photoelectron spectroscopy in combination with sputtering. The structures formed both by thermal nitriding and plasma ion implantation correlate very well with the Fe–N phase diagram, as the surface temperature and nitrogen concentration are decisive factors in developing specific crystalline phases. Only at lower temperatures, where chemical absorption and thermal diffusion effects are strongly limited, does the distribution of implanted nitrogen become substantially of the non-equilibrium type, and can almost be freely tailored. At low temperatures, however, the nitrided layer becomes extremely shallow (defined almost solely by the ballistic ion model), thereby limiting the applicability of this technology for iron-based materials. Hence, unless specific ferrous alloy materials are chosen which promote nitride formation and diffusion, e.g. chromium and iron-chromium alloys, the niche for nitrogen plasma ion implantation into ferrous materials seems to be limited to those cases where surface nitriding is desired, but where exposure of the workpiece to high temperature is forbidden.

Reactive sputter deposition of zirconium nitride/aluminum nitride multilayers: Chemical competition effects and structural characterizations

We have examined in detail the process of reactive sputtering of elemental Zr and Al targets simultaneously in an argon/nitrogen mixture. The total pressure and optical emission from both target plasma discharges have been monitored as a function of increasing nitrogen fraction. We compare this situation with the usual case of single target operation and demonstrate the existence of a chemical competition effect between the individual target plasma discharges, which manifests itself in preferential reaction of nitrogen with Zr and sequential nitriding of Zr and Al targets with increasing nitrogen fraction. We have further examined the structure and composition of single layer zirconium nitride and aluminum nitride films, deposited at different nitrogen fractions, by symmetrical and glancing angle x‐ray diffraction, and by electron probe microanalysis, and our results corroborate the existence of chemical competition effects. We demonstrate the possibility of synthesizing zirconium nitride/aluminum nitride...

Grain growth of rapid-thermal-annealed Y-Ba-Cu oxide superconducting thin films

A study of the microstructure of Cu‐rich and stoichiometric Y‐Ba‐Cu oxide thin‐film superconductors is presented. The films were deposited on 〈100〉 SrTiO3 by the nonvacuum technique of metalorganic deposition followed by rapid thermal annealing in oxygen. Analysis showed that for annealing temperatures below 900 °C, grain size increased with increased annealing temperature, with an enhancement in grain growth for the Cu‐rich films. Annealing near or above the melting point of the 1‐2‐3 phase causes only a slight increase in the rate of grain growth and no detectable effects of the excess Cu. Annealing above 920 °C produces segregated CuO islands 5–10 μm in size in the Cu‐rich films. Oriented grain growth was found for the 1‐2‐3 grains with their c axis perpendicular and parallel to the SrTiO3 substrates. Sheet resistivity measurements were correlated with grain size, phase separation, and oriented grain growth. An anomalous behavior in the resistance‐temperature plot at 220–240 K of the Cu‐rich films is s...

Determination of platinum in alumina-supported automotive catalyst material by electrothermal atomic absorption spectrometry

Abstract Platinum (0.01–0.2%) is determined after dissolution in sulfuric and hydrochloric acids and addition of palladium and rhodium to compensate for interelement effects. At the 0.06% level, the relative standard deviation is 2%. The results agree within 4% with those obtained by chemical methods.