Laser Melting Additive Manufacturing Research Articles

Effects of process parameters on microstructure properties of WE43 magnesium alloy by selective laser melting

Magnesium alloys have broad application in aerospace, biomedicine and automobile, et al. Selective Laser Melting (SLM) additive manufacturing of magnesium alloy can fabricate complex components with acceptable properties. However, the low evaporation heat of magnesium alloy at ambient temperature leads to vaporization instead of melting during the SLM forming process, posing significant challenges for achieving successful SLM fabrication of magnesium alloys. Hence, the objective of this paper is to analyze the impact of various process parameters on the distribution of macroscopic defects and the relative density during SLM additive manufacturing test of WE43 magnesium alloy samples. Additionally, it investigates the effect of forming parameters on the microstructure by examining molten pool morphology, grain size, and material composition. Mechanical property tests are conducted to establish correlations between relative density, microhardness, strength, and energy density in printed samples. Consequently, optimal SLM manufacturing parameters for WE43 magnesium alloy are determined as follows: laser power 200 W and scanning speed 800 mm/s. This study successfully achieves high-performance additive manufacturing of magnesium alloy materials.

A novel additive manufacturing strategy with high hydrogen production for ordered-porous stainless steel catalyst support

This paper proposes to improve hydrogen production performance of ordered-porous stainless steel by increasing its forming structure parameters. Firstly, selective laser melting additive manufacturing of ordered-porous stainless steel is carried out through designed orthogonal experiment table, to obtain its forming structure parameters under different manufacturing process parameters. Then, different forming structure parameters of ordered-porous stainless steel are converted into a comprehensive index by grey relation theory, which is grey relational degree (GRD). When powder thickness, scanning speed, scanning space and laser power are 30 μm, 800 mm/s, 90 μm and 60 W, respectively, the highest GRD of 0.930 is obtained, when those are 40 μm, 1200 mm/s, 70 μm and 60 W, respectively, the lowest GRD of 0.410 is gained. Finally, catalyst bonding strength and hydrogen production performance of the ordered-porous stainless steels with the above GRDs are verified. It is found that the ordered-porous stainless steel with the highest GRD has higher catalyst bonding strength and higher hydrogen production performance. When 12 mL/h injection rate of methanol–water solution and 250 ℃ reaction temperature are used, CH3OH conversion, H2 flowing rate and CO selectivity of the above ordered-porous stainless steel are 64.3%, 0.396 mol/h and 6.75%, respectively.

Impact of Heat Treatment and Building Direction on Tensile Properties and Fracture Mechanism of Inconel 718 Produced by SLM Process

In the selective laser melting (SLM) additive manufacturing process of Inconel 718, the emergence of Laves and δ precipitate phases in the γ matrix during or after heat treatment is a critical consideration. This study comprehensively assesses the microstructures and mechanical properties of Inconel 718 alloy produced through SLM under varied conditions: as-built (AB), homogenization + solution + aging (HSA), homogenization + aging (HA), and solution + aging (SA). Additionally, the impact of building orientation, whether horizontal (H) or vertical (V), is investigated. The AB specimens oriented horizontally display a columnar melt pool structure, with dimensions roughly between 300 and 400 μm. In contrast, the AB specimens aligned vertically show an elongated river-like structure of melt pools, with their sizes approximately at 250 μm. From the detailed microstructural analysis, the findings reveal that the as-built specimens lack γ′ and γ″ precipitates in their microstructure. Conversely, in heat-treated specimens, both the γ′ and γ″ phases are evident. Notably, Inconel 718 alloy specimens subjected to SLM fabrication and SA heat treatment demonstrate optimal mechanical performance. Notably, SA exhibits an average hardness of 476 HV for the horizontal specimen, which is 51.1% higher than that of AB specimens. The morphology and distribution of the δ phase in the γ matrix emerge as decisive factors influencing high-temperature performance. In SA specimens, the dissolution of brittle Laves phases occurs, and the presence of the δ phase at the grain boundary imparts superior properties during high-temperature tensile testing, including excellent yield and ultimate tensile strength. The presence of the granular-δ phase in the SA specimens resulted in a tensile strength of 1422 MPa and a yield strength of 1236 MPa, which are the highest values among all the specimens. SA has a tensile strength of 1120 MPa and a yield strength of 974 MPa at 650 °C.

Effect of heat treatment on the microstructure and mechanical properties of biocompatible Ti–Ta–Nb–Zr alloys prepared by selective laser melting

Abstract In this paper, a low elastic modulus, non-cytotoxic Ti-10Ta-2Nb-2Zr titanium alloy was prepared by selective laser melting additive manufacturing. The effect of annealing and solution heat treatment on the structure, mechanical properties, and tribological behavior were investigated. The results show that the microstructure was composed of the main α′ phase and a small amount of β phase. Heat treatment improved strength and elongation. The ultimate tensile strength (UTS) and elongation of the deposited specimen were 807 ± 8.74 MPa and 6.6 ± 0.75 %, respectively. After annealing, the UTS was nearly the same, but the elongation increased to 15.3 ± 0.95 %. After solution and aging, the UTS and elongation increased to 873 ∼ 813 MPa and 9.25–11.9 %, respectively. The elastic modulus of the deposited specimen was 120 ± 6.81 GPa. The elastic moduli of heat treated specimens ranged from 74 ± 4.04 to 96 ± 5.13 GPa. The elastic moduli of heat treated specimens were close to that of β-type titanium alloys. The wear mechanism was mainly abrasive wear and oxidative wear. Compared with the deposited and annealed specimens, the solution and age treated specimens had low friction coefficients and much better wear resistance. In terms of properties and cost, the designed alloy has great potential in the medical implant field.

Compressive properties of AlSi10Mg lattice structures with novel BCCZZ and FCCZZ configurations fabricated by selective laser melting

PurposeThis paper aims to examine the static compression characteristics of cell topologies in body-centered cubic with vertical struts (BCCZ) and face-centered cubic with vertical struts (FCCZ) along with novel BCCZZ and FCCZZ lattice structures.Design/methodology/approachThe newly developed structures were obtained by adding extra interior vertical struts into the BCCZ and FCCZ configurations. The samples, composed of the AlSi10Mg alloy, were fabricated using the selective laser melting (SLM) additive manufacturing technique. The specific compressive strength and failure behavior of the manufactured lattice structures were investigated, and comparative analysis among them was done.FindingsThe results revealed that the specific strength of BCCZZ and FCCZZ samples with 0.5 mm strut diameter exhibited approximately a 23% and 18% increase, respectively, compared with the BCCZ and FCCZ samples with identical strut diameters. Moreover, finite element analysis was carried out to simulate the compressive response of the lattice structures, which could be used to predict their strength and collapse mode. The findings showed that while the local buckling of lattice cells is the major failure mode, the samples subsequently collapsed along a diagonal shear band.Originality/valueAn original and systematic investigation was conducted to explore the compression properties of newly fabricated lattice structures using SLM. The results revealed that the novel FCCZZ and BCCZZ structures were found to possess significant potential for load-bearing applications.

Axiomatic Design of a Test Artifact for PBF-LM Machine Capability Monitoring

Powder Bed Fusion Laser Melting (PBF-LM) additive manufacturing technology is expected to have a remarkable impact on the industrial setting, making possible the realization of a metallic component with very complex designs to enhance product performance. However, the industrial use of the PBF-LM system needs a capability monitoring system to ensure product quality. Among the various studies developed, the investigation of methodology for the actual machine capability determination has been faced and still represents an open point. There are multiple authors and institutes proposing different investigation methods, ranging from the realization of samples (ex situ analysis) to installing monitoring devices on the machine (in situ analysis). Compared to other approaches, sample realization allows for assessing how the machine works through specimen analysis, but it is sensitive to the sample design. In this article, we first present an analysis of a well-known test artifact from an Axiomatic Design perspective. Second, based on the customer needs analysis and adjustments with respect to the use of hypothetical additive production lines, a new test artifact with an uncoupled design matrix is introduced. The proposed design has been experimentally tested and characterized using artifact made of Inconel 718 superalloy to evaluate its performance and representativeness in machine capability assessment. The results show an accurate identification of beam offset and scaling factor considering all the building platform positions. In addition, the artifact is characterized by a reduced building time (more than 90% with respect to the reference NIST artifact) and a halved inspection time (from 16 h to 8 h).

Microstructure and compression performance of novel AlSi10Mg composite auxetic structures fabricated by additive manufacturing

In order to further increase the mechanical properties of auxetic structures, a novel enhanced composite (NEC) auxetic structure was proposed and characterized by the combination of the enhanced re-entrant anti-trichiral and double arrow structures. The NEC structures were fabricated from AlSi10Mg powders through selective laser melting (SLM) additive manufacturing technology. The grain morphology and microstructure characteristic of the AlSi10Mg sample were comprehensively analyzed. Results indicate that both columnar and equiaxed grains can be observed in the SLM-fabricated sample. Columnar grains with the size around 52 μm are mainly distributed in the melt pool and equiaxed grains exist at the boundary of the melt pool. The columnar grains are approximately perpendicular to the boundary of the melt pool and grow towards the center of the melt pool, exhibiting <100> filamentous texture. The melt pool boundaries can be divided into three distinct regions, i.e., coarse grain zone, fine grain zone, and heat affected zone. The microstructure of the as-built sample consists of elongate cellular α-Al matrix decorated with eutectic Si network boundaries. The mechanical properties and energy absorption performance are systematically investigated by means of Finite Element Analysis (FEA) verified by the experimental results. It is found that the elastic modulus, compression strength, Poisson's ration and energy absorption of the NEC structures are sensitive to the structure parameters. i.e., the compression stress and energy absorption present an increasing trend with the increasing of α, decreasing of l1 and β, while l1, α and β exhibit opposite effect on the Poisson's ratio. Moreover, the rotational combination of varied structures can lead to an excellent energy absorption capacity of the NEC structures, which is significantly higher than that of other auxetic structures. The results will provide guidance for the structure design of lightweight auxetic structures with enhanced performance and outstanding auxeticity.

Room Temperature Corrosion Behavior of Selective Laser Melting (SLM)-Processed Ni-Fe Superalloy (Inconel 718) in 3.5% NaCl Solution at Different pH Conditions: Role of Microstructures

Inconel 718 (UNS N07718) is a nickel-base superalloy containing iron that is used at cryogenic temperatures (arctic pipe components) and at high temperatures (gas turbines). This alloy is also used in off-shore oil drilling due to its high overall strength and resistance to corrosion. Inconel 718 components are created by a selective laser melting (SLM) additive manufacturing route and result in isotropic fine-grained microstructures with metastable phases (such as Laves phases) that are not usually present in conventional manufacturing processes. In this work, SLM Inconel 718 alloy specimens were investigated in four different conditions: (1) As-manufactured (AS-AM), (2) Additively manufactured and hot isostatically pressed (AM-HIP), (3) As-manufactured and heat-treated (solution annealing followed by two-step aging), and 4) AM-HIP and heat-treated. Localized corrosion behavior was evaluated at room temperature in a 3.5% NaCl solution at three different pH conditions (pH 1.25, 6.25, and 12.25). Electrochemical tests, including linear polarization, cyclic polarization, potentiostatic conditioning, electrochemical impedance spectroscopy, and Mott–Schottky analyses, were used to compare the corrosion behaviors of the SLM specimens with that of the conventionally wrought IN718 samples. The results showed that the additively manufactured specimens showed better corrosion resistance than the wrought material in the acidic chloride solution, and the AM-HIP specimens exhibited superior corrosion resistance to the as-manufactured ones. Hot isostatic pressing resulted in the visible elimination of the dendritic structure, indicating compositional homogeneity as well as a significant decrease in porosity. In addition, the deleterious secondary phases, such as Laves and δ phases, were not observed in the microstructure of the HIPed samples. The AM-HIP material showed the highest corrosion resistance in all the pH conditions. The two-step aging treatment, in general, resulted in the deterioration of corrosion resistance, which could be attributed to the formation of γ′ and γ″ precipitates that increased the cathodic reaction catalytic activities. In the additively manufactured samples, the presence of the Laves phase was more detrimental to corrosion resistance than any other phases and MC carbide and grain boundary δ phase increased the susceptibility to corrosion in wrought materials.

Design optimization of 3D-manufactured monolithic stage for biomedical polishing applications by neural artificial network and teaching learning studying based optimization algorithm

Ultra-precision polishing engineering is a current trend in ensuring the good surface quality for biomedical applications. In precision engineering, compliant mechanism, so-called monolithic mechanism, has an increasing trend in alternating conventional rigid counterparts which can be utilized for biomedical polishing application. Therefore, this article proposes an optimal design for the monolithic stage. The stage is employed in driving the polishing head. The stage is operated within from several millimeters to hundreds of millimeters. In this article, the stage was tended to guide the head to polish the biomedical samples. Hypercube sampling design is combined with finite element method to collect the data. The teaching learning-based optimization algorithm is firstly coupled with the artificial intelligence in modeling the behaviors of the stage (resonant frequency, displacement, strain energy, and stress). Next, the teaching learning studying based optimization algorithm is extended to search the optimal parameters of the stage. Three single objective optimization scenarios and two multiobjective optimization scenarios of the monolithic stage are conducted to show the effectiveness of the offered method. The predictors were well-formed by using the teaching learning-based optimization-coupled artificial neural network. The results found that the performance indicators (R and R2) are almost equal to one with the mean square error (MSE) and root MSE values are very small. The optimal results that the stage can work with a highest frequency of 760.7903 Hz, a largest stroke of 0.7325 mm (about 732.5 μm), and a strain energy of 2.5999 mJ. Meanwhile, the von Mises stress is almost much lower than the yield strength of AL 7075-T73. The designed method can effectively use in designing the stage. The stage can be fabricated by using selective laser melting additive manufacturing technology, and it can be employed to guide the polishing head for biomedical samples.

Fatigue behavior of notched and unnotched AM Scalmalloy specimens subjected to different surface treatments

In the present work, the fatigue resistance values of Scalmalloy specimens obtained by selective laser melting (SLM) additive manufacturing (AM) are experimentally studied. The fatigue levels of specimens with and without notches after applying different surface treatments, such as sand blasting, shot peening, isotropic finishing, and polishing alone or in combination, are analyzed. To understand the fatigue behavior of this material, the surface finishes and internal residual stresses of the specimens are analyzed. Moreover, the fracture surface of each sample is observed by electron microscopy to determine the failure mechanism. There is a clear separation between two different types of failure: (1) rupture by a crack generated on the surface associated with high applied stress values and (2) failure by a crack generated on an internal defect associated with low applied stress values.

Influence of oxygen content on selective laser melting leading to the formation of spheroidization in additive manufacturing technology.

Selective laser melting (SLM) additive manufacturing technology with different oxygen contents leads to the appearance of spherical solids of different sizes on the surface of the part, which affects the mechanical properties of the part, surface roughness, etc. In this study, the SLM molding technique was applied using three different 316L metal powders with different oxygen contents. The spheroidization properties and morphology of the samples were observed using a Quanta 200 environmental scanning electron microscope (ESEM), and the samples were observed microscopically and subjected to EDX spectroscopy using metallographic microscopy, and the mechanical properties were investigated. The results of the study showed that when using gas atomized powders, no spheroidization occurred when the oxygen content of the powders was 5.44 ± 0.01% in all cases, whereas using water atomized powders produced spherical structures with larger dimensions. This observation was closely related to the shape and particle size of the powder. When 316L metal powder with an oxygen content of 4.52 ± 0.01% was used for molding, small spherical structures appeared on the surface of the samples. When metal powder with an oxygen content of 5.44 ± 0.01% was used for the molding, larger spherical structures appeared on the surface of the samples. When the powder with an oxygen content of 5.90 ± 0.01% was used for the molding, more small spherical structures and some large spherical structures appeared on the surface of the samples. This suggests that higher oxygen levels may inhibit the occurrence of spheroidization. EDX spectroscopic analysis revealed that the white matter on the surface of the samples without spheroidization was mainly composed of Fe and Cr, whereas the white matter on the surface of the large-sized spherical structures was mainly composed of Si and Mn, which may be related to the oxygenophilicity of the various substances.

Thermo-physical phase field model of laser powder melting additive manufacturing of 2D layered stainless steel structures

Additive manufacturing (AM) techniques based on laser melting of metal powders are experiencing tremendous growth and are rapidly becoming the preferred processing approach for metal parts. However, the effect of the different processing variables on microstructural and mechanical property outcomes is not yet fully understood. Modeling and simulation can provide an inexpensive and expedient way to probe the large parameter space and identify the most important correlations between processing degrees of freedom and output products. In this work, we develop a two dimensional thermo-physical phase model of laser melting additive manufacturing that captures solidification and melting, heterogeneous nucleation, and oriented grain growth to simulate layered microstructures grown by melting a metal layer connected to the underlying substrate by a set of orientation relations. The model solves the Allen-Cahn and heat diffusion system of equations on structured meshes, and simulates the motion of a laser spot across the specimen through a sequence of successive passes. The simulations best replicate the formation of columnar structures, as under high-power laser conditions or under rapid solidification kinetics, in good qualitative agreement with experimental observations. Our approach connects processing variables with the microstructural outcomes, thus capturing the effect of important inputs such as laser spot size, laser scan speed, and cross hatch fraction on grain size and structure.

Experimental investigation on microstructure and properties of Al alloy-PEEK joint with different surface structure obtained by hot-pressing

In this study, selective laser melting (SLM) additive manufacturing was used for the fabrication of Al alloy with the surface structure based on the construction of mechanical interlocking mechanism to complete the joining with polyetheretherketone (PEEK). The application of hot-pressing process provided a direct joining between Al alloy-PEEK at 460 °C for 40 min. This work characterized the forming of both cylindrical and trapezoidal structures, indicating that the structures were formed completely, and the gaps were clear. Although some dimples or micropores were generated in the forming solid, these defects in the forming were beneficial for the flowing and filling of PEEK during hot-pressing joint. The microstructure of Al plate fabricated by SLM showed typical parallel columnar grains perpendicular to the deposition direction and stacked and fish scale like feature in the deposition direction, respectively. The microstructure characterizations of Al alloy-PEEK joints showed that both materials were joined without gaps and formed a strong mechanical interlocking, guaranteeing a firm bond with maximal tensile shear strength up to 81 MPa for trapezoidal structure. By comparison, the joint with cylindrical structure possessed a low 65 MPa shear strength due to weak cuneiform anchor interlocking. Fracture surface was investigated in more detail. The result showed that the joint with cylindrical structure mainly showed interfacial failure and pulling-out, tilting deformation and fracture of the supporting, while the joint with trapezoidal structure exhibited a separation between the top surface of the supporting and the PEEK and brittle cohesive fracture of the PEEK between the gaps.

Influence of forming directions on surface quality of 316L produced by selective laser melting additive manufacturing

Different forming directions have significant impact on surface quality in additive manufacturing. This study is aimed at exploring how different forming directions influence surface quality in additive manufacturing (AM). First, experiments were designed to prepare 316L stainless steel by selective laser melting additive manufacturing (SLAAM) in different forming directions. Moreover, the surfaces of samples manufactured by AM were tested using a three-dimensional (3D) surface profiler and a scanning electron microscope. Furthermore, the surface quality was characterized using four parameters, maximum height, S z ; maximum valley depth, S v; standard deviation of height, S q ; and arithmetic average height, S a. The following results were obtained: (a) different forming directions corresponded closely to upper surface roughness S a values, the values of S a being 7.16 and 8.20 μm, respectively. S a was the smallest among the four parameters; it showed good stability and statistical significance. (b) In the same forming direction, the upper surface roughness values followed the order S z &gt; S v &gt; S q &gt; S a. S z was the largest, exceeding 800 μm; the average value S a was the smallest, reaching 7.36 μm. The values of S q , S z and S v vary when the forming direction changed. Specifically, all of them increased when the forming direction changed from a vertical direction to planar and lateral directions in turn. (c) In different forming directions, the values of S z , S v, S q and S a varied on different surfaces but their variations were basically similar. Meanwhile, the S z , S v, S q and S a values of the free surfaces were at least ten times greater than those of the printed surface. In the SLAAM process, it was necessary to select a forming direction reasonably for parts with different dimensional parameters on each side.

Experimental investigation on selective laser melting additive manufacturing of non-ferromagnetic heterogeneous material based on TiNi alloy with Ta coating

In order to manufacture non-ferromagnetic heterogeneous material by Selective Laser Melting (SLM), it is necessary to solve the separation problem of non-ferromagnetic mixed powders after SLM forming. This research presents how to resolve this problem using TiNi/Ta mixed powders by ultrasonic vibration screening method and the analysis of SLM manufacturing experiment for non-ferromagnetic heterogeneous material. The purity of TiNi and Ta powders after separation could reach 99.7087%wt% and 98.8501wt% respectively, which both reached a relatively high purity. A TiNi alloy sample with Ta coating and TiNi/Ta gradient transition was manufactured successfully by SLM. The material interface of the sample achieves metallurgical bonding, and the color of the sample profile shows a gradient transition. The EDS analysis shows that the material composition changes from Ta -&gt;Ta/TiNi gradient -&gt;TiNi from surface to inside of the sample. The Ta coating contains over 92.5wt% Ta, and the TiNi matrix contains over 98.69wt% TiNi. Along the powder laying direction, it is difficult to clean the small powder near the solid-powder or solid-solid interfaces made of two different materials, which causes micro polluted areas near the interfaces. This study also provides a new method for integrated manufacturing of TiNi alloy part with Ta coating.

Vibration characteristics of additive manufactured IWP-type TPMS lattice structures

Several research has been done on the conventional strut-based lattice structures, which have the problem of stress concentration in the application. In recent years, a new lattice structure, the triply periodic minimal surface (TPMS) lattice structure is increasingly gaining attention, but its vibrational properties have been less studied. In this study, the IWP-type TPMS lattice structures and ordinary body-centered cubic (BCC) counterparts with similar topology were prepared by selective laser melting (SLM) additive manufacturing (AM) technique. The compression behavior of the structures and the energy absorption capacity were determined by uniaxial compression tests. The frequency response and the damping ratio of the structure were calculated by dynamic vibration transfer rate tests. The results show that the stiffness and inherent frequency of the lattice structure are proportional to the volume fraction and inversely proportional to the cell size. Decreasing the volume fraction and increasing the cell size can be more beneficial to achieve low-frequency vibration isolation. Moreover, the IWP-type triply periodic minimal surface lattice structures have better mechanical properties than BCC structures and have good vibration isolation properties. Insights from this paper provide a reference for improving the load-carrying and vibration isolation performance of lightweight lattice structures.

A multi-physics material point method for thermo-fluid-solid coupling problems in metal additive manufacturing processes

The metal additive manufacturing (AM) process involves complex multi-physics coupling phenomena associated with the heat transfer, fluid flow, and solid mechanics that bring challenge to the current numerical methods. In this study, a multi-physics material point method is proposed for solving thermo-fluid–solid coupling problems in metal additive manufacturing processes. In this method, the material domain is discretized by a structured grid and a set of particles with corresponding variants for the heat transfer, fluid flow, and thermal stress evolution, under both Eulerian and Lagrangian descriptions. The interaction between these fields is naturally handled by the same structured grid and particles. Moreover, a semi-implicit local iteration technique is proposed to efficiently solve heat transfer with solid–liquid phase change, an improved Chorin’s projection method is introduced to handle Darcy’s damping, and a staggered derivation scheme with a sub-cell occupation technique is proposed to solve surface tension and Marangoni forces. A set of numerical examples, including the benchmark problems and the selective laser melting AM problems, is presented to validate the proposed method, where good agreements have been achieved with the analytical, numerical, and experimental data available in the literature. It is demonstrated that the proposed method is a powerful tool for thermo-fluid–solid coupling problems in metal additive manufacturing and other multi-physics problems.

Bio-inspired, metal additive manufacturing interlocked structures: Geometrically design and fracture performance analysis

Suture-inspired interlocked interfaces in nature exhibit promising industrial applications potentials in advanced mechanical structures, devices and equipment. In this paper, the parametric design of interlocked interfaces is performed, and selective laser melting (SLM) additive manufacturing tensile specimens and compact tension (CT) fracture specimens with sutured interfaces are harvested, where AlSi10Mg raw materials are used as constituent materials. Afterwards, compact tension tensile fracture experiments and corresponding finite element simulations were performed and compared, where force-displacement curves for different interface structural geometrical parameters were harvested. The mechanical properties and failure modes of the interlocked interface structures were analyzed through experiments and simulations verification. Crack-tip opening displacement (CTOD) and fracture energy criteria were used to evaluate the fracture toughness of the interlocked specimen interfaces. In addition, parametric analysis was carried out to investigate the influence of different interlocked structural parameters on the interface mechanical performances and failure features. Accordingly, it can be concluded that the interface strength, toughness, and failure mechanisms can be rationally tuned through given geometrical parameters of the re-entrant interface microstructures.

PRODUCTION OF OXIDE DISPERSION STRENGTHENED INCONEL 718 ALLOYS USING CONVENTIONAL POWDER METALLURGY AND ADDITIVE MANUFACTURING METHODS

Oxide dispersion strengthened (ODS) Ni-based alloys having a high density of nano-oxides (NOs) (&amp;lt;10 nm) are considered to be good candidates for extreme environments, such as high temperature, radiation, and corrosion. In this study, ODS IN718 alloys have been produced using conventional powder metallurgy (PM) and novel selective laser melting (SLM) additive manufacturing. The effect of processing routes on the microstructure, in particular on the nano-oxide formation and structure has been investigated. It has been found that the powder metallurgy method that consists of compressing followed by sintering at 1250 and 1500 °C results in a nano-granular structure with homogenously distributed fine nano-oxides having a high number density. Similarly, SLM results in a high number density of fine nano-oxides; however, the particles exist in groups with the grains/cells. The nano-oxides are determined to be Y2Ti2O7, Y2TiO5 or YTiO3 and Y-Al-O. The deviation in the lattice parameters of Y2Ti2O7 infers the existence of some Al in the structure. This study sheds light on producing ODS IN718 alloys with high-density nano-oxides using powder metallurgy and additive manufacturing methods.

Selective Laser Melting Additive Manufactured Tantalum: Effect of Microstructure and Impurities on the Strengthening-Toughing Mechanism.

The balance between the strength and the toughness of pure tantalum (Ta) fabricated with selective laser melting (SLM) additive manufacturing is a major challenge due to the defect generation and affinity for oxygen and nitrogen. This study investigated the effects of energy density and post-vacuum annealing on the relative density and microstructure of SLMed tantalum. The influences of microstructure and impurities on strength and toughness were mainly analyzed. The results indicated that the toughness of SLMed tantalum significantly increased due to a reduction in pore defects and oxygen-nitrogen impurities, with energy density decreasing from 342 J/mm3 to 190 J/mm3. The oxygen impurities mainly stemmed from the gas inclusions of tantalum powders, while nitrogen impurities were mainly from the chemical reaction between the molten liquid tantalum and nitrogen in the atmosphere. The proportion of <110> texture decreased after vacuum-annealing at 1200 °C, while that of the <100> texture increased. Concurrently, the density of dislocations and small-angle grain boundaries significantly decreased while the resistance of the deformation dislocation slip was significantly reduced, enhancing the fractured elongation up to 28% at the expense of 14% tensile strength.