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

Materials ◽  
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.

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

Materials ◽  
2020 ◽  
Vol 13 (3) ◽  
pp. 538 ◽  
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.

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

Materials ◽  
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.

The mechanism of process parameters influencing the AlSi10Mg side surface quality fabricated via laser powder bed fusion

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Shimin Dai ◽  
Hailong Liao ◽  
Haihong Zhu ◽  
Xiaoyan Zeng
Keyword(s):  
Surface Roughness ◽  
Surface Quality ◽  
Process Parameters ◽  
Laser Power ◽  
Side Surface ◽  
Laser Powder Bed Fusion ◽  
Scanning Velocity ◽  
Content Type ◽  
Powder Bed

Purpose For the laser powder bed fusion (L-PBF) technology, the side surface quality is essentially important for industrial applicated parts, such as the inner flow parts. Contour is generally adopted at the parts’ outline to enhance the side surface quality. However, the side surface roughness (Ra) is still larger than 10 microns even with contour in previous studies. The purpose of this paper is to study the influence of contour process parameters, laser power and scanning velocity on the side surface quality of the AlSi10Mg sample. Design/methodology/approach Using L-PBF technology to manufacture AlSi10Mg samples under different contour process parameters, use a laser confocal microscope to capture the surface information of the samples, and obtain the surface roughness Ra and the maximum surface height Rz of each sample after analysis and processing. Findings The results show that the side surface roughness decreases with the increase of the laser power at the fixed scanning velocity of 1,000 mm/s, the side surface roughness Ra stays within the error range as the contour velocity increases. It is found that the Ra increases with the scanning velocity increasing and the greater the laser power with the greater Ra increases when the laser power of contour process parameters is 300 W, 350 W and 400 W. The Rz maintain growth with the contour scanning velocity increasing at constant laser power. The continuous uniform contour covers the pores in the molten pool of the sample edge and thus increase the density of the sample. Two mechanisms named “Active adhesion” and “Passive adhesion” cause sticky powder. Originality/value Formation of a uniform and even contour track is key to obtain the good side surface quality. The side surface quality is determined by the uniformity and stability of the contour track when the layer thickness is fixed. These research results can provide helpful guidance to improve the surface quality of L-PBF manufactured parts.

scholarly journals Manufacturing Aluminum/Multiwalled Carbon Nanotube Composites via Laser Powder Bed Fusion

Materials ◽  
2020 ◽  
Vol 13 (18) ◽  
pp. 3927
Author(s):  
Eo Ryeong Lee ◽  
Se Eun Shin ◽  
Naoki Takata ◽  
Makoto Kobashi ◽  
Masaki Kato
Keyword(s):  
Elastic Modulus ◽  
Carbon Nanotube ◽  
Energy Density ◽  
Laser Power ◽  
Multiwalled Carbon Nanotube ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Multiwalled Carbon ◽  
Powder Bed ◽  
Scan Speed

This study provides a novel approach to fabricating Al/C composites using laser powder bed fusion (LPBF) for a wide range of structural applications utilizing Al-matrix composites in additive manufacturing. We investigated the effects of LPBF on the fabrication of aluminum/multiwalled carbon nanotube (Al/MWCNT) composites under 25 different conditions, using varying laser power levels and scan speeds. The microstructures and mechanical properties of the specimens, such as elastic modulus and nanohardness, were analyzed, and trends were identified. We observed favorable sintering behavior under laser conditions with low energy density, which verified the suitability of Al/MWCNT composites for a fabrication process using LPBF. The size and number of pores increased in specimens produced under high energy density conditions, suggesting that they are more influenced by laser power than scan speed. Similarly, the elastic modulus of a specimen was also more affected by laser power than scan speed. In contrast, scan speed had a greater influence on the final nanohardness. Depending on the laser power used, we observed a difference in the crystallographic orientation of the specimens by a laser power during LPBF. When energy density is high, texture development of all samples tended to be more pronounced.

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

2021 ◽  
Author(s):  
Di Wang ◽  
Sheng Li ◽  
Guowei Deng ◽  
Yang Liu ◽  
Moataz M. Attallah
Keyword(s):  
Energy Density ◽  
Process Parameters ◽  
Crack Formation ◽  
Crack Density ◽  
Chemical Compositions ◽  
Temperature Model ◽  
Powder Bed ◽  
Melt Pool ◽  
Melt Pool Temperature ◽  
The Impact

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.

Optimization of parameters for SLS of WC-Co

2017 ◽  
Vol 23 (6) ◽  
pp. 1202-1211 ◽  
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).

Focus Variation Measurement and Prediction of Surface Texture Parameters Using Machine Learning in Laser Powder Bed Fusion

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Tuğrul Özel ◽  
Ayça Altay ◽  
Bilgin Kaftanoğlu ◽  
Richard Leach ◽  
Nicola Senin ◽  
...  
Keyword(s):  
Machine Learning ◽  
Energy Density ◽  
Surface Topography ◽  
Process Parameters ◽  
Surface Texture ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Powder Bed ◽  
Texture Parameters ◽  
Focus Variation

Abstract The powder bed fusion-based additive manufacturing process uses a laser to melt and fuse powder metal material together and creates parts with intricate surface topography that are often influenced by laser path, layer-to-layer scanning strategies, and energy density. Surface topography investigations of as-built, nickel alloy (625) surfaces were performed by obtaining areal height maps using focus variation microscopy for samples produced at various energy density settings and two different scan strategies. Surface areal height maps and measured surface texture parameters revealed the highly irregular nature of surface topography created by laser powder bed fusion (LPBF). Effects of process parameters and energy density on the areal surface texture have been identified. Machine learning methods were applied to measured data to establish input and output relationships between process parameters and measured surface texture parameters with predictive capabilities. The advantages of utilizing such predictive models for process planning purposes are highlighted.

scholarly journals Laser Powder Bed Fusion of NiTiHf High-Temperature Shape Memory Alloy: Effect of Process Parameters on the Thermomechanical Behavior

Metals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1522
Author(s):  
Mohammadreza Nematollahi ◽  
Guher P. Toker ◽  
Keyvan Safaei ◽  
Alejandro Hinojos ◽  
S. Ehsan Saghaian ◽  
...  
Keyword(s):  
High Temperature ◽  
Energy Density ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Process Parameters ◽  
Thermomechanical Behavior ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Powder Bed ◽  
Actuation Strain

Laser powder bed fusion has been widely investigated for shape memory alloys, primarily NiTi alloys, with the goal of tailoring microstructures and producing complex geometries. However, processing high temperature shape memory alloys (HTSMAs) remains unknown. In our previous study, we showed that it is possible to manufacture NiTiHf HTSMA, as one of the most viable alloys in the aerospace industry, using SLM and investigated the effect of parameters on defect formation. The current study elucidates the effect of process parameters (PPs) on the functionality of this alloy. Shape memory properties and the microstructure of additively manufactured Ni-rich NiTiHf alloys were characterized across a wide range of PPs (laser power, scanning speed, and hatch spacing) and correlated with energy density. The optimum laser parameters for defect-free and functional samples were found to be in the range of approximately 60–100 J/mm3. Below an energy density of 60 J/mm3, porosity formation due to lack-of-fusion is the limiting factor. Samples fabricated with energy densities of 60–100 J/mm3 showed comparable thermomechanical behavior in comparison with the starting as-cast material, and samples fabricated with higher energy densities (>100 J/mm3) showed very high transformation temperatures but poor thermomechanical behavior. Poor properties for samples with higher energies were mainly attributed to the excessive Ni loss and resultant change in the chemical composition of the matrix, as well as the formation of cracks and porosities. Although energy density was found to be an important factor, the outcome of this study suggests that each of the PPs should be selected carefully. A maximum actuation strain of 1.67% at 400 MPa was obtained for the sample with power, scan speed, and hatch space of 100 W, 400 mm/s, and 140 µm, respectively, while 1.5% actuation strain was obtained for the starting as-cast ingot. These results can serve as a guideline for future studies on optimizing PPs for fabricating functional HTSMAs.

scholarly journals Melt Pool Features Analysis Using a High Speed Coaxial Monitoring System for Laser Powder Bed Fusion of Ti-6Al-4V Grade 23

2021 ◽  
Author(s):  
Aditi Thanki ◽  
Louca Goossens ◽  
Agusmian Partogi Ompusunggu ◽  
Mohamad Bayat ◽  
Abdellatif Bey-Temsamani ◽  
...  
Keyword(s):  
Energy Density ◽  
Laser Power ◽  
High Speed ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Porosity Formation ◽  
Powder Bed ◽  
Binary Images ◽  
Melt Pool ◽  
Scan Speed

Abstract In laser powder bed fusion (LPBF), defects such as pores or cracks can seriously affect the final part quality and lifetime. Keyhole porosity, being one type of porosity defects in LPBF, results from excessive energy density which may be due to changes in process parameters (laser power and scan speed) and/or result from the part’s geometry and/or hatching strategies. To study the possible occurrence of keyhole pores, experimental work as well as simulations were carried out for optimum and high volumetric energy density conditions in Ti-6Al-4V grade 23. By decreasing the scanning speed from 1000 mm/s to 500 mm/s for a fixed laser power of 170 W, keyhole porosities are formed and later observed by X-ray computed tomography. Melt pool images are recorded in real-time during the LPBF process by using a high speed coaxial Near-Infrared (NIR) camera monitoring system. The recorded images are then pre-processed using a set of image processing steps to generate binary images. From the binary images, geometrical features of the melt pool and features that characterize the spatter particles formation and ejection from the melt pool are calculated. The experimental data clearly show spatter patterns in case of keyhole porosity formation at low scan speed. A correlation between the number of pores and the amount of spatter is observed. Besides the experimental work, a previously developed, high fidelity finite volume numerical model was used to simulate the melt pool dynamics with similar process parameters as in the experiment. Simulation results illustrate and confirm the keyhole porosity formation by decreasing laser scan speed.

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