硬質合金是一種非常廣泛使用的粉末冶金產品，常使用在需要高磨耗以及硬度的產品上，例如做為金屬切削的刀具材料，然而傳統的粉末冶金製程會面臨一些問題，其製程步驟複雜且耗時，因而近期許多的研究都將此材料應用於雷射熔融積層製造上，而本研究主要是針對雷射參數對於材料巨觀結構(試片緻密度與表面品質)，微觀相組成與機械性質的影響，以及在選定好適當的雷射參數後對不同的三種硬質合金粉末經由雷射熔融積層製造後對其微結構與機械性質做分析， 因為雷射熔融積層製造中較高的冷卻速率以及雷射掃描的重複區域造成材料的微結構有相當大的影響，在製程中產生了一些脆性如W2C, M6C與石墨，而這些相的產生會對材料的性質造成一些不好的影響，因此在本研究中透過熱處理、對原始粉末添加碳以及使用其他優化的掃描策略嘗試去改變其微結構，本研究也成功透過這些方法將W2C與石墨的量降低許多，也提升了WC在微結構中的比例。

Cemented carbide is a very widely used powder metallurgy product, often used in products that require high wear resistance and hardness, such as tool materials for metal cutting. However, traditional powder metallurgy processes face some problems, such as complicated and time consuming process steps. Therefore, many recent studies have applied this material on SLM process. This study is mainly discussed the influence of laser parameters on the microscopic structure (sample density and surface quality), phase composition and mechanical properties. Then after selecting the appropriate laser parameters, I try to analyze the microstructure and mechanical property of the cemented carbide with different compositions. Due to the extremely high cooling rate during the SLM process, some brittle phases such as W2C, M6C and graphite are formed. The generation of these phases can have some adverse effects on the properties of the material. Therefore, in this study, through heat treatment, adding carbon to the original powder, and other optimized scanning strategies were used to attempt to change its microstructure. This study successfully reduced the amount of W2C and graphite by these methods, and also increased the proportion of WC in the microstructure.

Abstract I
摘要 II
致謝 III
List of Figures VI
List of Tables X
1.Introduction 1
2.Literature review 2
2.1 Cemented carbide 2
2.2 Traditional liquid phase sintering process 4
2.3 Selective laser melting 5
2.4 Relationship between laser parameters and properties 7
2.5 Post heat-treatment 9
2.6 The influence of powder composition and particle size 12
3. Experiments 14
3.1 Experimental procedure 14
3.2 Powders 14
3.3 SLM machine setting 19
3.4 Laser parameters test 19
3.5 Sample preparation and optical metallography analysis 20
3.6 XRD analysis 21
3.7 Scanning electron microscope 21
3.8 Vicker Hardness test 21
3.9 Flexural strength test 21
3.10 Post-heat treatment 21
3.11 Optimization of laser strategy 22
3.12 Carbon addition 22
4. Results and Discussion 23
4.1 Laser parameter tests 23
4.2 The effect of different laser parameters 26
4.2.1 Influence of laser parameters on microscopic structure 26
4.2.2 Influence of laser parameters on phase composition 29
4.2.3 Influence of laser parameters on Vicker hardness and Co content 34
4.3 Microstructures of different powders 36
4.4 Mechanical properties of different powders 49
4.5 Effect of repeating scanning 50
4.6 Effect of heat treatment 52
4.7 Comparison of Vickers hardness after heat treatment 58
4.7 Flexural strength after furnace heat treatment 59
4.8 Carbon addition 60
5. Conclusions 62
6.References 64

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