Anisotropic microstructure and superelasticity of additive manufactured NiTi alloy bulk builds using laser directed energy deposition

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Abstract

The microstructure and superelasticity in additive manufactured NiTi shape memory alloys (SMAs) were investigated. Using elementally blended Ni and Ti powder feedstock, Ni-rich build coupons were fabricated via the laser-based directed energy deposition (LDED) technique. The build volumes were large enough to extract tensile and compressive test specimens from selected locations for spatially resolving microconstituents and the underlying stress-induced martensitic phase transformation (SIMT) morphology. In the as-deposited condition, X-ray diffraction identified the B2 atomic crystal structure of the austenitic parent phase in NiTi SMAs, and Ni4Ti3 precipitates were the predominant microconstituent identified through scanning electron microscopy. The microstructure exhibited anisotropy, which was characterized by the Ni4Ti3 precipitate morphology being coarsest nearest the substrate, while a finer morphology was observed farthest from the substrate. In-situ full-field deformation measurements calculated using digital image correlation confirmed that the SIMT predominately occurred in the finer precipitate morphology. Heat treatment reduced the degree of anisotropy, and DIC analysis revealed localized SIMT strains increased compared to the as-deposited condition.

Original languageEnglish (US)
Pages (from-to)125-134
Number of pages10
JournalMaterials Science and Engineering A
Volume674
DOIs
StatePublished - Sep 30 2016

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phase transformations
Precipitates
precipitates
microstructure
Microstructure
Lasers
Phase transitions
shape memory alloys
Shape memory effect
lasers
Anisotropy
Crystal atomic structure
Dacarbazine
anisotropy
energy
Substrates
tensile tests
Powders
Feedstocks
heat treatment

All Science Journal Classification (ASJC) codes

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

Cite this

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title = "Anisotropic microstructure and superelasticity of additive manufactured NiTi alloy bulk builds using laser directed energy deposition",
abstract = "The microstructure and superelasticity in additive manufactured NiTi shape memory alloys (SMAs) were investigated. Using elementally blended Ni and Ti powder feedstock, Ni-rich build coupons were fabricated via the laser-based directed energy deposition (LDED) technique. The build volumes were large enough to extract tensile and compressive test specimens from selected locations for spatially resolving microconstituents and the underlying stress-induced martensitic phase transformation (SIMT) morphology. In the as-deposited condition, X-ray diffraction identified the B2 atomic crystal structure of the austenitic parent phase in NiTi SMAs, and Ni4Ti3 precipitates were the predominant microconstituent identified through scanning electron microscopy. The microstructure exhibited anisotropy, which was characterized by the Ni4Ti3 precipitate morphology being coarsest nearest the substrate, while a finer morphology was observed farthest from the substrate. In-situ full-field deformation measurements calculated using digital image correlation confirmed that the SIMT predominately occurred in the finer precipitate morphology. Heat treatment reduced the degree of anisotropy, and DIC analysis revealed localized SIMT strains increased compared to the as-deposited condition.",
author = "Bimber, {Beth A.} and Hamilton, {Reginald Felix} and Keist, {Jayme Scot} and Todd Palmer",
year = "2016",
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T1 - Anisotropic microstructure and superelasticity of additive manufactured NiTi alloy bulk builds using laser directed energy deposition

AU - Bimber, Beth A.

AU - Hamilton, Reginald Felix

AU - Keist, Jayme Scot

AU - Palmer, Todd

PY - 2016/9/30

Y1 - 2016/9/30

N2 - The microstructure and superelasticity in additive manufactured NiTi shape memory alloys (SMAs) were investigated. Using elementally blended Ni and Ti powder feedstock, Ni-rich build coupons were fabricated via the laser-based directed energy deposition (LDED) technique. The build volumes were large enough to extract tensile and compressive test specimens from selected locations for spatially resolving microconstituents and the underlying stress-induced martensitic phase transformation (SIMT) morphology. In the as-deposited condition, X-ray diffraction identified the B2 atomic crystal structure of the austenitic parent phase in NiTi SMAs, and Ni4Ti3 precipitates were the predominant microconstituent identified through scanning electron microscopy. The microstructure exhibited anisotropy, which was characterized by the Ni4Ti3 precipitate morphology being coarsest nearest the substrate, while a finer morphology was observed farthest from the substrate. In-situ full-field deformation measurements calculated using digital image correlation confirmed that the SIMT predominately occurred in the finer precipitate morphology. Heat treatment reduced the degree of anisotropy, and DIC analysis revealed localized SIMT strains increased compared to the as-deposited condition.

AB - The microstructure and superelasticity in additive manufactured NiTi shape memory alloys (SMAs) were investigated. Using elementally blended Ni and Ti powder feedstock, Ni-rich build coupons were fabricated via the laser-based directed energy deposition (LDED) technique. The build volumes were large enough to extract tensile and compressive test specimens from selected locations for spatially resolving microconstituents and the underlying stress-induced martensitic phase transformation (SIMT) morphology. In the as-deposited condition, X-ray diffraction identified the B2 atomic crystal structure of the austenitic parent phase in NiTi SMAs, and Ni4Ti3 precipitates were the predominant microconstituent identified through scanning electron microscopy. The microstructure exhibited anisotropy, which was characterized by the Ni4Ti3 precipitate morphology being coarsest nearest the substrate, while a finer morphology was observed farthest from the substrate. In-situ full-field deformation measurements calculated using digital image correlation confirmed that the SIMT predominately occurred in the finer precipitate morphology. Heat treatment reduced the degree of anisotropy, and DIC analysis revealed localized SIMT strains increased compared to the as-deposited condition.

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