臺灣博碩士論文加值系統

鈦合金具有高比強度、低彈性模量及良好的耐腐蝕性與優異的生物相容性等傑出性質，被廣泛應用於航空航太、汽車工業以及生物醫學領域。而近年來，相關研究添加不同β穩定元素的鈦合金，例如鈮和鉬，藉以開發具有較低彈性模數，以及更好生物相容性的低成本β型鈦合金。另一方面，目前中熵合金及高熵合金的製程多以電弧熔煉法為主，需耗費較多的能源且成本較高，在過程中容易因為元素的熔點、密度差異造成組織不均勻。因此近期開始研究以粉末冶金法製備，這是一種能製造具有複雜形狀的高質量鈦合金零件之經濟高效製程，其作為一種近淨成形技術，能夠降低生產成本、提升組織均勻性及減少材料浪費。
本研究以粉末冶金法製備鈦鈮鉬中熵合金，第一階段使用鈦粉、鈮粉、鉬粉與鎳粉四種純金屬粉末，配製成Ti-25Nb-25Mo-5Ni、Ti-25Nb-25Mo-10Ni、Ti-25Nb-25Mo-15Ni和Ti-25Nb-25Mo-20Ni 四種不同成分之中熵合金，於1175°C、1200°C和1225°C之溫度下進行真空燒結，並持溫一小時。而第二階段是以第一階段之最佳參數的鈦鈮鉬鎳中熵合金，分別加入1、3與5 wt%的碳化鉻微粉，並於1150°C、1175°C、1200°C和1225°C之溫度下進行真空燒結，持溫一小時。燒結完成之試片會進行體收縮率、視孔隙率、硬度、橫向破裂強度(TRS)及撓曲模數的測量與試驗來評估中熵合金的機械性質。並使用掃描式電子顯微鏡(SEM)、X光繞射(XRD)和光學顯微鏡(OM)進行顯微組織的觀察，並且會對第二階段綜合性質最佳之參數的Ti-25Nb-25Mo-15Ni-1Cr3C2複合材料，使用場發射電子微探儀(FE-EPMA)進行更進一步的顯微組織分析。
第一階段實驗結果顯示，燒結溫度為1225°C之Ti-25Nb-25Mo-15Ni中熵合金具有最佳之綜合性質，其體收縮率為30.55%，視孔隙率1.10%、硬度72.9 HRA、橫向破裂強度607.36 MPa以及撓曲模數54.9 GPa。因此，本研究第二階段選擇Ti-25Nb-25Mo-15Ni中熵合金添加Cr3C2微粉進行第二階段的後續分析；研究結果顯示，燒結溫度為1225°C之添加1 wt% Cr3C2的Ti-25Nb-25Mo-15Ni-1Cr3C2複合材料具有最佳之綜合性質，其體收縮率34.71%、視孔隙率0.17%、硬度75.88 HRA、橫向破裂強度為684.23 MPa以及撓曲模數69.64 GPa。研究結果亦顯示鈮、鉬及鉻能與鈦形成良好之固溶體，達成固溶強化之效果，同時鎳會與鈦生成TiNi及Ti2Ni金屬間化合物，散佈在基地中阻礙差排滑移，有效提升其機械性質。

Due to the high specific strength, low elastic modulus, good corrosion resistance, and superior biocompatibility, titanium alloys have been extensively used in aerospace, automotive industries, and biomedicine. In recent years, several Ti alloys with different β stabilizing elements, e.g., Nb and Mo, were studied to develop low-cost β-Ti alloys with lower Young's modulus and better biocompatibility. On the other hand, the process of producing medium entropy alloys and high entropy alloys is primarily vacuum arc remelting, which requires more energy and higher costs. In the process, inhomogeneous microstructures may occur due to differences in melting points and densities of the elements. As a result, studies have recently begun using powder metallurgy to produce these alloys, which is a cost- effective manufacturing method for high quality Ti alloy parts with complex shapes. As a near-net-shape technique, it reduces production costs, improves microstructural homogeneity, and minimizes material waste.
This study fabricated Ti-Nb-Mo medium entropy alloy by powder metallurgy. In the first part of this study, four different metal powders (Ti, Nb, Mo and Ni) were uniformly mixed and used to produce four different proportions medium entropy alloys: Ti-25Nb-25Mo-5Ni, Ti-25Nb-25Mo-10Ni, Ti-25Nb-25Mo-15Ni and Ti-25Nb-25Mo-20Ni. Furthermore, Ti-based medium entropy alloys were vacuum sintered at temperatures of 1175°C, 1200°C, and 1225°C for 1 h. In the second part of this study, the Ti-Nb-Mo-Ni medium entropy alloy with the optimal parameters from the first part was mixed with 1, 3, and 5 wt% of Cr3C2 powder, and vacuum sintered at temperatures of 1150°C, 1175°C, 1200°C, and 1225°C for 1 h, respectively. Then, the mechanical properties of the Ti-25Nb-25Mo-15Ni-1Cr3C2 composites were evaluated by measuring the volume shrinkage, porosity, hardness, TRS, and flexural modulus. Finally, the microstructures were examined with SEM, XRD, OM, and FE-EPMA to analyze the microstructures of the optimal sintered parameters of the second part.
The first part of the experimental results showed that the Ti-25Nb-25Mo-15Ni medium entropy alloys sintered at 1225°C for 1 h had the best overall properties, with volume shrinkage 30.55%, porosity 1.10%, hardness 72.9 HRA, TRS 607.36 MPa, and flexural modulus of 54.9 GPa. Accordingly, for the second part of this study, Ti-25Nb-25Mo-15Ni was selected with Cr3C2 powder added for further analysis. The results showed that Ti-25Nb- 25Mo-15Ni-1Cr3C2 composites with 1 wt% Cr3C2 added and sintered at 1225°C had the best overall properties, with volume shrinkage 34.71%, porosity 0.17%, hardness 75.88 HRA, TRS 684.23 MPa, and flexural modulus of 69.64 GPa. The research results show that niobium, molybdenum, and chromium can form a good solid solution with titanium to achieve the solid-solution strengthening effect. Moreover, nickel can form TiNi and Ti2Ni intermetallic with titanium, which are dispersed in the titanium matrix and effectively enhance its mechanical properties.

摘 要 i
ABSTRACT iii
誌謝 v
目錄 vi
表目錄 ix
圖目錄 xi
第一章 緒論 1
1.1 前言 1
1.2 研究目的與動機 2
第二章 文獻回顧 3
2.1 高熵合金 3
2.1.1 高熵合金簡介 3
2.1.2 高熵合金之四大效應 4
2.2 鈦及鈦合金 6
2.2.1 鈦合金的特性 7
2.2.2 鈦合金的分類 9
2.3 鈦合金內元素及碳化物之作用 13
2.3.1. 鈮(Niobium, Nb) 13
2.3.2. 鉬(Molybdenum, Mo) 14
2.3.3. 鎳(Nickel, Ni) 14
2.3.4. 碳化鉻(Chromium Carbide, Cr3C2) 15
2.4 粉末冶金(Powder Metallurgy, PM) 16
2.4.1 燒結原理 16
2.4.2 液相燒結(Liquid Phase Sintering) 17
2.4.3 反應燒結 18
2.5 強化機制 19
2.5.1 固溶強化(Solid Solution Strengthening) 19
2.5.2 細晶強化(Fine Grain Size) 21
2.5.3 析出強化(Precipitation Strangthening) 22
2.5.4 散佈強化(Dispersion Strengthening) 22
第三章 實驗流程與研究方法 23
3.1 實驗步驟與流程 23
3.1.1 粉末配製 24
3.1.2 混合粉末 24
3.1.3 成形 25
3.1.4 真空燒結 26
3.2 材料分析 27
3.2.1 雷射粒徑分析 27
3.2.2 結構組織分析 28
3.2.3 材料性質分析 33
第四章 結果與討論 36
4.1 分析粉末形貌與粒徑大小 36
4.1.1 基材粉末分析 36
4.1.2 混合後之Ti-25Nb-25Mo-xNi粉末 38
4.1.3 混合後之Ti-25Nb-25Mo-15Ni-xCr3C2粉末 38
4.2 鈦鈮鉬鎳中熵合金性質 39
4.2.1 燒結性質分析 39
4.2.2 顯微組織分析 42
4.2.3 機械性質分析 54
4.2.4 腐蝕特性分析 59
4.2.5 Ti-25Nb-25Mo-xNi中熵合金性質之小結 60
4.3 鈦鈮鉬鎳合金添加Cr3C2後之性質 61
4.3.1 分析添加Cr3C2後之燒結性質 61
4.3.2 分析添加Cr3C2後之顯微組織 64
4.3.3 分析添加Cr3C2後之機械性質 76
4.3.4 分析添加Cr3C2後之腐蝕特性 82
4.3.5 分析添加Cr3C2後之相組成與微結構 83
第五章 結論 92
參考文獻 94

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