摘要:
高压输电、核动力、航空航天、汽车、油气勘探等工程领域,均需形状记忆合金能够在较高的温度(>100℃)下驱动或过热预警等,因此高温形状记忆合金的研制和开发有重要的工程应用前景。作为可实用的高温形状记忆合金,除了具有较高的马氏体转变温度、良好的记忆和力学性能之外,还须具有组织和性能在高温下和热循环相变中的长期稳定性。本文选择双相韧化的Ni-Mn-Ga-Ti高温形状记忆合金为研究对象。制备了淬火态Ni55Mn25Ga18Ti2高温形状记忆合金,并对其在室温至480℃之间进行高达500次的相变热循环,获得了5,10,50,100和500次热循环态样品。采用X射线衍射、扫描电镜、能谱仪、同步热分析仪及室温压缩等实验方法,研究了淬火态和热循环态合金样品的微观组织、相变行为、力学及记忆性能,进而分析其热循环稳定性。研究结果表明:经500次循环后,Ni55Mn25Ga18Ti2合金相结构和显微组织未发生明显变化;随着循环次数增加,马氏体相变温度几乎不变,逆马氏体相变温度和相变滞后在循环5次后趋于稳定;抗压强度及压缩变形率波动幅度较小;形状记忆性能略有下降,但形状记忆应变仍保持在1.4%以上;Ni55Mn25Ga18Ti2高温形状记忆合金显示出良好的热循环稳定性。
Abstract:
The research of high temperature shape memory alloys (HTSMAs) has attracted much attention due to the control requirements of high-temperature drive (>100℃) and overheating warning in high voltage transmission, nuclear power, aerospace, automotive, oil exploration and other engineering fields. Besides the high transformation temperatures and good mechanical and shape memory properties, the thermal stability of microstructures and properties at high temperatures and after cycling transformations is also the important basis for evaluating the practicability of HTSMAs. The dual-phase Ni-Mn-Ga-Ti HTSMAs were chosen because of their good ductility. In this paper, the as-quenched Ni55Mn25Ga18Ti2 HTSMA is prepared and then the specimens are thermal-cycled between room temperature and 480 °C for 5, 10, 50, 100, 500 times. The thermal stability of microstructure, martensitic transformation temperatures and mechanical properties are studied by X-ray diffraction analysis, scanning electron microscopy, simultaneous thermal analyzer, and room-temperature compression analysis. The results show that no obvious changes in the phase structure and microstructure of Ni55Mn25Ga18Ti2 HTSMA are observed after 500 thermal cycles. With the increase of thermal-cycling times, the forward martensitic transformation temperatures are almost remain constant and the reverse martensitic transformation temperatures and the hysteresis run to steady when the thermal cycles exceed 5 times. After 500 thermal cycles, the compressive strength and compressive stain change little and the shape memory strain drops slightly but remains over 1.4%. The Ni55Mn25Ga18Ti2 HTSMA shows high thermal cycling stability.