Electrical property of rapidly solidified Co-Cu peritectic alloys

The microstructure formation and phase selection characteristics of Co-Cu peritectic alloys during rapid solidification are investigated experimentally. The relationships between such physical factors as cooling rate, microstructure morphology, crystal orientation, and alloy resistivity are further analyzed. The experimental results show that rapid solidification makes the Co solubility in (Cu) phase extend up to 20%Co. If Cu concentration is more than 80%Cu, the peritectic transformation L + αCo→ (Cu) is suppressed, and the (Cu) phase can directly precipitate from the undercooled alloy melt. When the Cu concentration is in the range of 40%-70%Cu, the liquid phase separation of the alloys is also suppressed, and the microstructure in the direction of ribbon thickness consists of two crystal zones. In the fine crystal zone, the αCo and (Cu) phases nucleate and grow competitively, the tiny equiaxed (Cu) dendrites are distributed in the αCo matrix homogeneously, whereas in the coarse crystal zone the αCo is the leading phase, where Cu-rich phase exists in the grain boundary of αCo dendrites. With the increase of cooling rate, the microstructure is refined and the amount of grain boundary increases, resulting in the rise of alloy resistivity. If the grain boundary reflection coefficient r = 0.996-0.999, the electrical resistivity of Co-Cu peritectic alloys can be predicted theoretically.