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Shan X, Pan Z, Gao M, Han L, Choi JP, Zhang H. Multi-Physics Modeling of Melting-Solidification Characteristics in Laser Powder Bed Fusion Process of 316L Stainless Steel. MATERIALS (BASEL, SWITZERLAND) 2024; 17:946. [PMID: 38399196 PMCID: PMC10890438 DOI: 10.3390/ma17040946] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2024] [Revised: 02/11/2024] [Accepted: 02/16/2024] [Indexed: 02/25/2024]
Abstract
In the laser powder bed fusion process, the melting-solidification characteristics of 316L stainless steel have a great effect on the workpiece quality. In this paper, a multi-physics model was constructed using the finite volume method (FVM) to simulate the melting-solidification process of a 316L powder bed via laser powder bed fusion. In this physical model, the phase change process, the influence of temperature gradient on surface tension of molten pool, and the influence of recoil pressure caused by the metal vapor on molten pool surface were considered. Using this model, the effects of laser scanning speed, hatch space, and laser power on temperature distribution, keyhole depth, and workpiece quality were studied. This study can be used to guide the optimization of process parameters, which is beneficial to the improvement of workpiece quality.
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Affiliation(s)
- Xiuyang Shan
- School of Mechanical and Electronic Engineering, Suzhou University, Suzhou 234000, China; (X.S.)
| | - Zhenggao Pan
- School of Information Engineering, Suzhou University, Suzhou 234000, China
| | - Mengdi Gao
- School of Mechanical and Electronic Engineering, Suzhou University, Suzhou 234000, China; (X.S.)
| | - Lu Han
- School of Mechanical and Electronic Engineering, Suzhou University, Suzhou 234000, China; (X.S.)
| | - Joon-Phil Choi
- Department of 3D Printing, Korea Institute of Machinery & Materials, Daejeon 34103, Republic of Korea
| | - Haining Zhang
- School of Information Engineering, Suzhou University, Suzhou 234000, China
- School of Mechanical and Aerospace, Nanyang Technological University, Singapore 639798, Singapore
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Kaess M, Werz M, Weihe S. Residual Stress Formation Mechanisms in Laser Powder Bed Fusion-A Numerical Evaluation. MATERIALS (BASEL, SWITZERLAND) 2023; 16:2321. [PMID: 36984200 PMCID: PMC10055713 DOI: 10.3390/ma16062321] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/15/2023] [Revised: 03/07/2023] [Accepted: 03/10/2023] [Indexed: 06/18/2023]
Abstract
Additive manufacturing methods, such as the laser powder bed fusion, do not need any special tool or casting mold. This enables the fast realization of complex and individual geometries with integrated functions. However, the local heat input during the manufacturing process often leads to residual stresses and distortion. This in turn causes poor quality, scrap parts or can even terminate a job prematurely if the powder recoating mechanism collides with a distorted part during the process. This study investigates the generation mechanisms of residual stresses and distortion during laser powder bed fusion (LPBF) of stainless steel 316L in order to reduce these effects and thus contribute to improved process safety and efficiency. Therefore, numerical investigations with a finite element model on the scale of a few melt tracks and layers serve to develop a detailed understanding of the mechanisms during production. The work includes an investigation of the build plate temperature, the laser power and speed and the layer thickness. The results show a strong dependency on the build plate preheating and energy per unit length. A higher build plate temperature and a reduction of the energy per unit length both lead to lower residual stresses.
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Ur Rehman A, Ullah A, Liu T, Ur Rehman R, Salamci MU. Additive manufacturing of Al 2O 3 ceramics with MgO/SiC contents by laser powder bed fusion process. Front Chem 2023; 11:1034473. [PMID: 36817171 PMCID: PMC9936093 DOI: 10.3389/fchem.2023.1034473] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2022] [Accepted: 01/20/2023] [Indexed: 02/05/2023] Open
Abstract
Laser powder bed fusion is a laser-based additive manufacturing technique that uses a high-energy laser beam to interact directly with powder feedstock. LPBF of oxide ceramics is highly desirable for aerospace, biomedical and high-tech industries. However, the LPBF of ceramics remains a challenging area to address. In this work, a new slurry-based approach for LPBF of ceramic was studied, which has some significant advantages compared to indirect selective laser sintering of ceramic powders. LPBF of Al2O3 was fabricated at different MgO loads up to 80 wt%. Several specimens on different laser powers (70 W-120 W) were printed. The addition of magnesia influenced the microstructure of the alumina ceramic significantly. The findings show that when the laser power is high and the magnesia load is low, the surface quality of the printing parts improves. It is feasible to produce slurry ceramic parts without binders through LPBF. Furthermore, the effects of SiC and MgO loads on the microstructure and surface morphology of alumina are compared and analysed.
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Affiliation(s)
- Asif Ur Rehman
- ERMAKSAN, Bursa, Türkiye
- Department of Mechanical Engineering, Faculty of Engineering, Gazi University, Ankara, Türkiye
- Additive Manufacturing Technologies Research and Application Center-EKTAM, Gazi University, Ankara, Türkiye
| | - Abid Ullah
- Department of Mechanical Engineering, Faculty of Engineering, Gazi University, Ankara, Türkiye
- Additive Manufacturing Technologies Research and Application Center-EKTAM, Gazi University, Ankara, Türkiye
- CAS Key Laboratory of Mechanical Behavior and Design of Materials, Department of Modern Mechanics, University of Science and Technology of China, Hefei, Anhui, China
| | - Tingting Liu
- School of Mechanical Engineering, Nanjing University of Science and Technology, Nanjing, Jiangsu, China
| | | | - Metin U. Salamci
- Department of Mechanical Engineering, Faculty of Engineering, Gazi University, Ankara, Türkiye
- Additive Manufacturing Technologies Research and Application Center-EKTAM, Gazi University, Ankara, Türkiye
- Advanced Manufacturing Technologies Center of Excellence-URTEMM, Ankara, Türkiye
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Bhagat K, Rudraraju S. A Numerical Investigation of Dimensionless Numbers Characterizing Meltpool Morphology of the Laser Powder Bed Fusion Process. MATERIALS (BASEL, SWITZERLAND) 2022; 16:94. [PMID: 36614432 PMCID: PMC9821554 DOI: 10.3390/ma16010094] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/11/2022] [Revised: 12/06/2022] [Accepted: 12/15/2022] [Indexed: 06/17/2023]
Abstract
Microstructure evolution in metal additive manufacturing (AM) is a complex multi-physics and multi-scale problem. Understanding the impact of AM process conditions on the microstructure evolution and the resulting mechanical properties of the printed component remains an active area of research. At the meltpool scale, the thermo-fluidic governing equations have been extensively modeled in the literature to understand the meltpool conditions and the thermal gradients in its vicinity. In many phenomena governed by partial differential equations, dimensional analysis and identification of important dimensionless numbers can provide significant insights into the process dynamics. In this context, we present a novel strategy using dimensional analysis and the linear least-squares regression method to numerically investigate the thermo-fluidic governing equations of the Laser Powder Bed Fusion AM process. First, the governing equations are solved using the Finite Element Method, and the model predictions are validated by comparing with experimentally estimated cooling rates, and with numerical results from the literature. Then, through dimensional analysis, an important dimensionless quantity interpreted as a measure of heat absorbed by the powdered material and the meltpool, is identified. This dimensionless measure of absorbed heat, along with classical dimensionless quantities such as Péclet, Marangoni, and Stefan numbers, are employed to investigate advective transport in the meltpool for different alloys. Further, the framework is used to study variations in the thermal gradients and the solidification cooling rate. Important correlations linking meltpool morphology and microstructure-evolution-related variables with classical dimensionless numbers are the key contribution of this work.
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Gatões D, Alves R, Alves B, Vieira MT. Selective Laser Melting and Mechanical Properties of Stainless Steels. MATERIALS (BASEL, SWITZERLAND) 2022; 15:7575. [PMID: 36363178 PMCID: PMC9654318 DOI: 10.3390/ma15217575] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/17/2022] [Revised: 10/07/2022] [Accepted: 10/17/2022] [Indexed: 06/16/2023]
Abstract
Metal additive manufacturing (AM) has been evolving in response to industrial and social challenges. However, new materials are hindered in these technologies due to the complexity of direct additive manufacturing technologies, particularly selective laser melting (SLM). Stainless steel (SS) 316L, due to its very low carbon content, has been used as a standard powder in SLM, highlighting the role of alloying elements present in steels. However, reliable research on the chemical impact of carbon content in steel alloys has been rarely conducted, despite being the most prevalent element in steel. Considering the temperatures involved in the SLM process, the laser-powder interaction can lead to a significant carbon decrease, whatever the processing atmosphere. In the present study, four stainless steels with increasing carbon content-AISI 316L, 630 (17-4PH), 420 and 440C-were processed under the same SLM parameters. In addition to roughness and surface topography, the relationship with the microstructure (including grain size and orientation), defects and mechanical properties (hardness and tensile strength) were established, highlighting the role of carbon. It was shown that the production by SLM of stainless steels with similar packing densities and different carbon contents does not oblige the changing of processing parameters. Moreover, alterations in material response in stainless steels produced under the same volumetric energy density mainly result from microstructural evolution during the process.
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Dąbrowska K, Nowak R, Rumianek P, Seńko J. Construction and Validation of Simulation Models of Samples Made from 316L Steel by Applying Additive Technique. MATERIALS (BASEL, SWITZERLAND) 2022; 15:6244. [PMID: 36143564 PMCID: PMC9501943 DOI: 10.3390/ma15186244] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/27/2022] [Revised: 09/02/2022] [Accepted: 09/02/2022] [Indexed: 06/16/2023]
Abstract
The main aim of the study includes research concerning the strength of samples printed out of 316L steel in the form of laminates and the creation of reflective simulation models with regard to the results obtained during the research. In addition, the tests addressed the effect of the arrangement of the printed layers on the final strength of the object. Static tensile tests allowed the material constants of 316L steel in the form of dimensionally printed laminate to be determined. Tests were conducted on samples with different printed angles. The tests also covered the impact of the printing envelope on samples with the printing angles. Based on the determined material constants, simulation models for calculations using the finite element method were created. Furthermore, the study includes analytical and simulation calculations of plain laminate in order to verify the accuracy of the Composite Layup module in Abaqus CAE software. The study was summarized by compiling and commenting on the results obtained from the conducted research. Tests showed that there is a possibility of simulating the strength of the printouts from 316L steel using the FEM calculations. It was shown that the FEM model results are similar to those obtained in the tests. The calculated errors were from 3.6 to 14.4%. The linear model describes well the first part of the stress-strain curve, but in further research, it is strongly recommended that a proper and checked nonlinear anisotropic one is presented.
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Mahmood MA, Ur Rehman A, Ristoscu C, Demir M, Popescu-Pelin G, Pitir F, Salamci MU, Mihailescu IN. Advances in Laser Additive Manufacturing of Cobalt–Chromium Alloy Multi-Layer Mesoscopic Analytical Modelling with Experimental Correlations: From Micro-Dendrite Grains to Bulk Objects. NANOMATERIALS 2022; 12:nano12050802. [PMID: 35269291 PMCID: PMC8912423 DOI: 10.3390/nano12050802] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/14/2021] [Revised: 02/13/2022] [Accepted: 02/24/2022] [Indexed: 11/25/2022]
Abstract
This study presents two analytical models for the laser powder bed fusion (LPBF) process. To begin, the single layer’s dimensions were measured using principal operating conditions, including laser power, laser scanning speed, powder layer thickness, and hatch distance. The single-layer printing dimensions were transformed into multi-layer printing using the hatch distance. The thermal history of the printed layers was used as an input to the Johnson–Mehl–Avrami-Kolmogorov model to estimate the average dendrite grain size. LPBF experiments were conducted for a Cobalt–chromium (Co–Cr) alloy to validate the developed model. The average dendrite grain size was estimated using a scanning electron microscope (SEM) combined with “Image J” software. The Vickers hardness test was performed to correlate the average dendrite grain size and operating conditions. A 10–15% mean absolute deviation was presented between experiments and simulation results. In all samples, a Co-based γ-FCC structure was identified. An inverse correlation was established between the laser power and smaller average dendrite grain, while a direct relationship has been determined between laser scanning speed and average dendrite grain size. A similar trend was identified between hatch distance and average dendrite grain size. A direct link has been determined between the average dendrite grain size and hardness value. Furthermore, a direct relationship has connected the laser volume energy density and hardness value. This study will help experimentalists to design operating conditions based on the required grain size and corresponding mechanical characteristics.
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Affiliation(s)
- Muhammad Arif Mahmood
- Mechanical Engineering Program, Texas A&M University at Qatar, Doha P.O. Box 23874, Qatar;
- Laser Department, National Institute for Laser, Plasma and Radiation Physics (INFLPR), 077125 Magurele, Ilfov, Romania; (G.P.-P.); (I.N.M.)
| | - Asif Ur Rehman
- ERMAKSAN, Bursa 16065, Turkey; (M.D.); (F.P.)
- Department of Mechanical Engineering, Gazi University, Ankara 06570, Turkey;
- Additive Manufacturing Technologies Research and Application Center-EKTAM, Gazi University, Ankara 06560, Turkey
- Correspondence: (A.U.R.); (C.R.); Tel.: +90-539-9387-8001 (A.U.R.); +40-214-574-243 (C.R.)
| | - Carmen Ristoscu
- Laser Department, National Institute for Laser, Plasma and Radiation Physics (INFLPR), 077125 Magurele, Ilfov, Romania; (G.P.-P.); (I.N.M.)
- Correspondence: (A.U.R.); (C.R.); Tel.: +90-539-9387-8001 (A.U.R.); +40-214-574-243 (C.R.)
| | | | - Gianina Popescu-Pelin
- Laser Department, National Institute for Laser, Plasma and Radiation Physics (INFLPR), 077125 Magurele, Ilfov, Romania; (G.P.-P.); (I.N.M.)
| | - Fatih Pitir
- ERMAKSAN, Bursa 16065, Turkey; (M.D.); (F.P.)
| | - Metin Uymaz Salamci
- Department of Mechanical Engineering, Gazi University, Ankara 06570, Turkey;
- Additive Manufacturing Technologies Research and Application Center-EKTAM, Gazi University, Ankara 06560, Turkey
| | - Ion N. Mihailescu
- Laser Department, National Institute for Laser, Plasma and Radiation Physics (INFLPR), 077125 Magurele, Ilfov, Romania; (G.P.-P.); (I.N.M.)
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Ur Rehman A, Saleem MA, Liu T, Zhang K, Pitir F, Salamci MU. Influence of Silicon Carbide on Direct Powder Bed Selective Laser Process (Sintering/Melting) of Alumina. MATERIALS 2022; 15:ma15020637. [PMID: 35057354 PMCID: PMC8778824 DOI: 10.3390/ma15020637] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/01/2021] [Revised: 12/09/2021] [Accepted: 12/14/2021] [Indexed: 01/27/2023]
Abstract
The powder bed selective laser process (sintering/melting) has revolutionised many industries, including aerospace and biomedicine. However, PBSLP of ceramic remains a formidable challenge. Here, we present a unique slurry-based approach for fabricating high-strength ceramic components instead of traditional PBSLP. A special PBSLP platform capable of 1000 °C pre-heating was designed for this purpose. In this paper, PBSLP of Al2O3 was accomplished at different SiC loads up to 20 wt%. Several specimens on different laser powers (120 W to 225 W) were printed. When the SiC content was 10 wt% or more, the chemical interaction made it difficult to process. Severe melt pool disturbances led to poor sintering and melting. The structural analysis revealed that the micro-structure was significantly affected by the weight fraction of SiC. Interestingly, when the content was less than 2 wt%, it showed significant improvement in the microstructure during PBSLP and no effects of LPS or chemical interaction. Particularly, a crack pinning effect could be clearly seen at 0.5 wt%.
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Affiliation(s)
- Asif Ur Rehman
- ERMAKSAN, Bursa 16065, Turkey;
- Department of Mechanical Engineering, Gazi University, Ankara 06570, Turkey;
- Additive Manufacturing Technologies Research and Application Center-EKTAM, Gazi University, Ankara 06560, Turkey
- Correspondence: (A.U.R.); (T.L.); Tel.: +90-539-938-780-01 (A.U.R.); +86-138-130-848-95 (T.L.)
| | - Muhammad Ahsan Saleem
- School of Mechanical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China; (M.A.S.); (K.Z.)
| | - Tingting Liu
- School of Mechanical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China; (M.A.S.); (K.Z.)
- Correspondence: (A.U.R.); (T.L.); Tel.: +90-539-938-780-01 (A.U.R.); +86-138-130-848-95 (T.L.)
| | - Kai Zhang
- School of Mechanical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China; (M.A.S.); (K.Z.)
| | | | - Metin Uymaz Salamci
- Department of Mechanical Engineering, Gazi University, Ankara 06570, Turkey;
- Additive Manufacturing Technologies Research and Application Center-EKTAM, Gazi University, Ankara 06560, Turkey
- Manufacturing Technologies Center of Excellence-URTEMM A.S., Ankara 06560, Turkey
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Mahmood MA, Ur Rehman A, Pitir F, Salamci MU, Mihailescu IN. Laser Melting Deposition Additive Manufacturing of Ti6Al4V Biomedical Alloy: Mesoscopic In-Situ Flow Field Mapping via Computational Fluid Dynamics and Analytical Modelling with Empirical Testing. MATERIALS (BASEL, SWITZERLAND) 2021; 14:7749. [PMID: 34947357 PMCID: PMC8705474 DOI: 10.3390/ma14247749] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/27/2021] [Revised: 12/03/2021] [Accepted: 12/13/2021] [Indexed: 01/18/2023]
Abstract
Laser melting deposition (LMD) has recently gained attention from the industrial sectors due to producing near-net-shape parts and repairing worn-out components. However, LMD remained unexplored concerning the melt pool dynamics and fluid flow analysis. In this study, computational fluid dynamics (CFD) and analytical models have been developed. The concepts of the volume of fluid and discrete element modeling were used for computational fluid dynamics (CFD) simulations. Furthermore, a simplified mathematical model was devised for single-layer deposition with a laser beam attenuation ratio inherent to the LMD process. Both models were validated with the experimental results of Ti6Al4V alloy single track depositions on Ti6Al4V substrate. A close correlation has been found between experiments and modelling with a few deviations. In addition, a mechanism for tracking the melt flow and involved forces was devised. It was simulated that the LMD involves conduction-mode melt flow only due to the coaxial addition of powder particles. In front of the laser beam, the melt pool showed a clockwise vortex, while at the back of the laser spot location, it adopted an anti-clockwise vortex. During printing, a few partially melted particles tried to enter into the molten pool, causing splashing within the melt material. The melting regime, mushy area (solid + liquid mixture) and solidified region were determined after layer deposition. This research gives an in-depth insight into the melt flow dynamics in the context of LMD printing.
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Affiliation(s)
- Muhammad Arif Mahmood
- National Institute for Laser, Plasma and Radiation Physics (INFLPR), Magurele, 077125 Ilfov, Romania;
| | - Asif Ur Rehman
- ERMAKSAN, Bursa 16065, Turkey;
- Department of Mechanical Engineering, Gazi University, Ankara 06570, Turkey;
- Additive Manufacturing Technologies Research And Application Center-EKTAM, Gazi University, Ankara 06560, Turkey
| | | | - Metin Uymaz Salamci
- Department of Mechanical Engineering, Gazi University, Ankara 06570, Turkey;
- Additive Manufacturing Technologies Research And Application Center-EKTAM, Gazi University, Ankara 06560, Turkey
- Manufacturing Technologies Center of Excellence-URTEMM A.S., Ankara 06980, Turkey
| | - Ion N. Mihailescu
- National Institute for Laser, Plasma and Radiation Physics (INFLPR), Magurele, 077125 Ilfov, Romania;
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Spatter Formation and Splashing Induced Defects in Laser-Based Powder Bed Fusion of AlSi10Mg Alloy: A Novel Hydrodynamics Modelling with Empirical Testing. METALS 2021. [DOI: 10.3390/met11122023] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Powder spattering and splashing in the melt pool are common phenomena during Laser-based Powder Bed Fusion (LPBF) of metallic materials having high fluidity. For this purpose, analytical and computational fluid dynamics (CFD) models have been deduced for the LPBF of AlSi10Mg alloy. The single printed layer’s dimensions were estimated using primary operating conditions for the analytical model. In CFD modelling, the volume of fluid and discrete element modelling techniques were applied to illustrate the splashing and spatter phenomena, providing a novel hydrodynamics CFD model for LPBF of AlSi10Mg alloy. The computational results were compared with the experimental analyses. A trial-and-error method was used to propose an optimized set of parameters for the LPBF of AlSi10Mg alloy. Laser scanning speed, laser spot diameter and laser power were changed. On the other hand, the powder layer thickness and hatch distance were kept constant. Following on, 20 samples were fabricated using the LPBF process. The printed samples’ microstructures were used to select optimized parameters for achieving defect-free parts. It was found that the recoil pressure, vaporization, high-speed vapor cloud, Marangoni flow, hydraulic pressure and buoyancy are all controlled by the laser-material interaction time. As the laser-AlSi10Mg material interaction period progresses, the forces presented above become dominant. Splashing occurs due to a combination of increased recoil pressure, laser-material interaction time, higher material’s fluidity, vaporization, dominancy of Marangoni flow, high-speed vapor cloud, hydraulic pressure, buoyancy, and transformation of keyhole from J-shape to reverse triangle-shape that is a tongue-like protrusion in the keyhole. In the LPBF of AlSi10Mg alloy, only the conduction mode melt flow has been determined. For multi-layers printing of AlSi10Mg alloy, the optimum operating conditions are laser power = 140 W, laser spot diameter = 180 µm, laser scanning speed = 0.6 m/s, powder layer thickness = 50 µm and hatch distance = 112 µm. These conditions have been identified using sample microstructures.
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Ur Rehman A, Mahmood MA, Pitir F, Salamci MU, Popescu AC, Mihailescu IN. Keyhole Formation by Laser Drilling in Laser Powder Bed Fusion of Ti6Al4V Biomedical Alloy: Mesoscopic Computational Fluid Dynamics Simulation versus Mathematical Modelling Using Empirical Validation. NANOMATERIALS 2021; 11:nano11123284. [PMID: 34947634 PMCID: PMC8707298 DOI: 10.3390/nano11123284] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/19/2021] [Revised: 11/27/2021] [Accepted: 11/30/2021] [Indexed: 01/21/2023]
Abstract
In the laser powder bed fusion (LPBF) process, the operating conditions are essential in determining laser-induced keyhole regimes based on the thermal distribution. These regimes, classified into shallow and deep keyholes, control the probability and defects formation intensity in the LPBF process. To study and control the keyhole in the LPBF process, mathematical and computational fluid dynamics (CFD) models are presented. For CFD, the volume of fluid method with the discrete element modeling technique was used, while a mathematical model was developed by including the laser beam absorption by the powder bed voids and surface. The dynamic melt pool behavior is explored in detail. Quantitative comparisons are made among experimental, CFD simulation and analytical computing results leading to a good correspondence. In LPBF, the temperature around the laser irradiation zone rises rapidly compared to the surroundings in the powder layer due to the high thermal resistance and the air between the powder particles, resulting in a slow travel of laser transverse heat waves. In LPBF, the keyhole can be classified into shallow and deep keyhole mode, controlled by the energy density. Increasing the energy density, the shallow keyhole mode transforms into the deep keyhole mode. The energy density in a deep keyhole is higher due to the multiple reflections and concentrations of secondary reflected beams within the keyhole, causing the material to vaporize quickly. Due to an elevated temperature distribution in deep keyhole mode, the probability of pores forming is much higher than in a shallow keyhole as the liquid material is close to the vaporization temperature. When the temperature increases rapidly, the material density drops quickly, thus, raising the fluid volume due to the specific heat and fusion latent heat. In return, this lowers the surface tension and affects the melt pool uniformity.
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Affiliation(s)
- Asif Ur Rehman
- ERMAKSAN, Bursa 16065, Turkey;
- Department of Mechanical Engineering, Gazi University, Ankara 06570, Turkey;
- Additive Manufacturing Technologies Research and Application Center-EKTAM, Gazi University, Ankara 06560, Turkey
- Correspondence: (A.U.R.); (M.A.M.); Tel.: +90-53993878001 (A.U.R.); +40-214574491 (M.A.M.)
| | - Muhammad Arif Mahmood
- National Institute for Laser, Plasma and Radiation Physics (INFLPR), Magurele, 077125 Ilfov, Romania; (A.C.P.); (I.N.M.)
- Correspondence: (A.U.R.); (M.A.M.); Tel.: +90-53993878001 (A.U.R.); +40-214574491 (M.A.M.)
| | | | - Metin Uymaz Salamci
- Department of Mechanical Engineering, Gazi University, Ankara 06570, Turkey;
- Additive Manufacturing Technologies Research and Application Center-EKTAM, Gazi University, Ankara 06560, Turkey
| | - Andrei C. Popescu
- National Institute for Laser, Plasma and Radiation Physics (INFLPR), Magurele, 077125 Ilfov, Romania; (A.C.P.); (I.N.M.)
| | - Ion N. Mihailescu
- National Institute for Laser, Plasma and Radiation Physics (INFLPR), Magurele, 077125 Ilfov, Romania; (A.C.P.); (I.N.M.)
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Ur Rehman A, Pitir F, Salamci MU. Laser Powder Bed Fusion (LPBF) of In718 and the Impact of Pre-Heating at 500 and 1000 °C: Operando Study. MATERIALS (BASEL, SWITZERLAND) 2021; 14:6683. [PMID: 34772210 PMCID: PMC8588267 DOI: 10.3390/ma14216683] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/04/2021] [Revised: 10/26/2021] [Accepted: 11/01/2021] [Indexed: 11/17/2022]
Abstract
The morphology of a melt pool has a critical role in laser powder bed fusion (LPBF). Nevertheless, directly characterizing the melt pool during LPBF is incredibly hard. Here, we present the melt pool flow of the entire melt pool in 3D using mesoscopic simulation models. The physical processes occurring within the melt pool are pinpointed. The flow patterns throughout the same are exposed and measured. Moreover, the impact of pre-heating at 500 and 1000 °C has been described. The study findings offer insights into LPBF. The findings presented here are critical for comprehending the LPBF and directing the establishment of improved metrics for process parameters optimization.
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Affiliation(s)
- Asif Ur Rehman
- ERMAKSAN, Bursa 16065, Turkey;
- Department of Mechanical Engineering, Gazi University, Ankara 06570, Turkey;
- Additive Manufacturing Technologies Application and Research Center—EKTAM, Gazi University, Ankara 06560, Turkey
| | | | - Metin Uymaz Salamci
- Department of Mechanical Engineering, Gazi University, Ankara 06570, Turkey;
- Additive Manufacturing Technologies Application and Research Center—EKTAM, Gazi University, Ankara 06560, Turkey
- Manufacturing Technologies Center of Excellence—URTEMM A.S., Ankara 06980, Turkey
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Full-Field Mapping and Flow Quantification of Melt Pool Dynamics in Laser Powder Bed Fusion of SS316L. MATERIALS 2021; 14:ma14216264. [PMID: 34771790 PMCID: PMC8585046 DOI: 10.3390/ma14216264] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/01/2021] [Revised: 10/07/2021] [Accepted: 10/13/2021] [Indexed: 11/26/2022]
Abstract
Laser powder bed fusion (LPBF) has a wide range of uses in high-tech industries, including the aerospace and biomedical fields. For LPBF, the flow of molten metal is crucial; until now, however, the flow in the melt pool has not been described thoroughly in 3D. Here, we provide full-field mapping and flow measurement of melt pool dynamics in laser powder bed fusion, through a high-fidelity numerical model using the finite volume method. The influence of Marangoni flow, evaporation, as well as recoil pressure have been included in the model. Single-track experiments were conducted for validation. The temperature profiles at different power and speed parameters were simulated, and results were compared with experimental temperature recordings. The flow dynamics in a single track were exposed. The numerical and experimental findings revealed that even in the same melting track, the melt pool’s height and width can vary due to the strong Marangoni force. The model showed that the variation in density and volume for the same melting track was one of the critical reasons for defects. The acquired findings shed important light on laser additive manufacturing processes and pave the way for the development of robust, computational models with a high degree of reliability.
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Microstructure Evolution in He-Implanted Si at 600 °C Followed by 1000 °C Annealing. MATERIALS 2021; 14:ma14175107. [PMID: 34501194 PMCID: PMC8434436 DOI: 10.3390/ma14175107] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/13/2021] [Revised: 09/02/2021] [Accepted: 09/04/2021] [Indexed: 11/24/2022]
Abstract
Si single crystal was implanted with 230 keV He+ ions to a fluence of 5 × 1016/cm2 at 600 °C. The structural defects in Si implanted with He at 600 °C and then annealed at 1000 °C were investigated by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The microstructure of an as-implanted sample is provided for comparison. After annealing, rod-like defects were diminished, while tangled dislocations and large dislocation loops appeared. Dislocation lines trapped by cavities were directly observed. The cavities remained stable except for a transition of shape, from octahedron to tetrakaidecahedron. Stacking-fault tetrahedrons were found simultaneously. Cavity growth was independent of dislocations. The evolution of observed lattice defects is discussed.
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