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Title: | 通電加熱對Ti-Ni及Ti-Ni-Cu形狀記憶合金線材之超彈性、彈熱效應與功能穩定性影響之研究 The Effect of Electric Current Heat Treatment on the Superelasticity, Elastocaloric Effect, and Functional Stability of Ti-Ni and Ti-Ni-Cu Shape Memory Wires |
Authors: | 鄭聿 Yu Cheng |
Advisor: | 陳志軒 Chih-Hsuan Chen |
Keyword: | TiNi基合金,形狀記憶線材,超彈性,彈熱效應,麻田散體相變態,功能穩定性,通電加熱, TiNi-based alloys,shape memory wires,superelasticity,elastocaloric effect,martensitic transformation,functional stability,electric current treatment, |
Publication Year : | 2024 |
Degree: | 博士 |
Abstract: | 本研究以電流對TiNi基合金進行熱處理。首先,以通電加熱(直流電)方式研究富Ni之Ti49Ni51形狀記憶線材每經歷100次超彈性循環後的修復效果,在不將Ti49Ni51線材(直徑0.5毫米)從拉伸試驗機上取出的情況下利用電流熱效應進行通電加熱,旨在實現在無需移動材料的情形下修復形狀記憶合金的效果。此外,本研究亦以脈衝電流對冷抽之富(Ni,Cu) Ti49Ni41Cu10形狀記憶線材進行退火,改善其功能穩定性;透過析出延性佳之Ti(Ni,Cu)2,成功製備了直徑同為0.5毫米之Ti49Ni41Cu10線材,接著再以額外具有非熱效應的高密度脈衝電流對線材進行高效率之退火,以獲得優秀的超彈性及彈熱冷卻效應穩定性。對於電流密度較低的情形(20.4 A/mm2),可以透過在每100次超彈性循環之後將材料加熱2分鐘以部份恢復Ti49Ni51線材衰退的超彈性及彈熱效應;通電3 ~ 4次後,Ti49Ni51線材的彈熱升溫能力及彈熱降溫能力趨於穩定,且與未經過任何熱處理的情況相比分別恢復了約14%與6%。此恢復現象的機制為Ti49Ni51線材內部在超彈性循環過程中產生的殘留麻田散體由於通電加熱(熱效應)發生麻田散體逆相變態而被消除。另一方面,由於額外的非熱效應之存在,可以透過高密度脈衝電流(60 A/mm2)在0.3秒內對冷抽之Ti49Ni41Cu10線材進行高效率的退火,讓線材產生再結晶的效果,晶粒尺寸則大約為20 ~ 30奈米。退火之Ti49Ni41Cu10線材具有優秀的超彈性及彈熱冷卻效應穩定性;在65 °C施加3.5%應變的情形下,該線材在50次超彈性循環後累積的殘留應變僅有0.15%,而彈熱降溫能力在50次循環內則大約維持在9.4 °C。此外,在施加3%應變的情形下,該線材在50 °C至100 °C的溫度範圍內的彈熱降溫能力為5.3 °C ~ 8.1 °C。退火之Ti49Ni41Cu10線材之優秀的功能穩定性可歸因於奈米晶粒結構以及B2與B19相之間優異的相容性。總體而言,本研究初步開發透過通電加熱來調整TiNi基合金的微觀結構;透過調整電流密度及通電時間,此方法可恢復衰退之彈熱效應或者獲得具有優秀之功能穩定性的材料,這些成果都將有助於固態冷卻材料的發展及應用。 In this study, electric current was utilized to treat TiNi-based alloys. First, direct current (DC) was employed to investigate the healing effects of an as-received Ni-rich Ti49Ni51 shape memory wire after every 100 superelastic cycles. For the Ti49Ni51 wire with a diameter of 0.5 mm, the electric current treatment was applied, taking advantage of its thermal effect, without removing the wire from the tensile machine, aiming for online healing of the shape memory alloy. In addition, pulsed electric current was applied to anneal a cold-drawn (Ni,Cu)-rich Ti49Ni41Cu10 shape memory wire to improve its functional performance. The Ti49Ni41Cu10 wire with the same diameter (0.5 mm) was successfully fabricated with the help of the existence of ductile Ti(Ni,Cu)2 precipitates. Subsequently, a high-density pulsed current, with an extra athermal effect, was utilized to efficiently anneal the wire and obtain superior superelasticity and stable elastocaloric cooling capacity. For the electric current treatment with a lower density (20.4 A/mm2), the degraded superelasticity and elastocaloric effect of the Ti49Ni51 wire after every 100 superelastic cycles could be partially restored by heating the material for 2 min. After 3–4 treatments, the elastocaloric temperature rise and drop of the Ti49Ni51 wire reached steady states and recovered about 14% and 6%, respectively, as compared with the case without any heat treatment. The mechanism of the recovery phenomenon lies in that the residual martensite introduced into the Ti49Ni51 wire during superelastic cycles could be eliminated due to reverse martensitic transformation through the electric current treatment (thermal effect). On the other hand, with the help of the extra athermal effect, the cold-drawn Ti49Ni41Cu10 wire could be effectively annealed through the high-density pulsed electric current (60 A/mm2) in only 0.3 sec, resulting in recrystallization in the wire, with a grain size of about 20–30 nm. The annealed Ti49Ni41Cu10 wire demonstrated superior stability in superelasticity and elastocaloric cooling capability. The accumulated residual strain was only 0.15% after 50 superelastic cycles with an applied strain of 3.5% at 65 °C, and the elastocaloric temperature drop of the wire remained at about 9.4 °C for 50 cycles. Moreover, under 3% applied strain, the wire exhibited elastocaloric temperature drops of 5.3 °C to 8.1 °C within the application window of 50 °C to 100 °C. The exceptional functional stability of the annealed Ti49Ni41Cu10 wire is attributed to the combination of nanocrystalline structure and high compatibility between the B2 and B19 phases. In summary, this study contributes to the development of using electric current treatment to tune the microstructure of TiNi-based alloys. By tuning the current density and treatment duration, it can recover the degraded elastocaloric effect or obtain materials with superior functional performance, both of which are viable for solid-state refrigeration applications. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/92997 |
DOI: | 10.6342/NTU202401170 |
Fulltext Rights: | 同意授權(全球公開) |
Appears in Collections: | 機械工程學系 |
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