鐵-8.0鋁-28.5錳-(5,10)鉻合金相變化

Abstract

在本論文中，我們利用穿透式電子顯微鏡以及X光能量散佈分析儀研究在鐵- 8.0鋁-28.5錳合金中添加 5.0和10.0鉻的相變化。在淬火狀態下，添加5.0鉻的合金中，其顯微結構為沃斯田鐵和肥粒鐵之雙相，而添加10.0鉻的合金之淬火顯微結構為單一肥粒鐵相。將合金做時效處理，在沃斯田鐵基地中均無析出物，而在肥粒鐵基地中隨著不同時效溫度會有不同析出物產生。當此二合金在350℃至450℃之間做時效處理時，規律的D03和A12 α-錳相皆可在肥粒鐵基地中被發現。除此之外，在高溫時效後，A13 b-錳析出物亦可在兩合金中被觀察到。在這二個合金中，發現隨著時效溫度的增加，在肥粒鐵相內之相變化均為 (α + A12 α-Mn + D03) → (α + A12 α-Mn) → (α + A13 β-Mn) → α 。 儘管這兩個合金的顯微結構變化順序是一樣的，但是由實驗結果可清楚知道，隨著鉻含量的增加，D03和A12 α-錳相皆可存在至更高的溫度。

Phase transformations in Fe- 8.0 wt. % Al -28.5 wt. % Mn alloy with 5.0 and 10.0 wt. % Cr have been investigated by means of optical microscopy, scanning transmission electron microscopy and energy-dispersive X-ray spectrometey. In the as-quenched condition, the microstructure in the Fe- 8.0 wt. % Al- 28.5 wt. % Mn-5.0 wt. % Cr alloy was a (ferrite) + g (austenite) duplex phases and only single a phase could be found in the Fe- 8.0 wt. % Al- 28.5 wt. % Mn-10.0 wt. % Cr alloy. When the Fe- 8.0 wt. % Al- 28.5 wt. % Mn-5.0 wt. % Cr alloy was aged at various temperatures, no precipitates could be found within the austenite matrix. However, different kinds of precipitates could be formed within the ferrite grains with increasing the aging temperature. When both alloys were aged at temperatures ranging from 350°C to 450℃, both ordered D03 and A12 α-Mn phases could be observed within the ferrite matrix. In addition to the D03 and A12 a-Mn phases, A13 b-Mn precipitates could also be found in both alloys aged at higher temperatures. In these two alloys, the phase transformation sequences in the ferrite grains as the aging temperature increased were found to be (α + A12 α-Mn + D03) → (α + A12 α-Mn) → (α + A13 β-Mn) → α. In spite of having the same microstructural developments in these two alloys, experimental results indicated that the existing temperatures of both the D03 and A12 a-Mn phases were increased with increasing the Cr content.