Abstract
The phase relations in the Ti-Nb-Co system are of great importance for the design of high temperature Ti alloys. The isothermal section of Ti-Nb-Co system at 1000°C has been established using one diffusion couple supplemented with 13 key alloys. Phase relations and ternary solubility of the binary compounds were determined using electron probe microscopy (EPMA), wave dispersive X-ray spectrometer (WDS) and X-ray diffraction (XRD) techniques. There are 19 two-phase equilibria and 9 three-phase equilibria in the isothermal section at 1000°C. The determined maximum solubility of Nb in TiCo3, TiCo2 (h), TiCo2 (c), TiCo, Ti2Co were 6.22, 17.21, 2.29, 22.88 and 2.49at.%, respectively. Nb2Co7, NbCo3, NbCo2, Nb6Co7 dissolves up about 0.33, 17.75, 13.26 and 10.81at.% Ti, respectively. All of the binary phases have a certain composition range at 1000°C except Nb2Co7. The phase diagram of Ti-Nb-Co system varied greatly when the temperature raised from 900°C to 950°C, but the changes was not so big when temperature increased from 950°C to 1000°C.
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