TiNi基形狀記憶合金箔帶之性能以及R相自我調適行為之研究

Abstract

本研究利用快速凝固製程(RSP)製備富鈦鈦鎳形狀記憶合金箔帶(ribbon)，並針對其麻田散體相變態、顯微結構、析出硬化以及形狀記憶特性進行探討。本研究所使用之試片包含Ti50.4Ni49.5Si0.1, Ti50.1Ni49.7Si0.2, Ti50.6Ni39.4Cu9.8Si0.2 and Ti50Ni25Cu25合金箔帶之性能。此外，本研究也包含高含鈦量之Ti50.92Ni48.94Si0.14箔帶中富鈦GP區(GP zone)析出物之顯微結構觀察。Ti50.4Ni49.5Si0.1及Ti50.1Ni49.7Si0.2此兩種合金箔帶於噴鑄狀態(as-spun)下包含大量奈米級Ti2Ni析出物，而經過500 ºC時效後皆產生未曾於塊材(bulk)富鈦鈦鎳形狀記憶合金中發現之R相相變態以及Ti3Ni4析出物。此奈米級Ti2Ni及Ti3Ni4析出物可有效產生析出硬化效果，強化箔帶之強度並且提升其形狀記憶特性。利用奈米壓痕超彈性試驗顯示Ti50.4Ni49.5Si0.1及Ti50.1Ni49.7Si0.2此兩種箔帶於50 mN之力量下皆有高於78 %之回復量，其性能較被報導的Ti49.8Ni50.2合金優異。Ti50.6Ni39.4Cu9.8Si0.2箔帶於噴鑄狀態僅部分結晶，其於550 ºC時結晶化並熱處理15分鐘後更可得到高達6.2%的形狀記憶效性回復量。Ti50Ni25Cu25箔帶於噴鑄狀態為非晶質，經過於500 ºC時結晶化並熱處理15分鐘後，由奈米壓痕超彈性測試可於2.5~3.0 GPa之平均壓力下達到最明顯之超彈性表現。由Ti50.92Ni48.94Si0.14箔帶中富鈦GP區析出物之顯微結構觀察，其結構為序化之C11b Ti2Ni以及Ti5Ni3兩次結構所組成，造成其繞射圖譜於0.4 q001及0.7 q001處有產生額外之繞射點。研究結果顯示利用RSP製成製造鈦鎳基形狀記憶合金薄帶可有效提升鈦鎳基形狀記憶合金之性能並得到優良的形狀記憶特性。透過利用電子背向散射繞射(EBSD)技術觀察R像自我調適行為(self-accommodation)提供更高解析度並且觀察不受晶粒方位所限制，可以更快速地分析R向自我調適之行為。

Characteristics of aging treatments, transformation sequence, phase identification, microstructures, precipitation hardening and shape memory performances of melt-spun Ti50.4Ni49.5Si0.1, Ti50.1Ni49.7Si0.2, Ti50.6Ni39.4Cu9.8Si0.2 and Ti50Ni25Cu25 ribbons were studied. Ti50.4Ni49.5Si0.1, Ti50.1Ni49.7Si0.2 and Ti50.6Ni39.4Cu9.8Si0.2 ribbons show significant precipitation hardening by GP zones and/or nanoscale Ti2Ni/Ti3Ni4 precipitates after aging treatment, which result in excellent shape memory performance. The recovery of both Ti50.4Ni49.5Si0.1 and Ti50.1Ni49.7Si0.2 ribbons during pseudoelasticity tests are higher than 78 % under nanoindentation load of 50 mN, which is significantly higher than conventional bulk Ti49.8Ni50.2 alloy. Additionally, the microstructure, precipitation phenomenon and shape memory properties of TiNiSi ribbons are found closely related to the slight variation of Ti/Ni ratio and Si content. For Ti50.6Ni39.4Cu9.8Si0.2 ribbon, shape memory effect with 6.2 % recoverable strain is obtained after crystallized and aged at 550 ºC for 15 min. Amorphous Ti50Ni25Cu25 ribbon becomes well-crystalized after being treated at 500 ºC for 15 min and shows pronounced pseudoelasticity response under average contact pressure between 2.5-3.0 GPa. The structure of GP zones in Ti-rich Ti50.92Ni48.94Si0.14 ribbon was studied and a hybrid structure composed of C11b Ti2Ni and Ti5Ni3 substructures is proposed to explain the appearance of these extra diffuse streaks. Experimental results indicate that performance of TiNi-based shape memory alloys can be effectively enhanced by fabricating the alloys with rapid solidification process. The self-accommodation morphologies of R-phase variants studied by an EBSD system provide a fast and high resolution method to study twinning relationship between R-phase variants.