Physical properties of TiMn2 and interaction with refractory TiN (system Ti-Mn-N)

Abstract

Mechanical (elastic) properties have been derived for polycristalline TiMn2 from micro-indentation and thermal expansion measurements. With a room temperature (RT) Vicker's hardness of ∼11 GPa, TiMn2 is a rather hard intermetallic material. The elastic modulus is E = 217 ± 4 GPa at RT. Physical properties (from 1.8 K to 300 K) including specific heat, electrical resistivity and magnetic susceptibility reveal temperature independent paramagnetism and metallic conductivity consistent with a Bloch-Grüneisen behavior.Based on experimental data (X-ray powder diffraction, metallography, SEM and EMPA on 30 alloys prepared by various methods employing arc melting, powder reaction sintering in closed crucibles as well as nitriding binary master alloys in 105 Pa nitrogen gas) phase relations in the ternary system Ti-Mn-N have been established and calculated for the isothermal section at 900 °C. The thermodynamic modelling relies on existing thermodynamic assessments of the Mn-N and Ti-N binary systems and on our recent modelling of the Ti-Mn system, which is characterized by a significantly higher thermodynamic stability of the C14-type Laves phase Ti1-xMn2+x than hitherto assumed in the literature. It is this higher stability, which is consistent with the experimental phase triangulation in Ti-Mn-N: as the most important consequence of the higher stability of Ti1-xMn2+x, compatibility exists between the only two congruently melting compounds Ti1-xMn2+x and TiN1-x. The high melting refractory solution TiN1-x dominates the liquidus surface pushing all monovariant melting lines close to the Ti-Mn binary.