It is well known that an abnormal expansion appears in Cu-Sn compacts during sintering. For the purpose of investigating the cause of this phenomenon, author carried out the dilatometric study on kinetics of sintering with Cu-Sn compacts containing about 10% Sn powder and 0.5% Zn-stearate.
Results obtained in this experiment were as follows ; the abnormal expansion appeared always at 798°C, which is the highest peritectic temperature in the Cu-Sn equilibrium diagram, and this expansion increased with increase of heating-rate ; from the microscopic examination, it is presumable that right below the peritectic temperature large amount of liquid phase regions accompanied by the β-phase regions were retained in the compact, however, just at this temperature or above, the β-phase must decompose to the α and liquid phase, subsequently the direct contact with the α-phase accelerates the diffusion of the liquid phase, consequently the liquid phase rapidly disappered above the peritectic temperature on heating ; the absorbed gas in the liquid phase was discharged by rapid solidification at 789°C, showing the dilatometric expansion and the enlarged porosity, judging from the following examination of gas atmosphare, the greater part of the absorbed gas can be estimated as H₂.
In order to eliminate the abnormal expansion, slow heating and, isothermal keeping right below the peritectic temperature are recommendable.