Abstract：The influences of W addition on microstructures and phase transformation behavior of as-cast TiNi shape memory alloy were investigated by differential scanning calorimeter（DSC）, X-ray diffraction(XRD) and scanning electron microscope(SEM). The results showed that the phase composition of TiNiW0.3 and TiNiW0.5 (atom fraction) alloy were B2 parent phase and Ti2（Ni,W）precipitate phase at room temperature; TiNiW3 and TiNiW6 alloy were composed of B2 parent phase, Ti2 (Ni,W) and W-rich solid solution phase（W-s）, and the shapes of Ti2（Ni,W）precipitated phases were irregular granular, strip, fence with the size ranging from several hundred nanometers to a few microns, while W-s phases were in non-uniform granular shapes, grew up in clusters and dispersed in matrix uniformly. After the addition of W, the grain size of as-cast ingot was refined, and effects of refined crystalline strengthening and solution strengthening were produced. The strength and hardness of the alloy increased with W content increasing. After solid solution treatment at 850℃ for 15 min, the phase transformation in cooling/heating process was A→M/M→A, and the phase transition temperature range became wide, the phase transition temperature reduced, and the reducing rate gradually decreased with the increase of W content.
[1] Li Yanfeng,Mi Xujun,Gao Baodong?,Tan Ji.Effects of thermomechanical cycling on the shape memory behavior and transformation temperatures of a Ni50.2Ti49.8 alloy[J]. Rare Metals, 2008, 27(5):522. [2] 贺志荣，王芳，周敬恩．TiNi合金的形状记忆效应及其工程应用研究进展[J]．材料热处理学报，2005，26(5)：21.[3] 刘礼华，赵连城，杨恒，王利明．镍钛形状记忆合金应用及产业化现状[J]．新材料产业，2002，8：64.[4] 蔡继峰，贺志荣，刘艳，李春月．TiNi基形状记忆合金及其应用研究进展[J]. 金属热处理，2009，34（5）：64.[5] 林海峰，曹继敏，杨宏进，杨华斌，罗斌莉. TiNi合金铸锭VAR熔炼化学成分均匀性控制技术研究[J]. 稀有金属，2010，34s：17.[6] Xu H B,Jiang C B,Gong S K.Phase transformation and hysteresis of TiNiFe shape memory alloys [J].Mater Sci Eng A,2000,281:234.[7] Wang Z G,Zu X T,You L P.Investigation on the two-way shape memory effect and alternating current -electrothermal driving characteristics of TiNiCu shape memory alloy [J].J. Mater. Sci. 2004,39(10):3391.[8] Okita K,Okabe N,Sato T,Nakao T.Appearance of two-way strain in shape memory effect of TiNiNb alloy influence of applied strain on two-way strain[J].Mater. Trans.,2006,47(3):753.[9] Yan X J ,Gugel H, Huth S,Theisen W.Microstructures and properties of laser cladding NiTi alloy with W for biomedical applications[J].Materials Letters,2011,65:2934.[10] Mehrabi K,Bahmanpour H,Shokuhfar A,Kneissl A.Influence of chemical composition and manufacturing conditions on properties of NiTi shape memory alloys[J].Materials Science and Engineering A,2008,481-482 :693.[11] Navjot Kaur,Davinder Kaur.Grain re?nement of NiTi shape memory alloy thin ?lms by W addition[J].Materials Letters,2013,91:202. [12] Pelton B L,Park M.Thermoelastic and superelastic Ni-Ti-W alloy[P].United States:US2010/0114295 A1,Oct.9,2003.[13] 长崎诚三．二元合金状态图集[M].刘安生．北京：冶金工业出版社，2004,498.[14] Buenconsejo P J S,?Zarnetta R,?Konig D,?Savan A,?Thienhaus S,?Ludwig A. A new prototype two-phase (TiNi)–(β-W) SMA system with tailorable thermal hysteresis[J].Advanced Functional Materials,2011,21(1):113.[15] MehrabiaK,Bahmanpour H,Shokuhfar A.Influence of chemical composition and manufacturing conditions on propertie of NiTi shape memory alloys[J].Materials Science and Engineering A, 2008,481-482:693.[16] Hsieha S F,Wub S K, Linc H C, Yangc C H.Transformation sequence and second phases in ternary Ti-Ni-W shape memory alloys with less than 2at.% W[J].Journal of Alloys and Compounds,2005,387:121. [17] 王磊．TiNi基形状记忆合金若干理论及应用问题的额研究[D]．沈阳：中国科学院金属研究所，2006：78.[18] 吕建民．合金化对TiNi合金马氏体相变影响的第一原理研究[D] ．沈阳：中国科学院金属研究所，2007：85.
2017, Vol. 24 
