The Heusler Phase Ti25(Fe50 − x Ni x )Al25 (0 ≤ x ≤ 50); Structure and Constitution

Abstract

Alloys with composition Ti 25 (Fe 50 2 x Ni x )Al 25 (0 £ x £ 50) were investigated employing electron probe microanalysis (EPMA) and X-ray powder diffraction (XPD). For TiFe 2 Al, in situ neutron powder diffraction (ND) was used for the inspection of phase constitution covering the temperature range from 27°C (300 K) to 1277°C (1550 K). Combined Rietveld refinement of ND and XPD data for TiFe 2 Al revealed that Fe atoms occupy the 8c site in space group Fm " 3m; Ti with a small amount of Al sharing the 4a site, and the remaining Ti and Al atoms adopting the 4b site. This structural model was successfully applied in the refinement of all alloys Ti 25 (Fe 50 2 x Ni x )Al 25 (0 £ x £ 50). Partial atom order exists on the Fe-rich side while complete order is observed for the Ni-rich side. Profiles recorded by in situ neutron powder diffraction for TiFe 2 Al in the range of investigated temperatures show two phases, namely Heusler phase and MgZn 2 -type Laves phase. Diffraction peaks from the Heusler phase dominate the profiles at lower temperatures but at higher temperatures the MgZn 2 -type Laves phase is the main phase. No CsCl-type phase was found in the alloy in the investigated temperature range. The thermal expansion coefficient of TiFe 2 Al is 1.4552310 25 K 21 .

First-Principles Investigations of the Structural, Anisotropic Mechanical, Thermodynamic and Electronic Properties of the AlNi2Ti Compound

“…In this study, the LTEC of AlNi 2 Ti is quite near to ZTA (7.0-9.5 × 10 −6 K −1 [90]) and Fe (9.2-16.9 × 10 −6 K −1 [91]), so the ZTA/Fe composite with AlNi 2 Ti at the interface will have excellent thermal shock resistance. [52]), which is higher than our result. In addition, the specific heats at constant pressure (Cp) and constant volume (Cv) are studied and their values follow the equation…”

“…The high temperature limit of C v tends to approaching the classic Dulong-Petit limit, and C p keeps growing due to the work done by the volumetric expansion. [52]), which is higher than our result. In addition, the specific heats at constant pressure (Cp) and constant volume (Cv) are studied and their values follow the equation…”

“…In order to explore the low-temperature heat capacity of AlNi2Ti with metallic features, Cp can be estimated from the calculations of the electronic structures and elastic constants, which is given by [67]. [52]), which is higher than our result. In addition, the specific heats at constant pressure (C p ) and constant volume (C v ) are studied and their values follow the equation…”

“…data measured by X-ray diffraction in [51]; k Exp. data in [52]; l Exp. data in [53]; m Calculated values from a thermodynamic database in [54]; n Data measured by high-temperature reaction calorimeter in [54].…”

On the Quaternary System Ti-Fe-Ni-Al

“…[35] In a previous investigation on a series of alloys Ti(Fe 50-x Ni x )Al, we elucidated atom site preferences for the Heusler phase in the quaternary system. [39] The purpose of the present work is (i) to clarify the homogeneity region of Laves phases in the quaternary system Ti-Fe-Ni-Al at 900°C, (ii) to define phase equilibria in which the Laves phase is involved at 900°C, and (iii) to determine the site occupancy of atoms in the quaternary phases, namely the Laves phase Ti(Ti,Fe,Ni,Al) 2 with MgZn 2 -type and the G phase with a Th 6 Mn 23 -derivative type structure.…”