本研究針對Ti48.7Ni51.3與Ti48.4Ni51.6形狀記憶合金(SMAs)之相變態、形狀記憶效應(SME)、超彈性(PE)與超彈性應力應變循環等性質作一系列的探討。900℃固溶處理1hr後水淬之Ti48.7Ni51.3與Ti48.4Ni51.6若未經任何時效處理強化者,硬度值分別為362HV及386HV,其PE性質由於SIM逆變態較少而使得殘留應變較多。常溫下之硬度實驗得知,Ti48.7Ni51.3在250℃時效者其硬度隨時效時間有兩個極大點;然Ti48.7Ni51.3在300℃~500℃時效者與Ti48.4Ni51.6在250℃~500℃時效者均只有一個極大點出現,本論文並就其產生極大點之原因做討論。本研究同時發現,Ti48.7Ni51.3在300℃時效10hrs及Ti48.4Ni51.6在350℃時效3hrs分別可達各時效溫度下之最大硬度值,各為415HV及455HV,顯示富Ni之TiNi合金其Ti3Ni4之析出硬化效果會因Ni含量的增加而增大,這可能與Ti3Ni4量的增多有關,同時其PE性能也較顯著,有較佳之應力應變循環的特性,也使能量儲存效率提升,但因奈米級Ti3Ni4析出物反而使其在SME/PE實驗中有較大之殘留應變。由DSC實驗結果可知,Ti48.7Ni51.3與Ti48.4Ni51.6時效於250℃、300℃及350℃等溫度,主要為B2↔R變態,B19’變態都不明顯;時效於400℃、450℃及500℃時,R相及B19’變態都非常明顯,為B2↔R↔B19’二階相變態。Ti48.7Ni51.3與Ti48.4Ni51.6在500℃時效10hrs之SME/PE可回復之應變量均最大,殘留應變量也最小,顯示高溫時效下其Ti3Ni4析出物已夠大,基地固溶之Ni量也降低,麻田散體變態之阻礙也變少,這反而使其在SME/PE測試時之塑性變形量最少。
In this study, the properties of shape memory effect (SME), pseudoelasticity (PE) and stress-strain (σ-ε) cycling exhibited in Ni-rich Ti48.7Ni51.3 and Ti48.4Ni51.6 shape memory alloys (SMAs) are investigated. These SMAs are solid-soluted(SS) at 900℃x 1 hr, water quenched, and then aged at 250℃~500℃ for various time. The hardnesses of as-SS Ti48.7Ni51.3 and Ti48.4Ni51.6 SMAs are 362HV and 386HV, respectively. The maximum hardness for SS and aged specimens is 415 HV for Ti48.7Ni51.3 SMA aged at 300℃x10 hrs, and is 455HV for Ti48.4Ni51.6 SMA aged at 350℃x3 hrs. In the early aging, the curve of hardness at room temperature v.s. aging time for Ti48.7Ni51.3 SMA aged at 250℃ has two maxima, but that for Ti48.7Ni51.3 SMA aged at 300℃~500℃ and that for Ti48.4Ni51.6 SMA aged at 250℃~500℃ have only one maximum. From DSC tests of Ti48.7Ni51.3 and Ti48.4Ni51.6 SMAs, B2↔R transformation mainly appears in specimens aged at 250℃~350℃, but B2↔R↔B19’ transformation occurs in specimens aged at 400℃~500℃. The tensile tests indicate that, in specimens of Ti48.7Ni51.3 and Ti48.4Ni51.6 SMAs aged at 500℃x10 hrs, their SME, PE and σ-ε cycling properties are better than other aging conditions due to Ti3Ni4 precipitates grow larger and the resistance for B19’ transformation is less.