발간논문

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The enthalpy relaxation behaviour for amorphous Fe_75Mo_7P_17 alloy that has a clear glass transition phenomenon has been examined calorimetrically. Upon heating the sample annealed at temperature below T_g, an endothermic reaction occurs above T_a and the temperature evolving the ΔC_(p.max)(T_m) increases with lnt_a. The annealing temperature depen-dence of the magnitude of reversible endothermic reaction shows two distinct stages ; a low temperature one which is appeared at about T₃=550∼575k(∼T_g -l50K) and a high temperature one near T_g Moreover, the activation energy of enthalpy relaxation increases with T_m from 1.6 eV at T_m=580K to 2.6 eV at T_m = 700K. It was interpreted that the increase in activation energy with the rise of temperature is due to the transition from local rearrangement among metal atoms to long-mange rearrangement of metal and metalloid atoms.

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The microstrure evolution of a 78.0 Cu-7.1 Sn-12.5 Fe-2.4 Pb(wt%) alloy, metal composition of a typical Cu-Sn base friction material, has been studied during pressure (1.5 Mpa) and pressureless sintering up to 810℃ for various times. Overall microstructural changes during sintering were found to be determined by the reaction between Cu and Sn. The Sn melts upon heating spread alone the capillaries leaving pores at their sites and form ε phase. The pores collapsed during subsequent pressure sintering at higher temperatures. Upon heating ε phase appeared to transform into γ and β phases, which remelted eventually by reverse peritectic reactions. Fores, however, formed again at the sites of the intermediate phases, when the sintering pressure was relieved in the temperature range of peritectic reactions. Remelting of the intermediate phases could thus enlarge the size of pores in Cu-Sn base materials. A good homogeneous microstructure was obtained after sintering at 810℃ for about 1 hr under 1.5 Mpa.

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