Effect of Aging Treatment on the Compressibility and Recovery of NiTi Shape Memory Alloys as Static Seals
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JMEPEG (2017) 26:3025–3033 DOI: 10.1007/s11665-017-2762-z
Effect of Aging Treatment on the Compressibility and Recovery of NiTi Shape Memory Alloys as Static Seals Xiaofeng Lu, Gang Li, Luwei Liu, Xiaolei Zhu, and Shan-Tung Tu (Submitted August 7, 2016; in revised form May 5, 2017; published online June 9, 2017) The improvement of the compressibility and recovery of the gaskets can decrease the leakage occurrence in bolted flange connections. In this study, the effect of aging treatment on the compressibility and recovery of NiTi shape memory alloys is investigated as static seals together with thermal analysis. The experimental results indicate that different phase transformations of NiTi alloys are exhibited in the DSC curves during aging treatment. The recovery coefficient of NiTi alloys aged at 500 °C for 2 h is quite low accompanied with a large residual strain. With increasing aging time at the aging temperature of 400 °C, the residual strain and area of hysteresis loop of NiTi alloys are both increased, whereas the recovery coefficient is decreased. Since the deformation associates the phase transformation behavior, aging treatment could improve the compressibility and recovery of NiTi alloys as static seals. Keywords
aging treatment, compressibility, NiTi alloys, phase transformation, recovery
1. Introduction Metallic static gaskets as primary seals are extensively used in bolted flange connections of petrochemicals, aerospace, submarine shipbuilding, and other industries (Ref 1, 2). The conventional metallic seals cannot meet the specific needs in the extreme situations because of the great possibility of the leakage. As advanced and attractive materials, shape memory alloys (SMAs) have been put forward to manufacture static gaskets due to their shape memory effect (SME), superelasticity and structural properties (Ref 3, 4). Owing to excellent superelastic and relatively low deformation resistance, the gaskets fabricated by NiTi SMAs could compensate the reduction in pre-tighten force and enhance sealing performance. Therefore, the gaskets of NiTi alloys can be effectively applied in severe rugged environments and have been attracted considerable attention in engineering. Tatsuoka et al. (Ref 5, 6) revealed that the gaskets of NiTi alloys possessed superior sealing performance to the conventional aluminum gaskets. Efremov (Ref 7, 8) considered that the gaskets with core of SMAs had a feature of negative creep effect and provided leaktight, automatic and continuous multiple seal under a variety of operating temperatures and internal pressures. The new gaskets with core of SMAs could inhibit operating creep relaxation and extend service life of bolted flange connections. As well known, heat treatment is a conventional method to control the microstructure and properties of NiTi alloys (Ref 9Xiaofeng Lu, Gang Li, Luwei Liu, and Xiaolei Zhu, School of Mechanical and Power Engineering, Nanjing Tech University, Nanjing 211800, China; and Shan-Tung Tu, School of Mechanical and Power Engineering, Nanjing Tech Universi
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