Impurities block the α to ω martensitic transformation in titanium

Richard G. Hennig, Dallas R. Trinkle, Johann Bouchet, Srivilliputhur G. Srinivasan, Robert C. Albers, John W. Wilkins

Research output: Contribution to journalArticlepeer-review

Abstract

Impurities control phase stability and phase transformations in natural and man-made materials, from shape-memory alloys to steel to planetary cores. Experiments and empirical databases are still central to tuning the impurity effects. What is missing is a broad theoretical underpinning. Consider, for example, the titanium martensitic transformations: diffusionless structural transformations proceeding near the speed of sound2. Pure titanium transforms from ductile α to brittle ω at 9 GPa, creating serious technological problems for β-stabilized titanium alloys. Impurities in the titanium alloys A-70 and Ti-6Al-4V (wt%) suppress the transformation up to at least 35 GPa, increasing their technological utility as lightweight materials in aerospace applications. These and other empirical discoveries in technological materials call for broad theoretical understanding. Impurities pose two theoretical challenges: the effect on the relative phase stability, and the energy barrier of the transformation. Ab initio methods4,5 calculate both changes due to impurities. We show that interstitial oxygen, nitrogen and carbon retard the transformation whereas substitutional aluminium and vanadium influence the transformation by changing the d-electron concentration 6. The resulting microscopic picture explains the suppression of the transformation in commercial A-70 and Ti-6Al-4V alloys. In general, the effect of impurities on relative energies and energy barriers is central to understanding structural phase transformations.

Original languageEnglish (US)
Pages (from-to)129-133
Number of pages5
JournalNature Materials
Volume4
Issue number2
DOIs
StatePublished - Feb 2005
Externally publishedYes

ASJC Scopus subject areas

  • General Chemistry
  • General Materials Science
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

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