Quantitative phase transformation behavior in TiNi shape memory alloy thin films

Bo Kuai Lai, H. Kahn, S. M. Phillips, Zentaro Akase, A. H. Heuer

Research output: Contribution to journalArticlepeer-review

13 Citations (Scopus)

Abstract

Phase transformations in near-equiatomic TiNi shape memory alloy thin films were studied, and the phase fraction evolutions were quantitatively correlated to the stress and resistivity of the films. TiNi thin films with compositions of 50.1, 51.1, and 51.7 at.% Ti all exhibited transformation temperatures between 65 and 100 °C, low residual stresses at room temperature (RT), and high recoverable stresses, thus making them suitable for microactuators in microelectromechanical systems. Low residual stresses at RT, less than 50 MPa, can be obtained even when only a small quantity of martensite, less than 30%, is present. Phase fraction evolution during complete thermal cycles (heating and cooling) was studied using elevated temperature x-ray diffraction, combined with quantitative Rietveld analysis. R-phase always appeared in these near-equiatomic TiNi thin films during cooling but did not have a noticeable effect on the stress-temperature hysteresis curves, which mainly depend on the phase fraction evolution of martensite. On the other hand, the occurrence of R-phase determined the variation of film resistivity. Martensite, austenite, and R-phase coexisting within a single grain were observed using transmission electron microscopy.

Original languageEnglish
Pages (from-to)2822-2833
Number of pages12
JournalJournal of Materials Research
Volume19
Issue number10
DOIs
Publication statusPublished - 2004 Oct 1
Externally publishedYes

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

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