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NiTi alloy has unique shape memory effect and superelasticity, but low strength limits its application. TiC has been identified as a suitable reinforcing phase for NiTi shape memory alloys (SMAs) since it does not undergo interface reactions and has a minimal impact on the shape memory effect. In this study, NiTi SMAs with 5 wt.% TiC addition are prepared by Laser Engineered Net Shaping (LENS). The incorporation of TiC and the fast cooling rate of LENS process generate significant residual stress, thus, heat treatment at 600 and 800 °C are performed for residual stress control. After heat treatment, the stress-induced martensite caused by residual stress disappears, where residual stress of NiTi SMAs decreases by 50-60% when compared to the sample without heat treatment. The optimal yield strength of 531 MPa is 47.1% higher than that of pure NiTi SMAs (361 MPa). Besides, NiTi SMAs undergoes a one-step phase transformation from austenite to martensite, while a two-step transformation including austenite-R phase-martensite is observed after heat treatment. [ABSTRACT FROM AUTHOR]

In this paper, the influences of two post-heat treatments on the structural, mechanical and corrosion resistance properties of additively manufactured Ti6Al4V alloys were discussed in detail. The materials were produced using the laser engineering net shaping (LENS) technique, and they were subjected to annealing without pressure and hot isostatic pressing (HIP) under a pressure of 300 MPa for 30 min at temperatures of 950 °C and 1050 °C. Annealing without pressure led to the formation of a thin plate structure, which was accompanied by decreasing mechanical properties and increasing elongation and corrosion resistance values. For the HIP process, the formation of a thick plate structure could be observed, resulting in the material exhibiting optimal mechanical properties and unusually high elongation. The best mechanical and corrosion resistance properties were obtained for the material subjected to HIP at 950 °C. [ABSTRACT FROM AUTHOR]

The low deposition efficiency in directed energy deposition (DED) has prompted the reuse of powders that do not fuse to the builds to make additive manufacturing more sustainable. It is unknown, however, how the properties of the powder and deposited parts change as powders are continuously reused. In this study, AlSi10Mg was investigated for five deposition cycles in DED. Exposing AlSi10Mg powder to DED conditions changes the morphology, size, and flowability. The mechanical properties of AlSi10Mg DED parts decreased after the feedstock powder was reused one time. Notably, no additional significant changes were observed when the powder was further reused. [ABSTRACT FROM AUTHOR]

The low deposition efficiency in directed energy deposition (DED) has prompted the reuse of powders that do not fuse to the builds to make additive manufacturing more sustainable. It is unknown, however, how the properties of the powder and deposited parts change as powders are continuously reused. In this study, AlSi10Mg was investigated for five deposition cycles in DED. Exposing AlSi10Mg powder to DED conditions changes the morphology, size, and flowability. The mechanical properties of AlSi10Mg DED parts decreased after the feedstock powder was reused one time. Notably, no additional significant changes were observed when the powder was further reused.

Cylindrical Inconel 718 specimens were fabricated via a blown-powder, laser-directed energy deposition (DED-L) additive manufacturing (AM) process equipped with a dual thermal monitoring system to learn key process–structure relationships. Thermographic inspection of the heat affected zone (HAZ) and melt pool was performed with different layer-to-layer time intervals of ~0 s, 5 s, and 10 s, using an infrared camera and dual-wavelength pyrometer, respectively. Maximum melt pool temperatures were found to increase with layer number within a substrate affected zone (SAZ), and then asymptotically decrease. As the layer-to-layer time interval increased the HAZ temperature responses became more repetitive, indicating a desirable approach for achieving a more homogeneous microstructure along the height of a part. Microstructural variations in grain size and the coexistence of specific precipitate phases and Laves phases persisted among the investigated samples despite the employed standard heat treatment. This indicates that the effectiveness of any post DED-L heat treatment depends significantly on the initial, as-printed microstructure. Overall, this study demonstrates the importance of part size, part number per build, and time intervals on DED-L process parameter selection and post-process heat treatments for achieving better quality control. [ABSTRACT FROM AUTHOR]

To investigate the thermal stress field and microstructure evolution of Ti-6Al-4V alloy component produced by laser engineered net shaping (LENS), numerical simulations are performed at both macroscale and mesoscale. At the macroscale, a finite element model is developed and validated by comparing the simulated residual stress with the measured residual stress. Meanwhile, the effect of scanning strategies on residual stress is analyzed. At the mesoscale, a three-dimensional (3D) cellular automaton model is established to analyze the growth mechanism of β-columnar grains. The results show that the maximum residual stress locates at the surrounding area at the interface between the substrate and the cladding layer. Based on the results under the unidirectional and reciprocating scanning strategies, the residual stress of the component is minimized by using the reciprocating alternating scanning strategy. Due to the higher temperature gradient at the bottom of the molten pool, β-columnar grains grow epitaxially from the pre-existing grains in the substrate. When the direction of dendritic growth is consistent with the direction of the temperature gradient, grain growth is faster and there is a clear preferred orientation, which ultimately forms β-columnar grain structures that tilt towards the scanning direction and penetrate multiple cladding layers. [ABSTRACT FROM AUTHOR]

In this paper, the influences of two post-heat treatments on the structural, mechanical and corrosion resistance properties of additively manufactured Ti6Al4V alloys were discussed in detail. The materials were produced using the laser engineering net shaping (LENS) technique, and they were subjected to annealing without pressure and hot isostatic pressing (HIP) under a pressure of 300 MPa for 30 min at temperatures of 950 °C and 1050 °C. Annealing without pressure led to the formation of a thin plate structure, which was accompanied by decreasing mechanical properties and increasing elongation and corrosion resistance values. For the HIP process, the formation of a thick plate structure could be observed, resulting in the material exhibiting optimal mechanical properties and unusually high elongation. The best mechanical and corrosion resistance properties were obtained for the material subjected to HIP at 950 °C.

Titanium alloys are prone to increased oxidation rates when exposed to higher temperatures during application. As a result, the components suffer mechanical failure due to the formation of the alpha-case layer at 500 °C. To improve its corrosion and oxidation properties, and ultimately its mechanical performance, it is necessary to modify its surface properties. In this study, a LENS 3D-printing system was used to fabricate titanium alloy sample coupons, while surface treatment was performed using laser shock processing (LSP) to improve the surface properties. The characterisation of the samples was performed to establish a basis for the corrosion behaviour of the 3D-printed material and the effect of LSP treatment on the rate of corrosion. The samples fabricated at the moderate laser energy density of 249 J/mm3 showed the best-performing properties as the microstructures that evolved showed elevated hardness profiles, which were associated with material property improvements such as high strength and corrosion resistance. After subjecting the samples to LSP treatment, the properties of the LENS samples showed a further improvement in corrosion resistance. [ABSTRACT FROM AUTHOR]

Cylindrical Inconel 718 specimens were fabricated via a blown-powder, laser-directed energy deposition (DED-L) additive manufacturing (AM) process equipped with a dual thermal monitoring system to learn key process–structure relationships. Thermographic inspection of the heat affected zone (HAZ) and melt pool was performed with different layer-to-layer time intervals of ~0 s, 5 s, and 10 s, using an infrared camera and dual-wavelength pyrometer, respectively. Maximum melt pool temperatures were found to increase with layer number within a substrate affected zone (SAZ), and then asymptotically decrease. As the layer-to-layer time interval increased the HAZ temperature responses became more repetitive, indicating a desirable approach for achieving a more homogeneous microstructure along the height of a part. Microstructural variations in grain size and the coexistence of specific precipitate phases and Laves phases persisted among the investigated samples despite the employed standard heat treatment. This indicates that the effectiveness of any post DED-L heat treatment depends significantly on the initial, as-printed microstructure. Overall, this study demonstrates the importance of part size, part number per build, and time intervals on DED-L process parameter selection and post-process heat treatments for achieving better quality control.

The gradual and uniform variation in the composition of the material, generally two, is called functionally graded materials (FGM). These FGM are used in practical applications to advantage both material properties. Several methods are used to fabricate the FGM components. The current article is research on the direct energy dispersive technique of 3D Printing employed for depositing the SS316L and Co-Cr-Mo alloy FGM samples. L9 orthogonal array of Taguchi method is used. Process parameters like laser power, powder feed rate and scan speed have been used for deposition. Their structural properties are analysed using scanning electron microscopy, X-ray diffraction, element dispersive technique, and Fourier transform impedance spectroscopy. The results reveal that defect-free samples were deposited, and all the samples have Body Centered Cubic structure except one. Good elemental bonding was observed between SS316L and Co-Cr-Mo alloy.

Laser engineered net shaping (LENS) is an advanced additive manufacturing technology combining rapid prototyping and synchronization technology. Its multi-powder feeder delivery system enables multi-materials building in single deposition, which is appropriate for additive manufacturing of functionally graded materials (FGMs). In this study, martensitic-stainless steel (MSS)/austenitic stainless steel (ASS) FGMs with composition transitioning from 100% MSS incrementally graded to 100% ASS by 25% composition gradients are fabricated by LENS. The Vickers hardness of MSS/ASS FGMs ranges from 358 to 170 HV. The decrease of hardness is found to relate to the grain-growth region with the increase of austenite. The obtained specimens of MSS/ASS FGMs show a tensile strength of 669 MPa and an elongation of 19%. In addition, the fracture location of MSS/ASS FGMs in tensile test is in the region of 100% ASS, which is dominated by austenite structure. Finally, the Scheil–Gulliver model is introduced to validate the phase formation of MSS/ASS FGMs’ failure region. Experimental and modeling results indicate that precipitation of α-ferrite in the austenite structure leads to reduced ductility of MSS/ASS FGMs.

Recently, additive manufacturing (AM) processes have expanded rapidly in various fields of the industry because they offer design freedom, involve layer-by-layer construction from a computerized 3D model (minimizing material consumption), and allow the manufacture of parts with complex geometry (thus offering the possibility of producing custom parts). Also, they provide the advantage of a short time to make the final parts, do not involve the need for auxiliary resources (cutting tools, lighting fixtures or coolants) and have a low impact on the environment. However, the aspects that make these technologies not yet widely used in industry are poor surface quality of parts, uncertainty about the mechanical properties of products and low productivity. Research on the physical phenomena associated with additive manufacturing processes is necessary for proper control of the phenomena of melting, solidification, vaporization and heat transfer. This paper addresses the relevant additive manufacturing processes and their applications and analyzes the advantages and disadvantages of AM processes compared to conventional production processes. For the aerospace industry, these technologies offer possibilities for manufacturing lighter structures to reduce weight, but improvements in precision must be sought to eliminate the need for finishing processes.

The gradual and uniform variation in the composition of the material, generally two, is called functionally graded materials (FGM). These FGM are used in practical applications to advantage both material properties. Several methods are used to fabricate the FGM components. The current article is research on the direct energy dispersive technique of 3D Printing employed for depositing the SS316L and Co-Cr-Mo alloy FGM samples. L9 orthogonal array of Taguchi method is used. Process parameters like laser power, powder feed rate and scan speed have been used for deposition. Their structural properties are analysed using scanning electron microscopy, X-ray diffraction, element dispersive technique, and Fourier transform impedance spectroscopy. The results reveal that defect-free samples were deposited, and all the samples have Body Centered Cubic structure except one. Good elemental bonding was observed between SS316L and Co-Cr-Mo alloy. [ABSTRACT FROM AUTHOR]

Titanium alloys are prone to increased oxidation rates when exposed to higher temperatures during application. As a result, the components suffer mechanical failure due to the formation of the alpha-case layer at 500 °C. To improve its corrosion and oxidation properties, and ultimately its mechanical performance, it is necessary to modify its surface properties. In this study, a LENS 3D-printing system was used to fabricate titanium alloy sample coupons, while surface treatment was performed using laser shock processing (LSP) to improve the surface properties. The characterisation of the samples was performed to establish a basis for the corrosion behaviour of the 3D-printed material and the effect of LSP treatment on the rate of corrosion. The samples fabricated at the moderate laser energy density of 249 J/mm3 showed the best-performing properties as the microstructures that evolved showed elevated hardness profiles, which were associated with material property improvements such as high strength and corrosion resistance. After subjecting the samples to LSP treatment, the properties of the LENS samples showed a further improvement in corrosion resistance.

Copyright of Laser Technology is the property of Gai Kan Bian Wei Hui and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The microstructure and magnetic performance of Fe49Co2V (Hiperco50) manufactured via laser‐directed energy deposition are determined. In the as‐printed form, the material displays a fine, equiaxed microstructure and magnetically "hard" behavior. With a customized post‐process annealing treatment, significant grain growth occurs, resulting in soft magnetic performance comparable to traditionally manufactured materials. An inverse correlation between laser power and post‐anneal grain size is observed, with lower laser powers resulting in samples with larger grain sizes after annealing. Samples printed with lower laser powers also display improvements in soft magnetic performance. This is consistent with the expected relationships between grain size, magnetic permeability, and magnetic coercivity, i.e., as grain size increases, magnetic permeability increases and magnetic coercivity decreases. A prototype magnetic shield for a Hall‐effect thruster is successfully printed. The magnetic performance of the printed and annealed shield is comparable to one that is traditionally manufactured. [ABSTRACT FROM AUTHOR]

Recently, additive manufacturing (AM) processes have expanded rapidly in various fields of the industry because they offer design freedom, involve layer-by-layer construction from a computerized 3D model (minimizing material consumption), and allow the manufacture of parts with complex geometry (thus offering the possibility of producing custom parts). Also, they provide the advantage of a short time to make the final parts, do not involve the need for auxiliary resources (cutting tools, lighting fixtures or coolants) and have a low impact on the environment. However, the aspects that make these technologies not yet widely used in industry are poor surface quality of parts, uncertainty about the mechanical properties of products and low productivity. Research on the physical phenomena associated with additive manufacturing processes is necessary for proper control of the phenomena of melting, solidification, vaporization and heat transfer. This paper addresses the relevant additive manufacturing processes and their applications and analyzes the advantages and disadvantages of AM processes compared to conventional production processes. For the aerospace industry, these technologies offer possibilities for manufacturing lighter structures to reduce weight, but improvements in precision must be sought to eliminate the need for finishing processes. [ABSTRACT FROM AUTHOR]

Background: Metal additive manufacturing has extensive application prospects in the aerospace, precision instrument, and biomedical fields, etc. However, the low manufacturing quality of key components is a bottleneck restricting the further development and application of this technology. Because of the extremely complex manufacturing environment, a real-time and online monitoring technology for the manufacturing quality remains lacking. Objective: For laser engineered net shaping (LENS), a mainstream technology of metal additive manufacturing, a hybrid method for the online evaluation of stress fields during laser cladding is developed in this paper that combines the real-time measured temperature field, three-dimensional deformation field and finite element method. Methods: The proposed method first designed the synchronous measurement optical paths of the temperature field and three-dimensional deformation field of the substrate, and the positions of the temperature and deformation field images were matched. A finite element model was established based on the printing parameters such as the layer thickness and printing speed, and the temperature field and three-dimensional deformation field synchronously measured at each moment were incorporated into the model as boundary conditions to obtain the deformation and stress information inside the model. Results: We compared the stress field obtained at the end of printing with the XRD (X-ray diffraction) measurement results to verify the effectiveness of the proposed method. The proposed method can obtain the three-dimensional stress distribution and evolution of the substrate and printed component. Conclusion: The proposed method can realize the online characterization of the three-dimensional stress field in the LENS printing process and provide important experimental guidance and data for the quality control of 3D printing. [ABSTRACT FROM AUTHOR]

Microstructural characteristics of additively manufactured Ti-6Al-4V specimens are analyzed in this study. Laser Engineered Net Shaping technology, a direct energy deposition additive manufacturing process, is used to fabricate specimens. Effects of process parameters including machine head laser power, head write speed, layer height, hatch spacing, and powder flow rate on the morphological features of the material are investigated. A first batch of samples is built with a combination of parameters leading to full density metal parts across each layer and near-zero defects likewise more conventional process techniques (i.e. wrought and casting). A second batch of samples is built with a set of processing parameters aimed to induce defects within the parts like voids and porosity. Samples from both batches were stress-relieved in order to remove internal residual stresses generated by the additive manufacturing process. Optical microscopy, scanning electron microscopy and X-ray diffraction were used to characterize the microstructure of all samples. Tensile properties were measured after the stress-relief heat treatment. It was found that Laser Engineered Net Shaping technology parts are strongly sensitive to variations of building process parameters. Different structure morphologies were observed for different incident energies and cooling rates due to the combination of laser power and head write speed. The grain size distribution and shape are influenced by the powder flow rate resulting in either equiaxed or columnar grain microstructures with the development of material defects such as pores, gas entrapment and lack of fusion. Non-porous specimens revealed comparable tensile and ductility properties with the wrought counterpart; however, porous specimens were found to have a reduced strength and ductility. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Fe-based amorphous materials offer new opportunities for magnetic sensors, actuators, and magnetostrictive transducers due to their high saturation magnetostriction (λs = 20-0 ppm) and low coercive field compared with polycrystalline Fe-based alloys, which have high magnetostriction but large coercive fields and Co-based amorphous alloys with small magnetostriction (λs = -3 to -5ppm). Additive layer manufacturing (ALM) offers a new fabrication technique for more complex net-shaping designs. This paper reviews the two different ALM techniques that have been used to fabricate Fe-based amorphous magnetic materials, including the structural and magnetic properties. Selective laser melting (SLM)--a powder-bed fusion technique--and laserengineered net shaping (LENS)--a directed energy deposition method--have both been utilised to fabricate amorphous alloys, owing to their high availability and low cost within the literature. Two different scanning strategies have been introduced by using the SLM technique. The first strategy is a double-scanning strategy, which gives rise to maximum relative density of 96% and corresponding magnetic saturation of 1.22 T. It also improved the glassy phase content by an order of magnitude of 47%, as well as improving magnetic properties (decreasing coercivity to 1591.5 A/m and increasing magnetic permeability to around 100 at 100 Hz). The second is a novel scanning strategy, which involves two-step melting: preliminary laser melting and short pulse amorphisation. This increased the amorphous phase fraction to a value of up to 89.6%, and relative density up to 94.1%, and lowered coercivity to 238 A/m. On the other hand, the LENS technique has not been utilised as much as SLM in the production of amorphous alloys owing to its lower geometric accuracy (0.25 mm) and lower surface quality, despite its benefits such as providing superior mechanical properties, controlled composition and microstructure. As a result, it has been commonly used for large parts with low complexity and for repairing them, limiting the production of amorphous alloys because of the size limitation. This paper provides a comprehensive review of these techniques for Fe-based amorphous magnetic materials. [ABSTRACT FROM AUTHOR]

This work investigates the effect of layer thickness on the microstructure and mechanical properties of M300 maraging steel produced by Laser Engineered Net Shaping (LENS®) technique. The microstructure was characterized using light microscopy (LM) and scanning electron microscopy (SEM). The mechanical properties were characterized by tensile tests and microhardness measurements. The porosity and mechanical properties were found to be highly dependent on the layer thickness. Increasing the layer thickness increased the porosity of the manufactured parts while degrading their mechanical properties. Moreover, etched samples revealed a fine cellular dendritic microstructure; decreasing the layer thickness caused the microstructure to become fine-grained. Tests showed that for samples manufactured with the chosen laser power, a layer thickness of more than 0.75 mm is too high to maintain the structural integrity of the deposited material.

Additive Manufacturing of aluminium alloys has become crucial for lightweight applications. However, new materials and techniques need to be developed in order to achieve more advanced properties and higher efficiency. Therefore, a new energy-efficient wire deposition strategy was developed for processing aluminium-silicon alloys with Laser Metal Wire Deposition. Three alloys with different Si-contents were studied: AlSi5, AlSi10Mg and AlSi12. Different thicknesses of partially melted zones were observed and explained. The previous layer was partly remelted only by the heat conduction in the melt pool. It was found that the thickness of the partially melted zone depends on the difference of temperature between the liquidus and solidus. [ABSTRACT FROM AUTHOR]

We investigated the complex solidification behaviour of Al 2 O 3 –Y 3 Al 5 O 12 eutectics prepared by laser engineered net shaping. Colony structure consisting of coupled irregular eutectic was dominant at interior region of as-fabricated specimens, and its growth behaviour was depicted by Magnin–Kurz model. In each deposited layer, The Y 3 Al 5 O 12 phase within irregular eutectic grew through a competitive mechanism from random to oriented, whereas the orientation of Al 2 O 3 remained unchanged. Transition from anomalous to colony coupled eutectics occurred at the bottom of each layer, and irregular to regular eutectics transition was recognized at outer region of as-built sample. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Yttria stabilized zirconia (YSZ) thin wall components were fabricated using laser engineered net shaping (LENS) technique. It was found that after LENS processing, the monoclinic (m) phase in as-received YSZ powders transformed to tetragonal (t) and cubic (c) phases with the lenticular shaped t-ZrO2 embedded in the c-ZrO2 matrix. The relative density of the parts reached up to 98.7%. Our investigation showed that micro cracks within the wall structure were reduced by judiciously choosing laser power parameter. The fabricated parts have surface roughness values that ranged from 20 to 40 μm. The maximum hardness and elastic modulus achieved from the LENSed YSZ parts were 19.8 GPa and 236.1 GPa, respectively. We also demonstrated that dark brown color of the LENSed parts could be removed via heat treatment. [ABSTRACT FROM AUTHOR]

Abstract Direct laser deposition (DLD) is one of the rapidly emerging laser-based additive manufacturing (LBAM) process. Laser Engineered Net Shaping (LENS) is one such DLD technique which was employed to fabricate one of the widely used Ti–6Al–4V implant material with enhanced surface-related properties compared to the wrought sample (commercially available). Wear and corrosion behavior of LENS fabricated Ti–6Al–4V (L-Ti64) was characterized using low-frequency reciprocatory wear tester and potentiostat. Sample hardness was determined using Vickers's microhardness test. Adhesion and morphology of Human mesenchymal stem cells (hMSCs) on the samples were examined using Scanning Electron Microscopy (SEM) and fluorescence microscope whereas the quantification of live cells was determined using MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide) assay. Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) was used to determine the concentration of leached-out metal ions during wear test. All the above mentioned surface-related properties were compared to that of wrought Ti-6Al-4V (W-Ti64) to standardize the efficiency of LENS-fabricated materials (L-Ti64) when compared to its wrought counterpart. The results clearly indicated stable passive behavior of L-Ti64, which was evident from the lower corrosion rate and high passive range obtained. L-Ti64 exhibited improved hardness level than W-Ti64 by 8% which enhanced the wear resistance and also prevented the release of wear debris. However, in presence of FBS, coefficient of friction (COF) increased by about 21 and 33% for L-Ti64 and W-Ti64 respectively, which inturn accelerated the wear rate of both the samples. Low cytotoxicity and well spread morphology of human Mesenchymal Stem Cells (hMSC's) affirmed higher level of biocompatibility of both the samples. However, no significant differences in the cellular behaviors were observed. Graphical abstract Unlabelled Image Highlights • Important surface related properties of LENS- fabricated Ti64 (L-Ti64) and wrought Ti64 (W-Ti64) were compared. • Higher cooling rates experienced by the specimens during the fabrication procedure resulted in the formation of martensite phases. • L-Ti64 specimens exhibited higher resistance to both wear and corrosion than W-Ti64. • The concentration of the leached-out metal ions during wear test was also found to be lower for L-Ti64 compared to W-Ti64. • L-Ti64 enabled the attachment and proliferation of hMSCs on its surface, suggesting that they were as cytocompatible as W-Ti64. [ABSTRACT FROM AUTHOR]

Oxide dispersion strengthened (ODS) alloys are attractive material candidates for advanced fission and fusion reactor application owing to their excellent radiation tolerance and high temperature creep strength but traditional manufacturing process encounters some difficulties in producing complex components. An ODS Fe-9Cr alloy with nominal composition of Fe-9Cr-1.5W-0.3Ti-0.3Y (wt%) were manufactured by laser engineered net shaping (LENS) method with different laser power. Equiaxed martensitic grains together with micro-pores were observed in the as-deposited alloys. With the increase of laser power, the density and size of pores decrease, the grain size of the alloys increases while the number density of nanoscale oxides decreases due to the formation of thicker Y-Ti-O-enriched and Al-O-enriched slag layer in the block surface. Hot isostatic pressing (HIP) processing of the as-deposited ODS alloy with low laser power reduces significantly the density of and the size of micro-pores, refines the grain size, and precipitates higher density of nanoscale oxides (Y 2 TiO 5 and Y 2 Ti 2 O 7), which improves significantly the tensile properties that is comparable at room temperature and is better at 873 K than ODS EUROFER steel produced by conventional powder metallurgy. • ODS alloy was successfully manufactured by laser engineered net shaping. • High-density of nanoscale Y 2 TiO 5 and Y 2 Ti 2 O 7 are formed. • The density of nanoscale oxides depends strongly on laser power. [ABSTRACT FROM AUTHOR]

Highlights • Laser additive processing for high-throughput analysis of high entropy alloys. • A combinatorial approach for assessing composition-microstructure-microhardness. • Compositionally graded AlCrFeMoVx (0 < x < 1) high entropy alloys (HEAs) assessed. • A new single solid solution bcc based equi-atomic HEA is reported. • High solubility of V offers a broad range of solid solution strengthening. Abstract The current study discusses a novel combinatorial high-throughput approach for assessing the composition-microstructure-hardness relationship, using laser deposited compositionally graded AlCrFeMoVx (0 < x < 1) high entropy alloy (HEA) as a candidate system. The composition gradient was achieved from AlCrFeMo (with 0.3 at. % V) to AlCrFeMoV (with 18.5 at. % V) over a length of ∼20 mm, deposited using the laser engineered net shaping process from a blend of elemental powders. Scanning electron microscopy, X-ray diffraction, and transmission electron microscopy were used to characterize the alloys. A single solid solution (SS) body-centered cubic (bcc) structure is observed throughout the compositional range. The high solubility of V in this novel alloy system offers a broad range of solid solution strengthening of a compositionally complex but structurally simple bcc matrix. The hardness of the alloy increases from 485 Hv to 581 Hv on increasing V from 0.3 to 18.5 at. %. The solid solution hardening model for dilute solutions underestimates the strengthening of the alloy. The current study presents a novel and efficient method for microstructural screening of the bulk alloys for optimization of the microstructure and properties. [ABSTRACT FROM AUTHOR]

The molten pool temperature during laser engineered net shaping (LENS) could directly affect the microstructure and phase compositions of materials in the molten pool, thereby affecting the mechanical properties of the fabricated parts. To achieve a well-built solid structure, the research on fundamentals and methods of molten pool thermal behavior monitoring is of great significance. Using a high-resolution infrared camera, this paper realized real-time temperature tracking of Inconel 718 deposition in the LENS process. The effects of deposition variables, such as laser power and scanning speed, on the molten pool temperature and cooling rate have been investigated. In addition, the effects of the molten pool temperature on the molten pool depth and dendrite arm spacing (DAS) have been analyzed. The results suggest that the molten pool temperature increases with increasing of the laser power while it drops first and then rises with increasing of the scanning speed. The molten pool temperature increases nonlinearly with increasing of the number of layers during the material deposition process. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Plasma sprayed hydroxyapatite (HA) coating is known to improve the osteoconductivity of metallic implants. However, the adhesive bond strength of the coating is affected due to a mismatch in coefficients of thermal expansion (CTE) between the metal and HA ceramic. In this study, a gradient HA coating was prepared on Ti6Al4V by laser engineered net shaping (LENS™) followed by plasma spray deposition. In addition, 1 wt% MgO and 2 wt% Ag 2 O were mixed with HA to improve the biological and antibacterial properties of the coated implant. Results showed that the presence of an interfacial layer by LENS™ enhanced adhesive bond strength from 26 ± 2 MPa for just plasma spray coating to 39 ± 4 MPa for LENS™ and plasma spray coatings. Presence of MgO and Ag 2 O did not influence the adhesive bond strength. Also, Ag+ ions release dropped by 70% less with a gradient HA LENS™ layer due to enhanced crystallization of the HA layer. In vitro human osteoblast cell culture revealed presence of Ag 2 O had no deleterious effect on proliferation and differentiation when compared to pure HA as control and provided antibacterial properties against E. coli and S. aureus bacterial strands. This study presents an innovative way to improve interfacial mechanical and antibacterial properties of plasma sprayed HA coating for load-bearing orthopedic as well as dental implants. Statement of significance Implants are commonly composed of metals that lack osteoconductivity. Osteoconductivity is a property where bone grows on the surface meaning the material is compatible with the surrounding bone tissue. Plasma sprayed hydroxyapatite (HA) coating improves the osteoconductivity of metallic implants, however, the adhesive bond strength can be weak. This study incorporates a gradient HA coating by using an additive manufacturing technique, laser engineered net shaping (LENS™), followed by plasma spray deposition to enhance the adhesive bond strength by incorporating a thermal barrier. The proposed system has not been well studied in the current literature and the results presented bring forth an innovative way to improve the interfacial mechanical and antibacterial properties of plasma sprayed HA coating for load-bearing orthopedic implants. [ABSTRACT FROM AUTHOR]

Fe-based amorphous materials offer new opportunities for magnetic sensors, actuators, and magnetostrictive transducers due to their high saturation magnetostriction (λs = 20–40 ppm) and low coercive field compared with polycrystalline Fe-based alloys, which have high magnetostriction but large coercive fields and Co-based amorphous alloys with small magnetostriction (λs = −3 to −5 ppm). Additive layer manufacturing (ALM) offers a new fabrication technique for more complex net-shaping designs. This paper reviews the two different ALM techniques that have been used to fabricate Fe-based amorphous magnetic materials, including the structural and magnetic properties. Selective laser melting (SLM)—a powder-bed fusion technique—and laser-engineered net shaping (LENS)—a directed energy deposition method—have both been utilised to fabricate amorphous alloys, owing to their high availability and low cost within the literature. Two different scanning strategies have been introduced by using the SLM technique. The first strategy is a double-scanning strategy, which gives rise to maximum relative density of 96% and corresponding magnetic saturation of 1.22 T. It also improved the glassy phase content by an order of magnitude of 47%, as well as improving magnetic properties (decreasing coercivity to 1591.5 A/m and increasing magnetic permeability to around 100 at 100 Hz). The second is a novel scanning strategy, which involves two-step melting: preliminary laser melting and short pulse amorphisation. This increased the amorphous phase fraction to a value of up to 89.6%, and relative density up to 94.1%, and lowered coercivity to 238 A/m. On the other hand, the LENS technique has not been utilised as much as SLM in the production of amorphous alloys owing to its lower geometric accuracy (0.25 mm) and lower surface quality, despite its benefits such as providing superior mechanical properties, controlled composition and microstructure. As a result, it has been commonly used for large parts with low complexity and for repairing them, limiting the production of amorphous alloys because of the size limitation. This paper provides a comprehensive review of these techniques for Fe-based amorphous magnetic materials.

The mechanical properties and microstructure evolution caused by dynamic loads of 316L stainless steel, fabricated using the Laser Engineered Net Shaping (LENS) technique and hot forging method were studied. Full-density samples, without cracks made of 316L stainless steel alloy powder by using the LENS technique, are characterized by an untypical bi-modal microstructure consisting of macro-grains, which form sub-grains with a similar crystallographic orientation. Wrought stainless steel 316L has an initial equiaxed and one-phase structure, which is formed by austenite grains. The electron backscattered diffraction (EBSD) technique was used to illustrate changes in the microstructure of SS316L after it was subjected to dynamic loads, and it was revealed that for both samples, the grain refinement increases as the deformation rate increases. However, in the case of SS316L samples made by LENS, the share of low-angle boundaries (sub-grains) decreases, and the share of high-angle boundaries (grains of austenite) increases. Dynamically deformed wrought SS316L is characterized by the reverse trend: a decrease in the share of high-angle boundaries and an increase in the share of low-angle boundaries. Moreover, additively manufactured SS316L is characterized by lower plastic flow stresses compared with hot-forged steel, which is caused by the finer microstructure of wrought samples relative to that of additive samples. In the case of additively manufactured 316L steel samples subjected to a dynamic load, plastic deformation occurs predominantly through dislocation slip, in contrast to the wrought samples, in which the dominant mechanism of deformation is twinning, which is favored by a high deformation speed and low stacking fault energy (SFE) for austenite.

The isothermal oxidation of Fe-28Al-5Cr (at%) intermetallic alloy microalloyed with Zr and B (

Abstract In the present work, the feasibility of additive laser deposition (ALD) of YSZ on IN625 substrate was studied using two different bond coats (BC) viz. NiCr and NiCrAlY and two different deposition schemes, consisting of direct deposition of YSZ (DI) and compositionally graded (CG) deposition of bond coat-YSZ. These deposits were examined for microstructural features, and their ability to provide thermal barrier to heat flow and to withstand thermal cycling were evaluated. It has been observed that DI and CG NiCr-YSZ coatings survive 240 cycles whereas CG NiCrAlY-YSZ samples survive <5 thermal cycles between 1100 °C and room temperature. The poor thermal cycling resistance of CG NiCrAlY-YSZ coatings is attributed to the formation of a brittle oxide layer at the interface of NiCrAlY and YSZ. Between all four combinations of BC and types of deposition, CG NiCr-YSZ coatings give the maximum temperature drop (350 °C) across the thickness when tested at 1000 °C as hot face temperature and for 600 s duration which, combined with good thermal cycling resistance, makes them potential candidates as thermal barrier coatings (TBCs) applied by additive laser deposition. Highlights • Additive laser deposition has the potential to fabricate thick TBCs of YSZ. • Functionally graded YSZ shows significant improvement in adhesion strength and thermal insulation property. • Large no. of metal-ceramic interfaces in functionally graded YSZ results in improved thermal insulation. [ABSTRACT FROM AUTHOR]

Laser engineered net shaping (LENS), developed from laser cladding and rapid prototyping, has different promising applications such as aerospace, automotive, marine, tool manufacturing, etc. Due to the features of LENS process, the capability of overhang structure deposition was limited and some geometrical structures cannot be perfectly built. Investigating overhang building mechanisms and angle accuracy are crucial. In this study, the effects of scanning patterns (reciprocating and unidirectional deposition way) and vertical increment (z-increment) on overhang structures in LENS have been investigated. It was found that the overhang deposited in a reciprocating way exhibited higher geometry accuracy than that deposited in a unidirectional way. By optimizing z-increment, the discrepancy between the designed and experimental inclined angles of overhangs greatly decreased. The effects of processing parameters, including laser power, scanning speed, and powder feed rate, on the optimal z-increment were also investigated. [ABSTRACT FROM AUTHOR]

Abstract A laser additive manufacturing technique, laser engineered net shaping (LENS), was successfully applied to manufacture a reduced activation ferritic/martensitic (RAFM) steel with nominal composition of Fe-9Cr-0.11C-1.5W-0.4Mn-0.2V-0.12Ta (wt%). The as-deposited LENS-RAFM steels were normalized and tempered. The microstructures of as-deposited and heat treated LENS-RAFM steels were characterized by using optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The tensile tests of as-deposited and heat treated samples in different directions were carried out at room temperature and 873 K. The results showed that columnar dendrites grow epitaxially along the direction of deposition in vertical section (YOZ) and a mixture of equiaxed and columnar grains appears in horizontal section (XOY). No precipitates are observed in the as-deposited sample while Cr-rich M 23 C 6 and Ta-rich MX type carbides appear in the heat treated sample. The as-deposited sample showed anisotropic tensile properties which could be eliminated by heat treatment. The tensile strength of the LENS-RAFM steel is similar to conventional RAFM steels such as EUROFER 97 and CLAM. Highlights • A RAFM steel has been successfully manufactured by laser engineered net shaping (LENS), which is one of laser additive manufacturing technologies. • Columnar dendrites in vertical section and a mixture of equiaxed and columnar grains in horizontal section have been observed. • The anisotropic tensile properties are induced by LENS process, which can be eliminated well through the heat treatment. [ABSTRACT FROM AUTHOR]

Titanium-based materials are widely used in various areas due to their unique combination of outstanding characteristics. Properties such as stiffness, strength and wear resistance of conventional titanium alloys can be further enhanced through development of titanium-based matrix composites (TMCs). Additive manufacturing (AM) technology provides a promising platform for highly efficient fabrication of complex-shaped titanium parts. Although AM of titanium and titanium alloys are increasingly being investigated, far less attention has been paid to AM of TMCs due to their additional processing complications. This study aims to review the current state-of-the-art in AM of TMCs as well as key aspects and research trends for the design, fabrication, and further development of high-performance TMCs. The review highlights the promising outlook for AM of TMCs. However, it also draws attention to critical aspects that require further investigation such as optimization of the processing parameters and additional understanding of melting/consolidating of matrix and reinforcement for AM of defect-free TMC components. [ABSTRACT FROM AUTHOR]

Laser engineered net shaping (LENS) technology, due to its ability in melting and solidification of neat ceramic materials, exhibits great potential for direct fabricating net-shaped ceramic structures. However, due to limitation of sample size, reports on the macro properties of fabricated ceramic structures are still extremely lacking. In the present work, large-sized Al 2 O 3 ceramic samples were prepared using LENS technology to perform microstructural analysis and macro properties testing. Phase composition, grain characteristics and chemical purity of prepared samples were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray fluorescence (XRF). Macro properties of large-sized samples, including the flexural strength and compressive strength, were given for the first time after being tested using a mechanical tester. Results show that microstructure of prepared Al 2 O 3 ceramics presents typical solidification characteristics and consists of grains that grow along the deposition height direction. Primary dendrite spacing of the Al 2 O 3 grains is about 60 µm. The phase is mainly composed of high-temperature-stable α-Al 2 O 3 and a relative density of 99.5% is obtained. No new impurities are introduced during the depositing process. Element type and element content of fabricated samples are highly consistent with those of original powder. Property test results show that, under current process conditions, the flexural strength and compressive strength of fabricated samples reaches the level of traditional sintering method, reaching the maximum of 350 MPa and 625 MPa respectively. [ABSTRACT FROM AUTHOR]

In the present paper, AISI 316L stainless steel hollow thin-walled cylinders were fabricated via laser engineered net shaping (LENS), which have been described in details. It is found that z-axis increment (delta Z) has significant effects on the geometrical features, mechanical, and metallurgical properties via single factor experiment in the condition of optimized processing parameters (laser power, powder feed rate, shielding gas flow rate and scanning speed) unchanged. Therefore, it is observed that deviations of the diameter are caused by unstable working distance, inclination angles, and preheating condition. As a result, through analyzing and modifying structural defects, an optimized delta Z, practical scanning strategies, and high surface quality of the cladding hollow thin-walled cylinder have been obtained. Expanding these conclusions to more complex build geometries and a more comprehensive variety of processing conditions would allow for a better understanding of the laser deposition process for more ubiquity of LENS in the industry. [ABSTRACT FROM AUTHOR]

The aim of this work is to study the effect of heat treatment on the microstructure, phase transformations, shape memory characteristics and corrosion behaviour of laser deposited equiatomic NiTi alloy. Dense samples of NiTi alloy were fabricated using Laser Engineered Net Shaping (LENS™) with two different laser energy densities by varying the scan speed and laser power. These samples were annealed for 30 min at 500 °C and 1000 °C in flowing argon, followed by furnace-cooling to room temperature. The resulting microstructures and properties were compared with the corresponding as-deposited samples. Microstructural analysis after heat treatment showed needle-shape martensite in the samples processed at lower laser energy density of 20 J/mm 2 , and lenticular or plate-like martensite in the samples processed at 80 J/mm 2 . The XRD results revealed relatively high concentration of martensite (B19′) in heat-treated NiTi alloy compared to as-processed samples. Furthermore, the heat treatment decreased the forward and reverse transformation temperatures of NiTi alloy from 80 – 95 °C to 20–40 °C, presumably due to annihilation of thermally induced defects. Interestingly, the samples annealed at 500 °C showed a measurable increase of 1–2% in the shape memory recovery, from the net recovery of 8% exhibited by the as-processed NiTi alloy. The corrosion resistance of laser-processed NiTi alloy decreased upon annealing. [ABSTRACT FROM AUTHOR]