Transformation kinetics of the ferromagnetic alloy Mn-Al-C

Mn
1-x-y
Al
x
C
y
forms a ferromagnetic metastable tetragonal τ-phase in the composition range
0.42 \leq x \leq 0.47
and
0 \leq y \leq 0.021
. Its high unaxial magnetocrystalline anisotropy makes it an interesting candidate for a permanent magnet. In order to investigate the kinetics of the transformations which occur in this system, we established the time-temperature-transformation diagram of a ternary alloy with the composition Mn
0.538
Al
0.446
C
0.016
. It was homogenized for 2 h at 1375 K, quenched, and subsequently isothermally annealed at temperatures between 625 K and 1025 K for various times ranging from one minute up to seven days. The quantitative phase analyses were performed by means of x-ray diffraction and stereological analysis of the microstructures. The addition of carbon increases the stability of the τ-phase, thereby allowing longer annealing times for the formation of single-phase samples.