Microstructure and shape memory behavior of [111]-oriented NiTiHfPd alloys

ACAR E., Tobe H., Karaca H. E., Noebe R. D., Chumlyakov Y. I.

SMART MATERIALS AND STRUCTURES, vol.25, no.3, 2016 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 25 Issue: 3
  • Publication Date: 2016
  • Doi Number: 10.1088/0964-1726/25/3/035011
  • Journal Name: SMART MATERIALS AND STRUCTURES
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Keywords: shape memory alloys, microstructure, elastic energy storage, NiTiHfPd, superelasticity, MARTENSITIC-TRANSFORMATION, STRENGTH, PSEUDOELASTICITY, PRECIPITATION, DEPENDENCE, AL
  • Erciyes University Affiliated: Yes

Abstract

The relationship between the microstructure and shape memory properties of [111]-oriented Ni45.3Ti29.7Hf20Pd5 (at%) single crystals was explored. In this precipitation-strengthened alloy, the size and volume fraction of precipitates and interparticle distances govern the martensite morphology and the ensuing shape memory responses. Aging of the solution-treated material, leading to a microstructure of fine, closely spaced precipitates, resulted in a material capable of a shape memory strain of 2.15% at 1000 MPa in compression. Larger precipitates formed after aging the as-grown single crystals (without a prior solution treatment) resulting in a shape memory strain of 2.5% at this same stress level in constant-stress thermal cycling experiments. Superelastic strains of 4% in compression without any residual strain were possible under various microstructural conditions and the stress hysteresis could be varied between nearly 500 and 1000 MPa depending on the microstructure.