Evaluation of the Characteristics of a Cu-Al-Ni-Ti-B Shape Memory Alloy

This study investigates the properties of a Cu–13Al–4Ni-0.8Ti-0.1B shape memory alloy prepared by the vacuum arc remelting process. Two alloys were cast: Cu–13Al–4Ni-0.8Ti (alloy 1) and Cu–13Al–4Ni-0.8Ti-0.1B (alloy 2). Microstructural features were investigated by Optical, scanning, and transmission electron microscopy. X-ray diffraction and energy-dispersive spectroscopy were employed to study the phases and their chemical compositions. Transformation temperatures were determined by differential scanning calorimetry. Tensile and shape memory properties were examined to evaluate mechanical characteristics. Microstructural analysis showed that boron addition, in combination with slight compositional variations, altered precipitate composition but did not significantly affect grain size. XRD analysis suggests the likely presence of TiB 2 and Ti-Ni-rich X-phase precipitates in the boron-containing alloy. Microscopic observations showed that alloy 2 consisted of martensite and austenite. It was found that adding boron decreases the transformation temperatures, although an increase in Al and Ni content may also contribute to this effect. The thermal hysteresis of alloy 2 was smaller than that of alloy 1. The fracture strain of alloy 1 and alloy 2 was 6.5±0.1% and 9.7±0.5%, respectively. Moreover, the fracture stress increased from 375±14 MPa for alloy 1 to 482±7 MPa for alloy 2. Shape memory effect testing showed 100% strain recovery after three cycles with a 2% pre-strain. Under bending conditions with a 2.4% pre-strain, 100% of the strain was recovered over 100 cycles. After four loading-unloading cycles at 150 o C, the fracture stress and strain at the same temperature were 437±11 MPa and 5.73±0.48%, respectively.