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標題: | 三元至五元FCC結構中/高熵合金Hall-Petch關係與晶粒成長之研究 A study on Hall-Petch relationship and grain growth of ternary to quinary FCC-structured medium/high entropy alloys |
作者: | Che-Hsuan Su 蘇哲萱 |
指導教授: | 吳錫侃 |
關鍵字: | 中/高熵合金,Hall-Petch關係,微硬度值,晶粒成長指數,晶粒成長活化能, Medium / High entropy alloys,Hall-Petch relationship,Hardness,Grain growth exponent,Activation energy of grain growth, |
出版年 : | 2018 |
學位: | 碩士 |
摘要: | 本文探討六種中/高熵合金FeCoNiCrMn、FeCoNiCrPd、FeCoNiCr、FeCoNiMn、CoNiCr以及CoNiMn經80%冷軋延後在不同的退火溫度及時間下之再結晶行為及晶粒成長特性。由各合金的δ、∆H_mix、VEC值以及XRD量測皆顯示此六種合金為單一FCC相的結構。再結晶後合金的硬度值會隨著晶粒大小的增加而下降並符合Hall-Petch關係式Hv=H0+KHd-1/2,其中KH值以三元的CoNiCr為最大,五元的FeCoNiCrPd為最小,此因後者之疊差能最大與剪力模數最小所致。又只經80%冷軋延的合金表面硬度,以CoNiCr為最硬,這顯示在中/高熵合金中,固溶硬化的程度並不會因為所添加的合金元素數的增加而上升,反而是與所添加的元素種類較相關。本文也對此六種80%冷軋延之合金做不同條件的退火處理以觀察其晶粒成長行為,發現晶粒成長指數1/n值在FeCoNiCrPd合金約為3.5,CoNiMn、FeCoNiCr、FeCoNiCrMn合金的1/n值接近於2.8,CoNiCr及FeCoNiMn合金的1/n值接近於2.9,此等1/n值皆大於純金屬的2。而晶粒成長的活化能則以FeCoNiCrPd合金最大,為831.9kJ/mol,CoNiMn合金最小,為325.1kJ/mol,但此等值也都比傳統合金高出甚多,顯示中/高熵合金之晶界移動易受溶質拖曳效應及緩慢擴散因素等的影響;此外,合金元素的自行擴散所需活化能的大小也會造成上述晶粒成長活化能的差異。 In this study, recrystallization behavior and grain growth characteristics of homogenized and 80% cold-rolled FeCoNiCrMn、FeCoNiCrPd、FeCoNiCr、FeCoNiMn、CoNiCr and CoNiMn multi-component equiatomic medium / high entropy alloys(MEAs/HEAs) heated at different annealing time and temperature are investigated. The values of δ、∆H_mix and VEC in these six alloys all indicate the formation of single-phase FCC structure. The hardness of recrystallized alloys decreases as the grain size increases, and obeys the Hall-Patch equation, Hv=H0+KHd-1/2. The ternary CoNiCr alloy has the highest KH value, whereas the quinary FeCoNiCrPd alloy has the lowest one. This phenomenum is caused by the largest stacking fault energy and smallest shear modulus exhibited in FeCoNiCrPd alloy. After 80% cold rolling, the surface hardness of the ternary CoNiCr alloy is hardest, indicating that solid solution hardening in MEAs/HEAs is not determined by the number of soluted elements but by the kind of the element. Furthermore, all six alloys have the grain growth exponents 1/n higher than 2 with FeCoNiCrPd alloy having the highest activation energy of grain growth, say 831.9kJ/mol which is much higher than that in the conventional alloys. This characteristic suggests that the effects of the solute drag and the sluggish diffusion control the grain boundary motion. Moreover, the self-diffusion activation energy of the element exhibited in the alloy also affects the MEAs/HEAs activation energy of grain growth. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/69367 |
DOI: | 10.6342/NTU201801426 |
全文授權: | 有償授權 |
顯示於系所單位: | 材料科學與工程學系 |
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