In sintered Cu-10wt% Sn alloy the effect of heating path on pore formation has been investigated to determine the optimum heating path to the sintering temperature. Mixtures of irregular fine Cu powder and -150+125 ㎛ spherical Sn powder has been used to make a clear observation of the microstructural changes.
When heated very slowly (4℃/min) to temperature just below the peritectic temperature of β phase (790℃), η and ε phases are formed around the Sn particle melt and Sn atoms diffuse to Cu particles leaving Kirkendall pores at the original Sn sites.
When heated rapidly to the sintering temperature (810℃), large pores are formed at the Sn sites surrounded by large amount of liquid which is trapped by α-bronze. Upon further sintering, the large pores expand while fine Kirkendall pores are formed in the liquid site.
When heated rapidly to 400℃ and held there for 15 min, Sn melt flows completely into the capillaries between Cu particles leaving spherical pores at the Sn sites. Upon heating to 810℃, the Sn liquid in the capillaries diffuse into Cu grains leaving pores.
Finally, some compacts have been heated rapidly to 790℃, held there for 15 min, and reheated rapidly to 810℃. The microstructural changes are similar to those which have been heated rapidly to 810℃.
From these results, the optimum heating path is determined to be rapid heating to about 400℃ to induce the flow of Sn melt into the capillaries between Cu particles and subsequent slow heating to the sintering temperature.
