Selective Laser Melting Parameters Research Articles

Correlation between selective laser melting parameters, pore defects and tensile properties of 99.9 % silver

In this study the relationship between Selective Laser Melting (SLM) process parameters, associated pore defects and resulting tensile properties of additively manufactured (AM) pure (99.9 %) silver structures are investigated using X-ray Computed Tomography (XCT) and 3D visualisation analysis. Yield strength, Young’s Modulus, failure strain and ultimate tensile strength of AM pure silver are reported. Furthermore, fracture surfaces of the samples are analysed using optical microscopy and Scanning Electron Microscopy (SEM) to investigate fracture surface porosity content and surface roughness is analysed using digital microscopy. Pore defect distribution, morphology and resultant pore surface area are reported, and average pore size calculated in relation to SLM process parameters variations. It was found that sample yield and ultimate tensile strengths of pure silver have a direct correlation with energy density at the powder bed related to SLM process parameters selected. However, Youngs Modulus values were found to be dependent on the average porosity pore size rather than sample density or number of pores. SLM pure silver bulk density was evaluated using XCT comparative analysis while varying SLM parameters and the resultant pore defect morphology and distribution discussed. The results reported in this work serve as a basis for further material development and mechanical property predictions utilising XCT analysis for pure silver and other nonstandard SLM materials.

Simulation of the Evolution of Thermal Dynamics during Selective Laser Melting and Experimental Verification Using Online Monitoring.

The process parameters of selective laser melting (SLM) significantly influence molten pool formation. A comprehensive understanding and analysis, from a macroscopic viewpoint, of the mechanisms underlying these technological parameters and how they affect the evolution of molten pools are presently lacking. In this study, we established a dynamic finite element simulation method for the process of molten pool formation by SLM using a dynamic moving heat source. The molten pool was generated, and the dynamic growth process of the molten pool belt and the evolution process of the thermal field of the SLM molten pool were simulated. Then, a deposition experiment that implemented a new measurement method for online monitoring involving laser supplementary light was conducted using the same process parameters as the simulation, in which high-speed images of the molten pool were acquired, including images of the pool surface and cross-section images of the deposited samples. The obtained experimental results show a good agreement with the simulation results, demonstrating the effectiveness of the proposed algorithm.

An effective rule for translating optimal selective laser melting processing parameters from one material to another

Selective Laser Melting (SLM) or Laser Powder Bed Fusion (L-PBF) is the most studied laser-based additive manufacturing process for metals and alloys. One important issue in SLM is the time-consuming identification of a process window leading to quasi fully dense parts (> 99.8%), usually based on trials and errors. As some metal powders may be very expensive, and therefore not suitable for a whole battery of tests, a method to infer optimal parameters from one material to another would be highly beneficial. In this study, we use bronze as a test material for optimizing SLM parameters, before translating these parameters to red gold and 316 L steel. The concept of normalized enthalpy is used to take into account the differences in thermal and optical properties among the different materials. A translation rule is derived for the prediction of optimal processing conditions, based on the ones found for the test material. One important input for this translation rule is the powder absorptivity, which is measured at the appropriate laser wavelength and at room temperature. This approach eventually leads to the highest reported density for an additive manufactured 18-carat gold alloy (99.81% relative density), to the authors' knowledge. Finite element (FEM) simulations justify the translation rule formulation by showing the importance of the laser/powder interactions during the SLM process, leading to a finite penetration depth of the laser in the powder bed due to multiple reflections. The FEM calculations indicate that a significant part of the laser energy is directly absorbed by the powder during the manufacturing process when operating in near-optimal conditions.

A detailed microstructural and corrosion analysis of magnesium alloy WE43 manufactured by selective laser melting

The production of magnesium alloy WE43 was achieved by selective laser melting (SLM). The alloy was investigated after SLM, hot isostatic pressing (HIP), and solutionising heat treatment. The microstructure and corrosion behaviour of the specimens were carefully characterised, whilst assessed and contrast relative to the conventionally cast alloy counterpart. The SLM prepared specimens possess a unique microstructure comprising fine grains growing with a strong [0001] texture along the building direction with a low fraction of process-induced and metallurgical defects, reaching < 0.1 %, after optimising the SLM parameters and the HIP treatment. Electrochemical measurements demonstrated that the SLM prepared WE43 is cathodically more active as compared with its cast counterpart. It is proposed that this behaviour is due to a high density of zirconium-rich oxide particles uniformly distributed throughout the alloy microstructure as well as the alterations in the chemical composition of the solid-solution matrix originating from the high cooling rates of SLM. It was also noted that the oxide particles are mainly sourced by powder. The present results suggest that the corrosion of SLM prepared Mg alloys could be greatly improved once the influence of powder characteristics is further understood and controlled.

SHS Produced TiB2-Si Powders for Selective Laser Melting of Ceramic-Based Composite

One of the main limitations for widespread additive manufacturing is availability and processability of the precursor materials feedstock. For the first time, this study reports the development of a “pomegranate-like” structured TiB2-Si ceramic-metalloid powder feedstock suitable for selective laser melting (SLM) of ceramic-based composite. The powder was produced via self-propagating high temperature synthesis (SHS) at a moderate combustion temperature of 1530 °C. The effective activation energy in the Ti-B-Si system for the slow step of the combustion process was estimated as 184 kJ. Conditions of SHS process demonstrated a strong influence on the properties of produced powders and, therefore, on SLM parameters and properties of the printed materials. The powders have demonstrated a high performance for manufacturing bulks of 56 wt%TiB2–44 wt%Si ceramic-based composite.

Surface Formation Mechanisms in Selective Laser Melting of Cobalt-Chromium-Molybdenum Powder

Selective laser melting (SLM) is a manufacturing technology of metal parts of any shapes with target mechanical properties by means of laser melting. This paper discusses the effect of SLM parameters: laser output power, laser movement velocity, scanning pitch and preheating temperature of a powdered material on surface formation mechanism, namely, its physical configuration when melting cobalt-chromium-molybdenum powdered material Со28Cr3Mo. The study points at structural differences of melted surfaces even under identical process parameters. Several types of surface formation are identified, e.g. homogenous melt, coagulated particles, and shapeless particles. Vapor pressure, Marangoni effect, and heat effect of a melted powder are stated to be key reasons for rough surface. This research is of high importance for understanding the effect of SLM parameters on formation of a target quality surface, positive stability and repeatable accuracy of the process.

The Mechanism of Forming Coagulated Particles in Selective Laser Melting of Cobalt-Chromium-Molybdenum Powder

Selective laser melting (SLM) is thought to be a prospective manufacturing technology of complex metal components. Formation of coagulated particles when melting is reported to be an important factor for target mechanical properties of the end product. This paper discusses the effect of SLM parameters, including laser output power, laser movement velocity, preheating temperature of the powder, laser beam diameter on the mechanism of forming coagulated particles in melting cobalt-chromium-molybdenum powdered material. The study shows that a rise of power to 60 W at a scanning velocity 6 mm/s causes coagulated particles to expand to 350 μm; that is far bigger than a size of powder in as delivered state (90 μm). The work investigates the effect of mechanical activation of cobalt-chromium-molybdenum powder on dimensions of coagulated particles. The research data can be applied to the improvement of up-to-date optimization approaches to manufacturing process parameters in SLM technology.

Improving the Mechanical Strength of Dental Applications and Lattice Structures SLM Processed.

To manufacture custom medical parts or scaffolds with reduced defects and high mechanical characteristics, new research on optimizing the selective laser melting (SLM) parameters are needed. In this work, a biocompatible powder, 316L stainless steel, is characterized to understand the particle size, distribution, shape and flowability. Examination revealed that the 316L particles are smooth, nearly spherical, their mean diameter is 39.09 μm and just 10% of them hold a diameter less than 21.18 μm. SLM parameters under consideration include laser power up to 200 W, 250–1500 mm/s scanning speed, 80 μm hatch spacing, 35 μm layer thickness and a preheated platform. The effect of these on processability is evaluated. More than 100 samples are SLM-manufactured with different process parameters. The tensile results show that is possible to raise the ultimate tensile strength up to 840 MPa, adapting the SLM parameters for a stable processability, avoiding the technological defects caused by residual stress. Correlating with other recent studies on SLM technology, the tensile strength is 20% improved. To validate the SLM parameters and conditions established, complex bioengineering applications such as dental bridges and macro-porous grafts are SLM-processed, demonstrating the potential to manufacture medical products with increased mechanical resistance made of 316L.

Phase structure and composition of nickel-based superalloy subject to synthesis by selective laser melting parameters and heat treatment

The structure of ZhS6K-VI alloy samples obtained by selective laser melting in a nitrogen atmosphere was studied at a scanning speed of 600, 1000 and 1200 mm/s, as well as after additional heat treatment. The distribution of alloying elements in the structure of synthesized and heat-treated samples, phase composition, morphology, and phase structure were studied by transmission electron microscopy. The effect of scanning speed on the structure of the synthesized material and distribution of alloying elements within the crystallization cells are shown.

Fabrication of three-dimensional connected W-Cu10Sn composites by selective laser melting

Three-dimensional connected W-Cu10Sn composites materials with high relative density (99.36%) were fabricated through selective laser melting (SLM). The densification process of the composite balanced the melting of W, evaporation of Cu/Sn and the spreading of melted α-Cu. Under the optimized SLM parameters, high laser power (LP) melted the most of W powder, the adjacent laser scanning track with small hatch space (HS) could fuse W phase together. With small HS and low scanning speed (SS), the spreading of melted α-Cu could fill up the pores caused by the evaporation of Cu/Sn. Finally, a three-dimensional connected structure is formed by W phase, and α-Cu phase occupied the gaps the gaps among W phase.

Effects of Micron/Submicron TiC on Additively Manufactured AlSi10Mg: A Comprehensive Study from Computer Simulation to Mechanical and Microstructural Analysis

The Al-based metal matrix composites (AMMCs) reinforced by micron- and submicron-scale TiC ceramic particles were manufactured by selective laser melting (SLM) additive manufacturing. The influences of SLM processing parameters such as volumetric energy density (ɛ) and laser absorptivity of powders on the densification, microstructural evolution, mechanical behavior and corrosion behavior of the AMMCs were systematically studied, based on which the strengthening mechanisms of the SLM-processed AMMC components were clarified. Finite element simulation was run to assist in revealing the underlying mechanism. Fundamental processes such as the Marangoni flow were discussed. Through these efforts, the as-printed AlSi10Mg/1 μm TiC was SLMed into crack-free, high-density parts (= 99.2%) when ɛ was > 65 J/mm3. For the as-printed AlSi10Mg/1 μm TiC samples prepared by the best SLM parameters, high tensile strength (470 ± 14 MPa) was achieved. Average hardness of ~ 169 HV0.1 and a considerably low friction coefficient with a mean value of ~ 0.3 were also obtained. The homogeneously distributed submicron TiC particles reduced the wear rate to 1.68 × 10−11 mm3/N/m. The as-printed AlSi10Mg/1 μm TiC parts showed better performance on corrosion resistance as well due to the high relative density achieved along with continuous and compatible bonding interfaces with the Al alloy matrix. Use of large-sized TiC (e.g., 30 μm) particles should be avoided, however, since they led to reduced mechanical properties and a poorer corrosion resistance.

Fabricating CoCrFeMnNi high entropy alloy via selective laser melting in-situ alloying

Quasi-equiatomic CoCrFeMnNi high entropy alloy (HEA) has been in-situ alloyed by selective laser melting (SLM) from a blend of CoCrFeNi pre-alloyed powder and Mn elemental powder. The blended powder shows good printability with various SLM parameters and the as-built HEA samples achieve a reliable forming quality. Despite the slight evaporation of Mn, energy dispersive spectrometer mapping and X-ray diffraction results show that the as-built HEA has a homogeneous chemical distribution and presents a single face-centred-cubic (fcc) phase, indicating successful in-situ alloying. The study has verified the feasibility of using blended powder to prepare high-quality HEA by SLM.

Dimensional Analysis of the Effect of SLM Parameters on Surface Roughness and Material Density

Additive Manufacturing (AM) based on Selective Laser Sintering (SLS) and Selective Laser Melting (SLM) is relatively widely used to manufacture complex shape parts made from metallic alloys, ceramic and polymers. One of the main problems is to guarantee surface quality of the manufactured product. This study investigated the effects of various SLS/SLM parameters such as the laser power, scanning speed, hatching, powder layer thickness and volumetric energy density on the surface roughness, porosity and material density of samples made from the CoCr powder. A mathematical model for the average surface roughness Ra based on the machining parameters and important thermo physical properties was established using the dimensional analysis. The results of this study show the significance of the correlation between the material density of the built part and its surface roughness.

A novel approach to the production of NiCrAlY bond coat onto IN625 superalloy by selective laser melting

The present study investigated for the first time the feasibility of producing by Selective Laser Melting (SLM) a NiCrAlY bond coat material directly onto an IN625 substrate itself produced by SLM. A typical parameters optimization was conducted by varying laser power (P) and scanning speed (v). Single-line scanning tracks and two-layer coatings were carried out and analyzed for 15 different P/v conditions. Several criteria were defined for the selection of appropriate SLM parameters. The results showed significant remelting of the underlying substrate, which is a typical feature of SLM manufacturing. This led to the formation of an intermediate dilution zone characterized by substantial mixing between IN625 superalloy substrate and NiCrAlY bond coat suggesting excellent metallurgical bonding. Optimum processing conditions were found for P = 250 W and v = 800 mm/s. It produced a dense 242 μm thick bond coat including a 36% dilution zone. The SLMed < NiCrAlY-IN625> system exhibited a smooth microhardness profile slightly increasing from 275 Hv in the bond coat to 305 Hv in the substrate. A progressive Al concentration distribution between the phases and low residual stress levels were found in the system. This suggested that SLM might be a valuable alternative manufacturing process for bond coat systems promoting excellent adhesion for high temperature applications.

Effect of 316L stainless steel powder size distribution on selective laser melting process

The product quality of selective laser melting (SLM) is closely related to the alloy powder size distribution. The small voidage of fine-sized alloy powder bed is beneficial to improve the density of SLM product. While, the fine-sized alloy powder would result in the poor powder spreading uniformity in the SLM equipment, which leads to the formation of holes in the SLM product. In this work, the 316L stainless steel powder was prepared by a vacuum atomization furnace and sieved into a coarse-sized distribution and a fine-sized distribution. Then, the coarse-sized powder and the fine-sized powder are mixed according to different ratios. The results show that, under the condition of same SLM parameters, the density and strength of the SLM sample gradually decrease, with the increasing amount of fine-sized powder. The main reason for this phenomenon is that the fine-sized powder, with the large specific surface, is easy to bond with the coarse-sized powder. It reduces the fluidity of powder, resulting in the pores and cracks during the SLM layering process. Furthermore, the addition of fine-sized powder to the coarse-sized powder results in a decrease in the elongation of SLM sample. However, with the increase of the addition amount of the fine-sized powder, the residual stress is released due to the formation of a large number of cracks and pores, so that the elongation of SLM sample is slightly increases.

Simulation, forming process and mechanical property of Cu-Sn-Ti/diamond composites fabricated by selective laser melting

Metal bond diamond abrasive tools with complex structure and high wear efficiency will be widely used in the geological drilling and mechanical processing industries, but are difficult to manufacture by traditional technology. In this paper, selective laser melting (SLM), as one of the additive manufacturing technologies, was used to fabricate Cu-Sn-Ti bonded diamond abrasive composites. Simulations, experiments and characterization were carried out to obtain the appropriate SLM process parameters. Results indicated that the optimal SLM parameters were laser power of 260 W, scanning speed of 300 mm/s and layer thickness of 0.09 mm. Furthermore, the wear resistant performance of SLM sample was compared with hot-pressed sintered sample in terms of mass loss rate, wear morphology and bonding condition. Results showed that diamond particles were seriously pulled-out from hot-pressed sintered sample while this hardly occurred from the wear surface of SLM sample, which was benefited from higher amounts of TiC around the diamond. Consequently, the bonding force to diamond was effectively improved for SLM sample. Therefore, SLM method cannot only fabricated sample with complex structures, but also with better performance. This study provides a novel approach for forming metal bonded diamond tools by SLM in the future.

Effect of rescanning cycles on the characteristics of selective laser melting of Ti6Al4V

Rescanning has been introduced as a new method to improve the performance of selective laser melting (SLM) in recent years. However, many of the related works were done on the investigating of the rescanning parameters and only one rescanning cycle was used. In this work, the influences of rescanning cycle on the relative density, microstructure, residual stress and mechanical properties of SLMed Ti6Al4V alloy were investigated. The results show that as the rescanning cycles increase from 0 to 4, the relative density and residual stress of the samples increase at first and then decrease, the highest relative density and residual stress are found when the number of rescanning cycle is one. The number of rescanning cycle has little effect on the microstructure. The microstructures all consist of the martensitic α′ laths which grow inside the columnar prior β grains. The ultimate tensile strength (UTS), yield strength, micro-hardness and micro-strain of the samples all increase as the rescanning cycles increase from 0 to 3, but decrease when the samples are rescanned fourth times. This research provides an insight in the influence of rescanning cycles on characteristics of SLM process and can be used to optimize the process parameters of SLM.

Influence of laser process parameters on the densification, microstructure, and mechanical properties of a selective laser melted AZ61 magnesium alloy

We present a detailed, systematic study of how laser process parameters affect the formation characteristics, densification, microstructure, and mechanical properties of AZ61 magnesium alloy specimens prepared by selective laser melting (SLM). The results allow us to develop a method to control defects and optimize the SLM parameters for the fabrication of a dense, bulk AZ61 magnesium alloy. A bulk AZ61 magnesium alloy prepared by SLM is used to investigate how hatch spacing, large-scale scanning speed, and energy input affect the macrosurface morphology (before and after polishing) and how the surface roughness and the relative density of the specimens affect the microstructure and mechanical properties of the dense bulk material. The results show that process parameters strongly influence the macrosurface topography, which we divide into four stages: a strong surface balling pore region, weak surface balling pore region, rough scan track region, and flat smooth region. In addition, the surface roughness changes from 18.95 to 7.49 μm. Two types of pore shapes (meniscus and circular) are governed by the scan speed, and pore size is a function of hatch spacing. We also obtain unusual X-ray diffraction results that depend on input energy in the range of 138.89–208.33 J/mm3. The α-Mg diffraction peak shifts to the right and reaches a maximum at 156.25 J/mm3 (scanning speed of 400 mm/s and hatch spacing of 0.06 mm), and the relative density reaches a maximum of 99.4% because the amount of Al in solid solution is maximized. The microstructure results show that the microstructure evolution involves dispersed α-Mg grains (refined equiaxed α-Mg grains) and coarsened equiaxed α-Mg grains with an average grain size ranging from 1.61 to 2.46 μm. The tensile properties of the as-built AZ61 Mg alloy at room temperature are superior to those of an as-cast AZ61 Mg alloy. The ultimate tensile strength of the as-built AZ61 is 93% greater than that of the as-cast AZ61 alloy, and the yield strength is increased by 136%.

Effect of selective laser melting process parameters on microstructure and mechanical properties of 316L stainless steel helical micro-diameter spring

The effects of process parameters on microstructure and mechanical properties of the 316L stainless steel helical micro-diameter spring (316L HMDS) fabricated by selective laser melting (SLM) were explored. By optimizing SLM process parameters, the near-full density (> 99%) SLM-316L HMDS can be manufactured. The SLM-316L HMDS exhibits typical layered morphology consisting of micron-sized melt pools and columnar grains whose growth orientations are consistent with the temperature gradient. Lower hatch space reduces the formation of voids, resulting in better density, elongation, and ultimate tensile strength of the SLM-316L HMDS. The form angle significantly affects the yield strength and ultimate tensile strength, and obvious dimples appear on the fracture surface, demonstrating toughness fracture. The experimental results establish the correlation between the process parameters of SLM and the microstructure and macro-mechanical properties of the SLM-316L HMDS.

The Influence of Selective Laser Melting Process Parameters on the Property of TiAlN/TiN Multilayer Coating on the 316L Steel

Selective laser melting (SLM) is an important advanced additive manufacturing technology. The existing SLM products cannot fully meet the requirements of high-precision and strength of the mechanical component because of their defects. The TiAlN/TiN multilayer coating can improve the surface property of SLM products. The present work aims to explore the influences of different process parameters of SLM on the property of TiAlN/TiN multilayer coating plating on the 361L specimen and the mechanism of these influences. Taking laser power, scanning speed, and scanning space as factors, an orthogonal experiment was designed. The TiAlN/TiN multilayer coating specimens can be obtained by plating on the 361L specimen, fabricated by the process parameters of SLM on the orthogonal experiment. The surface topographies and properties of TiAlN/TiN multilayer coating were tested, the influences of SLM process parameters on TiAlN/TiN multilayer coating were analyzed, and the optimal process parameter was obtained. The electron microscope images revealed that the surface morphology of TiAlN/TiN multilayer coating plating on the SLM specimen was relatively flat, and there were some macro-particles in different sizes and pin holes dispersed on it. The thickness of the TiAlN/TiN multilayer coating was 2.77–3.29 μm. The microhardness value of coating SLM specimen was more than four times that of the uncoated SLM specimen and the wear rates of the uncoated specimen were 2–4 times that of the corresponding coating specimen. The comprehensive analysis shows that the laser power had the greatest influence on the comprehensive property of the coating. The primary cause of the influence of SLM process parameters on the properties of the TiAlN/TiN multilayer coating was preliminarily discussed. When the laser power was 170 W, the scanning speed was 1,100 mm/s, and the scanning space was 0.08mm, the TiAlN/TiN multilayer coating plating on the SLM specimen had the best comprehensive property.