Study of the h.c.p.-f.c.c. phase transition in cobalt by acoustic measurements

Abstract

Acoustic measurements have been performed in the vicinity of the h.c.p.-f.c.c. phase transition in cobalt. The main results are the following: At low frequency (~ 1 Hz), a high transitory internal friction peak is observed. It is shown that this internal friction is a function of T/ v T temperature rate, v vibration frequency) but is not proportional to T/ v. This behavior is explained in the framework of a recent model based on a Clausius-Clapeyron-like equation expressing the coupling between stress and phase transition; At medium (~5 KHz) and high (~ 20 MHz) frequencies, the transitory internal friction becomes negligible. However, a small peak appears accompanied by an elastic modulus decrease. It is shown that these anomalies are related to the shear modes parallel to the transformation plane. Thus, they might be related to the motion of the partial dislocations composing the h.c.p.-f.c.c. interface.