Mechanism of fusing of Ni-Ti powder compact by self-exothermic reaction.

It was reported previously by the present authors that by quick heating in vacuum some gases evolved from the Ni-Ti compact during exothermic fusing reaction. It was also suggested that the gas evolution might take the part of triggering the self-exothermic reaction. Gas evolution of H2, and deposits of Na, Cl and O were confirmed by gas chromatography and Auger analysis.The mechanism of the reaction in Ni-Ti compacts was examined by a microscopic analysis on the semireacted specimens and the calculation of the exothermic heat quantity.The results showed that the exothermic fusing reactions of the Ni-Ti compact occurr in the composition range 48-56 at%Ni through step reactions of each intermetallic compounds, and that the reaction heat of NaCl and Na2O formation bring about the exothermic fusing reaction.