鐵基塊狀金屬玻璃熱塑成形性之研究;The study of thermoplastic forming ability on Fe-based bulk metallic glass

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Title:	鐵基塊狀金屬玻璃熱塑成形性之研究;The study of thermoplastic forming ability on Fe-based bulk metallic glass
Authors:	李鎮谷;Li,Chen-Ku
Contributors:	材料科學與工程研究所
Keywords:	鐵基非晶質合金;過冷液相區;熱塑成形;Bulk amorphous steel;Supercooled liquid region;Thermoplastic forming
Date:	2016-07-25
Issue Date:	2016-10-13 13:22:51 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究使用真空電弧熔煉結合真空吸鑄法製備Fe41Cr15Mo14C12B9Co7Y2合金，經由X光繞射與示差掃瞄熱分析結果初步判定為非晶結構，進一步由DSC的分析可得知其玻璃形成能力指標Trg為0.59、γ為0.4、γm為0.69，且其過冷液相區(ΔTx)為74 K。為了進一步了解鐵基非晶質合金的熱塑形成能力，使用熱機械分析儀測量於過冷液相區，觀察樣品隨著溫度變化所產生的形狀變化，得知鐵基非晶質合金熱塑變形軟化點為903 K，鐵基非晶質合金的黏滯流黏度隨溫度與應變速率上升均呈現下降趨勢。依據示差掃瞄熱分析與熱機械分析儀分析結果，在不同溫度(873 K、883 K、893 K與903 K)、不同應變速率下(5x10-2 s-1~1x10-3 s-1)下針對2 mm鐵基非晶質棒材進行壓縮測試，進一步探討在過冷液相區之變形行為。結果顯示，同溫度下，隨著應變速率上升、流變應力隨之增加；再者，當應變速率高於5x10-2 s-1時，所有試片於測試後均破裂。由於鐵基非晶質合金軟化點相對溫度較高，所需的升溫時間較長，鐵基非晶質合金內部開始產生結晶現象，因此當應變速率太低時會導致試片有硬化現象。綜觀加工溫度與應變速率工作窗，最佳熱塑成形加工條件為加工溫度873 K，應變速率2.5x10-3 s-1。 ;A Fe-based bulk amorphous steel (BAS), Fe41Cr15Mo14C12B9Co7Y2, was successfully fabricated by suction casting and confirmed its amorphous state by X-ray diffraction and differential scanning calorimetry analysis. The Tg, Tx, γ, γm and ΔT are 832 K, 906 K, 0.4, 0.69, and 74 K, respectively. The thermoplastic deformation during supercooled liquid region was firstly investigated by thermal mechanical analysis (TMA). TMA results reveal that the viscosity decreases with increasing temperature under the same strain rate and no specimen is deformable under the strain rate of 5x10-2 s-1 or higher. Based on the TMA results, the lowest viscosity is about 5x1010 Pa‧s. The thermoplastic deformation behavior of Fe-based BAS was investigated at different temperatures within the supercooled temperature region (namely 873 K, 883 K, 893 K, 903 K) with different strain rate (5x10-2 s-1~1x10-3s-1). The Fe-based BAS only exhibits Newtonian flow at lower strain rate (less than 5x10-3 s-1 at 873 K~883 K, and less than 7.5x10-3 s-1 at 893 K~903 K). Moreover, the Fe-based BAS was fractured during thermoplastic forming process at strain rate higher than 5x10-2 s-1. TEM analysis were carry out for further investigating the amorphous state of the as cast sample and the sample after thermoplastic forming. The Fe-based BAS sample after thermoplastic forming at 903 K with 2.5x10-3 s-1 strain rate was found to have some nano-size crystalline particles embedded locally in amorphous matrix.
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