This work studied the structural evolution of Cu-xMo (x = 5 and 8 wt.%) alloys processed by mechanical alloying using x-ray diffraction profiles, scanning electron microscopy, differential scanning calorimetric and microhardness. X-ray diffraction analysis was done using the modified Williamson-Hall and Warren-Averbach methods. These were used to determine structural properties, such as crystallite size, stacking fault probability and energy, dislocation density of metallic powder as a function of the amount of Mo and milling time. The main results obtained for both alloys were higher dislocation density and Vickers microhardness values were measured and crystallites sizes of around 10 nm were measured for both systems at 50 h of milling. Lattice defects increase the free energy and the free energy curves shift upwards, therefore the solubility limits change and Cu-Mo solid solution is formed. (C) 2012 Elsevier B.V. All rights reserved.

Tubular metal supported SOFC technology has successfully been developed over the past years with the aim at domestic CHP systems below 3 kWe. The basic cell structure consists of a metal porous support, a protective barrier layer, an anode and an electrolyte cofired at 1350ºC. Cathode and contacting layers are subsequently sintered at lower temperatures. The most significant results to date include successful thermal cycling of the cell and anodic connection during 450 cycles and 2000 hours, oxidation testing of the metal support for more than 2500 hours and a comparison of influence of porosity during 100 hours oxidation of metal porous substrates under high water vapour atmospheres.

Crofer can be considered as the reference interconnect material in solid oxide fuel cells (SOFCs) working under 800 degrees C. Thanks to its thermal expansion coefficient, it is suitable to replace ceramic components, such as the interconnect and the metal support, and it can be cost effective. Several research groups, including Ikerlan, have used porous substrates with the same composition as Crofer (PM from H. C. Starck GmbH, Goslar, Germany) as the metal support for their SOFC cells. The aim of this study is to determine the effect of certain variables (time, temperature, vapor content, cycling, porosity, and current flow), while other aspects are constant (sample composition and particle size and shape). [DOI: 10.1115/1.4001764]

A group of high strength, cost effective PM steels has been generated by combining alloying elements (e. g. Cr, Mo, Ni, Cu, Mn) in predetermined concentrations. The main aim was to optimise the balance between compressibility, hardenability and properties. Special efforts were devoted to identifying compositions and processing conditions giving specific proportions of transformation products (martensite, bainite, etc.) in an attempt to correlate microstructural characteristics with the mechanical properties of the sintered steels after tempering. Measuring dimensional changes after sintering as well as properties such as yield stress and hardness allowed processing conditions to be optimised for the composition and characteristics of the powder mixture.

The present paper focuses on the initial stage of the liquid phase sintering (LPS) of a commercially available P/M Al-Si alloy, with nominal composition A1-14Si-2.5Cu-0.5Mg (in wt%). The microstructural examination of the as-received powder showed that it is constituted by pure Al particles and master alloy particles with composition Al-28Si-5Cu-1 Mg (in wt%). Its compressibility is lower than for the conventional elemental P/M aluminium premixes, but it is still better than for prealloyed Al powders and other P/M powders. Thermogravimetry experiments showed that the elimination of the organic lubricant takes place between 275 and 490 degrees C during heating to the sintering temperature. The phase transformations leading to the formation of the liquid phase were studied by differential scanning calorimetry (DSC). The dimensional changes associated with the generation of the liquid were measured by dilatometry. Samples quenched into water from different temperatures (between 450 and 575 degrees C) and times (between 0 and 30 min) were studied to reveal the microstructural evolution of the alloy. The first liquid is formed inside the master alloy particles at around 505 degrees C. This liquid spreads across the compact, enhancing the chemical homogenization of the material. The alloying elements diffuse from the liquid inside the originally pure Al particles, reducing their melting temperature. This alloying process is almost concluded at around 535 degrees C. When the temperature is increased the liquid starts to be formed also in the originally pure Al particles. The melting of the FCC Al-rich phase finishes around 575-590 degrees C. The full melting of the alloy occurs at about 635-645 degrees C. After analyzing the different possible causes, it is concluded that the main swelling mechanism is the volume change associated with the melting of a fraction of the material when the temperature is increased. The phases detected by X-ray diffraction (XRD) in the as-received powder and in the sintered compact are FCC Al-rich solid solution, Si, theta-phase (CuAl(2)), and Q-phase (Cu(2)Mg(8)Si(6)Al(5)). (C) 2010 Elsevier B.V. All rights reserved.