As-built Specimens Research Articles

Experimental Analysis of the Effectiveness of Pre-Stressed Steel Strips for the Strengthening of Beam-Column Joints in Existing RC Buildings

Beam-column joints in existing Reinforced Concrete (RC) buildings are usually characterized by the absence of transverse reinforcement. The observation of post-earthquake damage, as well as several numerical and experimental studies, have soundly demonstrated the possible impact of the response of unreinforced joints on the damage – up to collapse – of existing RC buildings under seismic action. In this study, a possible strengthening approach for these elements, based on CAM® technology, is investigated through experimental tests. The results of these tests are reported, along with the results of a previous experimental campaign carried out on the same topic. Full-scale external beam-column joint specimens are tested, with and without strengthening, and with different characteristics in terms of amount of beam longitudinal reinforcement and concrete compressive strength. Different failure modes are observed for the as-built specimens (joint failure without (J) or after (BJ) beam flexural yielding). The effectiveness of the adopted strengthening approach is demonstrated, observing an increase in joint shear strength and subassemblage ductility and – unless a joint failure in compression occurs – a possible modification of the failure mode into a ductile, flexure-controlled response of the subassemblage, as for code-compliant beam-column joints.

Dislocation Density of Electron Beam Powder Bed Fusion Ti–6Al–4V Alloys Determined via Time-Of-Flight Neutron Diffraction Line-Profile Analysis

Ti–6Al–4V alloys undergo a multiple phase transformation sequence during electron beam powder bed fusion (EB-PBF) additive manufacturing, forming unique dislocation substructures. Thus, determining the dislocation density is crucial for comprehensively understanding the strengthening mechanisms and deformation behavior. This study performed time-of-flight neutron diffraction (TOF-ND) measurements of Ti–6Al–4V alloys prepared via EB-PBF and examined the dislocation density in the as-built and post-processed states using convolutional multiple whole profile (CMWP) fitting. The present TOF-ND/CMWP approach successfully determined the bulk-averaged dislocation density (6.8 × 1013 m−2) in the as-built state for the α-matrix, suggesting a non-negligible contribution of dislocation hardening. The obtained dislocation density values were comparable to those obtained by conventional and synchrotron X-ray diffraction (XRD) measurements, confirming the reliability of the analysis, and indicating that the dislocations in the α-matrix were homogeneously distributed throughout the as-built specimen. However, the negative and positive neutron scattering lengths of Ti and Al, respectively, lowered the diffraction intensity for the Ti–6Al–4V alloys, thereby decreasing the lower limit of the measurable dislocation density and making the analysis difficult.

Residual stress and microstructure in IN718-René41 graded superalloy fabricated by laser blown directed energy deposition

Additively printed Ni-based superalloy with a compositionally graded transition from IN718 to René41 was fabricated by laser blown-powder directed energy deposition (DED/LB-M), with the goals of meeting location-specific temperature capability and reducing component cost for hot gas path turbine components. Residual stress distribution in thin wall specimens with three sets of DED build parameters in the as-built and stress-relieved states was measured by neutron diffraction. For calculating residual stress, the calculated d0 method was found to be more appropriate as stress-free reference than using the lattice spacing measured from the stress-relief heat treated specimens. Longer dwell time (lower interpass temperature), higher energy input, smaller layer thickness resulted in a higher magnitude of tensile residual stresses at edges and compressive residual stresses at center of the specimens. The residual stress results did not show a strong dependence on graded compositions, indicating that the residual stress build-up was more geometry and process dependent. Non-destructive neutron imaging based on the attenuation coefficient qualitatively visualized the compositional variation in the bulk and showed good agreement with quantitative Electron Probe Micro-Analysis (EPMA) measurement. Grain structure, texture, and residual plastic strain along the build direction were characterized by Electron Backscatter Diffraction (EBSD). Long columnar grains with (001) preferred grain orientation were dominant along the build direction. Compositional change did not show an obvious effect on the epitaxial growth of dendrites and the continuation of the columnar grains. Residual plastic strain was relatively low in the as-built specimens.

Laser powder bed fusion of C18150 copper alloy with excellent comprehensive properties

Laser powder bed fusion (LPBF) of copper alloys is expected to revolutionize aerospace propulsion and related industries. This study reports an LPBF-fabricated C18150 copper alloy with excellent comprehensive properties, e.g., thermal conductivity and tensile properties, at both room and elevated temperatures (300 °C, 500 °C). The results show that the nearly full dense specimens are obtained by using optimal process parameters. The microstructure of both the as-built (AB) specimens and the direct aging (DA) specimens at different aging temperatures (480 °C, 530 °C, and 580 °C) with a constant aging time of 4 h mainly consisted of columnar grains, and the grain size remains almost unchanged after aging treatment. The Cr precipitates grow and aggregate with the increase in the aging temperature. The highest room temperature ultimate tensile strength (UTS) of 501 MPa is obtained for specimens aged at 480 °C due to the strong precipitation strengthening effect induced by the tiny and dispersed Cr nano-precipitates. The specimens aging at 580 °C show the highest thermal conductivity of 313 W m−1 K−1 due to the recovery of lattice distortion induced by the Cr atoms dissolution. The trends in tensile properties and thermal conductivity of samples tested at 300 °C are consistent with those at room temperature. When the test temperature is 500 °C, the AB specimens achieve the highest UTS of 274 MPa and thermal conductivity of 259 W m−1 K−1 due to the in-situ precipitation of Cr atoms. This work introduces LPBF C18150 specimens with excellent comprehensive properties and promotes the application of LPBF copper alloys in the industry at different service temperatures.

Role of microstructural phases in enhanced mechanical properties of additively manufactured IN718 alloy

The effect of different microstructural phases such as laves, metal carbides, δ, γ′, and γ′′ on mechanical and fatigue properties were extensively examined for additively manufactured Inconel 718 alloy at three different material conditions: as-built, as-built-machined, as-built-heat-treated. The as-built samples microstructure revealed the melt pools having the continuous structure of columnar and cellular dendrites of laves phases which form due to microsegregation of alloying elements. The machining of the as-built specimens reduced the surface roughness to 0.82μm and removed the micro-sized pores existing on the surfaces, thereby increasing the tensile and fatigue strength by 5% and 50%, respectively. However, the heat-treatment of as-built specimens resulted in dissolution of melt pool boundaries along with the breakdown of continuous dendritic structure of laves phase, and evolution of the strengthening phases. As a result, the mechanical and fatigue properties improved appreciably as compare to the as-built ones: the microhardness by 27%, the tensile strength by 23.20%, and the fatigue strength by 150% (at R=−1). The examination of damaged surfaces revealed the existence of four types of fatigue damage mechanisms: lack of fusion, surface roughness, facets, and gas porosities. The observed changes in mechanical and fatigue properties could be very well correlated with the changes in microstructural level and are discussed in this article.

Development of microstructure and high hardness of Ti6Al4V alloy fabricated using laser beam powder bed fusion: A novel sub-transus heat treatment approach

The present work aims to study the effect of novel sub-transus heat treatment on the microstructure evolution and hardness of Ti6Al4V alloy fabricated using laser based powder bed fusion. The results revealed that the as-built microstructure is α′ martensite which decomposes to α + β during sub-transus heat treatment at 970 °C for different soaking times. The formation of a bi-modal structure with approximately 25% globular primary α and transformed β is observed. The development of globular primary alpha is attributed to thermal grooving and boundary splitting. The resultant coarsening of these α/β grains was associated with a time-temperature combination and orientation relation (OR) to 45° [100]. Moreover, precipitation of fine Ti3Al intermetallic (α2) in plate form is observed predominantly inside the primary α grains. Owing to the faster cooling rate post soaking time resulted in Ti3Al precipitates which is the conversion of α to α2 precipitates. The average micro-hardness of the specimen heat-treated for 12 h at 970 °C is found to be 45% higher in comparison to the as-built specimen. Whereas, the micro-hardness differs between the primary α and transformed β region due to the alloy element partitioning effect. The average micro-hardness of 592 HV is observed in primary α grains in the specimen heat-treated for 12 h at 970 °C. The prior results are associated with the formation of intermetallic nano-sized Ti3Al (α2).

Additive manufacturing of CMCs with bimodal microstructure

The present work deal with the fabrication of TiC-based composites with green Fe-based binder via additive manufacturing such as selective laser melting/laser fusion bed process. The as-built specimen exhibits a bimodal microstructure consisting of fine/ultrafine dendritic and coarser TiC phases. By adopting a novel multiple scan strategy, process defects such as cracks were eliminated by careful control of the melt pool temperature/cooling rates. Even though the mechanical properties may be improved, the anisotropic distribution of the dual phase leads to anisotropic distribution of hardness within the CMC surface.

Combination of annealing and laser shock peening for tailoring microstructure and mechanical properties of laser directed energy deposited CrMnFeCoNi high-entropy alloy

In this study, a post-treatment method combining annealing and laser shock peening (LSP) is used to tailor the microstructure and mechanical properties of CrMnFeCoNi high-entropy alloy (HEA) prepared by laser directed energy deposition (LDED). The microstructure, microhardness, residual stress and tensile property of the as-built, annealed, LSP and annealed + LSP specimens are compared. Results indicate that LSP produces greater plastic deformation on the surface of annealed specimen compared to the pristine as-built specimen, as manifested by a thicker plastically-affected layer. Recrystallization, dislocation network annihilation and thermal stress relaxation caused by annealing contribute to an increase in the plasticity of LDED-prepared specimens, which provides great strengthening conditions for LSP. Gradient strain hardening and compressive residual stress are gained in the surface layer of the annealed specimen subjected to LSP. Moreover, plastic deformation induces a gradient microstructure consisting of ultra-fine grains, high-density mechanical twins and slip bands in order. An excellent strength–ductility synergy is achieved in LDED-prepared CrMnFeCoNi HEA after combined post-treatment of annealing and subsequent LSP.

On study of process induced defects-based fatigue performance of additively manufactured Ti6Al4V alloy

Additively manufactured Ti6Al4V are high strength alloys but associated with inferior ductility and inherent defects. These process-induced defects act as a stress raiser and deteriorates the mechanical and fatigue properties of the alloy. Post-processing is generally done to enhance the ductility and fatigue properties but at the expense of strength of the additively manufactured Ti6Al4V alloy. In this study, the effect of defects on mechanical properties and fatigue performance of additively manufactured (selective laser melting) Ti6Al4V alloy has been investigated based on experimentally calibrated defects-based model. The as-built specimens were subjected to different heat treatments in order to optimize their mechanical properties and the most optimum heat treatment was then selected for investigation of changes in fatigue properties. The beneficial effect of heat treatment on mechanical properties was mainly associated with the reduction in fraction of α ’-martensitic microstructure and increase in α -lamellae thickness. Most of the fatigue failures occurred from surface and sub-surface defects, owing to the high stress concentration factor associated with them, and improved fatigue lives as a result of optimum heat treatment. A process-structure–property (PSP) linkage has been established to predict the mechanical properties. Experimentally calibrated defects’ based fatigue model has been formulated to predict the fatigue performance using the experimentally observed data i.e. the process induced defects’ size and their locations. • Different post-processing of SLM-based AM Ti6Al4V was investigated. • Heat treatment was carried out, which improved both mechanical & fatigue properties. • A Process-Structure-Property (PSP) linkage was established. • A new defects-based model was proposed to predict the fatigue properties.

Analysis of hierarchical microstructural evolution in electron beam powder bed fusion Ti–6Al–4V alloys via time-of-flight neutron diffraction

Ti–6Al–4V alloys prepared via electron beam powder bed fusion (EB-PBF) generally exhibit a hierarchical microstructure consisting of columnar β-grains, an acicular α-matrix, and nanoscale β-precipitates at α-lath interfaces. In this study, we performed time-of-flight neutron diffraction measurements to investigate the texture and volume fraction of EB-PBF Ti–6Al–4V alloys via Rietveld texture analysis (RTA). The high-intensity neutron source enabled the analysis of the nanosized β-phase precipitates at the α-lath interfaces. The results indicate that the α- and β-textures of the as-built specimen can be ascribed to multiple Burgers orientation relationships among the prior β-phase, α-laths, and nanosized β-phase precipitates, which are not clearly understood. The as-built texture was maintained during post-processing, suggesting that texture manipulation in EB-PBF fabrication is important for controlling the crystallographic orientations of the built components, even after post-processing. RTA allowed a precise quantification of the β-phase fraction, which was found to have increased in post-processed specimens. The results would contribute to a comprehensive understanding of the microstructural evolution of such alloys, which is vital for the modeling and optimization of alloy performance.

Combined effects of heat treatment and TiB2 content on the high-temperature tensile performance of TiB2-modified Ni-based GH3230 alloy processed by laser powder bed fusion

Laser powder bed fusion (LPBF) is widely used to manufacture advanced nickel-based superalloys for aero-engine components. LPBF-formed GH3230 nickel-based superalloy, however, suffers cracking and high residual stresses. This study systematically investigated the effects of different contents of submicron TiB2 particles on crack suppression and post-heat treatment for residual stress relief and improved microstructure anisotropy. The introduction of both 0.5 wt% and 1 wt% TiB2 achieved complete crack suppression in the LPBF-manufactured GH3230 specimens. As-built specimens with 0.5 wt% and 1 wt% TiB2 exhibited a supersaturated solid-solution microstructure, with the solid elements (Cr, Mo and W) almost fully dissolved in the matrix and only a limited number of Mo and Cr enriched carbides precipitated at the grain boundaries. Electron backscattered diffraction (EBSD) characterization demonstrated that a large number of deformed grains remained in the as-built specimens. After heat treatment, the residual stresses were released and the number of deformed grains significantly reduced. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterization demonstrated the disappearance of the dense dislocation network in the as-built specimens after heat treatment, accompanied by the precipitation of a large number of W-rich M6C carbides. This paper also discusses elevated-temperature (900 °C) mechanical properties. The ultimate tensile strength (UTS) values of the as-built GH3230 with 0.5 wt% (GH-0.5) and 1 wt% TiB2 (GH-1) specimens were 255 and 290 MPa, respectively. Compared to the as-built materials, the UTS values decreased by 40 and 53.5 MPa, respectively, after heat treatment. The paper also discusses the effect weight of the second-phase, solid-solution and dislocation-strengthening mechanisms on the elevated-temperature mechanical properties. The findings indicate that the added 1 wt% TiB2 particles and the solid-solution elements contributed about 106.2 MPa and 111.5 MPa stress, respectively, in the heat-treated GH-1 specimen. The precipitated M6C carbides after heat treatment, however, were not found to significantly improve the high temperature strength. This work is expected to provide a reference for industrial applications to improve the LPBF formability of nickel-based superalloys and to acquire attractive microstructures.

Solidification behavior and porosity in electron-beam powder bed fusion of Co–Cr–Mo alloys: Effect of carbon concentrations

An increased carbon content strengthens Co–Cr–Mo alloys for use in a broad range of industrial applications. In this study, we investigated the influence of the carbon content (0.04–2.5 mass%) on the porosity and microstructure of Co–27Cr–6Mo (mass%) alloys during atomization and electron-beam powder bed fusion (EB-PBF). Quantitative X-ray computed tomography clarified that the volume fraction of pores in the raw powders monotonically increased with the carbon content, as a potential effect of the significant reduction in the liquidus temperature. In contrast, the porosity evolution in the investigated alloys during EB-PBF under identical building conditions suggested an influence of carbon concentration that was distinct from that in the powder. These alloys exhibited negligible porosity fraction for 0.04 and 0.22 mass% and a maximum volume fraction (∼0.3 vol.%) at 2.0 mass%, followed by a remarkable reduction caused by further carbon addition. The porosity of the as-built alloys could be correlated to the solidification behavior varying with carbon concentration. The smoother and more flat solidification front during the cellular (0.04 and 0.22 mass%) and eutectic (2.5 mass%) solidification could effectively eliminate the gas bubbles from the melt pool, whereas the complicated morphology at the solid–liquid interfaces during the dendritic growth (1.5 and 2.0 mass%) hindered the pore elimination in the melt pool. Adding carbon significantly increased the Rockwell hardness of the as-built specimens, reaching a significantly high value of HRC59 at 2.5 mass% of carbon, primarily due to the formation of hard carbide precipitates. The obtained findings could be beneficial to reduce entrapped gas pores thereby contributing to the development of highly durable metal components.

Effect of intrinsic heat treatment on microstructure and hardness of additively manufactured Inconel 625 alloy by directed energy deposition

The effect of intrinsic heat treatment (IHT) induced by cyclic heat input in laser additive manufacturing (LAM) has been receiving increasing attention in recent years. Herein, the feasibility of tailoring the microstructure and mechanical properties of Inconel 625 alloy to improve material properties and help achieve part quality consistency by controlling IHT in directed energy deposition (DED) is demonstrated. In this study, thermal monitoring was used to obtain thermal histories of as-built specimens to reveal the differences in thermal characteristics under different IHT. The results show that the variation of IHT has an important effect on the primary dendrite arm spacing (PDAS), the temperature and cooling rate of the molten pool, the morphology and content of Laves, and can initiate unusual δ precipitation in the interdendritic region which may be related to the dissolution of Laves. And this time-position-dependent IHT effect results in a hardness fluctuation of about 23.6 % in the bottom and top of the as-built specimen with a dwell time of 1 s, while the hardness is relatively uniform in the specimen with a dwell time of 10 s. Furthermore, by simulating the IHT variation process, its effect on precipitate and hardness was further confirmed.

Effects of HIP Conditions on the Microstructure and Creep Properties of Ni-base Superalloy Fabricated by Laser Powder Bed Fusion

Ni-base superalloy (IN718) manufactured by laser powder bed fusion (L-PBF) was subjected to hot isostatic pressing (HIP) under various conditions. The effects on microstructure and defects in the builds were investigated, and tensile strength at room and high temperatures and tensile creep properties were evaluated. After HIP at lower temperature, Laves phase in as-built specimen was dissolved and the δ phase was precipitated. However, the δ phase dissolved in the matrix as the HIP temperature increased. When the HIP temperature was less than 1323 K, the tensile strength was almost as high as the forged specimen. The creep rupture strain increased with increasing HIP temperature and was the highest at 1393 K. However, the strain was lower than that of the forged specimen. It was found that there was a factor that reduce the creep rupture strain specific to the HIP specimens.

Microstructural Control Strategy Based on Optimizing Laser Powder Bed Fusion for Different Hastelloy X Powder Size.

In additive manufacturing (AM), the powder properties and laser powder bed fusion (LPBF) process parameters influence the quality of materials and building parts. However, the relationship between the size of the powder, LPBF process parameters, and mechanical properties is not well-established. In addition, Hastelloy X (HX) is attracting attention for its excellent high-temperature properties, but it is difficult to process, such as by cutting and milling, because of its high hardness and high ductility. This can be overcome by applying the AM process. We compared the LPBF window process maps for two HX powders of different sizes. Despite their small difference of 19.7% in particle size, it was confirmed that the difference in laser power was more than 40 W, the difference in scan speed was more than 100 mm/s, and the difference in energy density was more than 20% under the optimal process conditions. The as-built specimen had a larger molten-pool size as the energy density was higher, which resulted in the differences in mechanical properties at room temperature and high temperature (816 °C). We considered the control of the size of the powder to obtain the properties required for each temperature condition. The microstructures and mechanical properties of the as-built LPBF specimens were also investigated and compared with those of cast HX. Because of the rapid melting and solidification processes in LPBF, the as-built HX exhibited nano-sized dendrite structures and large internal strain energy. This resulted in the as-built LPBF exhibiting a higher room-temperature tensile strength than the cast material. Under high-temperature conditions, the grain boundary of the as-built LPBF acts as a sliding path, and the as-built LPBF HX showed significantly better high-temperature tensile strength characteristics than the cast HX.

Tunable mechanical performance of additively manufactured plate lattice metamaterials with half-open-cell topology

Plate lattices are an emerging class of lightweight mechanical metamaterials that exhibit superior mechanical properties. The unique architectures of plate lattice metamaterials are regarded as the origin of achieving such advanced performance, but they lead to the difficulty of powder removal after the powder-bed-based additive manufacturing process. In the present work, plate lattice metamaterials with half-open-cell topology are proposed and fabricated via the laser powder bed fusion technique. To investigate their mechanical performance and deformation behaviours, numerical simulations and experimental tests are performed on finite element models and as-built specimens, respectively. Simulation results show that the mechanical properties and elastic anisotropy of half-open-cell plate lattice metamaterials are easily tunable when changing the geometric parameters, e.g., plate thickness or hole diameter. The elastic moduli and Poisson’s ratio are found to scale nonlinearly with the hole diameter for different plate thicknesses, and the elastic anisotropy approaches 1.0 for specific hole size. The specific energy absorption of half-open-cell plate lattice metamaterials is up to two times higher than that of truss lattice metamaterials. The porous architecture, lightweight body, superior and easily tunable mechanical performance of half-open-cell plate lattice metamaterials provide them application potential in the fields of load-bearing, energy absorption and biomedical engineering.

Crack-free in situ heat-treated high-alloy tool steel processed via laser powder bed fusion: microstructure and mechanical properties

In this study, high-alloy tool steel S390 was processed crack-free and dense for the first time using laser powder bed fusion (LPBF). The resulting mechanical properties and microstructure of the LPBF steel parts were investigated. High-alloy tool steels, such as high-performance high-speed Boehler S390 steel (containing 1.64 wt% C and W, Mo, V, Co, and Cr in the ratio 10:2:5:8:5 wt%), are prone to cracking when processed using LPBF because these steels have high carbon and carbide-forming alloying elements content. Cracks are induced by thermal stresses and solid-phase transformation, combined with weak grain boundaries caused by segregated primary carbides. Substrate plate heating reduces thermal stresses and enables in situ heat treatment, thus modulating solid-phase transformation and carbide precipitation and preventing cracking during cooling. The resulting microstructure, precipitations, and mechanical properties of the as-built LPBF specimens, which were in situ heat-treated at 800 °C, and the conventionally post-heat-treated specimens were assessed using optical microscopy, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, electron backscatter diffraction, X-ray diffraction, hardness testing, bending testing, and density measurement. In situ heat treatment impacts microstructure, precipitation behavior, and solid-phase transformation, causing a change in the microstructure of the material along the build direction due to different thermal histories. The as-built specimens exhibit a hardness gradient along the build direction of 500 HV1 to 800 HV1 in the top layer. The average bending strength is 2500 MPa, measured from the tensile stresses on the harder side and the compressive stresses on the softer side. Conventional post-heat treatment yields a mean hardness of 610 HV1 and a mean bending strength of 2800 MPa.

Microstructure and Mechanical Properties of an Al-Mg-Si-Zr Alloy Processed by L-PBF and Subsequent Heat Treatments.

The aim of this study was to develop a new Al–Mg–Si–Zr alloy with a high magnesium content to achieve a wide range of mechanical properties using heat treatment and at a lower cost. Additive manufacturing was conducted using a powder bed fusion process with various scan speeds to change the volumetric energy density and establish optimal process conditions. In addition, mechanical properties were evaluated using heat treatment under various conditions. The characterization of the microstructure was conducted by scanning electron microscopy with electron backscatter diffraction and transmission electron microscopy. The mechanical properties were determined by tensile tests. The as-built specimen showed a yield strength of 447.9 ± 3.6 MPa, a tensile strength of 493.4 ± 6.7 MPa, and an elongation of 9.6 ± 1.1%. Moreover, the mechanical properties could be adjusted according to various heat treatment conditions. Specifically, under the HT1 (low-temperature artificial aging) condition, the ultimate tensile strength increased to 503.2 ± 1.1 MPa, and under the HT2 (high-temperature artificial aging) condition, the yield strength increased to 467 ± 1.3 MPa. It was confirmed that the maximum elongation (14.3 ± 0.8%) was exhibited with the HT3 (soft annealing) heat treatment.

An Al-5Fe-6Cr alloy with outstanding high temperature mechanical behavior by laser powder bed fusion

This research aims to study the laser powder bed fusion ( L -PBF) processability, the microstructure and the tensile mechanical properties of an AlFeCr alloy at a wide range of temperatures. With this goal, Al-5Fe-6Cr (wt%) pre-alloyed powder was produced by casting and gas atomization. The microstructure of the as-atomized powders and the as-built specimens was characterized via scanning electron microscopy, x-ray diffraction, and transmission electron microscopy. Following a parameter optimization study, dense as-built specimens with a high relative density of 99.8% and a Vickers hardness at room temperature of 192 HV were fabricated. In addition, the newly developed AlFeCr alloy exhibits yield strength values of 273 ± 5 MPa and 179 ± 3 MPa at 300ºC and 400ºC, respectively. The exceptional strength of this alloy at high temperature is attributed to the homogeneous precipitation during processing of large density of nanoscale icosahedral (i-phase) and intermetallic phases, which are endowed with high thermal stability. These values are significantly higher than those corresponding to the conventional wrought Al7075 aluminum alloy in the T6 condition and to all Al alloys manufactured by L -PBF to date. The current research sheds guidelines for the design of high strength aluminum alloys containing transition alloying elements that are suitable to be processed by L -PBF for high temperature structural applications in a cost effective way.

Parameter optimization and mechanical properties of 42CrMo4 manufactured by laser powder bed fusion

To study the manufacturability and mechanical properties of a low alloy heat treatable medium carbon steel by additive manufacturing, 42CrMo4 (AISI4140) specimens were manufactured by laser powder bed fusion. Influences of processing parameters on relative density and crack density were investigated. Moreover, Charpy impact tests, microhardness, and tensile tests for specimens with and without preheating were also studied. Results showed that the primary defects in the microstructure of additively manufactured samples were the lack of fusion pores and microcracks. The variation of processing parameters influences the porosity and microcracks prominently. The impact toughness of specimens with preheating is around three times higher than specimens without preheating. However, post heat treatment for as-built specimens, such as tempering at different temperature ranges, did not improve the impact toughness further. The detailed fracture mechanism for the massive difference in the impact toughness was investigated.