Identifying the effects of heat treatment temperatures on the Ti50Ni45Cu5 alloy using dynamic mechanical analysis combined with microstructural analysis

The properties of NiTiCu alloys strongly depend on their microstructure, which is greatly influenced by the temperature of the heat treatment (HT) carried out as a final step in their processing. This study investigates the effect of HT temperatures on the Ti50Ni45Cu5 alloy using dynamic mechanical analysis (DMA). To confirm the results obtained by the DMA as regards the effects of HT on the microstructure, they were checked against differential scanning calorimetry (DSC), synchrotron X-ray diffraction (SXRD), hardness measurement and stress-strain tests. By combining all these experimental techniques with the DMA measurements, the effects of the HT were determined and attributed to different factors: density dislocation morphology introduced by prior cold work, recovery and recrystallization processes with texture changes, grain growth, precipitation processes and wt% of retained martensite. The results showed that low HT temperatures (400 and 450 °C) are not high enough to eliminate the effects of the cold work but do provide suitable mechanical properties and lower transformation temperatures. Medium temperatures (500-575 °C) lead to higher transformation temperatures and maximum martensitic transformation capacity (ΔH and tan δ) because of the recovery and recrystallization process, but they also cause a reduction in the mechanical properties (slip stress). High temperatures (600 and 650 °C) produce a reduction in transformation capacity and a huge decrease in the mechanical properties (slip stress and ultimate tensile stress).