The Ti-Mn system revisited: experimental investigation and thermodynamic modelling

As the Ti-Mn phase diagram is part of numerous ternary and higher order systems of technological importance, the present paper defines phase relations which have been experimentally established throughout this work from 800 °C to the melting range based on Differential Thermal Analyses (DTA), X-ray powder diffraction, metallography and Electron Probe Micro Analysis (EPMA) techniques on ∼50 alloys, which were prepared by arc melting or high frequency melting under high purity argon starting from freshly cleaned metal ingots. Novel compounds were identified and reaction isotherms were redefined accordingly. In the Ti-rich region a novel compound TiMn was detected, sandwiched between the known phases: TiMn 1− x (∼45 at% Mn) and TiMn 1+ x (∼55 at% Mn). In the Mn-rich region the hitherto unknown crystal structure of TiMn ∼3 was solved from X-ray single crystal diffraction data and found to be of a unique structure type Ti 6 (Ti 1− x Mn x ) 6 Mn 25 ( x = 0.462; space group Pbam (#55); a = 0.79081(3) nm, b = 2.58557(9) nm, c = 0.47931(2) nm), which consists of two consecutive layers of the hexagonal MgZn 2 -type Laves phase (TiMn 2 ) and a combined layer of alternate structure blocks of MgZn 2 type and Zr 4 Al 3 type. Whereas TiMn can be considered as a line compound (solubility range