Investigation of the effects of different minor Cr and V additions on thermal and structural properties of CuAlNi shape memory alloy

This study aims to investigate the thermodynamic and structural properties of Cu–Al–Ni–Cr and Cu–Al–Ni–V high temperature shape memory alloys (HTSMAs) produced by adding different minor ratios of Cr and V elements as the fourth element to Cu–Al–Ni alloy. The alloys were successfully produced by arc-melting method in argon atmosphere. X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), differential scanning calorimetry (DSC) and differential thermal analysis (DTA) measurement techniques were used for structural and thermal characterizations. Adding different additive elements to shape memory alloys (SMAs) is a well-known, simple and widely used method that the properties of SMAs such as thermal, shape memory effect, structural, mechanical etc. can be changed and improved. In this thesis, the effects of Cr and V additives added at different ratios on the properties of CuAlNi alloy were investigated. The obtained analysis results showed that the characteristic martensitic transformations and transformation temperatures, thermodynamic and structural shape memory effect properties of the produced CuAlNi base alloy changed according to both the additive element and the additive element ratio. Accordingly, it was determined that the Cr addition stabilized the phase transformations and increased the transformation or shape memory capacity; while the V addition increased the transformation temperatures. In all four alloys, all the reverse martensitic transformation temperatures were determined above 100°C; this showed that the alloys have suitable transformation temperatures for high temperature applications. In addition, the activation energies of the alloys were calculated by the Kissinger method using the peak maximum temperatures of the reverse transformations. Peaks belonging to martensite phases present in the alloys at room temperature were determined by XRD measurements. As a result, the addition of Cr and V elements with different ratios significantly affected the phase transformation behavior and structural properties of the produced CuAlNi alloys; making these alloys strong candidates for actuator and sensor systems operating at high temperatures. Keywords: Smart materials, CuAlNiCr, CuAlNiV, high temperature shape memory alloys, martensitic phase transformation, XRD, DSC, DTA