Experimental investigation of the Al-Mn-C system: Part I. Phase equilibria at 1200 and 1100 °C

Phase equilibria in the Al-Mn-C system at 1200 and 1100 °C were studied using DTA, X-ray diffraction, SEM and electron probe microanalysis. Using the results the isothermal sections at 1200 and 1100 °C for this system were constructed covering the whole concentration range. It was shown that the ternary compound Mn3AlC (κ-carbide) (antiperovskite structure CaTiO3-type, ≿Р5-Pm-3m) is stable at these temperatures and has a wide homogeneity range. It co-exists with the majority of solid phases (γMn), εAlMn, Mn5C2, Mn7C3, C and Al4C3 at 1200 °C, and at 1100 °C also with the phase εMn4С1-х. In addition to the κ-carbide also (γMn), εAlMn, εMn4С1-х and Mn5C2 show appreciable homogeneity ranges. The Mn5C2 carbide, which in the binary Mn-C system is stable below 1167 °C, participates in equilibria in the ternary system at 1200 and 1100 °C. The character of the phase equilibria at 1100 °C is practically similar to those at 1200 °C. The main difference involves the fact that the equilibrium (γMn) + Mn5C2 which is present in the Al-Mn-C system at 1200 °C, is absent at 1100 °C. Instead, the alternative equilibrium κ + εMn4C1-x is present at 1100 °C.