選擇性雷射燒熔粉末製程(Selective laser melting, SLM)為一金屬積層製造方法，可高速製造複雜幾何之構件；雖然如此，快速升降溫的過程可能造成不期望之幾何變異與材料強度缺陷。因此，本研究引用吉布斯自由能理論探索粉末燒熔於半固態過程中，壓力對體積作功與表面張力對表面積作功之平衡過程，可以控制幾何變異與材料強度。實驗結果證明，修正Gibbs自由能模型經有效實驗數據之校驗後，可用來計算壓力對體積作功與表面張力對表面積作功之能量值與貢獻占比，模型精度可達82.0%(R2)。驗證實驗中，全因子測試陣列所控制之雷射功率、掃描間距與掃描速度可將選擇性雷射燒熔之不鏽鋼粉末(ANSI 316L)接合於異質不鏽鋼基底(ANSI 316)，用於觀測熱效應。實驗結果顯示，雷射燒熔粉末之操作參數可影響熱平衡狀態所發生之溫度與層數，加工溫度變化趨勢可界定熱傳導總量之三種狀態: 熱消散(I)、熱飽和(II)與相變化(III)。統計檢定加工溫度之結果中，雷射功率(Fcal: 9.74)與掃描間距(Fcal: 9.26)具統計之顯著性，且因子貢獻度(PCR)各為33.2%與31.5%。在機械性質方面，分析積層材料硬度巨幅增加之原因為，雷射掃描速度與掃描間距所影響之掃描面積足以降低輸入之低體積能量密度，造成積層溫度下降與造成晶粒細化。當積層溫度上升時，可產生相變化之層狀結構(lamellar structure)與退火結構(annealing structure)。在幾何精度方面，當表面張力等於或大於體積膨脹作功時，雷射燒熔粉末可維持Z軸高度與減少直徑變化量，降低高度坍塌與直徑擴增。

Selective laser melting (SLM) is an additive manufacturing process that enables the high speed production of metallic components in complex geometry. However, the rapid heating and cooling cycles involved in the process can lead to undesired geometric variations and material strength defects. This study employs the Gibbs free energy theory to investigate the balance between pressure-induced volume changes and surface tension-induced surface area changes during the powder melting process, aiming to control geometric variations and enhance material strength. Experimental results demonstrate that the modified Gibbs free energy model, validated with effective experimental data, can be used to calculate the energy values and contribution ratios of pressure-induced work on volume and surface tension-induced work on surface area, with a model accuracy of 82.0% (R2). Verification experiments were conducted using a full-factorial test array, where laser power, scan spacing, and scanning speed were controlled to join ANSI 316L stainless steel powders onto a heterogeneous ANSI 316 stainless steel substrate for thermal effect observation. The experimental findings indicate that the operational parameters of laser melting powder significantly influencing the temperature and layer formation during the thermal equilibrium state. Moreover, the thermal effects can be categorized into three states of heat dissipation (I), thermal saturated (II), and phase transformation (III) based on the temperature variation trend. Statistical analysis of the processing temperature revealed the significant effects of laser power (Fcal: 9.74) and hatch distance (Fcal: 9.26), with respective contribution percentages (PCR) of 33.2% and 31.5%. Regarding mechanical properties, the substantial increase in material hardness in the layered structure can be attributed to the reduction of input low-volume energy density through laser scanning speed and hatch distance, leading to temperature decrease and grain refinement. As the layer temperature rises, the formation of lamellar structure, bimodal structure, and annealing structure can occur through phase transformation. In terms of geometric accuracy, when the surface tension is equal to or greater than the volume expansion work, laser melted powder exhibits maintained Z-axis height and reduced diameter variation, thus minimizing height collapse and diameter enlargement.

[1] A. Jadhav, V.S. Jadhav, A review on 3D printing: An additive manufacturing technology, Materials Today: Proceedings, (2022).
[2] D.M. Hajare, T.S. Gajbhiye, Additive manufacturing (3D printing): Recent progress on advancement of materials and challenges, Materials Today: Proceedings, (2022).
[3] J. Elambasseril, M. Brandt, Artificial intelligence: way forward to empower metal additive manufacturing product development – an overview, Materials Today: Proceedings, (2022).
[4] M. Liu, L.N.S. Chiu, C. Vundru, Y. Liu, A. Huang, C. Davies, X. Wu, W. Yan, A characteristic time-based heat input model for simulating selective laser melting, Addit. Manuf., 44 (2021).
[5] K. Antony, N. Arivazhagan, K. Senthilkumaran, Numerical and experimental investigations on laser melting of stainless steel 316L metal powders, Journal of Manufacturing Processes, 16 (2014) 345-355.
[6] A. Simchi, Direct laser sintering of metal powders: Mechanism, kinetics and microstructural features, Materials Science and Engineering: A, 428 (2006) 148-158.
[7] D. Wang, S. Wu, Y. Bai, H. Lin, Y. Yang, C. Song, Characteristics of typical geometrical features shaped by selective laser melting, J. Laser Appl., 29 (2017).
[8] R. Li, Y. Shi, Z. Wang, L. Wang, J. Liu, W. Jiang, Densification behavior of gas and water atomized 316L stainless steel powder during selective laser melting, Applied Surface Science, 256 (2010) 4350-4356.
[9] Z. Kazemi, M. Soleimani, H. Rokhgireh, A. Nayebi, Melting pool simulation of 316L samples manufactured by Selective Laser Melting method, comparison with experimental results, International Journal of Thermal Sciences, 176 (2022).
[10] Hiemenz, P.C., & Rajagopalan, R. (Eds.). (1997). Principles of Colloid and Surface Chemistry, Revised and Expanded (3rd ed.). CRC Press.
[11] C. Kuo, P. Ye, J. Liu, Effects of Elemental Alloying on Surface Integrity in Joining of Composite Powders with Heterogeneous Titanium Substrates Using Selective Laser Melting, International Journal of Precision Engineering and Manufacturing-Green Technology, 7 (2019) 815-827.
[12] A.M. Khorasani, I. Gibson, A.R. Ghaderi, Rheological characterization of process parameters influence on surface quality of Ti-6Al-4V parts manufactured by selective laser melting, The International Journal of Advanced Manufacturing Technology, 97 (2018) 3761-3775.
[13] S. Hocine, H. Van Swygenhoven, S. Van Petegem, Verification of selective laser melting heat source models with operando X-ray diffraction data, Addit. Manuf., 37 (2021).
[14] D. Dai, D. Gu, M. Xia, C. Ma, H. Chen, T. Zhao, C. Hong, A. Gasser, R. Poprawe, Melt spreading behavior, microstructure evolution and wear resistance of selective laser melting additive manufactured AlN/AlSi10Mg nanocomposite, Surface and Coatings Technology, 349 (2018) 279-288.
[15] A. Kumar Mishra, A. Kumar, Effect of surface morphology on the melt pool geometry in single track selective laser melting, Materials Today: Proceedings, 27 (2020) 816-823.
[16] X. Ding, L. Wang, S. Wang, Comparison study of numerical analysis for heat transfer and fluid flow under two different laser scan pattern during selective laser melting, Optik, 127 (2016) 10898-10907.
[17] S. Dwivedi, A. Rai Dixit, A. Kumar Das, Wetting behavior of selective laser melted (SLM) bio-medical grade stainless steel 316L, Materials Today: Proceedings, (2021).
[18] Austenitic Stainless Steels, in: M.F. McGuire (Ed.) Stainless Steels for Design Engineers, ASM International, (2008)
[19] T. Reza Tabrizi, M. Sabzi, S.H. Mousavi Anijdan, A.R. Eivani, N. Park, H.R. Jafarian, Comparing the effect of continuous and pulsed current in the GTAW process of AISI 316L stainless steel welded joint: microstructural evolution, phase equilibrium, mechanical properties and fracture mode, Journal of Materials Research and Technology, 15 (2021) 199-212.
[20] S. Astafurov, E. Astafurova, Phase Composition of Austenitic Stainless Steels in Additive Manufacturing: A Review, Metals, 11 (2021).
[21] D.R. Gaskell, D.E. Laughlin, Introduction to the Thermodynamics of Materials, Sixth Edition, CRC Press, (2017).
[22] S. Das, Physical Aspects of Process Control in Selective Laser Sintering of Metals, Advanced Engineering Materials, 5 (2003) 701-711.
[23] H. Zhang, D. Gu, C. Ma, M. Xia, M. Guo, Surface wettability and superhydrophobic characteristics of Ni-based nanocomposites fabricated by selective laser melting, Applied Surface Science, 476 (2019) 151-160.
[24] M. Guo, D. Gu, L. Xi, L. Du, H. Zhang, J. Zhang, Formation of scanning tracks during Selective Laser Melting (SLM) of pure tungsten powder: Morphology, geometric features and forming mechanisms, International Journal of Refractory Metals and Hard Materials, 79 (2019) 37-46.
[25] X. Wang, W. Yu, M. Wang, F. Wang, B. Wu, Spreading behavior of Sn droplets impacting Cu and stainless steel substrates, Surfaces and Interfaces, 29 (2022).
[26] X. Liu, C. Zhao, X. Zhou, Z. Shen, W. Liu, Microstructure of selective laser melted AlSi10Mg alloy, Materials & Design, 168 (2019).
[27] Y. Sun, E. Yousefi, A. Kunwar, N. Moelans, D. Seveno, M. Guo, Study of the interfacial reactions controlling the spreading of Al on Ni, Applied Surface Science, 571 (2022).
[28] C. Kuo, W. Peng, A. Chiang, Evaluations of Surface Integrity and Mechanical Performance in Laser Melting of Stainless Steel Powders with Heterogeneous Metal Substrates, International Journal of Precision Engineering and Manufacturing, 19 (2018) 431-439.
[29] F. Abe, M. Shiomi, K.J.P.e. Osakada, Solidifying behaviour of metallic powder in selective laser melting process, 207 (2017) 1188-1193.
[30] J. Gan, L. Duan, F. Li, Y. Che, Y. Zhou, S. Wen, C. Yan, Effect of laser energy density on the evolution of Ni4Ti3 precipitate and property of NiTi shape memory alloys prepared by selective laser melting, Journal of Alloys and Compounds, 869 (2021).
[31] G. Michal, F. Ernst, H. Kahn, Y. Cao, F. Oba, N. Agarwal, A. Heuer, Carbon supersaturation due to paraequilibrium carburization: Stainless steels with greatly improved mechanical properties, Acta Mater., 54 (2006) 1597-1606.
[32] A.d.A. Vicente, R.L.d. Souza, D.C. Romano Espinosa, R.R. de Aguiar, P. Paul, A.B. Botelho, Juni, Effect of Relative Plate Thickness in the Heat Flow and Cooling Rate during Welding of Super Duplex Stainless Steel, Saudi Journal of Engineering and Technology, 05 (2020) 244-250.
[33] H. Fukuyama, H. Higashi, H. Yamano, Thermophysical Properties of Molten Stainless Steel Containing 5 mass % B4C, Nuclear Technology, 205 (2019) 1154-1163.
[34] R. Brooks, P. Quested, The surface tension of steels, Journal of Materials Science - J MATER SCI, 40 (2005) 2233-2238.
[35] P. Pichler, T. Leitner, E. Kaschnitz, J. Rattenberger, G. Pottlacher, Surface Tension and Thermal Conductivity of NIST SRM 1155a (AISI 316L Stainless Steel), International Journal of Thermophysics, 43 (2022).
[36] M. Watanabe, Y. Watanabe, C. Koyama, T. Ishikawa, S. Imaizumi, M. Adachi, M. Ohtsuka, A. Chiba, Y. Koizumi, H. Fukuyama, Density, surface tension, and viscosity of Co-Cr-Mo melts measured using electrostatic levitation technique, Thermochimica Acta, 710 (2022).
[37] Q. Chen, G. Guillemot, C.-A. Gandin, M. Bellet, Numerical modelling of the impact of energy distribution and Marangoni surface tension on track shape in selective laser melting of ceramic material, Additive Manufacturing, 21 (2018) 713-723.
[38] Y. Li, K. Zhou, S.B. Tor, C.K. Chua, K.F. Leong, Heat transfer and phase transition in the selective laser melting process, International Journal of Heat and Mass Transfer, 108 (2017) 2408-2416.
[39] C. Hagenlocher, P. O’Toole, W. Xu, M. Brandt, M. Easton, A. Molotnikov, Analytical modelling of heat accumulation in laser based additive manufacturing processes of metals, Addit. Manuf., 60 (2022).
[40] I. Yadroitsev, Selective laser melting: Direct manufacturing of 3D-objects by selective laser melting of metal powders, (2009).
[41] S.D. Washko, G. Aggen, A.H. Committee, Wrought Stainless Steels, Properties and Selection: Irons, Steels, and High-Performance Alloys, ASM International, (1990).