INTERSTITIAL ORDER-DISORDER TRANSFORMATION IN TI-O SOLID SOLUTION .2. A CALORIMETRIC STUDY

Heat capacity of the solid solution of alpha-titanium with 8∼28 at% oxygen has been measured to investigate calorimetric effects associated with the interstitial order-disorder transformation of oxygen atoms. Anomalous heat absorption is observed in the temperature range from 300 to 600°C varying with oxygen contents. The transformation at oxygen contents higher than about 15 at% is characterized by the appearance of double peaks in the specific heat curve. In the light of the results of diffraction studies, the peaks are interpreted to be due to the two successive processes from the ordered phase α″ to the disordered solid solution α through the intermediate phase α′. The transformation energy and entropy as well as the critical temperature are determined as functions of composition. It is found that two maxima appear in the transition energy-composition curve around 15 and 24 at% O with nearly the same value of about 390 cal/mol, and that a similar behavior is also observed in the transition entropy-composition curve with the maximum values of about 0.3 R at these compositions. © 1969, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.