鈦鎳銅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2000rpm以及4000rpm Ti50Ni40Cu10合金箔帶(Ribbon)，並針對其麻田散體變態、顯微結構、析出硬化以及形狀記憶效應等進行探討。其中as-spun 2000rpm Ti50Ni40Cu10合金箔帶為完全結晶的，但as-spun 4000rpm Ti50Ni40Cu10合金箔帶為部分非晶質的，此因RSP製備時，其箔帶越薄，凝固時冷卻速度愈快導致過冷度太大所造成，其Wavenumber Qp、結晶起始溫度Tx以及結晶之活化能Ea皆較Ti-Ni二元合金箔帶及薄膜低，但較Ti50Ni25Cu25合金箔帶者高，可知箔帶中Cu含量越高，非晶質合金箔帶的熱穩定性也就越低。此兩種合金箔帶各別經過400℃以及 550℃時效後之相變態行為，皆與塊材(Bulk) Ti50Ni40Cu10形狀記憶合金之B2↔B19↔B19’二階相變態不同，而是產生兩個B2↔B19’相變態，透過DSC，XRD以及SEM分析結果顯示此種相變態是由於箔帶中晶粒大小的不同所造成的。奈米壓痕硬度試驗顯示，箔帶經過時效後有析出硬化之效果，其強化程度估計可高於0.3GPa(約30Hv)。此析出硬化提供Ti50Ni40Cu10形狀記憶合金箔帶之強化，並可有效提升其形狀記憶效應。奈米壓痕硬度試驗以及形狀記憶效應測試的結果顯示，影響可回復應變之主要因素為析出硬化之效果，較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。本研究之箔帶試片，不論是2000rpm或4000rpm者，其可回復應變量均高於5%，顯示經過時效處理之Ti50Ni40Cu10形狀記憶合金箔帶具有相當良好之形狀記憶效應。

2000/4000rpm Ti50Ni40Cu10 ribbons prepared by rapid solidification process were studied their transformation behavior, microstructure, precipitation hardening and shape memory effect (SME) properties. As-spun 2000rpm Ti50Ni40Cu10 ribbons are completely crystallized, but as-spun 4000rpm Ti50Ni40Cu10 ribbons are partially amorphous due to their thinner thickness leads to the higher degree of cooling rate. The crystallization behaviors of wavenumber Qp, the starting crystallization temperature Tx and the activation energy of crystallization Ea of as-spun 4000rpm ribbons are investigated and all are lower than those of binary TiNi thin films/ribbons, but higher than those of Ti50Ni25Cu25 thin films/ribbons. This feature indicates that the thermal stability of amorphous Ti50Ni50-xCux alloys is worse with the higher Cu content. Two B2↔B19’ phase transformations, instead of two stage B2↔B19↔B19’ are observed in both aged ribbons, which are caused by the quite different grain sizes existed inherently in ribbons. Nanoindentation tests indicate that precipitation hardening occurs and the hardness increment is 0.3GPa, which can decrease the plastic deformation and increase the SME strain in aged ribbons. Experimental results show the SME strain can reach above 5% in aged ribbons, indicating rather good shape memory properties exhibited in aged ribbons.