Investigation of Thermal Behavior and Microstructure of Carbon Added NiTi Shape Memory Alloys

Abstract

Original scientific paperThis study aims to examine the thermal and microstructural properties of NiTiC1 and NiTiC2 shape memory alloys (SMAs) produced by arc-melting method. It was observed that additive C did not alter the phase transformation order which remained as one-step (𝐵2 ↔ 𝐵19′). Additionally, the effect of C addition on thermal properties of the Ni-riched NiTi alloy(s), including temperature hysteresis, enthalpy, entropy, and Gibbs free energies were also determined. An increase in the amount of C noticeably reduced the detectable grain size and thus decreased the elastic energy of the alloy. In DSC analysis, the presence of martensitic phases in the alloys was determined below the room temperature. The presence of B2 austenite, Ni4Ti3 precipitate, and TiC phases were detected in XRD analyses, which were supported by SEM-EDX results. Grain boundaries were clearly observed and precipitates were found to be homogeneously distributed.