SLM Samples Research Articles

Effect of surface topography on the fatigue behavior of additively manufactured Ti6Al4V and CoCr alloys

Powder bed fusion (PBF), including selective laser melting and electron beam melting, fabricates complex, porous, osseointegrative implants for widespread clinical use. Fatigue testing is imperative for predicting long-term strength and durability of rough and surface porous implants while bone remodels around and grows into the implant. This study analyzes different materials (Ti6Al4V and Co28Cr6Mo) with varying topographies including as-printed surface roughness and the addition of a surface porous layer common to implants. The results are compared to wrought and PBF controls that are polished and machined. Moreover, different PBF techniques for titanium result in different as-printed surface roughness (∼0.07–17 μm) and microstructure. The fatigue data demonstrates that the surface finish impact was stronger in Ti6Al4V versus CoCr and SLM Ti6Al4V HIP + surface porous gyroid samples didn't perform worse than the roughest solid sample without surface porosity (EBM Ti6Al4V). With the same mechanical surface finishes, the SLM and wrought Ti6Al4V samples display similar fatigue resistance (800 and 850 MPa respectively), while EBM samples remain inferior (350 MPa). This study provides a foundation to compare fatigue resistance across materials and surface topographies through different fabrication techniques to optimize the lifespan of orthopedic implants while incorporating rough as printed surfaces and added surface porosity, both of which are essential for osseointegration.

Effect of Fabrication Method and Heat Treatment on the Properties of Co-Cr Bio Alloy

Co-Cr alloys are widely used in dental and medical equipment since the development of the first cast Co-Cr-Mo alloy. This is due to its high mechanical properties and high resistance to wear and corrosion. This research aims to study the effect of the fabrication method (Investment Casting and Selective Laser Melting SLM by 3D printing) and heat treatments on the mechanical and tribological properties of Co-Cr-Mo alloy. It was found that the Selective Laser Melting method in general increases the ultimate tensile strength, strain and hardness compared to the Investment Casting method. Also, solution treatment and aging reduce the strength and strain values of the SLM samples and have no obvious effect on the casting samples. The wear test shows that wear rate of casting samples is lower than that of SLM samples.

INVESTIGATION OF HARDNESS AND ELASTIC MODULUS OF MILLED AND SLM Ti6Al4V ALLOY

The aim of the present paper is to investigate the hardness and elastic modulus of Ti6Al4V alloy produced by CAD/CAM milling and selective laser melting. The Vickers micro-hardness is measured, while the modulus of elasticity is determined by new developed methodology consisting of bending test and finite element analysis. It was established that the manufacturing methodlead to differences in the micro-hardness and elastic modulus of the milled and SLM samples. The measured micro-hardness of the Ti6Al4V alloy was higher for the SLM samples (396 HV) compared to the milled ones (347 HV). The values of the modulus of elasticity of Ti6Al4V alloy are 180 GPa for the milled and 120 GPa for the SLM fabricated samples. They are higher than the data given in the literature or by the manufacturers. Subsequent heat treatment with porcelain firing modes slightly decreased the micro-hardness to 322 HV for the milled and 388 HV for the SLM produced samples and had almost no effect on the modulus of elasticity for both groups.

Experimental study on the influence mechanism of micro-abrasive air jet machining on the surface quality of Ti-6Al-4V titanium alloy formed by selective laser melting

This experiment studied the effect and mechanism of micro-abrasive air jet machining (AAJ) on the surface quality of SLM-formed TC4 titanium alloy specimens under different air pressures and jet angles. The results showed that the width of the AAJ processing area increased with the increase of air pressure but decreased with the increase of the injection angle. The surface quality of SLM samples could be improved effectively by AAJ processing. The optimized percentage of surface roughness value (Sa) was the largest, reaching 54% when the injection angle was 60ᵒ and the air pressure was 0.5 MPa; The surface hardness of the sample increased the maximum percentage, reaching 22% when the injection angle was 75ᵒ, and the air pressure was 0.5 MPa. The initial abrasive grains mainly had three shapes: flake, block, and column. The flaky abrasive grains had sharp edges, a good effect on matrix removal, large processing area but shallow depth of action; The block abrasive particles were mainly removed by extrusion and accompanied by severe friction with the substrate, and layered chips were generated; The columnar abrasive grains mainly scratched the surface of the substrate to generate scratches. The material's erosion rate (ER) was the largest, reaching 1.3%, and the processing efficiency was the highest when the injection angle was 60ᵒ and the air pressure was 0.4 MPa. The α′ martensite near the sample’s surface was elongated by AAJ processing, and the direction was parallel to the sample's surface. The depth of processing influence was the largest, reaching about 30 μm when the injection angle was 75ᵒ and the air pressure was 0.5 MPa.

Effects of build direction on thermal exposure and creep performance of SLM Ti6Al4V titanium alloy

With the development of typical additive manufacturing SLM, SLM Ti6Al4V has the potential to be used in high temperature vehicle structure. Mechanical properties after thermal exposure and creep performance of SLM Ti6Al4V and its build direction effects need to be studied in detail. In this paper, tensile and creep samples with 0°, 45° and 90° three build directions were designed and manufactured by SLM. Tensile tests were performed after 500 ℃ and 600 ℃ thermal exposure; And creep tests were carried out at 450 ℃ for all samples. The tensile properties after thermal exposure and the creep behaviors were studied and compared. The same size forged Ti6Al4V samples were manufactured and tested. It was shown that the yield strength (YS) and the ultimate tensile strength (UTS) of forged samples increased 24.23% and 16.70% after 500 ℃ exposure; while YS and UTS decreased after 600 ℃ exposure. The build direction had a significantly effect on the tensile ductility of SLM Ti6Al4V after thermal exposure. After 500 ℃ exposure, the tensile property of 90° sample was the best. Although the strength of 90° sample was slightly lower than that of 0° sample and 45° sample, the elongation was about 36.7% higher than that of 0° sample and 45° sample. After 600 ℃ exposure, 90° sample had both the highest strength and the elongation. Compared with forged samples, the SLM samples had longer creep ruptured time but lower ductility. For the SLM samples, 45° samples had best creep properties, while the properties of 0° samples were the worst. Fracture surfaces, failure modes and effects of build directions were investigated. Based on the features of SLM microstructures, two improved constitutive models were proposed and can be used to predict the anisotropic behavior of SLM material.

Influence of substructures on the selective laser melted Ti-6Al-4V alloy as a function of laser re-melting

This study investigates the effects of melting sequence on the microstructure, substructure, and mechanical properties of SLM Ti6Al4V alloys. Acicular α′ martensite was observed in all the SLM samples, and the dimensions of the α′ phase were changed with the melting sequence. Twins appear between acicular α′ martensite, and a large number of dislocations were observed in the material and within α′ martensite. The density of twins and dislocations increased with increasing melting sequence from single melting to triple melting. Tensile strength properties including ultimate tensile strength and yield stress, and hardness increased with increasing melting sequence from single melting to triple melting. The present results clearly prove that the melting sequence plays a significant role in determining the microstructure, substructure, and mechanical properties of the SLM as-built materials. • The as-built SLM shows high density of twins and dislocation. • The density of twins and dislocation increased with re-melting. • Ultimate tensile strength and yield stress increased with re-melting. • Re-melting–microstructure–substructure–mechanical property relationships are investigated.

Temperature and strain-rate dependence of the elevated temperature ductility of Inconel 718 prepared by selective laser melting

The elevated temperature tensile properties of SLM IN718 were measured as a function of strain rate and test temperature to better understand the time-dependent and thermal aspects of environmental sensitivity. SLM and wrought materials were solution treated, aged, and tested over the range of 550–750 °C and 10−3 to 10−6 s−1. The SLM material tested across all conditions had inferior strength and ductility compared to wrought material of the same heat treatment because of environmental sensitivity in the form of dynamic embrittlement. SLM samples show evidence of brittle intergranular fracture, crack growth, and oxidized NbC particles on the fracture surface, which all contribute to the observed poor ductility. These features, and subsequent embrittlement, are intensified with decreasing strain rate and increasing temperature. Higher strain rates and lower temperatures are shown to improve the ductility in SLM IN718 but despite this recovery it remains susceptible to environmental attack even in the extreme cases of the current study. The prevalence of NbC at grain boundaries in the SLM material is the principal source of dynamic embrittlement and environmental sensitivity.

THE INFLUENCE OF MINERALOGICAL COMPOSITION ON THE ADSORPTION CAPACITY OF HEAVY METALS SOLUTION BY JAVA NATURAL CLAY, INDONESIA

The adsorption capacity of four clay samples (Boyolali-BYL, Sleman-SLM, Gunungkidul-GK, and Pacitan-PCT) from Java, Indonesia, for copper (Cu) lead (Pb), zinc (Zn) and cadmium (Cd) solution was investigated by using batch equilibrium test. The adsorption data were presented using an isotherm curve, and adjusted to the Langmuir equation model, which produced the maximum adsorption capacity of the clay samples. The physical, chemical, and mineralogical analysis showed that the BYL and PCT samples have higher montmorillonite content, cation exchange capacity (CEC), and specific surface area (SSA) compared to SLM and GK clay samples. The batch equilibrium test revealed that the clay samples with higher montmorillonite content produced higher heavy metal adsorption capacity due to the higher cation exchange capacity (CEC), and specific surface area (SSA). The batch equilibrium test also show that the adsorption order for the metals cations followed the selectivity order Cu2+ > Pb2+ > Zn2+ >Cd2+. The Langmuir model resulted in the adsorption processes, offering maximum adsorption capacities from 196.08 to 769.23 mg/g for Cu, 217.39 to 416.67 mg/g for Pb, 106.38 to 114.94 mg/g for Zn and 104.17 to 113.24 mg/g for Cd of four clay samples studied. The highest adsorption capacity was achieved for the BYL sample. The lowest was the GK sample, in which the order of the maximum adsorption capacity of clay samples was BYL > PCT > SLM > GK sample. This research indicated that the proportion of montmorillonite content in the clay samples affected the maximum adsorption capacity of the heavy metal in the solution.

Isolating trabecular morphology to study bone damage

Bone structure is particularly complex and characterized by an intricate hierarchical architecture. Consequently, bone damage occurs at the multi-scale. Clinical applications typically analyze bone fractures at the macro-scale, but currently damage modes at lower scales are not fully understood yet. This research focuses on the understanding of meso-scale damage, characterized by a network of trabeculae of different thickness and spatial orientation. In order to isolate this articulated morphology, bone samples from porcine vertebrae are scanned through micro-computed tomography (micro-CT) and replicated by means of selective laser melting technique (SLM), obtaining Ti6Al4V specimens. This is particularly useful, because these samples are realized with a uniform material, permitting to isolate morphological features. The SLM samples, after a check of the internal morphology, are mechanically tested under static compression. The load-displacement curve shows a first linear elastic section, followed by a collapse of the structure. This behavior is similar to the one of porcine vertebrae. Starting from micro-CT volume reconstruction, three finite element models are implemented. A global preliminary model of the entire sample is developed and the area with the highest level of strain is identified. In order to understand the distribution of stresses and strains in the critical zone, a sub-region of the original cylinder is considered. The results of the simulations identify a homogeneous distribution of deformations over the entire geometry, with the exception of the region characterized by a thinning of the trabeculae, called the failure band of the sample. By implementing an additional sub-model, the most strained trabecula is identified as the critical location, causing the collapse of the structure. The numerical models are then validated by comparing the numerical and experimental stiffness. This will allow to perform further analyses by varying the trabecular architecture and quantitatively evaluate the effect of morphology.

Effect of microstructure and porosity of AlSi10Mg alloy produced by selective laser melting on the corrosion properties of plasma electrolytic oxidation coatings

In this work, PEO process was carried out on SLM samples of AlSi10Mg, characterized by different grades of porosity, in direct-current mode using high current densities and short time in a basic silicate electrolyte. For comparison, the PEO process was also performed on samples of conventional cast AlSi10Mg alloy. The microstructure and the composition of the coatings was evaluated with SEM and XPS, whereas the phase analysis was performed with XRD. The corrosion resistance was analyzed by potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) tests.The parameters used for PEO process allowed to obtain a continuous coating on all SLM samples, but its morphology resulted strongly influenced by the initial microstructure of the substrate. The coatings more homogeneous and less porous were produced on the samples with initial lower porosity. The corrosion performances of all SLM samples improved after PEO treatment and the PEO coatings with lower porosity resulted the more corrosion resistant.

Adhesively bonded joints in components manufactured via selective laser melting

Additive manufacturing has gained increasing attention in recent years in numerous industrial sectors due to its inherent characteristics, e.g. tool-free production and unprecedented freedom of design. However, in some applications such as heat exchangers the design has to follow certain restrictions, e.g. to allow for the removal of unfused powder, which can be enclosed in cavities. Moreover, in case multi-material parts are considered, the use of different powders during processing is often uneconomical since powder recycling is highly challenging. Therefore, the production of complex structures being characterized by limited accessibility and components made of different materials often require a subsequent joining process. Based on an analysis of state-of-the-art joining technologies employed for additively manufactured metal components, research gaps related to adhesive bonding are deduced. In light of the prevailing gaps, the influence of selective laser melting process parameters like laser power and build direction on the surface topography and, thus, on the bondability of the substrates are investigated. The mechanical tests reveal a high bond strength for the vertically oriented samples and the samples manufactured with a laser power of 400 W. Furthermore, a laser post-treatment of the SLM samples lead to an improvement of lap shear strength. Finally, results reporting on the ageing behaviour of these joints and an outlook on further research activities are given.

A novel post-processing method for 316L steel specimen generated by SLM using TiN/TiAlN multilayer coating

Purpose Selective laser melting (SLM) is an important advanced additive manufacturing technology. The existing SLM printing technology cannot manufacture the mechanical parts that fully meet the requirements of high precision and strength. This paper aims to explore a new post-processing method for SLM 316L specimen, namely, using of the TiN/TiAlN multilayer coating fabricated by multi-arc ion plating on the surface of SLM specimens, for improving the performance of SLM specimens. The other purpose of this paper is compared the performances of the TiAlN/TiN multilayer coating machined specimen and the TiN/TiAlN multilayer coating SLM specimen. Design/methodology/approach The TiN/TiAlN multilayer coating is fabricated by multi-arc ion plating on the surface of 316L specimens. The surface morphology and selected mechanical properties of TiN/TiAlN multilayer coating plating on the SLM substrate specimen and the machined substrate specimen were studied in this paper. The analyzed properties included surface topography, micro hardness, the adhesion, the thickness and the wear resistance of TiN/TiAlN multilayer coating plating on the SLM substrate specimen and the machined substrate specimen. Findings The electron microscope images reveal that surface morphology of TiN/TiAlN multilayer coating plating on the SLM specimens is relatively flat, and there are some micro-particles in different sizes and pin holes dispersed on them. After TiN/TiAlN multilayer coating, the performances of SLM samples, such as micro hardness, the thickness and the wear resistance, were significantly improved. The micro hardness of TiN/TiAlN multilayer coating machined specimen is higher than that of TiN/TiAlN multilayer coating SLM specimen. However, the adhesion of TiN/TiAlN multilayer coating machined specimen is less than that of TiN/TiAlN multilayer coating SLM specimen. Originality/value The study provides a new post-processing method for SLM 316L specimen to improve the performance of SLM specimens and to enable SLM specimens to be applied in the field of precision mechanical transmission.

Investigation of Mechanical Properties of Granulated Waste Rubber Aggregates Substituted Self-Compacting Concrete Mortar Produced with Different Cement

Storage or disposal of waste vehicle tires is difficult, costly and time consuming. Waste tires, which cause the release of pollutant gases to the environment due to its chemical structure in the process of destruction, are considered as an important recycling material in the context of developing and advancing technology and alternative products. Waste vehicle tires are granulated in certain sizes after the disintegration phase and reused in many different fields. With this experimental study, it is aimed to examine the fresh and hardened properties of 12 different self- setting mortar (SSM) samples of Ground Vehicle Tire Aggregates (GVTA), which are substituted with 5 different fine aggregates and prepared with two different cement types. The evaluation of the workability properties of fresh SLM samples prepared in accordance with EFNARC was done with mini spreading and mini V-hopper experiments. In order to determine the mechanical properties of the hardened SSM, pressure and three-point bending tests were performed on the 3rd, 7th and 28th days of prismatic samples in 40x40x160mm dimensions, and capillary water absorption test is carried out on cubic samples in 50x50x50 mm dimesions on the 28th day. The optimum usability rate of GVTA in SSM mixtures produced separately with CEM-V 42.5R and CEM-V 32.5R cement is interpreted through graphs and tables. With this study, it was observed that when the rate of GVTA was increased in the SSM mixture, the capillary water absorption amount increased, while the pressure and bending strengths decreased

Processing of AlSi9Cu3 alloy by selective laser melting

ABSTRACT Additive manufacturing of Al-alloys allows the production of components with a complicated structured shape, geometry composed by lattice structures, internal cooling, etc. The portfolio of Al-alloys for metal additive manufacturing is still under development and is strongly limited, compared to the conventional technology. The alloy AlSi9Cu3 is used in many applications, but its processing details are still missing. The main aim of this paper is to describe the laser process parameters for AlSi9Cu3, processed by SLM technology and manufactured from two powders of different shapes and particle sizes. The tested process parameters were laser power, laser speed, and hatch distance in the range of 100–400 W, 200–1500 mm · s−1 and 90–150 µm. These were tested using a single-track and cube test. Microstructure, mechanical properties and the fatigue of SLM samples were analysed and compared with as-casted material.

A comprehensive study on fused filament fabrication of Ti-6Al-4V structures

In metal additive manufacturing, microstructural inhomogeneities, like anisotropic mechanical strength and geometric limitations in directed energy deposition, electron beam melting, or selective laser sintering, have led to the exploration of alternative techniques in recent years. Among these techniques, fused filament fabrication is an attractive alternative due to its successes in producing dense parts, approaching traditional manufacturing specifications. Despite this success, many challenges remain to produce reliable parts with reproducible properties using FFF, particularly in the thermal treatment for part densification. Here are presented results of using a polyolefin-based binder system loaded with 55–59 vol. % Ti-6Al-4V powder to create a printable filament. Printed Ti-6Al-4V parts using these filaments were sintered at temperatures ranging from 900 to 1340 °C and evaluated by x-ray diffraction, scanning electron microscopy and optical microscopy. The sintered samples demonstrated a linear decrease in β-phase from 15 to 11 vol. % with increasing temperature, while residual stress and Young’s modulus increased. Additionally, the density of printed and sintered Ti-6Al-4V parts could be increased up to 91 % of the theoretical density of Ti-6Al-4V by increasing the sintering temperature up to 1340 °C. Samples that were sintered at 1340 °C showed a higher Young’s modulus compared to SLM samples, likely due to the increased α-phase in samples sintered at 1340 °C.

Effects of size and geometry on the thermomechanical properties of additively manufactured NiTi shape memory alloy

Effect of size and shape of the additively manufactured Nickel-Titanium (NiTi) alloys on their thermomechanical properties is experimentally studied. Although additive manufacturing is shown as a solution to the difficulties of machining of NiTi shape memory alloys (SMAs), our understanding of the effect of various processing (e.g., laser power, scanning pattern, etc.) and part characteristics (e.g., part geometry) on the resulting properties is not complete. During the SLM fabrication process, various factors influence the properties of the final product. In this study, we investigated the effect of size and shape of the SLM samples on the thermomechanical behavior of the parts. Tensile specimens with different thicknesses and shapes were fabricated for this investigation. The accuracy of fabrication is discussed for all of the specimens. Differential scanning calorimetry (DSC) measurements were conducted to compare the transformation temperatures of specimens with different size and shape. Moreover, tensile tests including loading, unloading, and heating were done for all of the specimens and the mechanical responses were compared with each other. Digital image correlation (DIC) was used for strain measurements as a more accurate strain measurement tool. The transformation temperatures of the fabricated parts were similar for parts with different shapes and sizes. From the mechanical tests, higher strength was observed for the thinner parts in both rectangular and oval specimens. Also, from the mechanical behavior of different shapes, it was observed that the rectangular showed higher critical stress than their equivalent oval specimens.

Thermal stability and crystallization of a Zr-based metallic glass produced by suction casting and selective laser melting

The thermal stability and crystallization mechanism of the Zr59.3Cu28.8Al10.4Nb1.5 (at%) metallic glass produced through selective laser melting SLM (from industrial grade material) was studied and compared with the same alloy produced by suction casting (from laboratory grade material of high purity). Oxygen- and Al-rich particles of a cubic phase (Fd3‾m) with a size of up to 200 nm are detected in the as-built selective laser melted samples by transmission electron microscopy.The crystallization process of the cast and SLM samples is investigated by in-situ X-ray diffraction experiments. In the cast samples, the initial crystallization occurs via the formation of a metastable tetragonal phase (Al2Zr3), together with tetragonal CuZr2 and hexagonal Al3Zr4 type structures, while the SLM samples initially crystallize through the formation of the metastable, oxygen- and Al-rich, cubic phase already present before annealing. The main phases present at the end of the crystallization for both type of samples are the same, mainly CuZr2 and Al3Zr4. The differences in the crystallization paths are attributed to differences in the oxygen levels. In general, the higher oxygen content (∼1 at%) of the SLM samples results in a decrease of the thermal stability of the alloy and promotes the formation of an oxygen-rich, metastable cubic phase.

The effect of thermal treatment on the properties of SLM samples with a bionic design

This article shows the possibility of additive technology applied to medical implants. It’s shown the difference of physical properties such as elastic module of bones, implants made of traditional technology and implants made of additive technology. Porous structure has been chosen for future implants through designing its and further calculation of its mechanical properties using software such as Solid Works, Logos and Ansys. To confirm the right choice of design of structure we manufactured samples with using Rosatom 3D printer, made heat treatment and tested them.

Elemental segregation in an AlCoCrFeNi high-entropy alloy – A comparison between selective laser melting and induction melting

Additive manufacturing of a high-entropy alloy, AlCoCrFeNi, was studied with selective laser melting from gas atomized powder. A wide process parameter window in the SLM process was investigated but it was impossible to produce crack-free samples, attributed to stresses that originate during the building processes. The microstructure and elemental segregation in the SLM samples were compared with induction-melted AlCoCrFeNi. The induction-melted sample crystallizes in randomly oriented large grains (several hundred microns). Dendritic and inter-dendritic areas with slightly different chemical composition can be observed. Within these areas a spinodal decomposition occurs with a separation into FeCr- and NiAl-rich domains. Further spinodal decomposition within the FeCr-rich regions into Cr- and Fe-rich domains was observed by atom probe tomography.In contrast, the SLM-samples crystallizes in much smaller grains (less than 20 μm) with a dendrite-like substructure. These dendrite-like features exhibit distinct chemical fluctuations on the nm-scale. During annealing more pronounced chemical fluctuations and the formation of Cr-rich and Cr-poor regions can be observed. The difference in microstructure and spinodal decomposition between the induction-melted and SLM samples is attributed to the significantly higher cooling rate for SLM. This study shows that, by using different synthesis pathways, it is possible to modify the microstructure and segregation of element within alloys. This can be used to tune the materials properties, if the cracking behavior is handled e.g. by change of alloy composition to minimize phase transformations or use of a heating stage.

Notched fatigue testing of Inconel 718 prepared by selective laser melting

AbstractSelective laser melting (SLM) was used to prepare notched high‐cycle fatigue test specimens made from nickel‐based superalloy Inconel 718. Samples were designed to have 1 of 3 different notch geometries, including V notches with Kt of 2.2 or 3.1, a U notch with Kt of 2.0, and were printed in either vertical or horizontal orientations. Samples were tested with as‐printed dimensions and surfaces after heat treatment, but a separate set of SLM samples were printed as plates and machined to final dimensions comporting to the V‐notch specimen with Kt = 3.1. High‐cycle fatigue testing showed that machined SLM specimens behaved similar to wrought Inconel 718 plate specimens, but testing with as‐produced surfaces led to a decrease in fatigue life. The explanation for this difference is based on approximations of linear elastic fracture mechanics solutions for short cracks emanating from notch roots, with intrinsic surface features of SLM materials serving as the cracks. Analysis of the actual notch geometries after SLM fabrication indicates that stress intensity in the presence of these features plays a prominent role in determining number of cycles before fatigue crack initiation and propagation occurs.