奈米沉積在形狀記憶上的影響和 富含鎳的NiTiHf高溫形狀記憶合金的材料性能

Abstract

1. 目的：了解奈米沉積在形狀記憶上的影響以及富含鎳的 NiTiHf 高溫形狀記憶合金的材料性能。 2. 過程及方法：○1使用石墨坩堝將Ni50.3Ti29.7Hf20合金感應熔化 ○2鑄錠在1050℃ 下均質 ○3使用低速旋轉鋸切下試片，並使用箱式爐在不同時間溫度下時效 ○4使用放電加工機切割壓縮試片 ○5使用差示掃描量熱儀測定TTs ○6在X光繞射儀中進行X射線繞射（XRD） ○7使用液壓高頻疲勞動態材料測試機框架和定置壓縮夾具進行 ○8使用高溫延伸計測量軸向應變 ○9使用穿透式電子顯微鏡進行材料的微觀結構分析。對試片進行機械拋光， 然後在維氏顯微硬度測試儀中使用100g負重在室溫下進行測量 3. 結果：○1時效可以用來定制TTs ○2熱處理可用於改變析出物的尺寸和整合，進而可影響所得麻田散鐵相的形 態，並且這兩個因素直接影響富含鎳的 Ni50.3Ti29.7Hf20 的形狀記憶和機械性能 ○3在 550℃ 時效 3h ，顯著改善了 Ni50.3Ti29.7Hf20 形狀記憶合金的機械性能 ○4因為過時效的原因，大析出物表現出相對較差的形狀記憶和超彈性特性

In this study the effects of various heat treatments on the shape memory properties of a polycrystalline Ni50.3Ti29.7-Hf20 alloy were investigated. The main findings can be summarized as follows. Aging can be used to tailor the TTs. Thermal treatments can be used to alter the size and coherency of the precipitates, which in turn can affect the morphology of the resulting martensite phase, and both factors directly influence the shape memory and mechanical properties of the Ni-rich Ni50.3Ti29.7Hf20. In particular, it was found that aging for 3 h at 550℃ resulted in large martensitic plates with no internal twins. The alloy aged for 3 h at 650℃ exhibited higher TTs than those of the as-extruded and the 550℃/3 h aged conditions. However, it exhibited relatively poor shape memory and superelastic properties due to a large precipitate size as a consequence of overaging. Aging increased the work output significantly due to the improvement in the transformation strain.