A new diffusion-multiple technique was proposed in order to permit mapping of quaternary phase diagrams. This technique involved a combination of diffusion-multiple techniques to introduce two-dimensional compositional gradients into a matrix phase and a conventional annealing heat treatment to produce precipitation reactions in the matrix. Phase equilibria at 800C in the semi-quaternary Fe3Al–Cr–Mo–C system were determined with the aid of this technique. The following carbide phases were precipitated in the Fe3Al matrix phase (B2) with compositional gradients of Cr, Mo and C: κ-Fe3AlC, M6CH, M6CL, Cr7C3 and M2C (M: Mo, Cr and Fe, the two M6C phases were distinguished by their C and Cr contents.). It was found from the diffusion-multiple technique that a 4-phase equilibrium of M6CH-M6CL-Cr7C3-B2 existed. Microstructural analysis of several bulk alloys as well as DM samples revealed that the 3-phase equilibrium of M6CL-κ-B2 in the Fe3Al–Mo–C system changed to that of M6CL-Cr7C3-B2 with increasing Cr content through the following three four-phase equilibria: (1) M6CH-M6CL-κ-B2, (2) M6CH-Cr7C3-κ-B2, (3) M6CH-M6CL-Cr7C3-B2. The M2C phase was thought to be not in equilibrium with the Fe3Al matrix phase at 800C.

Determination of Phase Equilibria in the Fe3Al–Cr–Mo–C Semi-Quaternary System using a New Diffusion-Multiple Technique. S.Kobayashi, S.Zaefferer: Journal of Alloys and Compounds, 2008, 452[1], 67-72