THE EFFECT OF LOW-LEVEL ADDITION OF CU AND FE TOGETHER ON MARTENSITIC TRANSFORMATION AND MICROSTRUCTURE IN THE NITI INTERMETALLIC


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Keskin B., Başlayici S., Derin C. B.

3rd International Natural Science, Engineering and Material Technologies Conference, Gazimagusa, Cyprus (Kktc), 21 - 23 September 2023, pp.54

  • Publication Type: Conference Paper / Summary Text
  • City: Gazimagusa
  • Country: Cyprus (Kktc)
  • Page Numbers: pp.54
  • Istanbul Medipol University Affiliated: Yes

Abstract

NiTi is a notable intermetallic known for its shape memory characteristics. It possesses a B2 crystal structure and can dissolve specific elements at elevated temperatures. In the study, the stoichiometry of NiTi (100 at.%) was retained, and by decreasing the atomic ratio of nickel within the B2 lattice, Cu and Fe were added in varying proportions to achieve a similar crystal structure through combustion synthesis. The exchange of nickel with Cu-Fe was restricted to 10 at.% ratio. The investigations were conducted using optical microscopy, XRD, and thermal analysis methods. XRD results revealed the presence of small amounts of Ti2Ni(Fe,Cu) precipitates alongside the B2 phase with high intensity. With increasing Fe content in the microstructure (approaching 10 at.%), the martensitic transformation shifted to lower temperatures, accompanied by unclear second martensitic peaks. Dendritic phases containing Fe were observed in the microstructure. Elevated Cu content led to a reduction in dendritic structures and a more homogeneous elemental distribution. As the Cu content approached 10 at.%, martensitic (B19') peaks became sharper due to the homogenization of the structure. This was attributed to the negative mixture enthalpy formed by Fe with other elements, except Ni-Ti. Consequently, Fe primarily engaged with Ti and Ni, forming NiTi(Fe) dendritic structures and segregating in the microstructure.