富鎳Ti48.9Ni51.1及Ti48.8Ni51.2形狀記憶合金相變態 行為之研究

Abstract

本研究探討富鎳Ti48.9Ni51.1及Ti48.8Ni51.2形狀記憶合金 (SMAs) 在固溶處理後及時效於250~600 ºC之相變態行為。當試片時效於250 ºC和300 ºC時，Ti48.9Ni51.1及Ti48.8Ni51.2 SMAs 發生一階B2↔R相變態；當試片時效於350 ºC和400 ºC時，兩SMAs 皆發生二階B2↔R↔B19’相變態；當試片時效於450 ºC時，兩SMAs 發生三階相變態。當試片時效於500 ºC時，由於Ti3Ni4析出物的大小及分布不均勻之關係，Ti48.9Ni51.1 SMA可觀察到四階相變態而Ti48.8Ni51.2 SMA可觀察到為三階相變態。當試片時效於550 ºC時，兩SMAs 皆在早期時效階段發生三階相變態，而於長時效時間發生二階B2↔R↔B19’相變態。當試片時效於600 ºC時，兩SMAs 皆在早期時效階段發生B2↔B19’1變態，中期時效階段發生B2↔B19’1與B2↔B19’2相變態，而於長時效時間只發生B2↔B19’2相變態，其中B2↔B19’1與Ti3Ni4析出物有關，而B2↔B19’2則與Ti2Ni3析出物相關。本研究透過時效450~600 ºC 後Ti48.9Ni51.1 SMA 之SEM圖來觀察顯微結構及析出物Ti3Ni4及Ti2Ni3之分布，同時也探討經過固溶處理後之Ti50-xNi50+x (x=1.0~1.3 at.%) SMAs之微硬度、熱物理性質及制振能特性等，發現固溶處理後之Ti49Ni51、Ti48.9Ni51.1、Ti48.8Ni51.2 SMAs皆發生B2↔B19’相變態，然而Ti48.7Ni51.3 SMA轉變為應變玻璃型態，且Ti48.7Ni51.3 SMA與Ti48.8Ni51.2 SMA之間的微硬度、熱物理性質等均有顯著的差異。

In this study, Ni-rich Ti48.9Ni51.1 and Ti48.8Ni51.2 shape memory alloys (SMAs) are systematically studied to investigate their transformation behaviors exhibited in as solution-treated specimens and then they are aged at 250 ºC to 600 ºC for different aging times by DSC tests. Both SMAs exhibit a B2↔R transformation when aged at 250 ºC and 300 ºC, and a B2↔R↔B19’ transformation occurs when the specimens aged at 350 ºC and 400 ºC. A three-stage transformation occurs in both SMAs aged at 450 ºC due to the compositional inhomogeneity. When the specimens aged at 500 ºC, the transformation sequence of Ti48.9Ni51.1 SMA is a quadruple-stage transformation, whereas Ti48.8Ni51.2 SMA behaves a three-stage transformation due to the inhomogeneous size and distribution of Ti3Ni4 precipitates at grain interior. When the specimens aged at 550 ºC, a three-stage transformation occurs in both SMAs for the early aging time, and a B2↔R↔B19’ transformation occurs for the longer aging time. Both SMAs’ specimens aged at 600 ºC exhibit B2↔B19’1 for the early aging time, behave B2↔B19’1 and B2↔B19’2 for the middle aging time, and show B2↔B19’2 for the longer aging time. SEM images of Ti48.9Ni51.1 specimens aged at 450~600 ºC are observed. At the same time, Vickers microharness, thermal physical properties and damping characteristics of as solution-treated Ti50-xNi50+x (x=1.0~1.3 at.%) SMAs are also studied. Experimental results indicate a B2↔B19’ martensitic transformation exhibits in as solution-treated Ti49Ni51, Ti48.9Ni51.1 and Ti48.8Ni51.2 SMAs; however, Ti48.7Ni51.3 SMA behaves a strain glass transition.