Investigation of thermal property of spark plasma sintered Ti-Zr-Ta shape memory alloys

Abstract

There is increasing demand for the performance improvement of novel shape memory alloys (SMAs), such as the Ti-Zr-based systems. The effects of fabrication parameters and material compositions are critical to the thermal properties of the alloys. This study is designed to investigate the effects of ternary Ta additions on the thermal properties of spark plasma sintered (SPSed) novel Ti-Zr based SMAs for high temperature applications. The SPSed Ti-Zr/Ta specimens were characterized for their microstructural and crystallographic features using scanning electron microscopy (SEM) incorporated with Energy Dispersive X-ray Spectroscopy (EDS), and X-ray powder diffractometry (XRD). Thermal property measurements were conducted using the Laser Flash technique to obtain the thermal diffusivity behaviour, while the phase transformation properties were determined by the differential scanning calorimetry (DSC). The presence of both alpha martensite, and beta structures were revealed by the SEM/EDX and XRD respectively. High thermal diffusivity values were obtained, and they show an increasing trend with temperature. The DSC measurement revealed high reversible martensitic transformation (above 200 deg Celcius) for all the alloys, a two-stage phase transformation in the binary alloy, and a single-phase transformation event in the ternary alloys. A downward parabolic gradient of the specific heat and thermal conductivity with respect to temperature was recorded in the alloys, thus revealing an interaction between phonon-mediated and electron-mediated thermal transport processes. Two-stage phase transformations, noticed in the binary alloy indicate the reversible transformation events of alpha-Ti and alpha-Zr phases at different temperatures to-and-fro the austenite phase, whereas, in the ternary phase the single transformation event indicates the presence of only alpha-Ti phase. These results further strengthen the understanding of material atomic compositions effect on the thermal behaviour of the as-sintered alloys. The high thermal diffusivity and high martensitic transformation behaviour of the Ti-Zr/Ta alloys suggest they can be suitable candidates for high temperature applications in the aerospace technologies.