https://scholars.lib.ntu.edu.tw/handle/123456789/74833
標題: | 形狀記憶合金性能增進之研究─子計畫三--增進鐵基形狀記憶合金記憶性能之研究(3/3) | 作者: | 林新智 | 關鍵字: | 鐵基形狀記憶合金;塑變織構;熱機訓練;壓縮應力鬆弛;熱循環;Fe-based shape memory alloy;Deformation texture;Thermo-mechanical training;Compressive stress relaxation;Thermal cycling | 公開日期: | 2005 | 出版社: | 臺北市:國立臺灣大學材料科學與工程學系暨研究所 | 摘要: | 本研究係三年期計畫,主要探討Fe59Mn30Si6Cr5 形狀記憶合金經不同程度之塑性變形和退火後,其內部織構的分布情形與形狀記憶效應之間的關係,及在不同回復溫度和拉伸應變下,其熱機訓練行為的差異。另外,也針對固定應變下,藉由不同程度之壓縮應力鬆弛試驗,觀察其差排或疊差的分布情形與鬆弛效應之關係,及在不同溫度之熱循環和恆溫環境中,循環次數與溫度對合金鬆弛量的變化。 實驗結果顯示,合金經不同熱機處理後,其主要的fiber 均為平行ND(normal direction) 的ζ-fiber。隨著不同加工量和形變溫度,會形成不同方向之形變織構或再結晶織構,其對形狀記憶效應則未有明顯之影響。合金經熱機訓練後,可造成母相中疊差的形成,提高疊差機率而降低應力誘發ε 麻田散體所需的臨界應力,使母相更容易變態為應力誘發ε 麻田散體。在較高回復溫度下,由於可有效消除因熱機訓練所導入之差排,減緩循環硬化效應,使應力誘發ε 麻田散體能完全變態為母相γ,進而提升形狀回復率。在常溫下,合金之壓縮鬆弛現象約在6 小時後便呈現穩定的狀態,隨時間增加幾乎不再有明顯的鬆弛。在拘束力下,熱循環過程牽涉到相變態,導致合金產生熱應力與形狀回復效應,在這雙重因素影響下,造成合金應力鬆弛之現象。當循環熱滯越大時,鬆弛現象越明顯,但經多次熱循環後,將趨於應力平衡狀態。由微結構之觀察得知,鬆弛效應是由於合金經過內部之調整,將結構內高應變能區域慢慢轉換為低應變能區域之穩定狀態,藉由差排或疊差的形成來降低內部應變能,使應力鬆弛現象和緩。但隨著熱循環次數增加,合金內部的疊差除了優選方位排列外,將會誘發第二方位甚至第三方位疊差之生成,其變形程度與循環溫度差成正比,造成合金微結構的不穩定,直接影響到鬆弛量變化,此結果將隨著熱循環次數增加而更為明顯。 The purpose of this three-year research is to investigate the relation between the deformation texture of FeMnSiCr shape memory alloy and the shape memory effect when the FeMnSiCr shape memory alloy is under various conditions of plastic deformation and annealing, and to show the difference of thermo-mechanical behavior of the FeMnSiCr shape memory alloy in various recovery temperature and tensile strain. In addition, the relation between the dislocations or stacking faults of the alloys and the relaxation effect is studied when the FeMnSiCr shape memory alloys are under various conditions of compressive stress relaxation tests. The difference of the stress relaxation of the alloys at various thermal cycling and constant temperatures is also examined.Experimental results showed that the major fiber of the FeMnSiCr alloy by different thermo-mechanical treatment is the ζ fiber which parallels to the normal direction. With various strain and deformation temperature, several directions of the deformation texture or reorientation texture can be formed. Stacking faults can be formed by thermo-mechanical training. Thus, the stacking fault probability increases, and the critical shear stress for inducing martensite is reduced. At higher recovery temperatures, the cyclic hardening effect can be reduced by eliminating the density of the dislocations, and the stress-induced martensite can recover to the parent phase γ completely. The relaxation phenomenon of the FeMnSiCr alloy becomes negligible after about six hours at room temperature. The thermal stress and shape recovery effect of the FeMnSiCr shape memory alloys cause the stress relaxation under the stress and thermal cycling. The relaxation is quite obvious when the hysteresis of the cycling raises, and it tends to the equilibrium state of stresses after several thermal cycling. The relaxation effect of the alloys is attributed to the transformation of the higher strain energy region into the lower one by the rearrangement of dislocations and stacking faults to reduce the internal strain energy. The stacking faults of the secondary orientation are also induced with increasing the numbers of thermal cycling in addition to the primary orientation arrays. The extent of the change is proportional to the cyclic temperature, and the unstable structure of the alloys directly affects the relaxation which increases with increasing the numbers of thermal cycling. |
URI: | http://ntur.lib.ntu.edu.tw//handle/246246/12498 | 其他識別: | 932216E002025 | Rights: | 國立臺灣大學材料科學與工程學系暨研究所 |
顯示於: | 材料科學與工程學系 |
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