Phase transformations in Ti2Ni3 precipitates

M. Nishida, C. M. Wayman

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Abstract

The morphology and crystallography of transformation products of Ti2Ni3 in an aged Ti-52.0 at. pct Ni alloy have been studied by means of optical and electron microscopy and electron diffraction. Band-shaped surface relief was observed in optical micrographs at room temperature. Needle and antiphase-like domains were observed in electron micrographs at room temperature. The former correspond to the band-shaped relief seen in optical micrographs. The crystal structure of Ti2Ni3 at room temperature was confirmed to be monoclinic by electron diffraction. The needle-like domains and matrix are twin-related with respect to the {120} plane of the monoclinic structure. Upon heating, first the needle-like domains (low temperature phase) shrank and disappeared at about 50 °C, and then the antiphase-like domains (intermediate phase) disappeared at about 100 °C. Upon subsequent cooling, antiphase-like domains appeared and then needle-like domains appeared. These transformations are reversible upon thermal cycling. The antiphase-like domains in the intermediate phase disappeared with the growth of the needle-like domains and new antiphase-like domains appeared within the needles. The sequence of transformation events in the Ti2Ni3 phase was deduced by electron microscopy and diffraction to be as follows: parent phase (tetragonal) → intermediate phase characterized by antiphase-like domain morphology (orthorhombic) → low temperature phase characterized by needle-like domain morphology (monoclinic). In spite of some differences in crystallographic and morphological changes, the above phenomena are much like the R-phase transition associated with CDW's in TiNiFe alloys.

Original languageEnglish
Pages (from-to)785-799
Number of pages15
JournalMetallurgical Transactions A
Volume18
Issue number6
DOIs
Publication statusPublished - Jun 1 1987

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All Science Journal Classification (ASJC) codes

  • Engineering(all)

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