The Co-Cr-Ta (Cobalt-Chromium-Tantalum) System
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Phase Diagram Evaluations: Section II
The Co-Cr-Ta (Cobalt-Chromium-Tantalum) System K.P. Gupta, The Indian Institute of Metals
Introduction Very little work has been done in the Co-Cr-Ta system. Only the face-centered-cubic (fcc) ␥Co phase boundary has been established at high temperature. The aging of Co-CrTa alloys has been studied and is reported here.
Binary Systems Two evaluated versions of the Co-Cr phase diagram are shown in Fig. 1(a) [1978All, 1990Gup] and (b) [Massalski2]. The two versions are in quite close accord except for the Co-rich region below ∼900 °C. The two agree with regard to the following. Above 1300 °C, the Co-Cr system is a simple eutectic system with the eutectic reaction, L ↔ (Cr) + (␥Co), occurring at 1395-1397 °C. At 1283 °C, the (Cr) solid solution undergoes a congruent transformation to a phase. A eutectoid reaction, (Cr) ↔ + (␥Co), occurs near 1260-1266 °C. A peritectoid reaction, (␥Co) + ↔ (Cr), occurs at 967 °C. Lack of agreement between the two evaluated diagrams occurs (a) in the composition region with compositions of
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