鉭添加對於Fe-30Mn-6Si-5Cr形狀記憶合金之效應

Abstract

Fe-Mn-Si-Cr形狀記憶合金具有良好的加工成形性、良好的形狀記憶效應、以及相對低廉的單位成本。除此之外，Fe-Mn-Si-Cr合金只具有單向記憶效應，一旦經過加熱回復形狀一次後，形狀就不會再隨溫度變化而改變。因此Fe-Mn-Si-Cr合金對於大尺度、只需要一次性變形的機構應用來說，是相當理想的材料。工業上應用的實例如連接管路用的套筒元件、連接軌道的魚尾板、以及鉚釘。本研究藉由添加0.1wt%以及1.0wt%的鉭元素於Fe-30Mn-6Si-5Cr合金中，搭配2小時500到800℃的時效處理，來改善其形狀記憶效應。其中添加1.0wt%鉭並經過2小時700℃時效處理後的合金，與未經添加與熱處理的合金相比，有最高的形狀回復率，其增加量達16%。經過時校處理後，在γ基地發現有TaC與χ相兩種不同的第二相顆粒，在不同的鉭添加與時效處理溫度下，這些析出物的大小與分佈也隨之不同。本研究發現，鉭添加對於改善形狀記憶效應的機制有以下數種：固溶強化與析出第二相強化 γ奧氏體母相、γ奧氏體母相的晶粒細化、析出物在γ晶粒內對於不同方向ε麻田散鐵成長的區隔效應、以及增加γ母相內的疊差機率。

Fe-Mn-Si-Cr based shape memory alloys (SMAs) have desirable formability, moderate shape memory effect (SME) and low cost. This makes ferrous SMAs highly potential in large-scaled applications such as pipe coupling, rail fish plates, and other smart construction methods. Also, Fe-Mn-Si-Cr alloys only have one-way shape memory effect, which is ideal for applications that require only-one-time shape recovery as the fixed structure shape. In this study, the shape memory effect of Fe-30Mn-6Si-5Cr (in wt%) SMAs are improved by adding 0.1 wt% and 1.0 wt% Ta along with ageing treatment from 500 to 800℃ for 2 hours. 1.0 weight percent Ta addition followed by ageing at 700℃ for 2 hours increases recovery ratio up to 16 percent. Precipitate particles such as TaC and χ were found in the aged samples with different size and distribution in the γ matrix. Mechanisms of improving SME by Ta addition are proposed in the work: Solid solution and precipitation strengthening on the γ matrix, grain refining of γ parent phase, domain effect of precipitate particles, and increasing of stacking fault probability.