Synthesis of NiTi microtubes via the Kirkendall effect during interdiffusion of Ti-coated Ni wires

A. E. Paz y Puente*, D. C. Dunand

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

28 Scopus citations

Abstract

An additive alloying method is developed to fabricate NiTi microtubes, consisting of two steps: (i) depositing a Ti-rich coating onto ductile, pure Ni wires (50 μm in diameter) via pack cementation, resulting in a Ni core coated with concentric NiTi2, NiTi and Ni3Ti shells, and (ii) homogenizing the coated wires to near equiatomic NiTi composition via interdiffusion between core and shells, while concomitantly creating Kirkendall pores. Because of the spatial confinement and radial symmetry of the interdiffusing core/shell structure, the Kirkendall pores coalesce near the center of the wire and form a continuous longitudinal channel, thus creating a microtube. To study the evolution of Ni-Ti phases and Kirkendall pores during homogenization, coated wires were subjected to ex situ homogenization followed by (i) metallography and (ii) X-ray tomographic imaging. Near equiatomic NiTi was obtained upon homogenization at 925 °C for 4 h with compositional fluctuations between 49 and 53 at.% Ni consistent with slight variations in initial coating thickness. Kirkendall pores initially formed near the NiTi/Ni3Ti and Ni3Ti/Ni interfaces and eventually merged into a continuous channel with an aspect ratio of at least 75.

Original languageEnglish (US)
Pages (from-to)42-48
Number of pages7
JournalIntermetallics
Volume92
DOIs
StatePublished - Jan 2018

Funding

AEPyP acknowledges the National Science Foundation Graduate Research Fellowship Program for funding support. The authors acknowledge the financial support from the Defense Advanced Research Projects Agency under award number W91CRB1010004 (Dr. Judah Goldwasser, program manager). They also thank Profs. Peter Voorhees and David Seidman (Northwestern University) for their helpful discussions, Dr. Dinc Erdeniz, and Ms. Shannon Taylor, Victoria Vaccarreza, and Sarah Plain (Northwestern University) for experimental assistance at APS, and Dr. Ashwin Shahani (Northwestern University) for assistance with the MATLAB script for 3-D visualization and measuring pore volume fraction. This work made use of the EPIC, Keck-II, and/or SPID facility(ies) of Northwestern University's NUANCE Center, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource ( NSF ECCS-1542205 ); the MRSEC program ( NSF DMR-1121262 ) at the Materials Research Center; the International Institute for Nanotechnology (IIN); the Keck Foundation; and the State of Illinois, through the IIN. This work also made use of the OMM facility which receives support from the MRSEC Program ( NSF DMR-1121262 ) of the Materials Research Center at Northwestern University.

Keywords

  • Diffusion coatings
  • Kirkendall effect
  • Microtubes
  • NiTi
  • Pack cementation

ASJC Scopus subject areas

  • General Chemistry
  • Mechanics of Materials
  • Mechanical Engineering
  • Metals and Alloys
  • Materials Chemistry

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