Technology Advances
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Technology Advances provides upto-date reports of materials developments that show potential to bridge the gap between research innovation and application of advanced materials technologies. If you encounter or are involved with materials research that shows potential for commercialization and would like to present these developments, contact Renée G. Ford, Renford Communications, Ltd., P.O. Box 72, Harrison, NY 10528-0072; tel. 914-967-0955; fax 914-967-7927; or e-mail [email protected].
MRS BULLETIN/OCTOBER 2000
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5 mm Figure 1. Optical micrographs of sections through Al-9wt%Si/SiCp composite foams, showing the versatility of the FORMGRIP process for control of the foam porosity level, P: (a) P = 69%, (b) P = 79%, and (c) P = 88%.
(e.g., titanium hydride, TiH2) is dispersed in a semiliquid metal-matrix composite (Al-9wt%Si alloy, reinforced with SiC particles) melt. A low-porosity (~14–25%) foamable precursor is produced by allowing this melt to solidify after casting. A key requirement for the effective preparation of the precursor material is that only a limited amount of hydrogen is evolved during this stage of the process. Two factors facilitate this objective. The first is a foaming-agent thermal-oxidation pretreatment sequence in air that results in changes in the hydrogen concentration in the hydride and formation of a diffusionbarrier oxide layer on the powder surface. Both of these phenomena are important for controlling the onset and kinetics of hydrogen evolution. The second factor is an increase in the melt viscosity by using semiliquid processing and/or a fine dispersion of ceramic material. The stock material is thus effectively a metal-matrix composite in which the size, shape, and level of the ceramic content can vary over a wide range. The foam invasion into the mold is induced by thermally activated gas release as remelting occurs. The
A Two-Step Deformation Technique Strengthens Pure Titanium to Greater Than 1000 MPa A two-step deformation process has been developed by researchers at Ufa State Aviation Technical University in Russia and Los Alamos National Laboratory (LANL) that more than doubles the strength of commercially pure titanium from about 400 MPa to greater then 1000 MPa. The process combines warm equal-channel angular (ECA) pressing to refine the grain size with cold deformation (rolling and/or extrusion) to further increase the density of
process provides for flexibility in the design of foam structures through control over both the kinetics of hydrogen evolution and the drainage processes that occur during foam evolution. This is facilitated by manipulating parameters such as thermal histories during the precursor baking and composite melt viscosities (ceramic particle content and size). Examples of typical foam macrostructures are shown in Figure 1. Opportunities The FORMGRIP method for processing metallic foams is still under development. The researchers at Cambridge are currently interested in undertaking further work in collaboration with commercial concerns.
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