Additive manufacturing (AM), particularly Selective Laser Melting (SLM) has enabled development of lattice structures with unique properties. Through control of various parameters lattice structures ...can produce unique mechanical, electrical, thermal and acoustic properties, and have received much research attention. Despite the increasing volume of published data on the mechanical response of specific SLM lattice structures, there exists no overarching analysis. This work addresses this identified deficiency by providing a comprehensive summary of the experimental data reported on the mechanical response of SLM lattice structures. The design, fabrication and performance of SLM lattice structures are reviewed and the quality of data reported is analysed to inform best-practice for future studies. This comprehensive data summary enables meta-analysis of the reported mechanical performance of SLM lattice structures, providing insight into the bounds of their technical capabilities. Correlations were identified between the relative density and mechanical properties of many unit cell topologies consistent with the predictions of the Gibson-Ashby model, indicating its usefulness in describing and predicting the behaviour of SLM lattice structures. This review provides designers with a compiled resource of experimental data and design for AM tools to inform future design applications of SLM lattice structures and facilitates their further commercial adoption.
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•A review of the design, fabrication and mechanical performance of Selective Laser Melting (SLM) lattice structures.•Reported data on the mechanical performance and properties of a broad range of SLM lattice structures is compiled.•Meta-analysis of reported data allows insights into the applicability of the Gibson-Ashby model to SLM lattice structures.
•To have consistent results an average surface Sa was selected and measured as a target.•Artificial neural network was used as an accurate tool for characterizing the interaction and effect of ...parameters on the surface of SLM parts.•The effect of SLM process parameters and heat treatment on the values of average surface were modeled accurately.
In this paper, we propose a model to predict the average surface roughness (Sa) and analyse the effect of related process parameters on laser powder bed fusion (LPBF) selective laser melting (SLM) of Ti-6Al-4 V. The additive manufacturing (AM) process has various independent parameters that affect the quality of the produced parts and is complex to analyse. Although the process parameters can be selected separately in LPBF, they do however affect each other. Therefore, large adjustments of process parameters is not possible due to the negative effect they have on each other which can lead to problems such as cracks, balling, unmelted powders, porosity, and distortion. A range of process parameters using Taguchi L25 design of experiment (DOE) with five repetitions for each sample has been selected. Then, an artificial neural network (ANN) is applied to the model to predict the value of (arithmetical mean height)/(average surface roughness) (Sa). The selected processing parameters are laser power, scan speed, hatch spacing, laser pattern increment angle, and heat treatment (HT) condition. The present work revolves around ANN modeling and using a wide parameter range and a large number of test samples under ASTM standards as well as adding HT to the DOE to analyse the simultaneous effect of HT and changing process parameters on surface characteristics. A large and precise data set with high generality and reliability obtained by 3750 profilometries on 125 samples. The contribution of this paper is using ANN as an accurate tool in surface modeling and characterizing the effective parameters on the surface of LPBF parts. The existence phenomena and governing factors were explained by introducing new parametric mechanisms in rheology of melting pool. In AM of metals, the variation of average roughness in overlap of hatches can be 5–7 times higher than the centre of the track. Therefore, Sa was selected to have consistency in the measured roughness values. Results showed heat treatment above beta phase transus leads to a local flow of material at the surface causing an increase of Sa. The ranking of influential factors on Sa from the highest to the lowest was found to be: heat treatment > laser power > scan pattern angle > hatch space > scan speed.
•Refined and homogenized cell structure was obtained after direct aging.•No obvious grain growth was observed after aging treatment.•Strength along building direction was significantly improved after ...aging.•The growth of defects was related to the formation of high energy zones.
For additive manufactured aluminum alloys, the inferior mechanical properties along the building direction have been a serious weakness. In this study, an optimized heat treatment was developed as a simple and effective solution. The effects of direct aging on microstructure and mechanical properties along the building direction of AlSi10Mg samples produced via selective laser melting (SLM) were investigated. The results showed that, compared with the conventional heat treatment at elevated temperatures, direct aging at temperatures of 130–190 °C could retain the fine grain microstructure of SLM samples and promote further precipitation of Si phase, however, the growth of pores occurred during direct aging. With increasing aging temperature, while finer cell structures were obtained, more and larger pores were developed, resulting in decreased density of the samples. Two types of pore formation mechanisms were identified. Considering the balance between the refinement of cell structure and the growth of pores, aging at 130 °C was determined as the optimized heat treatment for SLM AlSi10Mg samples. The tensile strength along the building direction of the 130 °C aged sample was increased from 403 MPa to 451 MPa, with relatively high elongation of 6.5%.
Laser melting deposition (LMD) and selective laser melting (SLM) are two major metal additive manufacturing technologies that explore the near-net shaping of large components and net shaping of small ...complex structures. In order to achieve subscale complex structures, researchers proposed LMD–SLM hybrid manufacturing processes. Ti6Al4V is an α–β dual-phase, moderate strength titanium alloy that is widely used in the fields of medicine, aeronautics, and astronautics. In this study, thin (1.5–2.5mm) horizontal, vertical SLM plate and rolled plate are used as substrate materials for the LMD process to analyze tensile properties, microhardness, microstructure, and internal defects. The results show that the LMD process forms a hybrid with the aforementioned plates. The relative density of hybrid-forming area can reach 99.5%, because of the existence of the pores with diameter <20µm. Tensile strength and elongation of the hybrid thus produced can reach respectively 918MPa and 11%, and fractures are located in the LMD zone. Internal layer fracture of the LMD zone increases elongation, whereas layer interface fracture decreases it. The laser deposition process epitaxially generates coarse columnar crystals, and laser remelting reduces the microhardness of the SLM substrate in the 2- to 3-mm-thick grain-increased heat-affected zone (HAZ). The microhardness distributions of the LMD zone, HAZ, and substrate material are found to be 344, 343, and 375 (horizontal SLM); 346, 334, and 386 (vertical SLM); and 351, 328, and 340HV (rolled plate), respectively.
Considerable studies on metal selective laser melting (SLM) have proved the necessity to refine microstructure parts fabricated by SLM in order to eliminate property anisotropy, hot-tearing and to ...increase the SLM-processability. In the present work, Ti nanoparticles, at the first time, were discovered to be an extremely effective inoculant for an SLMed 2024 aluminium alloy. 0.7 wt% addition of Ti nanoparticles was capable of substantially eliminating the hot-tearing cracks and columnar structure, and refining the grains in the SLMed 2024 alloy in a broad processing window. The substantial grain refinement in the Ti-inoculated 2024 alloy was attributed to the in-situ formation of Al3Ti nanoparticles with a L12 ordered structure, which formed a coherent interface with Al matrix and therefore significantly promoted the heterogeneous nucleation of the α-Al during solidification of melt pools in the SLM process. After a conventional T6 heat treatment, this SLMed alloy exhibited a superior balance of strength and ductility (tensile strength was up to 432 ± 20 MPa and elongation of 10 ± 0.8%), which was comparable to its wrought counterpart. This work can be considered as a breakthrough in research of fabricating high-strength aluminium alloys using SLM.
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The microstructure characteristics as well as the mechanical properties of an Inconel 625 alloy obtained by three processes: forging, SLM and LMD, are investigated. For the last two processes, known ...as “additive manufacturing”, the influence of printing parameters is considered as well as the role of possible heat treatments. First, microstructural analyses (SEM and EBSD) underline the presence of columnar dendrites with a very heterogeneous grain size for additive manufactured as-built materials. The microstructures appear highly textured, particularly for SLM ones which are also often finer than the ones obtained by LMD. Heat treatments and particularly a 1h-1100C∘ annealing is proven to improve the printed parts microstructure and to avoid a drastic decrease in terms of ductility, particularly for LMD parts. The LMD process with controlled laser power, coupled with appropriate heat treatment, finally produces materials with both microstructures and tensile mechanical properties close to or better than those of the wrought alloy.
An in-situ nano-TiB2 decorated AlSi10Mg composite (NTD-Al) powder was fabricated by gas-atomisation for selective laser melting (SLM). Fully dense and crack-free NTD-Al samples were produced using ...SLM. In contrast to the NTD-Al powder without cell-like microstructure, the SLMed NTD-Al had a textureless microstructure, consisting of fine grains and cells, with well dispersed nano-TiB2 particles inside the grains and rod-like nano-Si precipitates inside the cells. Both nano-TiB2 particles and nano-Si precipitates exhibited a highly coherent interface with the Al matrix, indicative of a strong interfacial bonding. The formation of this microstructure was attributed to the sequential solidification of non-equilibrium and eutectic Al-Si upon rapid cooling during SLM. As a result, the SLMed NTD-Al showed a very high ultimate tensile strength ∼530 MPa, excellent ductility ∼15.5% and high microhardness ∼191 HV0.3, which were higher than most conventionally fabricated wrought and tempered Al alloys, previously SLMed Al-Si alloys and nano-grained 7075 Al. The underlying mechanisms for this strength and ductility enhancement were discussed and a correlation between this novel microstructure and the superior mechanical properties was established. This study provides new and deep insights into the fabrication of metal matrix nanocomposites by SLM from in-situ pre-decorated composite powder.
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•A material model based on the SLM-built porous materials was proposed.•The detailed stress and strain distribution were predicted from the FE results.•The fracture can be predicted and was verified ...by the experimental testing.•The predicted mechanical responses match well with the experimental results.•The Gibson–Ashby formulations were obtained from the FE analysis.
Cellular structures with controllable mechanical properties and porous architecture are the most promising candidates for many applications such as bone implants. Selective laser melting (SLM), one of the additive manufacturing (AM) technologies, enables manufacturing of space filling lattice structures with exceptional load bearing efficiency, customizable stiffness, controllable cell topology, cell size, and porosity. In this work, Schoen Gyroid (SG) unit cell, a triply periodic minimal surface (TPMS) structure, was used to design the cellular structures. As opposed to many other types of unit cells, SG has superior characteristics of self-supporting and high manufacturability for AM technologies. The titanium alloy (Ti–6Al–4V) SG cellular structures were manufactured by SLM. Finite element (FE) method was employed to predict the elastic modulus, compressive yield strength and stress/strain distributions of the SG cellular structures, and the failure occurrence mechanisms were analyzed. The FE results were compared with the experimental data. The results show that through FE method, the mechanical responses of the SG cellular structures can be accurately described and it is possible to customize the mechanical properties of SLM-produced titanium alloy TPMS lattices.
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The performance of many metal biomedical implants – such as fusion cages for spines – is inherently limited by the mismatch of mechanical properties between the metal and the ...biological bone tissue it promotes. Here, an alloy design approach is used to isolate titanium alloy compositions for biocompatibility which exhibit a modulus of elasticity lower than the Ti-6Al-4V grade commonly employed for this application. Due to the interest in alloys for personalised medicine, additive manufacturability is also considered: compositions with low cracking susceptibility and with propensity for non-planar growth are identified. An optimal alloy composition is selected for selective laser melting, and its processability and mechanical properties tested. Additive manufacturing is used to engineer an heterogeneous microstructure with outstanding combined strength and ductility. Our results confirm the suitability of novel titanium alloys for lowering the stiffness towards that needed whilst being additively manufacturable and strong.
Scaling laws for the additive manufacturing Rubenchik, Alexander M.; King, Wayne E.; Wu, Sheldon S.
Journal of materials processing technology,
07/2018, Letnik:
257
Journal Article
Recenzirano
Odprti dostop
The evaluation of simple thermal model of selective laser melting (SLM) process shows that the temperature distribution in the sample is characterized by two dimensionless parameters: normalized ...enthalpy and the ratio of dwell time to the thermal diffusion time. We demonstrated that the melt depth data taken for different machines for different materials collapsed in one curve, making possible to rescale the optimal processing parameters between the different materials and machines. The melt pool depth, width and the length are the universal function of these two parameters. Within the operational range of parameters for SLM these functions can be interpolated by the simple algebraic expressions given the possibility to reduce the calculation of the melt pool characteristic to spreadsheet model.
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