Shape Memory Transformation in Mechanically Alloyed Ni-50at % Ti

Sarah Green, D. M. Grant, J. V. Wood

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Ni and Ti elemental powders have been mechanically alloyed within a horizontal attritor to produce a Ni-50at% Ti product that is amorphous upon XRD analysis. Heat treatment of this product at 500 °C within an Ar atmosphere has been shown to promote crystallisation into a Ni-Ti intermetallic of CsCl type parent phase crystallography. Upon cooling this parent phase undergoes a solid state thermoelastic shape memory type of phase transformation producing a monoclinic B 19' martensite. This reversible phase transformation has been characterised by differential scanning calorimetry and displays a Ms ←→ As transformation temperature hysteresis of less than 10 °C. This is significantly lower than that associated with commercially produced ingot origin parent phase Ni-Ti, for which a 30 °C transformation hysteresis is expected. XRD analysis of the crystallised Ni-Ti indicates an increase in the parent phase lattice parameter when compared to Ni-Ti synthesised by ingot route. It is proposed that the increased parent lattice parameter effectively reduces the overall lattice strain required for the martensitic phase transformation, enabling the transformation to occur at reduced undercoolings and superheats.
Original languageEnglish
JournalJournal de Physique 4
Issue numberC5
Publication statusPublished - 3 Mar 1997

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