富鎳Ti48.7Ni51.3及Ti48.4Ni51.6形狀記憶合金時效後之相變態與性能之研究

Abstract

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.