scholarly journals Effect of Carbon Content on the Processability of Fe-C Alloys Produced by Laser Based Powder Bed Fusion

2022 ◽  
Vol 8 ◽  
Author(s):  
William Hearn ◽  
Eduard Hryha
Keyword(s):  
Heat Treatment ◽  
Carbon Content ◽  
Cross Sections ◽  
Mitigation Strategies ◽  
Cold Cracking ◽  
Process Window ◽  
Powder Bed Fusion ◽  
Powder Bed ◽  
Lack Of Fusion ◽  
Melt Pool

The present study examines the processability of Fe-C alloys, with carbon contents up to 1.1 wt%, when using laser based powder bed fusion (LB-PBF). Analysis of specimen cross-sections revealed that lack of fusion porosity was prominent in specimens produced at low volumetric energy density (VED), while keyhole porosity was prominent in specimens produced at high VED. The formation of porosity was also influenced by the carbon content, where increasing the carbon content reduced lack of fusion porosity, while simultaneously increasing the susceptibility to form keyhole porosity. These trends were related to an improved wettability, viscosity, and flow of the melt pool as well an increased melt pool depth as the carbon content increased. Cold cracking defects were also observed in Fe-C alloys that had an as-built hardness ≥425 HV. Reducing the carbon content below 0.75 wt% and increasing the VED, which improved the intrinsic heat treatment during LB-PBF, were found to be effective mitigation strategies to avoid cold cracking defects. Based upon these results, a process window for the Fe-C system was established that produces high density (>99.8%), defect-free specimens via LB-PBF without the requirement of build plate preheating.

Thermal Based Process Monitoring for Laser Powder Bed Fusion (LPBF)

2021 ◽  
Vol 1161 ◽  
pp. 123-130
Author(s):  
Dieter Tyralla ◽  
Thomas Seefeld
Keyword(s):  
Process Monitoring ◽  
Cross Sections ◽  
Observation System ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Destructive Testing ◽  
Camera System ◽  
Powder Bed ◽  
Post Process ◽  
Melt Pool

Laser powder bed fusion (LPBF) is a frequently used manufacturing process due to its advantages in lightweight construction, design possibilities and functionalization of geometry. However, the printed parts will often have to undergo time and cost expensive non-destructive testing by sophisticated methods like X-CT. Thus, there is a strong demand to identify suitable online process monitoring techniques that allow to reduce or substitute post-process NDT effort. The temperature field reacts sensitively to deviations during processing, thus online temperature monitoring is a promising approach. In the present work a spatially resolved temperature measurement, based on 2-channel-pyrometry, is used for process monitoring in LPBF. The camera system is coaxially integrated into the beam guidance of the LPBF system. The coaxial observation enables a lateral resolution better than 10 μm over the whole build-up area of 250 x 250 mm2. Single tracks were welded with different parameters and observed by the camera system to identify thermal indicators. Metallographic cross-sections of the tracks were compared with the melt pool width measured by the online observation system. The deviation was ca. 3 %. In addition, cubes of 10 mm by 10 mm by 10 mm are built up. The melt pool area is identified as useful indicator for the process behavior and for the first time the assessment of part density is demonstrated in LPBF during process by the help of a thermal monitoring system.

scholarly journals Processability and Optimization of Laser Parameters for Densification of Hypereutectic Al–Fe Binary Alloy Manufactured by Laser Powder Bed Fusion

Crystals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 320
Author(s):  
Wenyuan Wang ◽  
Naoki Takata ◽  
Asuka Suzuki ◽  
Makoto Kobashi ◽  
Masaki Kato
Keyword(s):  
Energy Density ◽  
Binary Alloy ◽  
Process Window ◽  
Process Conditions ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Powder Bed ◽  
Melt Pool ◽  
Deposited Energy ◽  
Scan Speed

Centimeter-sized samples of hypereutectic Al–15 mass% Fe alloy were manufactured by a laser powder bed fusion (L-PBF) process while systematically varying laser power (P) and scan speed (v). The effects on relative density and melt pool depth of L-PBF-manufactured samples were investigated. In comparison with other Al alloys, a small laser process window of P = 77–128 W and v = 0.4–0.8 ms−1 was found for manufacturing macroscopically crack-free samples. A higher v and P led to the creation of macroscopic cracks propagating parallel to the powder-bed plane. These cracks preferentially propagated along the melt pool boundaries decorated with brittle θ-Al13Fe4 phase, resulting in low L-PBF processability of Al–15%Fe alloy. The deposited energy density model (using P·v−1/2) would be useful for identifying the optimum L-PBF process conditions towards densification of Al–15%Fe alloy samples, in comparison with the volumetric energy density (using P·v−1), however, the validity of the model was reduced for this alloy in comparison with other alloys with high thermal conductivities. This is likely due to inhomogeneous microstructures having numerous coarsened θ–Al13Fe4 phases localized at melt pool boundaries. These results provide insights into achieving sufficient L-PBF processability for manufacturing dense Al–Fe binary alloy samples.

scholarly journals A Single Crystal Process Window for Electron Beam Powder Bed Fusion Additive Manufacturing of a CMSX-4 Type Ni-Based Superalloy

Materials ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 3785
Author(s):  
Julian Pistor ◽  
Christoph Breuning ◽  
Carolin Körner
Keyword(s):  
Additive Manufacturing ◽  
Single Crystal ◽  
Single Crystals ◽  
Process Window ◽  
Powder Bed Fusion ◽  
Powder Bed ◽  
Melt Pool ◽  
High Fraction ◽  
Scanning Strategies ◽  
Melt Pool Size

Using suitable scanning strategies, even single crystals can emerge from powder during additive manufacturing. In this paper, a full microstructure map for additive manufacturing of technical single crystals is presented using the conventional single crystal Ni-based superalloy CMSX-4. The correlation between process parameters, melt pool size and shape, as well as single crystal fraction, is investigated through a high number of experiments supported by numerical simulations. Based on these results, a strategy for the fabrication of high fraction single crystals in powder bed fusion additive manufacturing is deduced.

scholarly journals A new approach for automated measuring of the melt pool geometry in laser-powder bed fusion

2021 ◽  
Author(s):  
Simon Schmid ◽  
Johannes Krabusch ◽  
Thomas Schromm ◽  
Shi Jieqing ◽  
Stefan Ziegelmeier ◽  
...  
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Energy Input ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
New Approach ◽  
Powder Bed ◽  
Part Quality ◽  
Melt Pool ◽  
Process Disturbances

AbstractAdditive manufacturing (AM) offers unique possibilities in comparison to conventional manufacturing processes. For example, complex parts can be manufactured without tools. For metals, the most commonly used AM process is laser-powder bed fusion (L-PBF). The L-PBF process is prone to process disturbances, hence maintaining a consistent part quality remains an important subject within current research. An established indicator for quantifying process changes is the dimension of melt pools, which depends on the energy input and the cooling conditions. The melt pool geometry is normally measured manually in cross sections of solidified welding seams. This paper introduces a new approach for the automated visual measuring of melt pools in cross-sections of parts manufactured by L-PBF. The melt pools are first segmented in the images and are then measured. Since the melt pools have a heterogeneous appearance, segmentation with common digital image processing is difficult, deep learning was applied in this project. With the presented approach, the melt pools can be measured over the whole cross section of the specimen. Furthermore, remelted melt pools, which are only partly visible, are evaluated. With this automated approach, a high number of melt pools in each cross-section can be measured, which allows the examination of trends over the build direction in a specimen and results in better statistics. Furthermore, deviations in the energy input can be estimated via the measured melt pool dimensions.

scholarly journals Process characterization and analysis of ceramic powder bed fusion

2021 ◽  
Author(s):  
Kevin Florio ◽  
Dario Puccio ◽  
Giorgio Viganò ◽  
Stefan Pfeiffer ◽  
Fabrizio Verga ◽  
...  
Keyword(s):  
High Speed ◽  
Ceramic Powder ◽  
Integrating Sphere ◽  
Alumina Powder ◽  
Powder Bed Fusion ◽  
Single Track ◽  
Ceramic Powders ◽  
Pure Alumina ◽  
Powder Bed ◽  
Melt Pool

AbstractPowder bed fusion (PBF) of ceramics is often limited because of the low absorptance of ceramic powders and lack of process understanding. These challenges have been addressed through a co-development of customized ceramic powders and laser process capabilities. The starting powder is made of a mix of pure alumina powder and alumina granules, to which a metal oxide dopant is added to increase absorptance. The performance of different granules and process parameters depends on a large number of influencing factors. In this study, two methods for characterizing and analyzing the PBF process are presented and used to assess which dopant is the most suitable for the process. The first method allows one to analyze the absorptance of the laser during the melting of a single track using an integrating sphere. The second one relies on in-situ video imaging using a high-speed camera and an external laser illumination. The absorption behavior of the laser power during the melting of both single tracks and full layers is proven to be a non-linear and extremely dynamic process. While for a single track, the manganese oxide doped powder delivers higher and more stable absorptance. When a full layer is analyzed, iron oxide-doped powder is leading to higher absorptance and a larger melt pool. Both dopants allow the generation of a stable melt-pool, which would be impossible with granules made of pure alumina. In addition, the present study sheds light on several phenomena related to powder and melt-pool dynamics, such as the change of melt-pool shape and dimension over time and powder denudation effects.

scholarly journals Carbon Particle In-Situ Alloying of the Case-Hardening Steel 16MnCr5 in Laser Powder Bed Fusion

Metals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 896
Author(s):  
Matthias Schmitt ◽  
Albin Gottwalt ◽  
Jakob Winkler ◽  
Thomas Tobie ◽  
Georg Schlick ◽  
...  
Keyword(s):  
Laser Beam ◽  
Mechanical Strength ◽  
Carbon Content ◽  
Metal Powder ◽  
Case Hardening ◽  
Powder Bed Fusion ◽  
Powder Bed ◽  
Carbon Particles ◽  
Case Hardening Steel

The carbon content of steel affects many of its essential properties, e.g., hardness and mechanical strength. In the powder bed fusion process of metals using a laser beam (PBF-LB/M), usually, pre-alloyed metal powder is solidified layer-by-layer using a laser beam to create parts. A reduction of the carbon content in steels is observed during this process. This study examines adding carbon particles to the metal powder and in situ alloying in the PBF-LB/M process as a countermeasure. Suitable carbon particles are selected and their effect on the particle size distribution and homogeneity of the mixtures is analysed. The workability in PBF-LB is then shown. This is followed by an evaluation of the resulting mechanical properties (hardness and mechanical strength) and microstructure in the as-built state and the state after heat treatment. Furthermore, potential use cases like multi-material or functionally graded parts are discussed.

scholarly journals Laser Powder Bed Fusion Processing of Fe-Mn-Al-Ni Shape Memory Alloy—On the Effect of Elevated Platform Temperatures

Metals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 185
Author(s):  
Felix Clemens Ewald ◽  
Florian Brenne ◽  
Tobias Gustmann ◽  
Malte Vollmer ◽  
Philipp Krooß ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Crack Formation ◽  
Microstructural Analysis ◽  
Tensile Load ◽  
Grain Structure ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Cyclic Heat Treatment ◽  
Powder Bed ◽  
Cyclic Heat

In order to overcome constraints related to crack formation during additive processing (laser powder bed fusion, L-BPF) of Fe-Mn-Al-Ni, the potential of high-temperature L-PBF processing was investigated in the present study. The effect of the process parameters on crack formation, grain structure, and phase distribution in the as-built condition, as well as in the course of cyclic heat treatment was examined by microstructural analysis. Optimized processing parameters were applied to fabricate cylindrical samples featuring a crack-free and columnar grained microstructure. In the course of cyclic heat treatment, abnormal grain growth (AGG) sets in, eventually promoting the evolution of a bamboo like microstructure. Testing under tensile load revealed a well-defined stress plateau and reversible strains of up to 4%.

scholarly journals Optimization of Laser Powder Bed Fusion Processing Using a Combination of Melt Pool Modeling and Design of Experiment Approaches: Density Control

2019 ◽  
Vol 3 (1) ◽  
pp. 21 ◽  
Author(s):  
Morgan Letenneur ◽  
Alena Kreitcberg ◽  
Vladimir Brailovski
Keyword(s):  
Scanning Speed ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Powder Bed ◽  
Density Prediction ◽  
Melt Pool ◽  
Density Control ◽  
Pool Model ◽  
Conventional Material ◽  
Prediction Approach

A simplified analytical model of the laser powder bed fusion (LPBF) process was used to develop a novel density prediction approach that can be adapted for any given powder feedstock and LPBF system. First, calibration coupons were built using IN625, Ti64 and Fe powders and a specific LPBF system. These coupons were manufactured using the predetermined ranges of laser power, scanning speed, hatching space, and layer thickness, and their densities were measured using conventional material characterization techniques. Next, a simplified melt pool model was used to calculate the melt pool dimensions for the selected sets of printing parameters. Both sets of data were then combined to predict the density of printed parts. This approach was additionally validated using the literature data on AlSi10Mg and 316L alloys, thus demonstrating that it can reliably be used to optimize the laser powder bed metal fusion process.

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