本研究主要以積層製造技術-擇區雷射熔融法(Selective Laser Melting, SLM)製作碳化鎢超硬合金(WC-based Cemented Carbide)並針對其材料特性進行深入分析與研討。本研究可分為三部分，分別為擇區雷射熔融法製作鑄造型碳化鎢WC/W2C、鍍鎳鑄造型碳化鎢WC/W2C-8.3 wt.% Ni超硬合金微結構分析與抗磨耗測試、擇區雷射熔融製程對WC/W2C-20 wt.% NiAlCoCrCuFe超硬合金之微結構與機械性質分析，以及運用於擇區雷射熔融製程合金粉末之回收再使用機制研究。
在第一部份研究中，我們以擇區雷射熔融製成結合優化之雷射參數製作含高比例碳化鎢相之超硬合金，並詳細分析其微結構特徵，高能量密度之雷射參數引致之複雜微結構特徵包含：部分熔融之碳化鎢、再析出之碳化物以及碳化物之樹枝狀微結構；透過XRD, SEM, EBSD, TEM等分析方法，鑑定出四個主要的相，包含MC, M2C, FCC 以及 η-碳化物(M6C)。我們運用CALPHAD-based Thermo-Calc相圖模擬軟體建構相圖，並嘗試闡明在擇區雷射熔融製程中各分相的生成次序。我們發現，即使原始成分相對簡單，擇區雷射熔融製程會將碳化鎢分解並引致複雜樹枝狀微結構生成與碳化物再析出。
在第二部份研究中，我們將材料系統替換成了含有高熵合金金屬黏結相之WC/W2C-20 wt.% NiAlCoCrCuFe，並以最佳化之製程參數於INVAR合金基板上製作高緻密度之超硬合金樣品。針對樣品截面進行微結構、成分與機械性質之分析，發現其沿著積層方向(building direction, z-axis)之微結構梯度與成分梯度可歸因於底板成分之交互擴散與較低熔點合金黏結相成分之汽化。在樣品的下半部(接近底板位置)，可發現金屬黏結相形成顯著之成分梯度伴隨著大量的η-碳化物(M6C)生成。在樣品的上半部，金屬黏結相的成分梯度變化趨緩，並有WC, W2C, FCC 以及 η-碳化物(M6C)較均勻的分布及析出。針對機械性質表現部分，樣品下半部因其較高比例之金屬黏結相而導致較低的維氏硬度，介於711.7 HV1 (樣品底部) 至1178.6 HV1 (距離底板表面高1 mm位置)；而樣品上半部的維氏硬度受較低比例金屬黏結相之影響而提升，介於1306.8 HV1 至 1413.4 HV1 以及破裂韌性表現介於9.74 MPa m1/2 至 13.29 MPa m1/2。
在第三部分中，我們針對運用於SLM積層製造中的IN718合金粉末之回收篩選再利用機制進行研討。粉末可回收再使用為SLM製程之特性與優勢，與傳統減法製程相比，可降低大量材料端之成本。在積層製造中，粉末受雷射影響之狀態並不均一，而粉末性質為影響製品品質的直接因素之一，因此必須建立一套回收粉之篩選機制以確保製品性質。本研究首先制定一套標準積層製造流程，包含SLM積層製造塊材樣品，以及使用過粉末(舊粉)之回收篩選分級。使用固定之SLM製程參數條件製作塊材樣品，同時產生舊粉以進行回收。我們使用同一批IN718粉末重複此標準流程共5批次，過程中並無加入新粉。針對各批次回收粉之基本性質，包含流動性、粒徑分布與化學成分，進行分析與監測。以積層製作之塊材樣品進行相同條件之熱處理，並以室溫之機械性質(降伏強度、抗拉強度、延伸率)作為判斷回收粉末再利用性之依據。我們發現，經過五次粉末回收篩選再利用之流程，經嚴格控管粉末之基本性質(流動性、粒徑分布與化學成分)，均可控制如原始粉末之性質，接著，將各批次製作之塊材樣品進行室溫拉伸測試並互相比較，可得具有高度一致性、高度再現性之室溫拉伸性質。

This research presents detailed characterization of cemented carbide material system fabricated by selective laser melting process.
In the first part, cast tungsten carbide powders (WC/W2C) and Ni-coated cast tungsten carbide powders (WC/W2C-8.3wt.%Ni) were used. The selective laser melting process induced complex microstructure consisting of partially-melted carbide, carbide precipitates and dendritic microstructure. Four phases were identified, i.e. WC, W2C, FCC and -carbide in the as-built specimen. CALPHAD phase diagram was utilized to describe possible phase formation sequence during selective laser melting process, which involved melting, solidification and repeated heating. Although the composition of initial powder was very simple (spherical WC/W2C and Ni), selective laser melting allowed the decomposition of initial carbides, subsequent formation of dendritic structure and precipitation of additional carbides.
In the second part, the characterization focused on the influence of selective laser melting (SLM) process on microstructure and property of a cemented carbide system combining with high entropy alloy binders. Analysis along the building direction indicated variation of chemical composition and microstructure, and this was influenced by two effects, firstly the dilution effect due to elemental diffusion from the baseplate and secondly the elements evaporation caused by high-power laser. At the lower half of the specimen, high fraction of η-carbide formed near the level of baseplate, and there were chemical gradients of major binder elements along the building direction. At the upper half of the specimen, there were relatively less variation in chemical composition and more homogeneously distributed phases including WC, W2C, η-carbide and FCC metal binder. The hardness of the lower half specimen varied from 711.7 HV1 (bottom of the specimen) to 1178.6 HV1 at 1 mm height. For the upper half of the specimen, hardness values could range from 1306.8 HV1 to 1413.4 HV1 and fracture toughness varied from 9.74 MPa m1/2 to 13.29 MPa m1/2.
In the third part, the mechanism of recycling and reuse of alloy powders for SLM process has been investigated. For the powder-bed SLM process, the reuse of powder materials is beneficial for saving the manufacturing cost on raw materials; however, powders are heterogeneously-affected by either the laser beam or the other process settings. The properties of the used and recycled powders, which directly influence the properties of the built object, can be different from the virgin powders. Thus, a reliable mechanism for recycling and sieving the used powders should be validated. In this research, a batch of IN718 alloy powder had gone through a series of standard process, including fabrication of bulk specimens by SLM process and recycling/sieving of the used powders for five cycles without the addition of fresh powders. The used powders were then sieved and graded by powder size. The powder size distribution, Carr’s compressibility index and chemical composition were the target properties to be analyzed. Specimens for room temperature tensile test were cut from the heat-treated SLM IN718 bars, and the tensile mechanical properties were used as a guide for the quality-control of the recycled powders. For the 5 batches of recycled powders, the powder size distribution can be controlled by properly sieving; the Carr’s compressibility indices remained lower than 15 % and ensured a high quality of the powder bed; furthermore, the chemical compositions were similar to the virgin powders and within the commercial regulation. As a result, we obtained highly-consistent tensile properties for IN718 alloy made from different batches of recycled powders.

摘 要 I
Abstract III
誌 謝 V
Table of Contents VII
List of Tables IX
List of Figures XI
1. Background 1
2. Literature Review 2
2.1 Additive Manufacturing Process and Selective Laser Sintering/Melting Process 2
2.2 Manufacturing and Applications of Cemented Carbide 4
2.3 Alternative Metallic Binder Phase for Cemented Carbide 7
2.4 The Development of Cemented Carbide Fabricated by SLS/SLM Processes 11
3. Research Scope 13
4. Results and Discussion 14
4.1 Microstructure Characterization of Cemented Carbide Fabricated by Selective Laser Melting Process 14
4.2 On the Microstructure and Properties of an Advanced Cemented Carbide System Processed by Selective Laser Melting 48
4.3 On the Investigation of Recycling and Reuse of Alloy Powder for Selective Laser Melting Process 83
5. Conclusion 102
6. Future Topics 105
Reference 106

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