Instrumented micro-indentation of NiTi shape-memory alloys

K. Gall, K. Juntunen, H. J. Maier, H. Sehitoglu, Y. I. Chumlyakov

Research output: Contribution to journalArticlepeer-review


We study the instrumented Vickers micro-indentation of single-crystal Ti-50.9 at% Ni shape-memory alloys with systematically varied surface normal orientations ([100], [210], [111] and [221]) and Ti3Ni4 precipitate sizes (0 nm, 10 nm, 50 nm, 100 nm, 300 nm and 500 nm). Based on transmission electron microscopy observations, indentation of solutionized NiTi induces inelastic deformation via dislocation activity and a stress-induced martensitic transformation. The room-temperature hardness, Hv, and recoverable energy, Er, of NiTi are shown to be a maximum for very small precipitate sizes, decrease for intermediate precipitate sizes, and increase for large precipitate sizes. The maximization of Hv and Er at small precipitate sizes (10 nm) is attributed to the relatively high resistance to both dislocation motion and a recoverable stress-induced martensitic transformation. The decreases in Hv and Er at intermediate precipitate sizes (50-300 nm) are attri buted to a decrease in the resistance to dislocation motion and a measured increase in the transformation temperatures with respect to the indentation temperature. The increases in Hv and Er at large precipitate sizes (500 nm) are attributed solely to measured decreases in the transformation temperatures with respect to the indentation temperature, since the resistance to dislocation motion remains constant as the precipitates grow from 300 nm to 500 nm. For nearly all heat treatments, the [100] and [221] surfaces demonstrate the highest and lowest values of Hv and Er, respectively, an effect attributed primarily to orientation of favorable slip systems.

Original languageEnglish (US)
Pages (from-to)3205-3217
Number of pages13
JournalActa Materialia
Issue number16
StatePublished - Sep 20 2001


  • Annealing
  • Dislocations
  • Hardness testing
  • NiTi shape-memory alloys
  • Phase transformations
  • Transmission electron microscopy (TEM)

ASJC Scopus subject areas

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


Dive into the research topics of 'Instrumented micro-indentation of NiTi shape-memory alloys'. Together they form a unique fingerprint.

Cite this