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

Author(s)
A. U. Khan, P. Broz, M. Premovic, J. Pavlu, J. Vrestal, X. Yan, D. Maccio, A. Saccone, G. Giester, P. Rogl
Abstract

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-xMn

x)

6Mn

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

4Al

3 type. Whereas TiMn can be considered as a line compound (solubility range <∼1 at%), the homogeneity regions of the Ti-Mn compounds are significant (determined by EPMA): TiMn

1-x (44.0 to 46.6 at% Mn), TiMn

1+x (54.6 to 56.3 at% Mn), Ti

1+xMn

2-x (MgZn

2-type, 59 to 69 at% Mn at 1000 °C: -0.08 < x < 0.23), TiMn

∼3 (unique type; 74 to 76.5 at% Mn) and TiMn

∼4 (R-phase: Ti

8(Ti

xMn

1-x)

6Mn

39, 80 to 84 at% Ti). Supported by ab initio calculations of the ground state energy for the Laves phase, the new experimental results enabled thermodynamic modelling of the entire Ti-Mn phase diagram providing a complete and novel set of thermodynamic data thus providing a sound basis for future thermodynamic predictions of higher order Ti-Mn-X-Y systems.

Organisation(s)
Department of Physical Chemistry, Department of Mineralogy and Crystallography, Department of Materials Chemistry
External organisation(s)
Rutgers University, Masaryk University, University of Prishtina, Università degli Studi di Genova, Technische Universität Wien
Journal
Physical Chemistry Chemical Physics
Volume
18
Pages
23326-23339
No. of pages
14
ISSN
1463-9076
DOI
https://doi.org/10.1039/c6cp04542a
Publication date
09-2016
Peer reviewed
Yes
Austrian Fields of Science 2012
104017 Physical chemistry, 105113 Crystallography, 103006 Chemical physics
Keywords
ASJC Scopus subject areas
General Physics and Astronomy, Physical and Theoretical Chemistry
Portal url
https://ucrisportal.univie.ac.at/en/publications/f34c5adb-0383-40b3-b04c-5ba0316fde85