Phase equilibria of the Co–Mo–Ti system at 950°C

The phase equilibria at 950 °C of the Co–Mo–Ti system was investigated by a combination of a diffusion couple technique and equilibrated alloys. The samples were examined by means of optical microscopy, scanning electron microscopy, electron probe microanalysis, and X-ray diffraction analysis. The isothermal section of the Co–Mo–Ti system at 950 °C consists of 7 three-phase fields and 15 two-phase fields. The following five three-phase equilibria were well determined: (1) TiCo2 (h) + MoCo3 + Mo6Co7, (2) TiCo2 (c) + TiCo2 (h) + TiCo, (3) TiCo2 (h) + TiCo + Mo6Co7, (4) TiCo + Ti2Co + (Mo,Ti), and (5) TiCo + Mo6Co7 + (Mo,Ti). The solubility of Ti in Mo6Co7 was determined to be 23.1 at.% Ti. The solubilities of Mo in TiCo2 (h), TiCo2 (c), and TiCo were measured to be 11.4, 4.7, and 5.4 at.% Mo, respectively. The solubility of Mo in Ti2Co is about 0.3 at.% Mo. The two-phase region of TiCo3 + MoCo3 was found to be very narrow and close to the TiCo3 side.