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Metallography, Microstructure, and Analysis

, Volume 7, Issue 4, pp 476–486 | Cite as

Effect of Hafnium Addition in 60NiTi Alloy Hardened Under Open Atmosphere Conditions

  • Khashayar Khanlari
  • Maziar Ramezani
  • Piaras Kelly
  • Thomas Neitzert
Technical Article

Abstract

Vacuum furnaces or furnaces backfilled with inert argon gas are commonly employed to conduct hardening treatment on 60NiTi alloy. However, vacuum furnaces with the possibility of drop-quenching the solutionized parts are not easily available, and backfilling the furnaces with inert argon gas is costly. In this research, the hardening treatments were carried out in an air-exposed environment. As expected, reaction of Ti with oxygen gas existing in air during heat treatment resulted in formation of an oxide layer on the surface. This led to the depletion of Ti from the NiTi matrix and consequent formation of Ni-rich zones causing precipitation of soft Ni-rich phases. It was found that the addition of 1 at.% hafnium (Hf) prevented the soft Ni-rich phases formation in the matrix of the outer surface regions. This result suggests that Hf addition can be considered as a solution to harden a 60NiTi alloy under cost-effective open atmosphere heat treatment conditions.

Keywords

Intermetallics 60NiTi Hf addition Open atmosphere heat treatment 

Notes

Acknowledgment

The authors would like to thank Dr. Christopher DellaCorte and Dr. Ronald D. Noebe, National Aeronautics and Space Administration (NASA), Glenn Research Center, Cleveland, Ohio, for their generous technical assistance and continuous support. Patrick Conor, Auckland University of Technology, is appreciated for his assistance in conducting scanning electron microscopy studies.

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Copyright information

© Springer Science+Business Media, LLC, part of Springer Nature and ASM International 2018

Authors and Affiliations

  • Khashayar Khanlari
    • 1
  • Maziar Ramezani
    • 1
  • Piaras Kelly
    • 2
  • Thomas Neitzert
    • 1
  1. 1.Department of Mechanical EngineeringAuckland University of TechnologyAucklandNew Zealand
  2. 2.Department of Engineering ScienceUniversity of AucklandAucklandNew Zealand

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