富鈦鈦鎳形狀記憶合金箔帶麻田散體變態及其性能之研究

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效應進行探討。本研究所使用之試片包含2000/4000rpm Ti51Ni49以及4000rpm Ti52Ni48合金箔片。在此三種合金箔片經過400/500℃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。透過XRD以及TEM之分析結果顯示此R相相變態是由於奈米級Ti2Ni析出物與TiNi基地間之整合型介面所誘發產生的。奈米壓痕硬度試驗顯示此奈米級Ti2Ni具有析出硬化之效果，其強化程度估計可高於1GPa(約100Hv)。此析出硬化現象提供富鈦鈦鎳形狀記憶合金之強化，並可有效提升形狀記憶合金之效能。由形狀記憶效應之研究可歸納出兩個主要影響可回復應變量之因素：一為析出硬化之效果，即試片硬度；另一為變態潛熱，即ΔH值。高的析出硬化效果可降低塑性變形量，使得可回復之變形量增加；高的變態潛熱提供較多可變態之材料體積，使相變態所產生之變形量較高。本研究中之箔帶試片其可回復應變量可高於5.2%，顯示經過時效處理之富鈦鈦鎳形狀記憶合金具有相當良好之形狀記憶效能。

2000/4000rpm Ti51Ni49 and 4000rpm Ti52Ni48 Ti-rich TiNi ribbons prepared by rapid solidification process were studied to investigate the transformation behavior, microstructure, precipitation hardening effect and mechanical properties. Premartensitic R phase transformation, which has not been occurred in bulk Ti-rich TiNi SMAs, is observed in all of these ribbons after aging at 400℃/500℃using DSC and XRD tests. TEM observations show the R phase transformation is induced by the coherent strain between TiNi matrix and nano-scale Ti2Ni precipitates. Nanoindentation tests indicates that precipitation hardening by nano-scale Ti2Ni precipitates in Ti-rich TiNi SMAs does occur, and an increase of hardness of 1GPa is observed. This feature provides a new way to improve the properties of Ti-rich TiNi SMAs. The shape memory property of these aged ribbons is concluded to be related to two factors: the degree of precipitation hardening effect and the value of transformation latent heat. The reversible strains of SME tests can reach > 5.2% in these ribbons, indicating good shape memory property exhibited in ribbons of aged Ti-rich TiNi SMAs.