Ta至HfNbTaTiZr等莫耳體心立方系列合金巨觀機械性質之研究

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研究生：	顧瑜 Ku, Yu
論文名稱：	Ta至HfNbTaTiZr等莫耳體心立方系列合金巨觀機械性質之研究 Study on Macro-scale Mechanical Properties of Body-centered Cubic Equimolar Alloys from Ta to HfNbTaTiZr
指導教授：	林樹均 Lin, Su-Jien
口試委員:	張守一 Chang, Shou-Yi 洪健龍 Hong, Jian-Long 李勝隆 Lee, Sheng-Long
學位類別：	碩士 Master
系所名稱：	工學院 - 材料科學工程學系 Materials Science and Engineering
論文出版年：	2020
畢業學年度：	107
語文別：	中文
論文頁數：	146
中文關鍵詞：	高熵合金、耐火高熵合金、機械性質、高溫拉伸
外文關鍵詞：	High-entopy Alloys, Refractory High Entropy Alloys, Mechanical Properties, High-temperature Tensile Test
相關次數：	點閱：3 下載：0
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本研究旨在針對含有不同元素數目等原子比的BCC系列合金之巨觀性質進行研究，目的為觀察合金從低熵到高熵的變化趨勢，探討高熵固溶、遲緩擴散、晶格扭曲及雞尾酒共四大核心效應在多主元素合金中，對機械性質的影響與具體表現。2011年首次發表的BCC耐火高熵合金HfNbTaTiZr因為在室溫壓縮試驗中同時具有良好的強度與極佳的延展性而受到注目，雖然其理論熔點較低導致高溫表現普通，但仍為極有代表性的耐火高熵合金之一，故選擇以此合金做為高熵性質的研究主體。設計Ta至HfNbTaTiZr，一元至五元等莫耳的系列合金，除為維持合金均為單一BCC結構，添加元素順序安排熔點由高至低，命名為1B到5B，均進行相同的製程與測試以作為對照。以真空電弧融煉製備系列合金之長條鑄錠後，在室溫下冷輥軋至厚度縮減量70%，而後封於真空石英封管中，在700度至1300度每間隔50度進行退火處理，皆持溫一小時，以水淬冷卻，並進行金相觀察、硬度測試、結構分析、掃描式電子顯微鏡分析與常溫至高溫的拉伸測試。研究結果顯示，增加元素種類後有明顯固溶強化效應，3B至5B鑄造硬度均大於300 HV。再結晶溫度隨著元素數目增加有先升後降的趨勢，應是增加其他元素提高了擴散阻礙以及降低整體熔點增進擴散能力兩者的影響。4B與5B在中溫區間退火後有析出的情形，但在更高的溫度熱處理後合金就呈現單相，為高熵效應可降低自由能、穩定固溶相的展現。在常溫及高溫拉伸中，系列合金的降伏強度均隨溫度提高而下降，5B則因具有遲緩擴散效應與高熵效應，在除了常溫以外的測試中，強度數值均為系列合金中最高，高溫與常溫的降伏強度比值亦為最高。系列合金隨溫度提高後的延展性趨勢為先降後升，推測延性下降原因在低熵系統中應為動態應變時效，中熵及高熵系統中則推測是因為原子重排形成結構短程有序及析出。到800度延性提升則可能是因為發生了動態再結晶。本研究中首次對耐火高熵合金HfNbTaTiZr成功地進行了多個溫度在大氣環境中的高溫拉伸試驗，亦對合金高熵化後巨觀的物理與機械性質有了初步的分析，未來以本研究成果為基礎，藉由更精密之儀器與不同條件可深入探討多主元素之合金在高溫變形時與傳統合金機制的差異。

High-entropy alloys (HEAs) consist of five or more principle elements, creating a new era of metallic materials other than conventional alloys. Four core effects including high entropy-caused solid-solution formation, sluggish diffusion, lattice distortion and cocktail effect assist HEAs in demonstrating several superior properties. Refractory high alloy is a subclass of HEAs, and has been viewed as a promising candidate for replacing advanced Ni-based superalloy in aerospace and elevated-temperature application. Among them, single-phase body-centered cubic (BCC) HfNbTaTiZr possesses good strength and excellent ductility in uniaxial compression test at room temperature, and thus has drawn great attention since publication. Most of the recent researches on HEAs focus mainly on alloy design and fabrication. There is still very limited research on the deformation mechanism of them.
The objective of this research is to investigate the difference between low-entropy system and high-entropy one in mechanical properties and their evolution in macro-scale mechanical tests. A series of alloy were designed and investigated in this research, from one component to five with each element in equimolar chemical composition. The alloy ingots were prepared by vacuum arc-melting, and then cold rolled to thickness reduction 70%. Subsequent heat treatment with annealing temperature ranging from 700 C to 1300 C for 1 hour followed by water quenching were conducted. Analysis includes metallurgic observation, hardness test, crystal structure and electronic microscopy. Tensile tests at room temperature, 400 C, 600 C and 800 C were performed in air. Pronounced solid solution strengthening phenomenon had shown while the number of elements in the system increased. Alloy composed of more than four elements would precipitate at intermediate temperatures, and become single phase at higher temperatures, which further confirm high-entropy effect. In tensile tests, the yield strength of BCC-series alloys decreased with rising temperature. HfNbTaTiZr with highest configurational entropy had the highest yield strength values in all elevated-temperature tests, suggesting the sluggish diffusion effect and high entropy effect could enable the structure to be more stable than low entropy system.

摘要    I
Abstract    III
致謝    V
目錄    VII
圖目錄    XII
表目錄    XXI
壹、    前言    1
貳、    文獻回顧    4
1 高熵合金High-entropy Alloys    4
1.1. 高熵效應    5
1.2. 晶格扭曲效應    6
1.3. 遲緩擴散效應    8
1.4. 雞尾酒效應    10
2 HfNbTaTiZr高熵合金    14
2.1. 耐火高熵合金    14
2.2. 基本特性    15
2.3. 析出現象    18
2.4. 織構    24
2.5. 機械性質    26
參、    實驗方法    33
1 合金製備及實驗流程    33
1.1. 合金設計    33
1.2. 實驗流程    35
1.3. 真空電弧融煉    36
1.4. 輥軋    37
1.5. 熱處理    38
2 X-Ray 繞射分析    39
3 微結構觀察    40
3.1. 光學顯微鏡    40
3.2. 掃描式電子顯微鏡    41
4 硬度測試    42
5 常溫及高溫拉伸試驗    42
肆、    結果與討論    44
1 鑄造態及輥軋態分析    44
1.1. 硬度    44
1.2. SEM與成分分析    46
1.2.1. 2B    46
1.2.2. 3B    48
1.2.3. 4B    50
1.2.4. 5B    52
1.3. XRD結構分析    54
1.3.1. 鑄造態    54
1.3.2. 輥軋態    56
2 退火態分析    57
2.1. 1B    57
2.1.1. 金相觀察    57
2.1.2. 退火硬度    60
2.2. 2B    61
2.2.1. 金相觀察    61
2.2.2. 退火硬度    63
2.3. 3B    64
2.3.1. 金相觀察    64
2.3.2. 退火硬度    67
2.4. 4B    68
2.4.1. 金相觀察    68
2.4.2. 退火硬度    71
2.4.3. XRD分析    72
2.4.4. SEM觀察    74
2.5. 5B    79
2.5.1. 金相觀察    79
2.5.2. 退火硬度    82
2.5.3. XRD分析    83
2.5.4. SEM觀察    84
2.6. 綜合分析    87
3 拉伸試驗    90
3.1. 常溫拉伸    90
3.2. 400 C拉伸    95
3.3. 600 C拉伸    98
3.4. 800 C拉伸    101
3.5. 綜合分析    103
3.6. 破裂面分析    116
3.6.1. 1B    116
3.6.2. 2B    119
3.6.3. 4B    122
3.6.4. 5B    124
伍、    結論    128
陸、    研究貢獻與建議未來研究工作    131
1 研究貢獻    131
2 建議未來研究工作    131
柒、    參考資料    133
捌、    部分其餘實驗結果    141
1 5B    141
2 4B    145


                                

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