Mechanical properties of Ti–Ni Shape Memory Alloys in Micro-nano Scale

形狀記憶合金的超彈性行為是由於結晶可逆之熱彈性麻田散體變態，雖然這個性質在宏觀尺度下已經被廣泛研究,但是在微奈米尺度下關於超彈性行為的研究卻很少，由於微奈米機電的發展促使形狀記憶合金超彈性行為在微奈米尺度下被探討，因此本研究為在微奈米尺度下觀察其力學及相變態行為，製備之試片為三種不同成分的鈦鎳形狀記憶合金，成分分別是Ti49.05Ni50.95, Ti49.49Ni49.71Fe0.8, Ti49.93Ni50.07的塊材，透過DSC量測相變態溫度，這些材料的沃斯田鐵相變態結束溫度分別是–29.2 ºC, 10.0 ºC, 95.1 ºC，並且利用XRD確認常溫下的相結構，在常溫下Ti49.05Ni50.95, Ti49.49Ni49.71Fe0.8利用奈米壓痕試驗機的圓錐針頭在不同力量時探討超彈性行為，Ti49.93Ni50.07在不同溫度下利用奈米壓痕試驗機探討不同程度之超彈性現象，除了利用奈米壓痕試驗研究區域超彈性，我們也執行微奈米柱壓縮試驗研究整體超彈性行為，最後利用不同大小的探針壓痕，觀察探針尺度效應對形狀記憶合金的超彈性之影響，本研究發現形狀記憶合金具有往微奈米機電領域發展的潛力，成為新一代的功能性微奈米元件。Pseudoelasticity of shape memory alloy (SMA) results from the reversible thermoelastic martensitic transformation. Although this property has been studied extensively at the macroscale, the study of this pseudoelastic behavior at the micro-nano scale is sparse. Recent demands for micro- and nano-electro-mechanical systems (MEMS and NEMS) have prompted the studies of pseudoelasticity of SMA at the micro-nano scale. In the present study, we developed TiNi-based SMAs for applications at the micro-nano scale, such as the actuators. To achieve this, we processed three TiNi-based SMAs, Ti49.05Ni50.95, Ti49.49Ni49.71Fe0.8 and Ti49.93Ni50.07, which had different austenite finish temperatures of –29.2 ºC, 10.0 ºC and 95.1 ºC, respectively. Nanoindentations performed on Ti49.05Ni50.95 and Ti49.49Ni49.71Fe0.8 at room temperature and different peak loads revealed the pseudoelastic behavior. For Ti49.93Ni50.07, nanoindentations performed at various temperatures showed different degrees of pseudoelasticity because of the different amounts of stress-induced martensitic transformation taking place during the indentation process. In addition to performing nanoindentation to study the localized pseudoelastic behavior of TiNi-based SMAs at the nano scale, micropillar compression tests were also performed to study the global pseudoelastic behavior. The findings of this work demonstrate the potential of integrating TiNi-based SMAs into MEMS and NEMS components that exhibit pseudoelasticity which, in turn, would result in a new generation of functional micro- and nanodevices