CoCr alloy processed by Selective Laser Melting (SLM): effect of Laser Energy Density on microstructure, surface morphology, and hardness

Additive manufacturing (AM) combines materials to create parts from three-dimensional model data, often layer by layer. AM is mainly deployed to fabricate complicated geometrical components with high efficiency and low cost. Selective laser melting (SLM) is an AM method that uses a high-power laser beam to melt powder material layer upon layer completely. Multi-material in SLM is due to its potential for specific applications where different material properties achieve comprehensive performance at different locations of the directly manufactured parts. The process parameters (PP) used in SLM are layer thickness (LT), laser power (LP), hatch spacing (HS), and scanning speed (SS). It mainly impacts the porosity, residual stress, fatigue, surface roughness, density, mechanical properties, and product microstructure. This article investigates the selection of suitable PP’s and the influence of SLM PP’s on the quality of parts fabricated from different materials and combinations of multi-materials structures. Finally, it helps to understand each process parameter of SLM, and the future trends of AM in different areas are concluded. 

A process parameters review on Selective laser melting-based additive manufacturing of Single and Multi-Material: Microstructure, Properties, and machinability aspects

Laser powder bed fusion of AlSi10Mg: Influence of energy intensities on spatter and porosity evolution, microstructure and mechanical properties

The microstructural development of 316L stainless steel (SS) was investigated over a wide range of systematically varied laser powder bed fusion (LPBF) parameters, such as laser power, scan speed, hatch spacing and volumetric energy density. Relative density, melt pool width and depth, and the size of sub-grain cellular structure were quantified and related to the temperature field estimated by Rosenthal solution. Use of volumetric energy density between 46 and 127 J/mm3 produced nearly fully dense (≥99.8%) samples, and this included the best parameter set: power = 200 W; scan speed = 800 mm/s; hatch spacing = 0.12 mm; slice thickness = 0.03; energy density = 69 J/mm3). Cooling rate of 105 to 107 K/s was estimated base on the size of cellular structure within melt pools. Using the optimized LPBF parameters, the as-built 316L SS had, on average, yield strength of 563 MPa, Young’s modulus of 179 GPa, tensile strength of 710 MPa, and 48% strain at failure.

Process Optimization and Microstructure Analysis to Understand Laser Powder Bed Fusion of 316L Stainless Steel

Selective laser melting (SLM) is a 3D printing technology with a high near-net-shape ability and forming accuracy. However, the inevitable internal defects significantly hinder its development. Therefore, it is essential to fully understand the causes of internal defects in SLM processing and minimize the defects to achieve quality control accordingly. This work reviews the recent studies on internal defects in SLM, presenting the main internal defects of SLM as impurities, lack of fusion, gas pores, and micro-crack. These internal defects occur on the various phenomena in the laser-powder-melt pool (LPMP) stage. The formation of SLM internal defects is mainly affected by oxidation, denudation, balling, spatter, and keyholes; here, balling, spattering, and the keyhole phenomenon are the main factors causing internal defects in LPMP. Hence, this paper focuses on reviewing the balling effect, spatter behavior, and keyhole phenomenon, introducing the action mechanism of the above three phenomena under different process conditions. Additionally, the spatter behavior when forming internal defects is proposed. This review also considers the correlation between the spatter behavior and keyhole phenomenon and makes an important contribution to understanding and reducing SLM internal defects. It presents a reliable opinion on real-time monitoring and machine intelligent learning for SLM processing in the future, as well as supporting a systematic thinking for the suppression of defect formation in SLM. 

Quality Control: Internal Defects Formation Mechanism of Selective Laser Melting Based on Laser-powder-melt Pool Interaction: A Review

is an open access repository that collects the work of Arts et Metiers ParisTech researchers and makes it freely available over the web where possible. This is an author-deposited version published in: https://sam.ensam.eu Handle ID A B S T R A C T The systematic occurrence of porosities inside selective laser melted (SLM) parts is a well-known phenomenon. In order to improve the density of SLM parts, it is important not only to assess the physical origin of the different types of porosities, but also to be able to measure as precisely as possible the porosity rate so that one may select the optimum manufacturing parameters. Considering 316 L steel parts built with different input energies, the current paper aims to (1) present the different types of porosities generated by SLM and their origins, (2) compare different methods for measuring parts density and (3) propose optimal procedures. After a preliminary optimization step, three methods were used for quantifying porosity rate: the Archimedes method, the helium pycnometry and micrographic observations. The Archimedes method shows that results depend on the nature and temperature of the fluid, but also on the sample volume and its surface roughness. During the micrographic observations, it has been shown that the results depend on the magnification used and the number of micrographs considered. A comparison of the three methods showed that the optimized Archimedes method and the helium pycno-metry technique gave similar results, whereas optimized micrographic observations systematically underestimated the porosity rate. In a second step, samples were analyzed to illustrate the physical phenomena involved in the generation of porosities. It was confirmed that: (1) low Volume Energy Density (VED) causes non-spherical porosities due to insufficient fusion, (2) in intermediary VED the small amount of remaining blowhole porosities come from gas occlusion in the melt-pool and (3) in excessive VED, cavities are formed due to the keyhole welding mode.

https://hal.archives-ouvertes.fr/hal-02292119/document

Optimization and comparison of porosity rate measurement methods of Selective Laser Melted metallic parts

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Optimization and comparison of porosity rate measurement methods of Selective Laser Melted metallic parts