Powder characterization and part density for powder bed fusion of 17-4 PH stainless steel

Purpose Characteristics of the metal powder are a key factor in the success of powder bed fusion (PBF) additive manufacturing. Powders for PBF from different manufacturers may have a different particle size and/or bulk packing and flow behavior. Powder properties change as the powder is reused for multiple builds. This study seeks to measure the variability of commercial 17-4 PH stainless steel powders to determine the effect of powder variability on part density and demonstrate characterization methods that ensure part quality. Design/methodology/approach Commercial atomized metal powders from four different vendors were produced with two different atomizing gases (N2 and argon). Powder was characterized in both new and extensively reused conditions. All powders were characterized for flow and packing behavior, particle size and internal porosity. Coupons were manufactured using the laser PBF process with optimized scan strategy and exposure parameters. The quality of fabricated parts was measured using bulk density measurement. Findings Despite differences in powder flowability and particle size, fully dense parts (>99 per cent) were produced using all powders, except one. Residual porosity in these parts appeared to result from gas trapped in the powder particles. The powder with extensive reuse (400+ h in machine fabrication environment) exhibited reduced flowability and increased fraction of fine particles, but still produced full density parts. Originality/value This study demonstrates that full density parts can be fabricated using powders with a range of flowability and packing behavior. This suggests that a single flowability measurement may be sufficient for quality assurance in a production environment.

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Controlling the porosity of 316L stainless steel parts manufactured via the powder bed fusion process

Rapid Prototyping Journal ◽

10.1108/rpj-11-2017-0226 ◽

2019 ◽

Vol 25 (1) ◽

pp. 162-175 ◽

Cited By ~ 7

Author(s):

Abdullah AlFaify ◽

James Hughes ◽

Keith Ridgway

Keyword(s):

Stainless Steel ◽

Layer Thickness ◽

Exposure Time ◽

Process Parameters ◽

Pulsed Laser ◽

Powder Bed Fusion ◽

Content Type ◽

Powder Bed ◽

Point Distance ◽

Part Density

Purpose The pulsed-laser powder bed fusion (PBF) process is an additive manufacturing technology that uses a laser with pulsed beam to melt metal powder. In this case, stainless steel SS316L alloy is used to produce complex components. To produce components with acceptable mechanical performance requires a comprehensive understanding of process parameters and their interactions. This study aims to understand the influence of process parameters on reducing porosity and increasing part density. Design/methodology/approach The response surface method (RSM) is used to investigate the impact of changing critical parameters on the density of parts manufactured. Parameters considered include: point distance, exposure time, hatching distance and layer thickness. Part density was used to identify the most statistically significant parameters, before each parameter was analysed individually. Findings A clear correlation between the number and shape of pores and the process parameters was identified. Point distance, exposure time and layer thickness were found to significantly affect part density. The interaction between these parameters also critically affected the development of porosity. Finally, a regression model was developed and verified experimentally and used to accurately predict part density. Research limitations/implications The study considered a range of selected parameters relevant to the SS316L alloy. These parameters need to be modified for other alloys according to their physical properties. Originality/value This study is believed to be the first systematic attempt to use RSM for the design of experiments (DOE) to investigate the effect of process parameters of the pulsed-laser PBF process on the density of the SS316L alloy components.

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Plasma Spheroidisation of Irregular Ti6Al4V Powder for Powder Bed Fusion

Metals ◽

10.3390/met11111763 ◽

2021 ◽

Vol 11 (11) ◽

pp. 1763

Author(s):

Nthateng Nkhasi ◽

Willie du Preez ◽

Hertzog Bissett

Keyword(s):

Particle Size ◽

Additive Manufacturing ◽

Particle Size Distribution ◽

Size Distribution ◽

Metal Powder ◽

Weight Ratio ◽

High Strength ◽

Powder Bed Fusion ◽

Metal Powders ◽

Powder Bed

Metal powders suitable for use in powder bed additive manufacturing processes should ideally be spherical, dense, chemically pure and of a specified particle size distribution. Ti6Al4V is commonly used in the aerospace, medical and automotive industries due to its high strength-to-weight ratio and excellent corrosion resistance properties. Interstitial impurities in titanium alloys have an impact upon mechanical properties, particularly oxygen, nitrogen, hydrogen and carbon. The plasma spheroidisation process can be used to spheroidise metal powder consisting of irregularly shaped particles. In this study, the plasma spheroidisation of metal powder was performed on Ti6Al4V powder consisting of irregularly shaped particles. The properties of the powder relevant for powder bed fusion that were determined included the particle size distribution, morphology, particle porosity and chemical composition. Conclusions were drawn regarding the viability of using this process to produce powder suitable for additive manufacturing.

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Influence of the particle size distribution of monomodal 316L powder on its flowability and processability in powder bed fusion

Progress in Additive Manufacturing ◽

10.1007/s40964-021-00240-z ◽

2021 ◽

Author(s):

Marvin A. Spurek ◽

Lukas Haferkamp ◽

Christian Weiss ◽

Adriaan B. Spierings ◽

Johannes H. Schleifenbaum ◽

...

Keyword(s):

Particle Size ◽

Particle Size Distribution ◽

Powder Bed Fusion ◽

Median Particle Size ◽

Distribution Width ◽

Powder Bed ◽

Melt Pool ◽

Powder Flowability ◽

Median Particle ◽

Part Density

AbstractPowder bed fusion (PBF) is the most commonly adopted additive manufacturing process for fabricating complex metal parts via the layer-wise melting of a powder bed using a laser beam. However, the qualification of PBF-manufactured parts remains challenging and expensive, thereby limiting the broader industrialization of the technology. Powder characteristics significantly influence part properties, and understanding the influencing factors contributes to effective quality standards for PBF. In this study, the influence of the particle size distribution (PSD) median and width on powder flowability and part properties is investigated. Seven gas-atomized SS316L powders with monomodal PSDs, a median particle size ranging from 10 μm to 60 μm, and a distribution width of 15 μm and 30 μm were analyzed and subsequently processed. The PBF-manufactured parts were analyzed in terms of density and melt pool dimensions. Although powder flowability was inversely related to the median particle size, it was unrelated to the distribution width. An inverse relationship between the median particle size and the part density was observed; however, no link was found to the distribution width. Likely, the melt pool depth and width fluctuation significantly influence the part density. The melt pool depth decreases and the width fluctuation increases with an increasing median particle size.

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The influence of spreading metal powders with different particle size distributions on the powder bed density in laser-based powder bed fusion processes

10.6028/nist.ams.100-17 ◽

2018 ◽

Cited By ~ 1

Author(s):

Gregor Jacob ◽

Christopher U Brown ◽

Alkan Donmez

Keyword(s):

Particle Size ◽

Size Distributions ◽

Powder Bed Fusion ◽

Metal Powders ◽

Particle Size Distributions ◽

Powder Bed

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Influence of processing parameters on the density of 316L stainless steel parts manufactured through laser powder bed fusion

Proceedings of the Institution of Mechanical Engineers Part B Journal of Engineering Manufacture ◽

10.1177/0954405420911768 ◽

2020 ◽

Vol 234 (9) ◽

pp. 1246-1257 ◽

Cited By ~ 4

Author(s):

João PM Pragana ◽

Pedro Pombinha ◽

Valdemar R Duarte ◽

Tiago A Rodrigues ◽

João P Oliveira ◽

...

Keyword(s):

Stainless Steel ◽

316L Stainless Steel ◽

Processing Parameters ◽

Powder Bed Fusion ◽

Aisi 316L ◽

Laser Powder Bed Fusion ◽

Optimal Range ◽

Powder Bed ◽

Density Measurements ◽

Part Density

Additive manufacturing technologies are becoming more popular, as they allow the fabrication of specific parts with complex geometries not achievable by conventional manufacturing. In metal additive manufacturing, one of the most widely used technologies is laser powder bed fusion. This work focuses on the influence of different processing parameters on the density of AISI 316L stainless parts obtained through this technology. The article presents a review of published works on the deposition of AISI 316L stainless steel using laser powder bed fusion to define an optimal range of parameters to produce parts with densities above 99%, complemented by density measurements for new sets of laser powder bed fusion processing parameters within the defined optimal range. The investigation provides a further insight on the effect of operating parameters such as vector size and gas atmosphere (Nitrogen and Argon) on the part density. The density measurements were performed using two techniques: micrograph analysis and Archimedes method. Results reveal that an increase in vector size has a negative influence on part density. With the Archimedes method, a maximum relative density of 99.87% was achieved using Nitrogen atmosphere, showing that it is possible to produce near fully dense parts by laser powder bed fusion without post-processing by laser re-melting.

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Effects of layer thickness in laser-powder bed fusion of 420 stainless steel

Rapid Prototyping Journal ◽

10.1108/rpj-10-2019-0279 ◽

2020 ◽

Vol 26 (7) ◽

pp. 1197-1208

Author(s):

Subrata Deb Nath ◽

Gautam Gupta ◽

Martin Kearns ◽

Ozkan Gulsoy ◽

Sundar V. Atre

Keyword(s):

Tensile Strength ◽

Stainless Steel ◽

Layer Thickness ◽

Powder Bed Fusion ◽

Laser Powder Bed Fusion ◽

Corrosion Properties ◽

Content Type ◽

Powder Bed ◽

Heat Treated ◽

Mechanical And Corrosion Properties

Purpose The purpose of this paper is to investigate effects of layer thickness on densification, surface morphology, microstructure and mechanical and corrosion properties of 420 stainless steel fabricated by laser-powder bed fusion (L-PBF). Design/methodology/approach Standard specimens were printed at layer thickness of 10, 20 and 30 µm to characterize Archimedes density, surface roughness, tensile strength, elongation, hardness, microstructural phases and corrosion performance in the as-printed and heat-treated condition. Findings Archimedes density slightly increased from 7.67 ± 0.02 to 7.70 ± 0.02g/cm3 and notably decreased to 7.35 ± 0.05 g/cm3 as the layer thickness was changed from 20 µm to 10 and 30 µm, respectively. The sensitivity to layer thickness variation was also evident in properties, the ultimate tensile strength of as-printed parts increased from 1050 ± 25 MPa to 1130 ± 35 MPa and decreased to 760 ± 35 MPa, elongation increased from 2.5 ± 0.2% to 2.8 ± 0.3% and decreased to 1.5 ± 0.2, and hardness increased from 55 ± 1 HRC to 57 ± 1 HRC and decreased to 51 ± 1 HRC, respectively. Following heat treatment, the ultimate tensile strength and elongation improved but the general trends of effects of layer thickness remained the same. Practical implications Properties obtained by L-PBF are superior to reported properties of 420 stainless steel fabricated by metal injection molding and comparable to wrought properties. Originality/value This study successfully the sensitivity of mechanical and corrosion properties of the as-printed and heat-treated parts to not only physical density but also microstructure (martensite content and tempering), as a result of changing the layer thickness. This manuscript also demonstrates porosity evolution as a combination of reduced energy flux and lower packing density for parts processed at an increasing layer thickness.

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