The Thermal and Transport Properties of Annealed Ni-rich Ti48.7Ni51.3 Shape Memory Alloys

• Main Authors: Ming-Lung Ko, 柯明輪
• Other Authors: Yung-Kang Kuo
• Format: Others
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/36233624244068585803

碩士 === 國立東華大學 === 物理學系 === 103 === In this thesis, we report on the measurements of temperature-dependent electrical resistivity (ρ), Seebeck coefficient (S), specific heat (CP) and thermal conductivity (κ) in the temperature range 10 to 350 K on the shape memory alloy Ti48.7Ni51.3 annealed at 523 K with various annealing time (1 hr to 50 hrs). It was found that the resistivity of these alloys shows a semiconducting behavior, and the negative temperature coefficient in (T) curve is a characteristic of the strain glass transition that occurs in the Ni-rich TiNi alloys due to the local stress induced by the excess Ni in the TiNi lattice. The overall resistivity of Ti48.7Ni51.3 alloy was found to decrease with increasing annealing time, presumably attributed to the reduction in lattice defects. Seebeck coefficients of these Ti48.7Ni51.3 alloys were found to be positive, suggesting the hole-type carriers dominate the thermoelectric transport. Besides, the Seebeck coefficients of all studied samples exhibit a typical metallic behavior throughout the temperature range investigated, suggesting that the semiconducting behavior revealed from resistivity measurements is due to the influence of the strain glass transition. Anomalous behaviors are observed in both cooling and heating cycles in specific heat for the Ti48.7Ni51.3 alloys after annealing treatments, corresponding to the transformation between the R-like and austenite phases (B2) as a result of the nano-sized precipitation during annealing processes. It is clearly seen that the anomalous peaks in CP increase significantly and move toward to higher temperatures with increasing annealing time. We argue that the precipitation causes a decrease of the Ni content in the Ti48.7Ni51.3 matrix, which may facilitate the R-like phase transformation after the annealing treatments.