On the constitution and thermodynamic modeling of the phase diagramsnNb-Mn and Ta-Mn

Result code in IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F68081723%3A_____%2F21%3A00540495" target="_blank" >RIV/68081723:_____/21:00540495 - isvavai.cz</a>

Result on the web

<a href="https://www.sciencedirect.com/science/article/pii/S0925838821001225?via%3Dihub" target="_blank" >https://www.sciencedirect.com/science/article/pii/S0925838821001225?via%3Dihub</a>

DOI - Digital Object Identifier

<a href="http://dx.doi.org/10.1016/j.jallcom.2021.158715" target="_blank" >10.1016/j.jallcom.2021.158715</a>

Result language

angličtina

Original language name

On the constitution and thermodynamic modeling of the phase diagramsnNb-Mn and Ta-Mn

Original language description

The constitution of the two phase diagrams Nb-Mn and Ta-Mn has been determined from light optical andntransmission and scanning electron microscopy (LOM, TEM and SEM) with energy dispersive (EDX) as wellnas wavelength dispersive (WDX) X-ray spectroscopy, X-ray powder (XPD) and single crystal diffractionn(XSCD), differential thermal analysis (DTA) and/or differential scanning calorimetry (DSC). The Laves phasesnNbMn2 and TaMn2 are the only binary compounds in these systems. High-temperature differential thermalnanalyses revealed congruent melting for NbMn2 with Tm(NbMn2) = 1515 ± 15 °C, whereas TaMn2 melts incongruently with Tm(TaMn2) = 1797 ± 40 °C close to a depleted peritectic reaction. Both Lavesnphases engage in eutectic reactions ℓ ↔ (Mn) + Nb(Ta)Mn2 (Teut = 1220 ± 10 °C at 4.9 at% Nb andnTeut = 1234 ± 10 °C at 0.7 at% Ta, respectively). NbMn2 also forms a eutectic with (Nb): ℓ ↔ (Nb) + NbMn2 atnTeut = 1493 ± 15 °C and 53.2 at% Nb. Mn shows remarkably large maximum solid solubilities of 19.4 at% Mn inn(Nb) as well as of 21.3 at% Mn in (Ta). Detailed atom site distribution has been established for the Lavesnphases by means of temperature dependent X-ray single crystal data (both C14 - MgZn2-type). Combinedndata from XPD, EDX/WDX and SEM microstructure indicate that for both Laves phases extended homogeneity regions exist: Nb1+xMn2−x (62.5–73.0 at% Mn at 950°C: −0.19≤x≤0.125) and Ta1+xMn2−x (59.5–68.5 atn% Mn: −0.055≤x≤0.215). Density functional theory (DFT) calculations favor Nb(Ta)/Mn antisite occupationnrather than defects. The phases, “NbMn” and “TaMn”, adopted earlier in the literature as binary systemninherent compounds, were shown (TEM, WDX electron microprobe data and X-ray Rietveld refinements) tonbe oxygen stabilized phases of the Ti4Ni2O type (so-called eta(η)-phases) with modified Nb(Ta)/Mn sitensubstitution to comply with the formula Nb(Ta)3−xMn3+xO1−y (defect η-W3Fe3C-type). From magnetic susceptibility and magnetization measurements, both oxide stabilized eta phases η-Nb3Mn3O1−y andnη-Ta3Mn3O1−y were found to order ferromagnetically below Tc ~ 77 K, but the Laves phases NbMn2, TaMn2nreveal weakly temperature dependent paramagnetism. No trace of the rhombohedral μ-phase (W6Fe7-type)nhas been encountered in our investigation of the two binary phase diagrams. Thermodynamic and transportnproperties (specific heat, electrical resistivity and magnetic susceptibility/magnetization) classify the Lavesnphases with metallic behavior whilst mechanical properties (elastic moduli from DFT and nanoindentationnas well as hardness and thermal expansion) group both Laves phases among rather hard and brittle intermetallics. Based on (i) the experimentally derived constitution of the Nb-Mn and Ta-Mn systems, and (ii) on new own DFT data of the energy of formation of the Laves phases, a CALPHAD (CALculation of PHAsenDiagrams) calculation of both systems was made providing a complete set of optimized thermodynamicndata. Furthermore, the DFT calculations provided information on the instability of the η-Ta3Mn3 structurenand the atom-site specific stabilization effect of oxygen.

Czech name

—

Czech description

—

Type

J_imp - Article in a specialist periodical, which is included in the Web of Science database

CEP classification

—

OECD FORD branch

10403 - Physical chemistry

Project

Result was created during the realization of more than one project. More information in the Projects tab.

Continuities

P - Projekt vyzkumu a vyvoje financovany z verejnych zdroju (s odkazem do CEP)

Publication year

2021

Confidentiality

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů

Name of the periodical

Journal of Alloys and Compounds

ISSN

0925-8388

e-ISSN

1873-4669

Volume of the periodical

865

Issue of the periodical within the volume

JUN

Country of publishing house

CH - SWITZERLAND

Number of pages

19

Pages from-to

158715

UT code for WoS article

000626334500027

EID of the result in the Scopus database

2-s2.0-85101302402