A study on the thermo-structural and functional properties of NiTiCoB shape memory alloys

Saǧlr B., Klllç G., Abboosh O., Daǧdelen F., Aydoǧdu A., Kök M., ...Daha Fazla

Open Physics, cilt.24, sa.1, 2026 (SCI-Expanded, Scopus)

  • Yayın Türü: Makale / Tam Makale
  • Cilt numarası: 24 Sayı: 1
  • Basım Tarihi: 2026
  • Doi Numarası: 10.1515/phys-2025-0322
  • Dergi Adı: Open Physics
  • Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Anahtar Kelimeler: energy activation, microstructure, NiTiCoB, phase transformation, shape memory alloy
  • Gazi Üniversitesi Adresli: Evet

Özet

This study investigates the effect of the Ni/Ti ratio on the thermo-structural and functional properties of NiTiCoB shape memory alloys with nominal compositions of Ni42-x Ti53+x (Co4.5B0.5) (x = 0-2.0at.%), while maintaining constant Co and B contents. The alloys were produced by vacuum arc melting followed by homogenization at 900°C for 24h. Differential scanning calorimetry (DSC) was used to characterize phase transformation behavior and estimate apparent activation energies using the Kissinger and Ozawa methods. X-ray diffraction (XRD), optical microscopy, and Vickers microhardness measurements were employed for structural and microstructural characterization. The DSC results showed an overall tendency toward higher transformation temperatures with increasing nominal Ti content, although individual transformation temperatures exhibited non-monotonic variations. The apparent activation energies decreased overall from 395.7-380.87kJmol-1 to 269.2-260.57kJmol-1 according to the Kissinger and Ozawa methods, respectively. XRD revealed B2-NiTi, B19′-NiTi, NiTi2, and α-Ti-related phases, while the XRD-derived crystallite size generally decreased with increasing nominal Ti content. Microhardness exhibited an overall increase, reaching 325 ± 2 HV0.3. A preliminary single-specimen shape-recovery test indicated approximately 68% recovery. These findings demonstrate that the nominal Ni/Ti ratio influences the thermal, structural, mechanical, and functional behavior of NiTiCoB alloys under fixed Co and B contents.