Selective Laser Melting Parameters Research Articles

High strength and ductility of titanium matrix composites by nanoscale design in selective laser melting

• SLM parameters play a major role in densification and microstructure. • Nanosized secondary particle additions promote densification. • Nanosized BN additions produce fine, high aspect ratio TiB reinforcement. • TiB morphological evolution during SLM and heat treatment impacts properties. • High tensile strength and ductility through high aspect ratio TiB nanowhiskers. The use of selective laser melting (SLM) to produce titanium matrix composites (TMCs) with high strength while retaining sufficient tensile ductility suitable for structural applications is emerging as an attractive opportunity in the field of advanced manufacturing. However, the presence of coarse ceramic reinforcements as well as difficulties in optimizing the SLM process is a barrier to the application of TMCs. In this study, we demonstrated the production of TMCs reinforced with in situ high aspect ratio TiB nanowhiskers by selective laser melting using nanosized BN powder additions. Pure Ti with 2.5 vol.% nanosized BN powder showed promise for producing high performance TMCs with retained ductility. BN acted to produce TiB nanowhiskers with diameter < 50 nm. Further, by controlling post process furnace annealing TiB retained a low diameter but exhibited a high aspect ratio, up to 400. In addition to TiB refinement, nanosized BN addition promoted grain refinement during SLM, both acting as a solute to induce nucleation events and, as TiB is formed, providing nucleation sites leading to an ultrafine grain structure in as printed samples and after annealing. The produced TMCs exhibit high tensile yield strength, up to 1392 MPa, while retaining tensile ductility up to 10%. This study has shown how nanoscale design in powder bed fusion additive manufacturing techniques can be used to produce high performance TMCs through a combination of refined grain structure and high aspect ratio TiB leading to TMCs with significant improvement in strength, isotropic properties and retained tensile ductility.

Influence Mechanism of Process Parameters on Relative Density, Microstructure, and Mechanical Properties of Low Sc-Content Al-Mg-Sc-Zr Alloy Fabricated by Selective Laser Melting

Additive manufacturing of Al-Mg-Sc-Zr alloys is a promising technique for the fabrication of lightweight components with complex shapes. In this study, the effect of the process parameters of selective laser melting (SLM) on the surface morphology, relative density, microstructure, and mechanical properties of Al-Mg-Sc-Zr high-strength aluminum alloys with low Sc content was systematically investigated. The results show that the energy density has an important effect on the surface quality and densification behavior of the Al-Mg-Sc-Zr alloy during the SLM process. As the energy density increased, the surface quality and the number of internal pores increased. However, the area of the fine-grained region at the boundary of the molten pool gradually decreased. When the laser energy density was set to 151.52 J/mm3, a low-defect sample with a relative density of 99.2% was obtained. After heat treatment, the area of the fine grains at the boundary increased significantly, thereby contributing to the excellent mechanical properties. The microstructure was characterized by a unique “fan-shaped” heterogeneous structure. As the energy density increased, the microhardness first increased and then decreased, reaching a maximum value of 122 HV0.3. With the optimized process parameters, the yield strength (YS), ultimate tensile strength (UTS), and elongation of the as-built Al-Mg-Sc-Zr alloys were 346.8 ± 3.0 MPa, 451.1 ± 5.2 MPa, 14.6% ± 0.8%, respectively. After heat treatment at 325 °C for 8 h, the hardness increased by 38.5% to 169 HV0.3, and the YS and UTS increased by 41.3% and 18.1%, respectively, to 490.0 ± 9.0 MPa and 532.7 ± 7.8 MPa, respectively, while the elongation slightly decreased to 13.1% ± 0.7%.

Structure, Mechanical and Magnetic Properties of Selective Laser Melted Fe-Si-B Alloy.

Original 1CP powder was studied and it was founded that powder material partially consists of the amorphous phase, in which crystallization begins at 450 °C and ends at 575 °C. Selective laser melting parameters were investigated through the track study, and more suitable ones were found: laser power P = 90, 120 W; scanning speed V = 1200 mm/s. Crack-free columnar elements were obtained. The sample obtained with P = 90 W, contains a small amount of amorphous phase. X-ray diffraction of samples shows the presence of α-Fe(Si) and Fe2B. SEM-image analysis shows the presence of ordered Fe3Si in both samples. Annealed samples show 40% less microhardness; an annealed sample containing amorphous phase shows higher soft-magnetic properties: 2.5% higher saturation magnetization, 35% higher residual magnetization and 30% higher rectangularity coefficient.

Determining the Optimum Process Parameters of Selective Laser Melting via Particle Swarm Optimization Based on the Response Surface Method

Determining the Optimum Process Parameters of Selective Laser Melting via Particle Swarm Optimization Based on the Response Surface Method

Effect of process parameters on microstructures and properties of Al–42Si alloy fabricated by selective laser melting

In this paper, high-silicon Al–42Si alloy was prepared by selective laser melting (SLM) with different process parameters. Microstructures evolution and defects formation were studied and process parameters were optimized. The results shown that the density of SLM-fabricated Al–42Si alloy increases as input energy density increases. The highest and lowest density of SLM-fabricated Al–42Si alloy are obtained, when input energy density is 42.9J/mm3 and 33.8J/mm3 respectively. The microstructures of Al–42Si alloy fabricated by selective laser melting is mainly composed of primary silicon phase and eutectic silicon phase, which is distinct from casting alloy because of diffient grains size and shapes of the primary silicon. With higher energy density, larger size of the primary silicon observed during process due to higher heat released by powder. The size of primary silicon phase particles is in the range of 2.9–9.4μm, and the size of molten pool during SLM process is in the range of 125 ± 10μm–140 ± 10μm in this study. Also the hardness of SLM-fabricated Al–42Si alloy increases as input energy density increases between 40.0J/mm3 and 42.9J/mm3. After heat treatment, the residual stress is eliminated, microstructure stability and homogeneous of SLM-fabricated Al–42Si alloy are improved. The silicon distribution is more uniform and sizes increases about 1∼2μm, and the hardness decreases after heat treatment. The optimal SLM parameters for Al–42Si alloy are laser power of 320W, scanning speed of 1355 mm/s, layer thickness of 50μm and scanning space of 110μm.

Effects of fabrication parameters and post-processing treatments on the mechanical and tribological behavior of surface-enhanced copper based materials by selective laser melting

Selective laser melting (SLM), which is an advanced manufacturing method developed in recent years, produces parts with complex shapes and critical dimensions using metallic powder and laser beam. In this study, copper based conductive materials with silver networks were fabricated by electroless silver coating and SLM. The effects of laser power, scanning speed, hatch spacing, build orientation and post treatments on the mechanical and tribological properties of SLM compacts manufactured from core-shell particles were investigated. After the mechanical tests, higher stress and elongation values were obtained in the sample positioned horizontally on the build platform with a laser power of 100 W, scanning speed of 250 mm/s and hatch spacing value of 45%. After that SLM process, the post-processes were applied to the samples and the physical and mechanical properties improved significantly. The highest density value was obtained by the rolling process at 900 °C, and an increase of approximately 35.6% was obtained compared to the sample without post-processing. The lowest wear rate among all samples was obtained in the hot-pressing process at 750 °C. • Silver coating of copper particles by electroless silver plating method. • Production of copper-based compacts by SLM using core-shell particles. • Investigation of critical SLM parameters on the properties of SLMed parts. • Investigate the effect of post treatments on SLMed parts. • Obtaining the improved properties by electroless coating, SLM, post treatments.

Surface Roughness Improvement by Sliding Friction Burnishing of Parts Produced by Selective Laser Melting of Ti6Al4V Titanium Alloy

Selective laser melting is a frequently used, powder bed fusion additive manufacturing technology for producing metallic parts. However, appropriate surface quality cannot be achieved, so post-processing is often necessary. Subsequent machining of surfaces serves multiple objectives such as improvement of dimensional accuracy, changing surface roughness and modification of the residual stress state for higher surface hardness. Beyond its several advantageous properties, Ti6Al4V material has, as its weaknesses, low tribological behavior and wear resistance. Sliding friction burnishing is a conventional chipless and coolant-free environmentally conscious technology for surface modification that is appropriate for simultaneously decreasing surface roughness and increasing surface hardness. Until now, there has been a research gap regarding the diamond burnishing of selective laser melted Ti6Al4V parts. In this study, we investigated how the surface roughness of selective laser melted parts can be modified via sliding friction burnishing. 2D and 3D characteristics of surface roughness were measured by a chromatic roughness measuring device. Indices of surface roughness improvement were defined and studied as a function of selective laser melting parameters. Optimal manufacturing parameters of laser power—P = 280 W and scanning speed u = 1200 mm/s—for effective surface improvement via burnishing are proposed.

Hybrid prediction-optimization approaches for maximizing parts density in SLM of Ti6Al4V titanium alloy

It is well known that the processing parameters of selective laser melting (SLM) highly influence mechanical and physical properties of the manufactured parts. Also, the energy density is insufficient to detect the process window for producing full dense components. In fact, parts produced with the same energy density but different combinations of parameters may present different properties even under the microstructural viewpoint. In this context, the need to assess the influence of the process parameters and to select the best parameters set able to optimize the final properties of SLM parts has been capturing the attention of both academics and practitioners. In this paper different hybrid prediction-optimization approaches for maximizing the relative density of Ti6Al4V SLM manufactured parts are proposed. An extended design of experiments involving six process parameters has been configured for constructing two surrogate models based on response surface methodology (RSM) and artificial neural network (ANN), respectively. The optimization phase has been performed by means of evolutionary computations. To this end, three nature-inspired metaheuristic algorithms have been integrated with the prediction modelling structures. A series of experimental tests has been carried out to validate the results from the proposed hybrid optimization procedures. Also, a sensitivity analysis based on the results from the analysis of variance was executed to evaluate the influence of the processing parameter and their reciprocal interactions on the part porosity.

Process Parameter Optimization on Selective Laser Melting of CuSn10 Powders Based on Response Surface Methodology

Abstract A shaping test of CuSn10 powders was carried out by using the selective laser melting (SLM) technology to study influences of process parameters of SLM on compactness of specimens. Meanwhile, process parameters were optimized based on the response surface methodology. Meanwhile, phase composition and microstructure of formed part were analyzed by XRD and OM. Results demonstrated that as the energy density of laser body increases from 146.7 J·mm-3 to 181.3 J·mm-3, pores of samples decrease and the compactness increases from 98.97% to about 99.7%. Subsequently, the compactness begins to decrease with the continuous increase of laser energy density. The incomplete melting of powder under low energy density and gasification of powders under high energy density are major factors that influence the compactness. Over low or high laser energy density is disadvantageous for the improvement of compactness. A mathematical model of interaction between three factors (laser power, laser scanning speed and scanning space) and response value (compactness) was built up by using the BBD principle design test of response surface methodology. The degree of fitting (R2) and correction coefficient (R2 adj) of the model were 0.9952 and 0.9866, which agree well with the fitting degree of experimental tests. Among three factors, influences of laser power and scanning speed on compactness are equivalent and more significant than scanning space. The optimal process parameters which were predicted by the model were laser power=331.471 W, scanning speed=648.045 mm·s-1, scanning space=69.9302 μm. Under this circumstance, the compactness of CuSn10 powders after SLM is 99.75%. According to experimental verification, the practical value of compactness is 99.74%, showing a very small relative error. This proves that the BBD model is reliable. The shaped part is mainly composed of α-Cu phase and metastable phase β’-Cu13.7Sn. Compared with the original powders, the content of metastable phase β’ increases significantly, while the δ-Cu41Sn11 phase disappears.

The manufacturing process optimization and the mechanical properties of FeCoCrNi high entropy alloys fabricated by selective laser melting

The quality of metal parts fabricated by selective laser melting (SLM) is strongly depended on the manufacturing process parameters. The establishment of relationship between manufacturing parameters and the formability is the effective way to obtain forming parts with high density, defect-free and excellent mechanical properties by SLM. In this study, the effect of SLM process parameters on the relative density (RD) and mechanical properties of FeCoCrNi high entropy alloys (HEAs) were systematically investigated, involving single tracks, single layers and block samples. By optimizing the laser power, scanning speed and hatching space, the highest RD of 99.85% was obtained under the moderate energy density of 95.24 J/mm3, with no defect as prosity, cracks, un-melted powders and spheroidization under other SLM parameters. The tiny changes in RD significantly affected the mechanical properties of FeCoCrNi HEAs. The highest RD sample corresponded to the optimal comprehensive mechanical properties of 585 MPa in yield strength, 714 MPa in ultimate strength and 45.30% in elongation. The elevation of mechanical properties attributed to the high RD, defect-free, grain refinement and the unique cellular substructure.

Microstructure and mechanical behavior of TiCN reinforced AlSi10Mg composite fabricated by selective laser melting

Although Al alloys have been extensively used for additive manufacture, TiCN reinforced Al composites have rarely been investigated for the feasibility of additive manufacture. In this study, TiCN reinforced AlSi10Mg composite was fabricated by selective laser melting (SLM). The key SLM process parameters, including laser power, scanning speed, as well as hatch spacing were optimized through design of experiment (DOE) and the effects of these parameters on relative density of SLMed AlSi10Mg - 5 vol% TiCN composite were investigated. In addition, the effect of T6 heat treatment after SLM processing on microstructure and mechanical properties of AlSi10Mg - 5 vol% TiCN composite was also studied. Research results show that the optimal SLM parameters are laser power of 370 W, scanning speed of 1760 mm/s, and hatch spacing of 0.063 mm, corresponding to the maximum relative density of 98.5% for SLMed AlSi10Mg - 5 vol% TiCN. Noticeable diffusion of Al and Si elements from matrix to TiCN particles occurs while there is no observed new phase formation between TiCN and Al matrix during SLM process, which enhanced the bonding strength between the TiCN and AlSi10Mg matrix. As compared with the SLMed pure AlSi10Mg, AlSi10Mg–TiCN shows apparently higher hardness, ultimate tensile strength and compression strength due to the significant refinement of AlSi10Mg matrix and the strengthening effect from TiCN particles.

Investigation of the influence of the parameters of selective laser fusion of metal powders and cold isostatic pressing on the structure and mechanical properties of a nickel-based heat-resistant alloy

The influence of the parameters of selective laser melting (SLM) of metal powders and cold isostatic pressing (CIP) of samples from a high-chromium heat-resistant alloy on the microstructure of the processed alloy, the size and number of formed pores is investigated. The use of HIP for SLM alloys makes it possible to reduce the number and size of pores. The strengthening effect of deformation (increase in hardness) at normal temperature is established. Keywords: selective laser melting, additive manufacturing, track, pores, cold isostatic pressing, mechanical properties, microstructure. remshev@mail.ru, Galina@mail.ru, grisha.afimin@mail.ru, gulyarenko@mail.ru

Fatigue life optimization for 17-4Ph steel produced by selective laser melting

PurposeThe mechanical characterization of selective laser melting (SLM) parts is an industrial challenge. This paper aims to propose a methodology to control the fatigue life of 17-4Ph stainless steel by selecting the most relevant manufacturing parameters: i.e. laser power, laser travel speed, hatch spacing and laser defocusing.Design/methodology/approachA rough and refined design of experiment (DOE) is carried out to target the best combination of process parameters. A response surface model is then constructed to predict the parameter combination that optimizes the fatigue performance.FindingsThis study results show that the fatigue limit of the specimens manufactured by SLM (471.7 MPa at 107 cycles) has reached near 90% of the value found in samples machined from a bar. This demonstrates the applicability of the method proposed to optimize the SLM process and control the fatigue life of 17-4Ph stainless steel. The study results are compared with other research works and provide an increase of 18% to the fatigue limit.Originality/valueThis study showcases a DOE methodology to optimize the SLM parameters to achieve fatigue performance as great as that of solid 17-4Ph stainless steel.

Towards predicting process parameters for selective laser melting of titanium alloys through the modelling of melt pool characteristics

Various researchers have investigated the use of experimental melt pool characterization to speed up the optimisation process of selective laser melting parameters and found this to be possible. From their studies, it has become clear that the incorporation of modelling into this approach could provide efficient and predictable results that would minimise the experimental validation work required. This paper reports on progress made towards characterising the melt pool through simulation. The development of a numerical model is discussed. Subsequently, experimental validation of the numerical model is presented. This is done through a comparison of the simulation results with the experimentally determined cross-sectional geometry of single tracks created with various sets of process parameters. Melt pool size and shape are considered. Based on these results, it is concluded that using an identical simulation setup, verified simulation method, and verified material properties, it was possible to accurately determine the melt pool geometry for some, but not all process parameters.

Influence of selective laser melting process parameters on the characteristics of SiC/Ti6Al4V(ELI) single tracks

Process parameters of selective laser melting, such as track height, track width and depth of penetration, affect the characteristics of laser fused single tracks. The properties of additively manufactured 3D parts depend strongly on the quality of laser melted single tracks and resultant single layers. Layers formed with a good depth of laser penetration provide strong bonding between consecutive layers and the substrate. Poor depth of laser penetration leads to delamination of layers. In this study the effect of the critical process parameters of laser power, laser scanning speed, and laser linear energy density on the characteristics of SiC/Ti6Al4V(ELI) single tracks at different SiC volume fractions (5 %, 10 %, 15 %, 20 %, 25 % and 30%) was investigated. Phenomena, such as the keyhole effect, pre-balling, and balling of single tracks, were also investigated. The obtained results showed that increase of power at a constant speed increase both the track width and depth of penetration but the track height above the substrate is decreased.

3D Multi-Track and Multi-Layer Epitaxy Grain Growth Simulations of Selective Laser Melting.

An integrated simulation framework consisting of the 3D finite element method and 3D cellular automaton method is presented for simulating the multi-track and multi-layer selective laser melting (SLM) process. The framework takes account of all the major multi-physics phenomena in the SLM process, including the initial grain structure, the growth kinetics, the laser scanning strategy, the laser–powder and laser–matter interactions, the melt flow, and the powder-to-liquid-to-solid transformations. The feasibility of the proposed framework is demonstrated by simulating the evolution of the epitaxy grain structure of Inconel 718 (IN718) during a 15-layer SLM process performed using a bi-directional 67° rotation scanning strategy and various SLM process parameters. The simulation results are found to be in good agreement with the experimental observations obtained in the present study and in the literature. In particular, a strong (001) texture is observed in the final component, which indicates that the grains with a preferred <001> orientation win the competitive epitaxy grain growth process. In addition, the size and shape of the IN718 grains are governed primarily by the cooling rate, where the cooling rate is determined in turn by the SLM parameters and the build height. Overall, the results show that the proposed framework provides an accurate approach for predicting the final microstructures of SLM components, and therefore, it can play an important role in optimizing the SLM processing parameters in such a way as to produce components with the desired mechanical properties.

Effects of Static Magnetic Field on the Microstructure of Selective Laser Melted Inconel 625 Superalloy: Numerical and Experiment Investigations

A number of researchers have reported that a static magnetic field (SMF) will affect the process of selective laser melting (SLM), which is achieved mainly through affecting molten pool evolution and microstructure growth. However, its underlying mechanism has not been fully understood. In this work, we conducted a comprehensive investigation of the influence of SMF on the SLM Inconel 625 superalloy through experiments and multi-scale numerical simulation. The multi-scale numerical models of the SLM process include the molten pool and the dendrite in the mushy zone. For the molten pool simulation, the simulation results are in good agreement with the experimental results regarding the pool size. Under the influence of the Lorentz force, the dimension of the molten pool, the flow field, and the temperature field do not have an obvious change. For the dendrite simulation, the dendrite size obtained in the experiment is employed for setting up the dendrite geometry in the dendrite numerical simulation, and our findings show that the applied magnetic field mainly influences the dendrite growth owing to thermoelectric magnetic force (TEMF) on the solid–liquid interface rather than the Lorentz force inside the molten pool. Since the TEMF on the solid–liquid interface is affected by the interaction between the SMF and thermal gradient at different locations, we changed the SLM parameters and SMF to investigate the effect on the TEMF. The simulation shows that the thermoelectric current is highest at the solid–liquid interface, resulting in a maximum TEMF at the solid–liquid interface and, as a result, affecting the dendrite morphology and promoting the columnar to equiaxed transition (CET), which is also shown in the experiment results under 0.1 T. Furthermore, it is known that the thermoelectric magnetic convection (TEMC) around the dendrite can homogenize the laves phase distribution. This agrees well with the experimental results, which show reduced Nb precipitation from 8.65% to 4.34% under the SMF of 0.1 T. The present work can provide potential guidance for microstructure control in the SLM process using an external SMF.

Effects of process parameters and scanning patterns on quality of thin-walled copper flanges manufactured by selective laser melting

A thin-walled copper flange was prepared by the selective laser melting (SLM) method (with the average particle size of pure spherical copper powder of about 35 μm and the focal spot diameter of the single-mode fiber laser of 50 μm). The results show that the wall thickness (about 400 μm) of the obtained sample is significantly larger than that (200 μm, namely desired wall thickness) of the model set before the test. In this study, the wall thickness of the model was set as 50 μm and the linear scanning was adopted. On this basis, the influence laws of SLM parameters (laser power, scanning speed and hatch spacing) on forming quality (relative density, surface roughness and wall thickness) of the thin-walled copper flange sample were studied through an orthogonal test. Moreover, two groups of parameters of the sample with good forming quality were obtained. The thin-walled copper sample with the relative density of about 99.8%, wall thickness of about 200 μm and variance of height of rough surface morphologies (reflecting surface roughness) of 29–36 μm was obtained under linear scanning. Compared with SLM under linear scanning, the surface flatness of the sample is obviously improved and the variance of height of rough surface morphologies is reduced to 13–15 μm after SLM under circular scanning. In this way, the capability of SLM in preparing thinner components is significantly enhanced. The analysis shows that the area of a laser-heated region under scanning along the direction of wall thickness of the copper flange (linear scanning) is about 1.196 times that of the desired shape, and the heated region is wavy with several semicircles connected. Therefore, this is unfavorable for ensuring forming quality and dimensional accuracy of the sample prepared by SLM.

Laser Fusion of Aluminum Powder Coated with Diamond Particles via Selective Laser Melting: Powder Preparation and Synthesis Description

This work aims to study the possibility of obtaining Al–C composite from AlSi10MgCu aluminum matrix with the addition of 500 nm-sized diamond particles by selective laser melting (SLM) process. Al–C composite powder was prepared by mechanical mixing to form a uniform cover along the surface of aluminum particles. The diamond content in the resulting AlSi10MgCu-diamond composite powder was equal to 0.67 wt %. The selection of the optimal SLM parameters for the obtained composite material is presented. For materials characterization, the following methods were used: scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy. X-ray photoelectron spectroscopy (XPS) was applied after SLM printing for a detailed investigation of the obtained composites. The presence of carbon additives and the formation of aluminum carbides in the material after the SLM process were demonstrated.

Predictive models for an optimized fabrication of 18Ni300 maraging steel for moulding and tooling by Selective Laser Melting

Powder bed fusion (PBF) technologies have gained increased attention in the automotive sector for the manufacturing of mould tooling and inserts. These technologies can expressively reduce lead time and waste of material, while allowing extraordinary freedom to design new geometries. The performance of the produced parts is highly dependent on processing parameters. In this work, 18Ni300 maraging steel, a widely used material in mould and tooling industries, was selected to be transformed by Selective Laser Melting (SLM) using a previous defined framework of SLM variables, among them laser power (Lp), point distance (Pd), exposure time (Et) and hatch distance (Hd). The experimental results demonstrated that these parameters have vital importance to produce fully dense and micro-hardness improved parts. Furthermore, results showed that the energy density per se does not explain the final properties of 18Ni300 produced by SLM. Maximized density (99.99%) was achieved using (Lp, Pd, Et, Hd) (275.0 W, 60 μm, 65.0 μs, 110 μm), corresponding to 2.71 J/mm2 planar energy density, while maximized micro-hardness (350 HV2) was achieved using (Lp, Pd, Et, Hd) (337.5 W, 70 μm, 52.5 μs, 95 μm), corresponding to 2.66 J/mm2 planar energy density. The statistical relationship between SLM parameters and final density and micro-hardness of the parts was established using the so-called Response Surface Methodology (RSM), resulting in two predictive models, for density and micro-hardness. The most influential (single and combined factors), for both models, were then determined using analysis of variance (ANOVA). The outcomes of the ANOVA analysis revealed a predicted coefficient of determination, R2(pred.), of 93.73% and 98.98% for density and micro-hardness models, respectively, revealing that the developed models have high accuracy for the prediction of both properties on 18Ni300 steel parts produced by SLM.