Formation of metastable phases in magnesium-titanium system by high-pressure torsion and their hydrogen storage performance

Kaveh Edalati, Hoda Emami, Aleksandar Tsekov Staykov, David J. Smith, Etsuo Akiba, Zenji Horita

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

No binary phases exist in the Mg-Ti binary equilibrium phase diagram and the two elements are totally immiscible even in liquid form. This study shows that four metastable phases (two with the bcc and fcc structures and two with the hcp structures) are formed in the Mg-Ti system by severe plastic deformation (SPD) through the process of high-pressure torsion (HPT). Investigation of hydrogenation properties reveals that these metastable phases are decomposed to pure Mg and Ti during heating before they can absorb the hydrogen in the form of ternary Mg-Ti hydrides. First-principles calculations show that the hydrogenation reaction should occur thermodynamically, and ternary Mg-Ti hydrides with the cubic structure should form at low temperature. However, the slow kinetics for this reaction appears to be the limiting step. Calculations show that the binding energy of hydrogen increases and the thermodynamic stability of hydrides undesirably increases by addition of Ti to Mg.

Original languageEnglish
Pages (from-to)150-156
Number of pages7
JournalActa Materialia
Volume99
DOIs
Publication statusPublished - Aug 13 2015

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Metastable phases
Hydrogen storage
Titanium
Hydrides
Torsional stress
Magnesium
Hydrogenation
Hydrogen
Binding energy
Phase diagrams
Plastic deformation
Thermodynamic stability
Heating
Kinetics
Liquids
Temperature

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Polymers and Plastics
  • Metals and Alloys

Cite this

Formation of metastable phases in magnesium-titanium system by high-pressure torsion and their hydrogen storage performance. / Edalati, Kaveh; Emami, Hoda; Staykov, Aleksandar Tsekov; Smith, David J.; Akiba, Etsuo; Horita, Zenji.

In: Acta Materialia, Vol. 99, 13.08.2015, p. 150-156.

Research output: Contribution to journalArticle

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AB - No binary phases exist in the Mg-Ti binary equilibrium phase diagram and the two elements are totally immiscible even in liquid form. This study shows that four metastable phases (two with the bcc and fcc structures and two with the hcp structures) are formed in the Mg-Ti system by severe plastic deformation (SPD) through the process of high-pressure torsion (HPT). Investigation of hydrogenation properties reveals that these metastable phases are decomposed to pure Mg and Ti during heating before they can absorb the hydrogen in the form of ternary Mg-Ti hydrides. First-principles calculations show that the hydrogenation reaction should occur thermodynamically, and ternary Mg-Ti hydrides with the cubic structure should form at low temperature. However, the slow kinetics for this reaction appears to be the limiting step. Calculations show that the binding energy of hydrogen increases and the thermodynamic stability of hydrides undesirably increases by addition of Ti to Mg.

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