A Melt Pool Temperature Model in Laser Powder Bed Fabricated CM247LC Ni Superalloy to Rationalize Crack Formation and Microstructural Inhomogeneities

AbstractThis study of the laser powder bed fusion (LPBF) of γ′-strengthened Ni superalloy CM247LC focuses on the development of a melt pool temperature model to predict crack density within the alloy. This study also analyzes spatter and elemental evaporation, which might cause defects and inhomogeneities, at different melt pool temperatures. The melt pool temperature model provides more accurate predictions than the widely used energy density model. Spatter particles were collected and characterized to study their sizes and chemical compositions, compared with the virgin powder, recycled powder, and as-built samples, to probe the impact of their entrapment into the melt pool. This study also investigated Al evaporation, revealing that its extent does not correlate with the laser energy density and is believed to be rather limited by comparing the chemistry of the virgin powder and the build. Last, the impact of LPBF process parameters on the formation of these inhomogeneities, and accordingly crack formation, was studied using finite element analysis by estimating the maximum melt pool temperature and correlating it with the formation of the microstructural inhomogeneities. The morphology of the various cracking modes was associated with the process parameters.

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Influence of Laser Powder Bed Fusion Process Parameters on Voids, Cracks, and Microhardness of Nickel-Based Superalloy Alloy 247LC

Materials ◽

10.3390/ma13173770 ◽

2020 ◽

Vol 13 (17) ◽

pp. 3770

Author(s):

Olutayo Adegoke ◽

Joel Andersson ◽

Håkan Brodin ◽

Robert Pederson

Keyword(s):

Energy Density ◽

Process Parameters ◽

Laser Power ◽

Crack Density ◽

Void Formation ◽

Void Content ◽

Laser Powder Bed Fusion ◽

Powder Bed ◽

Nickel Based Superalloy ◽

Density Threshold

The manufacturing of parts from nickel-based superalloy Alloy 247LC by laser powder bed fusion (L-PBF) is challenging, primarily owing to the alloy’s susceptibility to cracks. Apart from the cracks, voids created during the L-PBF process should also be minimized to produce dense parts. In this study, samples of Alloy 247LC were manufactured by L-PBF, several of which could be produced with voids and crack density close to zero. A statistical design of experiments was used to evaluate the influence of the process parameters, namely laser power, scanning speed, and hatch distance (inherent to the volumetric energy density) on void formation, crack density, and microhardness of the samples. The window of process parameters, in which minimum voids and/or cracks were present, was predicted. It was shown that the void content increased steeply at a volumetric energy density threshold below 81 J/mm3. The crack density, on the other hand, increased steeply at a volumetric energy density threshold above 163 J/mm3. The microhardness displayed a relatively low value in three samples which displayed the lowest volumetric energy density and highest void content. It was also observed that two samples, which displayed the highest volumetric energy density and crack density, demonstrated a relatively high microhardness; which could be a vital evidence in future investigations to determine the fundamental mechanism of cracking. The laser power was concluded to be the strongest and statistically most significant process parameter that influenced void formation and microhardness. The interaction of laser power and hatch distance was the strongest and most significant factor that influenced the crack density.

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On the Relevance of Volumetric Energy Density in the Investigation of Inconel 718 Laser Powder Bed Fusion

Materials ◽

10.3390/ma13030538 ◽

2020 ◽

Vol 13 (3) ◽

pp. 538 ◽

Cited By ~ 6

Author(s):

Fabrizia Caiazzo ◽

Vittorio Alfieri ◽

Giuseppe Casalino

Keyword(s):

Surface Roughness ◽

Energy Density ◽

Process Parameters ◽

Vickers Hardness ◽

Powder Bed Fusion ◽

Processing Conditions ◽

Laser Powder Bed Fusion ◽

Powder Bed ◽

Fractional Density ◽

Experimental Variation

Laser powder bed fusion (LPBF) can fabricate products with tailored mechanical and surface properties. In fact, surface texture, roughness, pore size, the resulting fractional density, and microhardness highly depend on the processing conditions, which are very difficult to deal with. Therefore, this paper aims at investigating the relevance of the volumetric energy density (VED) that is a concise index of some governing factors with a potential operational use. This paper proves the fact that the observed experimental variation in the surface roughness, number and size of pores, the fractional density, and Vickers hardness can be explained in terms of VED that can help the investigator in dealing with several process parameters at once.

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Optimizing Laser Powder Bed Fusion Parameters for IN-738LC by Response Surface Method

Materials ◽

10.3390/ma13214879 ◽

2020 ◽

Vol 13 (21) ◽

pp. 4879

Author(s):

Mireia Vilanova ◽

Rubén Escribano-García ◽

Teresa Guraya ◽

Maria San Sebastian

Keyword(s):

Response Surface ◽

Response Surface Method ◽

Process Parameters ◽

Crack Density ◽

Processing Parameters ◽

Optimum Process ◽

Powder Bed Fusion ◽

Laser Powder Bed Fusion ◽

Powder Bed ◽

Surface Method

A method to find the optimum process parameters for manufacturing nickel-based superalloy Inconel 738LC by laser powder bed fusion (LPBF) technology is presented. This material is known to form cracks during its processing by LPBF technology; thus, process parameters have to be optimized to get a high quality product. In this work, the objective of the optimization was to obtain samples with fewer pores and cracks. A design of experiments (DoE) technique was implemented to define the reduced set of samples. Each sample was manufactured by LPBF with a specific combination of laser power, laser scan speed, hatch distance and scan strategy parameters. Using the porosity and crack density results obtained from the DoE samples, quadratic models were fitted, which allowed identifying the optimal working point by applying the response surface method (RSM). Finally, five samples with the predicted optimal processing parameters were fabricated. The examination of these samples showed that it was possible to manufacture IN738LC samples free of cracks and with a porosity percentage below 0.1%. Therefore, it was demonstrated that RSM is suitable for obtaining optimum process parameters for IN738LC alloy manufacturing by LPBF technology.

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A processing diagram for high-density Ti-6Al-4V by selective laser melting

Rapid Prototyping Journal ◽

10.1108/rpj-11-2017-0228 ◽

2018 ◽

Vol 24 (9) ◽

pp. 1469-1478 ◽

Cited By ~ 15

Author(s):

Yinmin (Morris) Wang ◽

Chandrika Kamath ◽

Thomas Voisin ◽

Zan Li

Keyword(s):

Mechanical Properties ◽

Energy Density ◽

Processing Parameters ◽

High Density ◽

Low Density ◽

Laser Powder Bed Fusion ◽

Content Type ◽

Powder Bed ◽

Melt Pool ◽

Hatch Spacing

Purpose Density optimization is the first critical step in building additively manufactured parts with high-quality and good mechanical properties. The authors developed an approach that combines simulations and experiments to identify processing parameters for high-density Ti-6Al-4V using the laser powder-bed-fusion technique. A processing diagram based on the normalized energy density concept is constructed, illustrating an optimized processing window for high- or low-density samples. Excellent mechanical properties are obtained for Ti-6Al-4V samples built from the optimized window. Design/methodology/approach The authors use simple, but approximate, simulations and selective experiments to design parameters for a limited set of single track experiments. The resulting melt-pool characteristics are then used to identify processing parameters for high-density pillars. A processing diagram is built and excellent mechanical properties are achieved in samples built from this window. Findings The authors find that the laser linear input energy has a much stronger effect on the melt-pool depth than the melt-pool width. A processing diagram based on normalized energy density and normalized hatch spacing was constructed, qualitatively indicating that high-density samples are produced in a region when 1 < E* < 2. The onset of void formation and low-density samples occur as E* moves beyond a value of 2. The as-built SLM Ti-6Al-4V shows excellent mechanical performance. Originality/value A combined approach of computer simulations and selected experiments is applied to optimize the density of Ti-6Al-4V, via laser powder-bed-fusion (L-PBF) technique. A series of high-density samples are achieved. Some special issues are identified for L-PBF processes of Ti-6Al-4V, including the powder particle sticking and part swelling issues. A processing diagram is constructed for Ti-6Al-4V, based on the normalized energy density and normalized hatch spacing concept. The diagram illustrates windows with high- and low-density samples. Good mechanical properties are achieved during tensile tests of near fully dense Ti-6Al-4V samples. These good properties are attributed to the success of density optimization processes.

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Influence of Material Property Variation on Computationally Calculated Melt Pool Temperature during Laser Melting Process

Metals ◽

10.3390/met9040456 ◽

2019 ◽

Vol 9 (4) ◽

pp. 456 ◽

Cited By ~ 4

Author(s):

Sazzad H. Ahmed ◽

Ahsan Mian

Keyword(s):

Thermal Conductivity ◽

Specific Heat ◽

Process Parameters ◽

Laser Power ◽

Laser Scanning ◽

Peak Temperature ◽

Powder Layer ◽

Laser Melting ◽

Melt Pool ◽

Melt Pool Temperature

Selective Laser Melting (SLM) is a popular additive manufacturing (AM) method where a laser beam selectively melts powder layer by layer based on the building geometry. The melt pool peak temperature during build process is an important parameter to determine build quality of a fabricated component by SLM process. The melt pool temperature depends on process parameters including laser power, scanning speed, and hatch space as well as the properties of the build material. In this paper, the sensitivity of melt pool peak temperature during the build process to temperature dependent material properties including density, specific heat, and thermal conductivity are investigated for a range of laser powers and laser scanning speeds. It is observed that the melt pool temperature is most sensitive to melt pool thermal conductivity of the processed material for a set of specific process parameters (e.g., laser power and scan speed). Variations in the other mechanical–physical properties of powder and melt pool such as density and specific heat are found to have minimal effect on melt pool temperature.

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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 ◽

10.3390/nano11123284 ◽

2021 ◽

Vol 11 (12) ◽

pp. 3284

Author(s):

Asif Ur Rehman ◽

Muhammad Arif Mahmood ◽

Fatih Pitir ◽

Metin Uymaz Salamci ◽

Andrei C. Popescu ◽

...

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Energy Density ◽

Operating Conditions ◽

Dynamics Simulation ◽

Powder Layer ◽

Powder Bed Fusion ◽

Laser Powder Bed Fusion ◽

Powder Bed ◽

Melt Pool

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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Laser Powder Bed Fusion (LPBF) of In718 and the Impact of Pre-Heating at 500 and 1000 °C: Operando Study

Materials ◽

10.3390/ma14216683 ◽

2021 ◽

Vol 14 (21) ◽

pp. 6683

Author(s):

Asif Ur Rehman ◽

Fatih Pitir ◽

Metin Uymaz Salamci

Keyword(s):

Critical Role ◽

Simulation Models ◽

Parameters Optimization ◽

Powder Bed Fusion ◽

Laser Powder Bed Fusion ◽

Physical Processes ◽

Mesoscopic Simulation ◽

Powder Bed ◽

Melt Pool ◽

The Impact

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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Experimental analysis of the influence of process parameters on the melt pool formation and stability in powder bed laser

International Congress on Applications of Lasers & Electro-Optics ◽

10.2351/1.5062886 ◽

2013 ◽

Cited By ~ 1

Author(s):

Runchen Cao ◽

Pascal Aubry ◽

Kevin Verdier

Keyword(s):

Process Parameters ◽

Experimental Analysis ◽

Influence Of Process Parameters ◽

Powder Bed ◽

Melt Pool ◽

Pool Formation

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Optimization of parameters for SLS of WC-Co

Rapid Prototyping Journal ◽

10.1108/rpj-10-2016-0168 ◽

2017 ◽

Vol 23 (6) ◽

pp. 1202-1211 ◽

Cited By ~ 11

Author(s):

Sanjay Kumar ◽

Aleksander Czekanski

Keyword(s):

Energy Density ◽

Process Parameters ◽

Laser Power ◽

Laser Energy ◽

Beam Diameter ◽

Content Type ◽

Powder Bed ◽

Scan Speed ◽

New Equation ◽

Hatch Spacing

Purpose WC-Co is a well-known material for conventional tooling but is not yet commercially available for additive manufacturing. Processing it by selective laser sintering (SLS) will pave the way for its commercialization and adoption. Design/methodology/approach It is intended to optimize process parameters (laser power, hatch spacing, scan speed) by fabricating a bigger part (minimum size of 10 mm diameter and 5 mm height). Microstructural analysis, EDX and hardness testing is used to study effects of process parameters. Optimized parameter is ascertained after fabricating 49 samples in preliminary experiment, 27 samples in pre-final experiment and 9 samples in final experiment. Findings Higher laser power gives rise to cracks and depletion of cobalt while higher scan speed increases porosity. Higher hatch spacing is responsible for delamination and displacement of parts. Optimized parameters are 270 W laser power, 500 mm/s scan speed, 0.04 mm layer thickness, 0.04 mm hatch spacing (resulting in energy density of 216 J/mm3) and 200°C powder bed temperature. A part comprising of small hole of 2 mm diameter, thin cylindrical pin of 0.5 mm diameter and thin wall of 2 mm width bent up to 30° angle to the base plate is fabricated. In order to calculate laser energy density, a new equation is introduced which takes into account both beam diameter and hatch spacing unlike old equation does. In order to calculate laser energy density, a new equation is formulated which takes into account both beam diameter and hatch spacing unlike old equation does. WC was not completely melted as intended giving rise to partial melting-type binding mechanism. This justified the name SLS for process in place of SLM (Selective Laser Melting). Research limitations/implications Using all possible combination of parameters plus heating the part bed to maximum shows limitation of state-of-the-art commercial powder bed fusion machine for shaping hardmetal consisting of high amount of WC (83 wt. per cent). Practical implications The research shows that microfeatures could be fabricated using WC-Co which will herald renewed interest in investigating hardmetals using SLS for manufacturing complex hard tools, molds and wear-resistance parts. Originality/value This is the first time micro features are successfully fabricated using WC-Co without post-processing (infiltration, machining) and without the help of additional binding material (such as Cu, Ni, Fe).

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