Laser powder bed fusion of nitihf high-temperature shape memory alloy: Effect of process parameters on the thermomechanical behavior

Mohammadreza Nematollahi, Guher P. Toker, Keyvan Safaei, Alejandro Hinojos, S. Ehsan Saghaian, Othmane Benafan, Michael J. Mills, Haluk Karaca, Mohammad Elahinia

Research output: Contribution to journalArticlepeer-review

4 Scopus citations

Abstract

Laser powder bed fusion has been widely investigated for shape memory alloys, primarily NiTi alloys, with the goal of tailoring microstructures and producing complex geometries. However, processing high temperature shape memory alloys (HTSMAs) remains unknown. In our previous study, we showed that it is possible to manufacture NiTiHf HTSMA, as one of the most viable alloys in the aerospace industry, using SLM and investigated the effect of parameters on defect formation. The current study elucidates the effect of process parameters (PPs) on the functionality of this alloy. Shape memory properties and the microstructure of additively manufactured Ni-rich NiTiHf alloys were characterized across a wide range of PPs (laser power, scanning speed, and hatch spacing) and correlated with energy density. The optimum laser parameters for defect-free and functional samples were found to be in the range of approximately 60–100 J/mm3. Below an energy density of 60 J/mm3, porosity formation due to lack-of-fusion is the limiting factor. Samples fabricated with energy densities of 60–100 J/mm3 showed comparable thermomechanical behavior in comparison with the starting as-cast material, and samples fabricated with higher energy densities (>100 J/mm3) showed very high transformation temperatures but poor thermomechanical behavior. Poor properties for samples with higher energies were mainly attributed to the excessive Ni loss and resultant change in the chemical composition of the matrix, as well as the formation of cracks and porosities. Although energy density was found to be an important factor, the outcome of this study suggests that each of the PPs should be selected carefully. A maximum actuation strain of 1.67% at 400 MPa was obtained for the sample with power, scan speed, and hatch space of 100 W, 400 mm/s, and 140 µm, respectively, while 1.5% actuation strain was obtained for the starting as-cast ingot. These results can serve as a guideline for future studies on optimizing PPs for fabricating functional HTSMAs.

Original languageEnglish
Article number1522
Pages (from-to)1-21
Number of pages21
JournalMetals
Volume10
Issue number11
DOIs
StatePublished - Nov 2020

Bibliographical note

Funding Information:
The authors would like to acknowledge the financial support of the Ohio Federal Research Network and the NASA Glenn Research Center. O.B. acknowledges support from the NASA Aeronautics Research Mission Directorate (ARMD), Transformational Tools and Technologies (TTT) projects. Electron microscopy was performed at the Center for Electron Microscopy and Analysis (CEMAS) at The Ohio State University.

Funding Information:
Acknowledgments: The authors would like to acknowledge the financial support of the Ohio Federal Research Network and the NASA Glenn Research Center. O.B. acknowledges support from the NASA Aeronautics Research Mission Directorate (ARMD), Transformational Tools and Technologies (TTT) projects. Electron microscopy was performed at the Center for Electron Microscopy and Analysis (CEMAS) at The Ohio State University.

Publisher Copyright:
© 2020 by the authors. Licensee MDPI, Basel, Switzerland.

Keywords

  • 3D printing
  • Additive manufacturing
  • HTSMA
  • Laser powder bed fusion
  • NiTiHf
  • Shape memory alloy
  • Smart materials

ASJC Scopus subject areas

  • Materials Science (all)
  • Metals and Alloys

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