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Phase Diagram Evaluations: Section II

Al-Co-Fe-Ti (Aluminum-Cobalt-Iron-Titanium) V. Raghavan

The data on this quaternary system are limited to the B2-L21-B2 phase boundaries on the CoAl-CoTi-FeTi-FeAl plane of the composition tetrahedron [2002Ish].

Binary and Ternary Systems An update of the Al-Ti phase diagram appears in this issue. For brief descriptions of the Co-Al and Co-Ti systems, see the Al-Co-Ti update in this issue. For Co-Fe phase diagram, see the Al-Co-Fe update by [2005Rag]. For descriptions of the Al-Fe and Fe-Ti phase diagrams, see the Al-Fe-Ti update by [2002Rag]. Recent updates on the ternary systems are: Al-Co-Fe [2005Rag], Al-Co-Ti (this issue), Al-Fe-Ti [2002Rag], and Co-Fe-Ti [2003Rag].

Quaternary Phase Equilibria With starting metals of 99.99+ % Al, 99.9+ % Co, 99.9+ % Fe, and 99.5+ % Ti, [2002Ish] melted in an arc furnace under Ar atmosphere a limited number of alloy compositions that lie on the CoAl-CoTi-FeTi-FeAl plane. Diffusion couples prepared by welding were annealed at the desired

temperatures. The compositions of the coexisting phases were measured by energy dispersion x-ray spectroscopy. The binary phases CoAl, CoTi, FeTi, and FeAl all have the CsCl-type B2 structure. Complete solid solubility exists along the CoAl-FeAl and CoTi-FeTi joins. The Heuslertype L21 phase Co2AlTi is present along the CoAl-CoTi join. The phase relationships on the CoAl-CoTi-FeAl-FeTi plane determined by [2002Ish] at 1300, 1200, and 1000 °C are redrawn in Fig. 1. The B2-L21 and L21-B2 boundaries are second-order boundaries without a two-phase region. Only at 1000 °C is the two-phase region seen in a narrow composition range close to the CoAl-CoTi line. References 2002Ish: K. Ishikawa, R. Kainuma, I. Ohnuma, K. Aoki, and K. Ishida, Phase Stability of the X2AlTi (X: Fe, Co, Ni, and Cu) Heusler and B2-Type Intermetallic Compounds, Acta Mater., Vol 50, 2002, p 2433-2443 2002Rag: V. Raghavan, Al-Fe-Ti (Aluminum-Iron-Titanium), J. Phase Equilibria, Vol 23 (No. 4), 2002, p 367-374 2003Rag: V. Raghavan, Co-Fe-Ti (Cobalt-Iron-Titanium), J. Phase Equilibria, Vol 24 (No. 2), 2003, p 175-176 2005Rag: V. Raghavan, Al-Co-Fe (Aluminum-Cobalt-Iron), J. Phase Equilibria, Vol 26 (No. 1), 2005, p 57-58

Fig. 1 Al-Co-Fe-Ti partial B2-L21-B2 phase equilibria on the CoAl-CoTi-FeTi-FeAl plane of the composition tetrahedron [2002Ish]

Journal of Phase Equilibria and Diffusion Vol. 26 No. 2 2005

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