Forma？？o dos aluminetos de níquel a partir de pós metálicos

the exothermic behavior of nickel aluminides formation from its elemental constituents and its high energy release rate represents a big potential for use in many industrial processes. in this work it was studied the formation reaction of nial from ni and al powders, looking for its use as bonding material for solid state diffusion joining of nickel and titanium aluminides. the reaction？s generated heat is released directly at the bonding zone, promoting the diffusion and making possible the joining at lower temperatures than usual. in this investigation green compacts from a nickel and aluminium were prepared in an equimolar blend; the reactions occurring in the blends were studied by differential scanning calorimetric tests on both, compacted performed calorimetric tests on both, compacted and non compacted powders. reaction products characterized by scanning electron microscopy and chemically analyzed by energy dispersive x-rar spectroscopy. non compacted powders ere also characterizes by x-ray diffraction. differential scanning calorimetric experiments confirmed the exothermic behavior of the reaction between nickel and aluminium, showing that heat release is not an explicit function of heating rate. that release？s intensity is conditioned by the heating rate, being higher for faster heating rates; this effect is enhanced by powders compaction pressure, being higher for higher pressures. before the reaction, non compacted powders remain metallic but, after the reaction several intermetallics are formed, ni3al, nial e ni2al3, resulting in a composition gradient across the particles. compacted powders also present similar composition gradient. an exception was noticed for powders compacted at 637mpa; when heated at 30oc/min. up to 750oc they show a homogeneous composition of nial.