Immiscible systems produced by squeeze casting of engineered metallic foams

摘要: A large number of liquid systems, such as Al-Bi, AlIn and Al-Pb, exhibit limited miscibility. They are often referred to the immiscibles characterized by their unique thermodynamic features, positive enthalpy mixing [1]. The thermophysical properties some immiscible systems summarized in Table I [2]. These have great potential applications bearing electrical contacts superconducting devices [3]. Unfortunately, it is technically difficult produce these alloys [1, 4]. During early stage cooling a homogeneous liquid, frequently encountered density difference between two liquids leads rapid spatial separation buoyant force, resulting two-layer structure. Owing this phenomenon, no casting process under terrestrial conditions has yet been able desired dispersion microstructure, even when extremely high solidification rates were achieved Many tests performed during space experiments achieve an appropriate phase distribution microgravity results, however, rather disappointing, because coarse occurs [4]. development new processing techniques, therefore, becomes inevitable task facing both materials community automobile industry. As consequence, several techniques emerged where controlled Marangoni motion—strip castings [5] or magnetic fields [6] introduced counterbalance gravity influence. But results still unsatisfactory, particles found concentrate middle strip castings. High energy processes also developed microstructure [7–9] all laboratory scale due cost difficulties controlling microstructure. More recently, novel rheomixing machine (twinscrew extruder) employed study behavior monotectic Fan et al. [10]. Due limitation barrier screw (currently made steel), laboratoryscale further that low melting point non-reactive with materials, for example, Ga-Pb. solution problem comes from modern composite theory, learning metal-ceramic combining distinct phases (normally ceramic having wettability matrix alloy), thus logical evolution develop employing those used composites production. Among squeeze method most commonly which allows production near net-shape components good tolerance surface finish [11]. key step obtain preforms later melt infiltration. It recently well-developed metallic foams provides optimum opportunity [12]. This refers foam suitable two-phase system. differences temperature (Table I) make feasible prepare system infiltration reticulated higher alloy temperature. origin present aims engineered foams. Al-Pb was chosen model demonstrate principles. commercial open-cell aluminum (Duocel, ERG, Okland, CA) pure lead process. placed steel die preheated together 200–220 ◦C followed molten 380– 400 using caster fitted evacuating After maximum pressure 50 MPa maintained until cooled solidified. samples polished examined Jeol JXA840 scanning electron microscope (SEM). relative 7% shown Fig. 1a produced therefrom