選擇性雷射熔融技術是積層製造的一種，積層製造具有傳統製造無法取代的優勢，如生產週期短、材料利用率高、自由成形三維物件，於材料及產業應用越來越廣，特別是選擇性雷射熔融技術於製造金屬物件上有非常大的發展潛力。傳統實驗中多以嘗試錯誤法取得最佳化參數，但會耗費許多人力及成本，且無法掌握關鍵技術，若將實驗結合數值模擬，利用參數調控獲得變化趨勢，同樣可提供製程改善資訊且有效降低實驗成本，因此本研究將以實驗方法作為數值模擬與實驗的驗證橋樑。
本研究使用的材料為H13工具鋼，利用選擇性雷射熔融技術製作堆疊基礎的單條融道，實驗方法為選用單一製程參數以雷射熔化鋪於H13塊材上的H13金屬粉末，雷射路徑將形成融道。針對形成的融道量測其形貌尺寸，並使用SEM、EBSD分析，輔助觀察H13融道橫截面重融區的微觀結構，將實驗結果與數值模擬結果結合探討融道形成的過程。
實驗量測得重融區平均寬度為112.5 m，平均高度為32.6 m及平均深度為55 m，將製程參數提供數值模擬進行預測，取得良好形貌驗證。數值模擬指出融道形成的過程中，有機會發生材料蒸發現象，因此於微觀結構觀察到雷射直接作用區域的固液界面為外延成長。

關鍵字：選擇性雷射熔融、單條融道、微結構、外延成長

In this study, selective laser melting technique was used to produce a single track of H13 steel, where H13 powders were melted on H13 substrate using moving laser source. SEM and EBSD analysis techniques were employed to observe the morphology and the microstructure of the track cross-section in this single track.
The microstructure revealed two types of grain in the melted zone, one is fine grains and the other is coarse grains due to epitaxial growth. The formation of coarse grains occurred during the evaporation process. The results of microstructures were similar to these predicted by the numerical simulation. Furthermore, the heat affected zone was identified by the profile of the measured value of micro-hardness.

Key words: Selective laser melting, single track, microstructure, epitaxial growth.

參考文獻
1. 林得耀, 林敬智, 莊傳勝, 黃偉欽, 吳誌賢, 劉松河, 積層製造成形技術與應用. 工業材料雜誌, 2016. 357: p. 093-105.
2. C.Y. Yap, C.K. Chua, Z.L. Dong, Z.H. Liu, D.Q. Zhang, L.E. Loh, and S.L. Sing, Review of selective laser melting: Materials and applications. Applied Physics Reviews, 2015. 2: p. 041101.
3. W. Meiners, K. Wissenbach, and A. Gasser, Shaped body especially prototype or replacement part production. DE Patent, 1998. 19.
4. X. Zhou, K. Li, D. Zhang, X. Liu, J. Ma, W. Liu, and Z. Shen, Textures formed in a CoCrMo alloy by selective laser melting. Journal of Alloys and Compounds, 2015. 631: p. 153-164.
5. B. Song, X. Zhao, S. Li, C. Han, Q. Wei, S. Wen, J. Liu, and Y. Shi, Differences in microstructure and properties between selective laser melting and traditional manufacturing for fabrication of metal parts: A review. Frontiers of Mechanical Engineering, 2015. 10: p. 111-125.
6. R. Li, J. Liu, Y. Shi, L. Wang, and W. Jiang, Balling behavior of stainless steel and nickel powder during selective laser melting process. The International Journal of Advanced Manufacturing Technology, 2012. 59: p. 1025-1035.
7. N.W. Makoana, H. Moller, H. Burger, M. Tlotleng, and I. Yadroitsev, Evaluation of Single Tracks of 17-4ph Steel Manufactured at Different Power Densities and Scanning Speeds by Selective Laser Melting. South African Journal of Industrial Engineering, 2016. 27: p. 210-218.

8. I. Yadroitsev, A. Gusarov, I. Yadroitsava, and I. Smurov, Single track formation in selective laser melting of metal powders. Journal of Materials Processing Technology, 2010. 210: p. 1624-1631.
9. M. Khan and P. Dickens, Selective laser melting (SLM) of gold (Au). Rapid Prototyping Journal, 2012. 18: p. 81-94.
10. W. Di, Y. Yongqiang, S. Xubin, and C. Yonghua, Study on energy input and its influences on single-track,multi-track, and multi-layer in SLM. The International Journal of Advanced Manufacturing Technology, 2011. 58: p. 1189-1199.
11. I. Yadroitsev and I. Smurov, Surface Morphology in Selective Laser Melting of Metal Powders. Physics Procedia, 2011. 12: p. 264-270.
12. P. Laakso, T. Riipinen, A. Laukkanen, T. Andersson, A. Jokinen, A. Revuelta, and K. Ruusuvuori, Optimization and Simulation of SLM Process for High Density H13 Tool Steel Parts. Physics Procedia, 2016. 83: p. 26-35.
13. U. Scipioni Bertoli, A.J. Wolfer, M.J. Matthews, J.P.R. Delplanque, and J.M. Schoenung, On the limitations of Volumetric Energy Density as a design parameter for Selective Laser Melting. Materials & Design, 2017. 113: p. 331-340.
14. K. Kempen, B. Vrancken, L. Thijs, S. Buls, J. Van Humbeeck, and J.P. Kruth. Lowering thermal gradients in selective laser melting by pre-heating the baseplate. in Solid freeform fabrication symposium proceedings. 2013.
15. P. Mercelis and J.P. Kruth, Residual stresses in selective laser sintering and selective laser melting. Rapid Prototyping Journal, 2006. 12: p. 254-265.
16. M. Shiomi, K. Osakada, K. Nakamura, T. Yamashita, and F. Abe, Residual Stress within Metallic Model Made by Selective Laser Melting Process. CIRP Annals - Manufacturing Technology, 2004. 53: p. 195-198.
17. I. Yadroitsev, P. Krakhmalev, I. Yadroitsava, S. Johansson, and I. Smurov, Energy input effect on morphology and microstructure of selective laser melting single track from metallic powder. Journal of Materials Processing Technology, 2013. 213: p. 606-613.
18. P. Yuan, D. Gu, and D. Dai, Particulate migration behavior and its mechanism during selective laser melting of TiC reinforced Al matrix nanocomposites. Materials & Design, 2015. 82: p. 46-55.
19. A. Gusarov, I. Yadroitsev, P. Bertrand, and I. Smurov, Heat transfer modelling and stability analysis of selective laser melting. Applied Surface Science, 2007. 254: p. 975-979.
20. A. Hussein, L. Hao, C. Yan, and R. Everson, Finite element simulation of the temperature and stress fields in single layers built without-support in selective laser melting. Materials & Design, 2013. 52: p. 638-647.
21. I. Kovaleva, O. Kovalev, and I. Smurov, Model of heat and mass transfer in random packing layer of powder particles in selective laser melting. Physics Procedia, 2014. 56: p. 400-410.
22. P. Yuan and D. Gu, Molten pool behaviour and its physical mechanism during selective laser melting of TiC/AlSi10Mg nanocomposites: simulation and experiments. Journal of Physics D: Applied Physics, 2015. 48: p. 035303.
23. S.A. Khairallah, A.T. Anderson, A. Rubenchik, and W.E. King, Laser powder-bed fusion additive manufacturing: physics of complex melt flow and formation mechanisms of pores, spatter, and denudation zones. Acta Materialia, 2016. 108: p. 36-45.
24. Y. Lee, M. Nordin, S.S. Babu, and D.F. Farson, Effect of Fluid Convection on Dendrite Arm Spacing in Laser Deposition. Metallurgical and Materials Transactions B, 2014. 45: p. 1520-1529.
25. D. Dai and D. Gu, Effect of metal vaporization behavior on keyhole-mode surface morphology of selective laser melted composites using different protective atmospheres. Applied Surface Science, 2015. 355: p. 310-319.
26. B. Zhang and C. Coddet, Selective laser melting of iron powder: observation of melting mechanism and densification behavior via point-track-surface-part research. Journal of Manufacturing Science and Engineering, 2016. 138: p. 051001.
27. D. Wang, C. Song, Y. Yang, and Y. Bai, Investigation of crystal growth mechanism during selective laser melting and mechanical property characterization of 316L stainless steel parts. Materials & Design, 2016. 100: p. 291-299.
28. Z.H. Liu, D.Q. Zhang, C.K. Chua, and K.F. Leong, Crystal structure analysis of M2 high speed steel parts produced by selective laser melting. Materials Characterization, 2013. 84: p. 72-80.
29. M.J. Holzweissig, A. Taube, F. Brenne, M. Schaper, and T. Niendorf, Microstructural Characterization and Mechanical Performance of Hot Work Tool Steel Processed by Selective Laser Melting. Metallurgical and Materials Transactions B, 2015. 46: p. 545-549.
30. B. AlMangour, D. Grzesiak, and J.M. Yang, Nanocrystalline TiC-reinforced H13 steel matrix nanocomposites fabricated by selective laser melting. Materials & Design, 2016. 96: p. 150-161.
31. D. Cormier, O. Harrysson, and H. West, Characterization of H13 steel produced via electron beam melting. Rapid Prototyping Journal, 2004. 10(1): p. 35-41.
32. H.J. Shin and Y.T. Yoo, Microstructural and hardness investigation of hot-work tool steels by laser surface treatment. Journal of Materials Processing Technology, 2008. 201: p. 342-347.
33. J. Yang, J. Han, H. Yu, J. Yin, M. Gao, Z. Wang, and X. Zeng, Role of molten pool mode on formability, microstructure and mechanical properties of selective laser melted Ti-6Al-4V alloy. Materials & Design, 2016. 110: p. 558-570.
34. W.E. King, H.D. Barth, V.M. Castillo, G.F. Gallegos, J.W. Gibbs, D.E. Hahn, C. Kamath, and A.M. Rubenchik, Observation of keyhole-mode laser melting in laser powder-bed fusion additive manufacturing. Journal of Materials Processing Technology, 2014. 214: p. 2915-2925.
35. K.A. Chiang and Y.C. Chen, Numerical modeling and experimental investigation of the superficial layer of SKD61 steel during laser surface hardening. Journal of the Chinese Institute of Engineers, 2006. 29: p. 717-724.
36. L. Tang and R.G. Landers, Melt Pool Temperature Control for Laser Metal Deposition Processes—Part II: Layer-to-Layer Temperature Control. Journal of manufacturing science and engineering, 2010. 132: p. 011011-011019.
37. R. Li, J. Liu, Y. Shi, M. Du, and Z. Xie, 316L Stainless Steel with Gradient Porosity Fabricated by Selective Laser Melting. Journal of Materials Engineering and Performance, 2009. 19: p. 666-671.
38. Y.C. Wu, Numerical modeling of melt pool behavior in selective laser melting with random powder distribution and its experimental validation. Materials, 2017. Submit.
39. D. Cong, H. Zhou, M. Yang, Z. Zhang, P. Zhang, C. Meng, and C. Wang, The mechanical properties of H13 die steel repaired by a biomimetic laser technique. Optics & Laser Technology, 2013. 53: p. 1-8.
40. K.H. Lee, S.W. Choi, J. Suh, and C.Y. Kang, Effect of laser power and powder feeding on the microstructure of laser surface alloying hardened H13 steel using SKH51 powder. Materials & Design, 2016. 95: p. 173-182.
41. S. Das, Physical aspects of process control in selective laser sintering of metals. Advanced Engineering Materials, 2003. 5: p. 701-711.