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Three 50Cr6Ni2Y + x wt.% TiC (x = 1.5, 3.0, 4.5) alloy steel coatings were prepared using direct laser deposition (DLD) technology. The microstructure, microhardness, and wear resistance of DLD samples were studied. The results indicate that DLD coatings were composed of α-Fe (Fe-Cr-Ti), γ-Fe (Fe-Ni), and TiC. When the added TiC content was 3.0 wt.%, the DLD coating without cracks was fabricated, and TiC particles were well embedded in the sample. In addition, the coating demonstrated the best performance, with a microhardness of 758 ± 23.3 HV0.2, an average friction coefficient of 0.58, and a wear rate of 0.37 %. The addition of an appropriate amount of TiC as a reinforcing phase, on the one hand, had played a role in the second phase strengthening. On the other hand, the diffusion interfaces formed between TiC particles and the matrix allowed some Ti elements to melt into the matrix and formed a solid solution, playing a role in solid solution strengthening. The results could provide a reference for the preparation and repair of laser additive manufacturing high-performance wear-resistant parts.

The present paper focuses on the technological approach to manufacturing composite in the form of Inconel 625 reinforced with tungsten carbide particles. Twenty-four samples with reinforcement amounts ranging from 30 to 90% (wt.%) and different numbers of deposited layers were manufactured with the use of Laser Engineered Net Shaping (LENS®). The metallurgical quality, microstructure, chemical and phase composition as well as hardness of the produced composites were determined. Digital microscopy, X-ray powder diffraction and SEM-EDS were employed for this purpose. Despite numerous cracks, the fabricated samples exhibited a greater hardness than single-layer coatings of analogous composition also produced by additive techniques. This phenomenon is likely a result of repeated crystallization of the composites in remelted areas. A dual mechanism of material strengthening is observed in the additively manufactured composites, both by the presence of reinforcing particles and precipitates of secondary phases.

The results of studies on the influence of the modes of shielded arc welding with a non-consumable electrode on the mechanical properties of parts manufactured from EK-61 powder alloy by direct laser deposition are presented. The results of metallographic studies of the weld and heat-affected zone are described. The possibility of obtaining high-quality welds using shielded arc welding of such products is shown. The influence of the number of passes on the quality of the weld is noted. [ABSTRACT FROM AUTHOR]

In response to the problem of low hardness and poor wear resistance of TC4 coatings prepared by laser additive manufacturing, three titanium alloy coatings with different Si contents were prepared on a TC4 substrate by direct laser deposition (DLD) technology. The evolution of the microstructure and wear mechanism of the coatings were studied. The addition of the Si element facilitated the formation of Ti5Si3 hard phase, which exhibited a uniform mesh form. The strengthening effect of the hard phase in the prepared coating increased with its proportion, demonstrating a positive correlation with the incremental addition of an Si element. However, the excessive addition of the Si element resulted in the surface cracking of the coating. The optimal DLD Ti-Al-Si coating was obtained when the Si content was 10 wt. %, with an average microhardness of 801 ± 24 HV0.2, 2.5 times greater than that of the TC4 substrate. The average friction coefficient of the Ti-Al-Si coating was 0.39, and the wear rate was 1.9%. The hard phase was uniformly distributed in a mesh form, which not only refined the wear debris and suppressed the shear force of the wear debris during wear but also slowed down the continuous wear of debris on the worn surface. The results of this study could provide a reference for preparing high-hardness and wear-resistant titanium alloy coatings by DLD. [ABSTRACT FROM AUTHOR]

The present paper focuses on the technological approach to manufacturing composite in the form of Inconel 625 reinforced with tungsten carbide particles. Twenty-four samples with reinforcement amounts ranging from 30 to 90% (wt.%) and different numbers of deposited layers were manufactured with the use of Laser Engineered Net Shaping (LENS). The metallurgical quality, microstructure, chemical and phase composition as well as hardness of the produced composites were determined. Digital microscopy, X-ray powder diffraction and SEM-EDS were employed for this purpose. Despite numerous cracks, the fabricated samples exhibited a greater hardness than single-layer coatings of analogous composition also produced by additive techniques. This phenomenon is likely a result of repeated crystallization of the composites in remelted areas. A dual mechanism of material strengthening is observed in the additively manufactured composites, both by the presence of reinforcing particles and precipitates of secondary phases. [ABSTRACT FROM AUTHOR]

Multi-material structures with variable functionalities can lead to unique solutions for engineering problems compared to single-material structures. Additive manufacturing of Functionally Graded Materials (FGMs) using Direct Laser Deposition for the multi-material deposition of Stellite6 and 17–4 PH stainless steel has been investigated in this study. Process parameter design was successfully applied to achieve FGM structures with expected composition ratio and defect free. Results revealed that clads with insufficient laser power had unmelted 17-4 PH powders, while those with excessive power resulted in micro-cracks and disrupting the expected composition for the previous layer. Energy Dispersive Spectroscopy analysis results showed that the composition was almost as expected, with less than 10% deviation. The Stellite6 composition in FGM exhibits a minimum ratio near the substrate due to the penetration of 17-4 PH elements. Meanwhile, in multi-track clads, the Stellite6% decreases along the transverse direction due to increased heat input, multiple cladding tracks, higher dilution, and slower solidification rate. The results of the micro-hardness tests illustrated the gradual evolution of micro-hardness along the build direction starting from the base metal, which had a hardness of approximately 300 HV for 17-4 PH and for the compositions of 25%, 50%, 75%, and 100% Stellite6 showed increases of 10%, 39%, 43%, and 63% respectively, reaching up to 490 HV for fully Stellite6 at the top of the specimen.

Functionally graded materials (FGM) do not show special processing in the composite structure due to the combination of mechanical, thermal, magnetic and stress gradient properties. The aim of this study is to produce IN718/St6 FGM samples by direct laser deposition method. The product of this model should enable the development of mechanical products. Best of all, this can be done without significant reduction in texture and case to residual stress that are a consequence of rapid changes in mechanical and thermal properties in non-FGM samples. To fabricate part, direct laser deposition system equipped with a 1 kW continuous fiber laser is used, SEM/EDS analysis and microhardness testing to measure porosity, chemical composition, and quantify gradient mechanical properties is used. In this study, the cladding composition is selected from 100% IN718 to 100% St6 with a 25% change in St6 composition. To prevent the formation of defects, both single-parameter modes and individual layering are examined, considering the diverse nature of the combination. The result shows that using an individual layering structure, reduces 100% Lack of fusion defects in the IN718/St6 structure. EDS analysis confirmed that the St6 content gradually increased from the first to the fifth layer. The substrate hardness gradually increases from 200 Vickers hardness to 550 Vickers hardness, showing an almost linear trend. Moreover, by using individual layering, the coaxial structure is reduced by 55% and the relative orientation of the vertical line is reduced by 18° compared to using the St6 directly (non-FGM).

Direct laser deposition (DLD) requires high-energy input and causes poor stability and portability. To improve the deposited layer quality, conducting online measurements and feedback control of the dimensions, temperature, and other melt-pool parameters during deposition is essential. Currently, melt-pool dimension measurement is mainly based on machine vision methods, which can mostly detect only the deposition direction of a single melt pool, limiting their measurement range and applicability. We propose a binocular-vision-based online measurement method to detect the melt-pool width during DLD. The method uses a perspective transformation algorithm to align multicamera measurements into a single-coordinate system and a fuzzy entropy threshold segmentation algorithm to extract the melt-pool true contour. This effectively captures melt-pool width information in various deposition directions. A DLD measurement system was constructed, establishing an online model that maps the melt-pool width to the offline deposited layer width, validating the accuracy of the binocular vision system in measuring melt-pool width at different deposition angles. The method achieved high accuracy for melt-pool measurements within certain deposition angle ranges. Within the 30°–60° measurement range, the average error is 0.056 mm, with <3% error. The proposed method enhances the detectable range of melt-pool widths, improving cladding layers and parts. [ABSTRACT FROM AUTHOR]

The mechanical properties of direct laser deposition (DLD) parts are crucial for engineering applications, which are determined by the microstructure and texture. To achieve fine microstructure and higher mechanical performance, pulsed laser deposition is used to generate less heat accumulation and a higher cooling rate. However, the relationship between microstructure and thermal history is difficult to investigate due to the transient temperature change. In this work, a three-dimensional numerical model is developed to study the thermal behavior of the molten pool in the continuous laser deposition (CLD), the continuous pulsed laser deposition (CPLD), and the interval pulsed laser deposition (IPLD) processes. The microstructure of the deposition samples is investigated by optical microscope and electron back-scattered diffraction. The mechanical response of the deposition samples is investigated by tensile test and microhardness test. Compared with the CLD, CPLD, and IPLD result in higher temperature gradient and cooling rate, long columnar grains, and a strong fiber texture. However, grains with larger sizes and a texture with a herringbone pattern due to the change of heat flow are obtained in CLD samples. The test values of IPLD samples show higher tensile strength, higher yield strength, lower ductility, and higher hardness values. This research brings about a perspective for studying the thermal effects of deposition layers and a novelty deposition process to obtain specific microstructures and better mechanical properties.

The main advantages of direct laser deposition (DLD) of large-sized products are discussed by the example of the internal core baffle of a pressurized water reactor (VVER core baffle). The problem of product damage during operation as a part of reactor is considered. Powder materials made of 08Cr18Ni10Ti and 10Cr16Ni25MoTi stainless steels are produced to develop the DLD process. Optimization of the core baffle design is carried out to improve operating reliability. Samples and experimental small fragments of the core baffle for complex research and tests are manufactured by the DLD method. The concept of an experimental DLD unit for large-scale parts is advanced. [ABSTRACT FROM AUTHOR]

An unfavourable combination of metallurgical factors and high stresses may result in the fracture of additively manufactured parts, especially in the case of high-strength alloys. Frequently in direct laser deposition (DLD) fabrication of large-scale parts, it is impossible to obtain desirable structural-phase composition and required mechanical properties of the depositing metal due to the low inter-pass temperature. Thereby, the stress and strain levels must be reduced to prevent fracture of the build part. The present work seeks to analyse the effectiveness of the proposed approaches for reducing residual stresses and strains by (i) local adjustment of the buildup geometry and (ii) addition of a ductile transition layer. The process conditions were close to those used to produce large-scale parts by the DLD method, resulting in the buildup having the same thermal history. The following cases are analysed: a single-wall buildup of Ti-6Al-4V alloy with flat-faced and concave fillets, and a single-wall buildup with a ductile transition layer of commercially pure titanium between the rigid substrate and rest buildup of the Ti-6Al-4V. A simulation procedure based on the implicit finite element method was adopted for the theoretical study of the stress-strain field evolution. It was found that the addition of flat-faced fillets has little effect on the magnitude of the accumulated plastic strain. On the other hand, concave fillets result in considerable plastic strain reduction compared to buildup without fillets by a factor of 2.8 for 14-mm fillet radius and 5.8 for 28-mm fillet radius. The addition of a transition layer of a less strong and more ductile alloy than the rest buildup causes non-uniform deformation of the buildup. The more brittle buildup part of the Ti-6Al-4V practically does not deform plastically and has a considerably lower peak stress than the buildup entirely composed of the Ti-6Al-4V. [ABSTRACT FROM AUTHOR]

The laser-based additive manufacturing techniques are widely used for the refurbishment of worn-out components. The post-processing treatments on additive manufactured parts will improve the material properties and meet the functional requirements. In this study, the multilayered deposition of Inconel 718, a nickel-based alloy is performed using fiber-coupled diode laser with 4 kW maximum output and 5.5 mm spot diameter of direct laser deposition technique. The fabricated samples were subjected to two different stages of heat treatment namely (i) solution-treated and (ii) solution-treated plus direct aged, aiming to study both stages of microstructural and mechanical properties of the deposit. Microstructural observations are carried out using SEM with EDS and microhardness measurements through Vickers indentation method. Further, the influence of different stages of heat treatment on microstructure formation is investigated individually for all multilayered samples. The heat treatment results show that, at different stages, the morphology and hardness differ irrespective of the number of layers. In addition, solution treatment with direct aging reveals precipitation of γ′ (Ni3Ti) and γ′′ (Ni3Nb) phases in the Ni-γ matrix. Further, a 40 to 50% increment in microhardness was obtained and the two-stage heat treatment process has given better results. [ABSTRACT FROM AUTHOR]

With the development of high-speed and heavy-haul railway transportation, the surface failure of rail turnouts has become increasingly severe due to insufficient high hardness-toughness combination. In this work, in situ bainite steel matrix composites with WC primary reinforcement were fabricated via direct laser deposition (DLD). With the increased primary reinforcement content, the adaptive adjustments of the matrix microstructure and in situ reinforcement were obtained at the same time. Furthermore, the dependence of the adaptive adjustment of the composite microstructure on the composites' balance of hardness and impact toughness was evaluated. During DLD, the laser induces an interaction among the primary composite powders, which leads to obvious changes in the phase composition and morphology of the composites. With the increased WC primary reinforcement content, the dominant sheaves of the lath-like bainite and the few island-like retained austenite are changed into needle-like lower bainite and plenty of block-like retained austenite in the matrix, and the final reinforcement of Fe3W3C and WC is obtained. In addition, with the increased primary reinforcement content, the microhardness of the bainite steel matrix composites increases remarkably, but the impact toughness decreases. However, compared with conventional metal matrix composites, the in situ bainite steel matrix composites manufactured via DLD possess a much better hardness-toughness balance, which can be attributed to the adaptive adjustment of the matrix microstructure. This work provides a new insight into obtaining new materials with a good combination of hardness and toughness. [ABSTRACT FROM AUTHOR]

Today's manufacturing industry requires novel technologies capable to improve process versatility, rapidity as well as the surface quality of the parts fabricated through additive manufacturing. A cost/process-effective manufacturing solution capable to meet these requirements is represented by the direct laser deposition (DLD) technology. DLD is essentially an additive manufacturing (AM) process that can accurately fabricate complex freeform geometries. The main drawback of DLD is constituted by the reduced surface quality that is in fact an unavoidable characteristic of the AM processes. It was found that the best areal surface roughness (Sa) occurs on the front wall characterized by a +90° angle (or clockwise rotation) between DLD feed and flow vectors. More specifically, while the front wall is characterize by Sa = 0.704µm, the rear/back wall (-90° or counterclockwise rotation) is characterized by Sa = 3.861µm because powder is distributed and affixed in an already solidifying molten pool. To counteract this DLD process inconsistency, high-speed laser polishing (LP) can be used as a post processing technique capable to significantly improve the post-DLD surface quality. Along these lines, LP can eliminate and/or reduce the time and the cost of post-DLD surface finishing operations. Preliminary experimental results demonstrate that LP improves the quality of DLDgenerated surfaces by decreasing with up to 70% the surface roughness (Sa LP(90deg) = 0.211 µm, Sa LP(-90deg) = 0.444 µm) through a redistribution of melted micro-peaks into micro-valleys. The combination of these two laser-based technologies offers an economic, ergonomic, and ecologic fabrication option and opens up avenues for future implementations of computer-based adaptive control, self-optimization, and online monitoring techniques. [ABSTRACT FROM AUTHOR]

Inconel 625 is a corrosion-resistant alloy with excellent mechanical properties, which has many applications in the oil, gas, and aerospace industries. Considering that the statistical modeling of the cladding indicates the final quality of the laser cladding; therefore, in this work, the geometric characteristics of a single-track on a substrate similar to the coating material were investigated. The impact of main process parameters in direct laser deposition, including the powder feeding rate, laser power, and scanning speed, on the geometric features of single-pass, such as height, dilution, width, and wetting angle, was investigated by the response surface method and linear regression. According to the results, the single-pass width directly correlates with the power and inversely correlates with the scan rate. The height of a single pass has a direct relationship with the powder feeding rate and the power, while it inversely correlates with the scan rate. Dilution directly correlates with the scanning velocity and the powder feeding rate, but it has little correlation with the laser power. The wetting angle directly correlates with the scanning rate and the powder feeding rate, while having an inverse correlation with the power of the laser. [ABSTRACT FROM AUTHOR]

A neutron diffraction method has been used to study residual stresses in corrosion-resistant martensitic steel AISI 410 plates of the composition (wt %): 0.15 С, 13 Cr, < 1 Mn, < 1 Si, and Fe for balance obtained by direct laser deposition. The plates are deposited on rigid substrates, which are commonly used in practice in the production of large parts. It has been shown that in plates of different thicknesses (2.2 and 7.4 mm) and the same length and width (70 × 30 mm), the patterns of the stress distribution curves are very close, however, the stresses in a 7.4-mm-thick plate are lower than in a 2.2-mm-thick plate. In both plates (2.2/7.4 mm), the maximum normal tensile stresses (~450/350 MPa) are induced near lateral edges of the substrate. The maximum tensile longitudinal stresses (~400/250 MPa) are induced in the middle section of the plate near the upper edge. In the middle section of a 7.4-mm-thick plate, a stress distribution over the thickness is observed: the stresses near the side surfaces are higher than in the middle section. The thickness distribution becomes more uniform by approaching the plate edges. The stress distribution pattern in plates obtained by direct laser deposition strongly depends on the rigidity of the substrate and, to a lesser extent, on the material and deposition technology. [ABSTRACT FROM AUTHOR]

The seawater circulation pump is a significant piece of equipment in coastal nuclear power plants that is susceptible to erosion and corrosion in the seawater. In this work, CeO2-modified cobalt-based composite coatings were prepared on the surface of martensitic stainless steel by direct laser deposition. The effect of CeO2 on the phase composition, microstructure, microhardness, corrosion resistance, and erosion properties of the cobalt-based composite coatings was systematically investigated. While the addition of CeO2 did not affect the phase composition of the coatings that comprised γ-Co, γ-Ni, M7C3, and M23C6 (M = Cr, W, Fe) metallic carbides, the eutectic organization showed an obvious phenomenon of contiguous aggregation. Microscopic pores were found in the coatings with 2 wt.% CeO2, and the number of pores increased with the increase in CeO2 content. Despite the higher self-corrosion potential (−0.27668 V) of cobalt-based alloy coating compared to the substrate (−0.37019 V), indicating enhanced corrosion resistance, the difference in self-corrosion potential among coatings with varying CeO2 addition amounts is small (0.027 V), and the corrosion current densities are within one order of magnitude (10−8 A/cm2). These findings suggest that the addition of CeO2 has no significant impact on the coating's corrosion resistance. [ABSTRACT FROM AUTHOR]

Recent studies have shown the benefits of utilizing ceramic particles as reinforcement in metal alloys; nevertheless, certain drawbacks, including loss of ductility, embrittlement, and decreases in toughness, have been noted. For the objective of obtaining balanced performance, experts have suggested the addition of metal particles as supplement to the ceramic reinforcement. Consequently, high-performance metal hybrid composites have been developed. However, achieving the optimal mix for the reinforcement combination with regards to the optimal performance of developed composite remains a challenge. This research aimed to determine the optimal mixture of Al50Cu10Sn5Mg20Zn10Ti5 lightweight high-entropy alloy (LHEA), B4C, and ZrO2 for the fabrication of trihybrid titanium composites via direct laser deposition. A mixture design was involved in the experimental design, and experimental data were modeled and optimized to achieve the optimal performance of the trihybrid composite. The ANOVA, response surface plots, and ternary maps analyses of the experimental results revealed that various combinations of reinforcement particles displayed a variety of response trends. Moreover, the analysis showed that these reinforcements significantly contributed to the magnitudes and trends of the responses. The generated models were competent for predicting response, and the best formulation consisted of 8.4% LHEA, 1.2% B4C, and 2.4% ZrO2. [ABSTRACT FROM AUTHOR]

The direct laser deposition (DLD) process has seen rigorous research in the past two decades due to its ability to directly manufacture products followed by minimal machining. The process input variables play a vital role in determining the properties achieved in the products manufactured by the DLD method. Inconel 625, a nickel-based superalloy with exceptional mechanical performance and corrosion resistance, has been used in critical applications within the aerospace, process, and marine industry. However, its poor machinability and higher load requirements for plastic deformation have been challenging for manufacturers. Therefore, many studies have explored the additive manufacturing of Inconel 625 to overcome these problems. This article focuses on the DLD of Inconel 625 and its composites, presenting the state-of-the-art, drawing a relation among laser processing parameters and resulting material properties, microstructure and phase evolution, and the high-temperature performance of DLD Inconel 625. The paper highlights the areas on which further studies may focus. [ABSTRACT FROM AUTHOR]

The 70Cr8Ni2Y coatings were prepared by direct laser deposition (DLD) with different scanning speeds. The microstructure evolution and the relationship between microstructure and properties of the coatings were studied. The results demonstrated that the microstructure of DLD 70Cr8Ni2Y coatings was martensite, and the phases were α ′ (Fe-Cr) and γ -Fe (Fe-Ni). With the increased of scanning speed, the martensite size decreased from 5.42 ± 0.04 μm to 4.42 ± 0.01 μm and 3.20 ± 0.02 μm. When the scanning speed was 20 mm s ^−1 , the fabricated coating displayed the highest average microhardness (883 ± 37 HV) and the lowest mass wear rate (0.061 mg mm ^−1 ) without pores. The combined strengthening effect of fine grain strengthening and solid solution strengthening, as well as good formability, were the fundamental reasons for the high hardness and wear resistance of the coating. The results of this study can provide an experimental basis for the DLD alloy coatings with high hardness and wear resistance.

The Hugoniot elastic limit and spall strength were measured for a heat-resistant metal-matrix composite Inconel 625–5%NiTi–TiB2 alloy additive manufactured (AM) by direct laser deposition. The strength characteristics of the alloy were obtained from the analysis of the complete wave profiles recorded with a VISAR laser Doppler velocimeter during shock-wave loading of the samples. The samples were loaded using a PP50 pneumatic gun or ad hoc explosive devices along and across the material deposition direction in order to determine the strength anisotropy of the AM alloy under study. The maximum shock compression pressure was ~7 GPa, and the strain rate under tension before spalling varied in the range of 105–106 s–1. Kinetic dependencies of elastic/plastic transition and critical fracture stresses vs. loading conditions were plotted. It was shown that the Hugoniot elastic limit of the alloy under study decreases as the shock wave travels into the sample, while the spall strength increases as the material's strain rate increases at the moment of spall fracture. A comparison of the strength characteristics of the Inconel 625–NiTi–TiB2 composite alloy with the original Inconel 625 alloy has shown that an addition of 5% of powder based on NiTi-TiB2 leads to a decrease in its elastic limit and critical fracture stresses upon spalling by more than 10%. The alloy under study demonstrates anisotropy of strength properties relative to the material deposition direction. [ABSTRACT FROM AUTHOR]

The difficulty of getting a correct distribution of the reinforcement in the metal matrix and the complexity for achieving a good-metallurgy matrix-reinforcement bonding has limited the development of additive manufacturing of metal matrix composites. This research proposes the use of a reactive atmosphere during the fabrication process to obtain titanium matrix composites reinforced with TiN. The relation between the carrying gas and the process parameters used with the presence of porous and defects, the microstructure, and microhardness has been obtained. Nitrogen was used as the carrying gas of the titanium powder. Under laser irradiation, the particles melt and react with nitrogen, resulting in the formation of a titanium matrix composite highly reinforced with TiN. The composite obtained had a microhardness increase between 50 and 100% in comparison with titanium samples fabricated in the same conditions in an argon atmosphere. Three reaction mechanisms have been proposed to take place in the microstructure, depending on the amount of nitrogen in the titanium particles, and its diffusion in them during the manufacture. [ABSTRACT FROM AUTHOR]

The field of additive manufacturing (AM) of various materials is rapidly developing. At the stage of designing and growing products and for the quality control of finished parts, non-destructive methods of analysis, in particular X-ray computed tomography (CT), are in demand. In addition to the advantages of non-destructive imaging of a wide range of materials in three dimensions, modern CT scanners offer a high contrast and high spatial resolution to provide digital information about their three-dimensional geometry and properties. Within the framework of this article, CT was used to follow the structural evolution of a TiNi–TiB2 metal–ceramic composite obtained by direct laser deposition. The relationship has been established between the additive method of production (layered direct laser deposition) and the formed layered structure of the product in the direction of growth. The porosity of the sample was calculated for each scan direction, and the average for the sample was 1.96%. The matrix of the TiNi–TiB2 composite is characterized by the presence of pores of various sizes, shapes and locations. Spherical voids prevail, but keyhole pores are also found. The heterogeneity of the structure was revealed in the form of clearly traced boundaries of the print layers, as well as differences in the density of the inner and outer regions of the composite. [ABSTRACT FROM AUTHOR]

The paper presents the results of experimental studies on the synthesis of a metal-matrix composite by direct laser deposition, including the assessment of optimum irradiation modes to make such a material free of defects (pores, cracks, etc.). It is shown that in-situ synthesis is provided by laser irradiation of a powder mixture composed of polycrystalline boron and titanium alloy Ti64 in a ratio of 1 : 9 wt %. According to X-ray diffraction analysis with synchrotron radiation, scanning electron microscopy, and nanoindentation, the deposited material contains second phases in the form of TiB and TiB2 ceramics. According to mechanical tests, the elastic modulus and the hardness of the Ti64 metal matrix are Eav = 159.7 GPa and Hav = 7 GPa, and those of synthesized particles (whiskers) are Eav = 321.6 GPa and Hav = 19.7 GPa, respectively. [ABSTRACT FROM AUTHOR]

The results of studying the mechanical properties of the Ti–4.25Al–2V titanium alloy produced by direct metal deposition with use of the equipment developed by the St. Petersburg State Marine Technical University are described. The mechanical properties of the deposited metal are compared with those of the cast and forged metal blanks. It is shown that the superior properties of the former in comparison with cast metal are associated with differences in the structure (in particular, with a high degree of dispersity). [ABSTRACT FROM AUTHOR]

Nowadays, research on additive manufacturing of Ti6Al4V alloy is growing exponentially but there are just a few studies about additive manufacturing of metal matrix composite components. In this work, highly reinforced Ti6Al4V matrix composites with SiC particles have been additively manufactured by direct laser deposition (DLD). Ti6Al4V powder and SiC particles have been deposited layer by layer to form an additive thin wall structure. The geometry, microstructure, and microhardness of the samples are strongly influenced by the laser scanning speed used during de fabrication process. In addition, the effect of the SiC increment in reinforcement concentrations and the influence of SiC particle sizes in the microstructure have been evaluated, and the reaction mechanisms have been established. The percentage of reinforcement measured is lower than expected due to the reinforcement-matrix reactivity that results in partially dissolved SiC particles and the formation of a TiC and Si5Ti3 ring around them. The size and number of particles and reaction products depend on the initial size and percentage of reinforcement and the DLD scanning speed. The higher the size and percentage of SiC particles and reaction products in the matrix, the higher the hardening effect of the composite matrix. [ABSTRACT FROM AUTHOR]

This paper studies the impact of the mass fraction of NiTi–TiB2 particles obtained by the method of self-propagating high-temperature synthesis (SHS) on the phase composition, structure, and mechanical properties of composites made by direct laser deposition from an Inconel 625–NiTiz–TiB2 powder mixture. Composites were obtained from a powder mixture with the mass fraction of particles at 5–10 wt%, and they consisted of an Inconel 625 metal matrix wherein ceramic inclusions of titanium diboride TiB2 were distributed. Increasing the mass fraction of SHS-produced NiTi particles from 30 to 95 wt% led to the emergence of a NiTi intermetallide phase in the matrix material as well as an increase in the average TiB2 particle size and formation of their agglomerates. In addition, an increase in the microhardness of the materials was observed. The graph of tensile strength of Inconel 625–NiTi–TiB2 samples has a parabolic shape with a maximum at 1000 MPa (when the mass fraction of SHS-produced NiTi–TiB2 particles is at 30 wt%). A further increase in the mass fraction of NiTi–TiB2 led to a decrease in the tensile strength down to 400 MPa. Here the deformation of samples decreases linearly as the ratio of composite particles in the initial mixture increases. From a comparative analysis of the results obtained, the optimal mass fraction of composite NiTi–TiB2 particles in the Inconel 625-NiTi–TiB2 powder mixture was found to be 5 wt%. [ABSTRACT FROM AUTHOR]

Titanium alloys require a special protecting atmosphere during the fabrication process due to their strong affinity with oxygen and nitrogen elements at high temperatures. In this study, the effects of different protection conditions on microstructure, phase characteristics, interstitial elements absorption and microhardness of additively manufactured Ti–6Al–4V alloy by direct laser deposition method have been investigated. Fabrication of specimens with similar laser parameters was carried out in three different protection conditions consist of air, closed box and argon shower. Characterization of samples was performed by utilization of OM, SEM, XRD, inert gas fusion method, micro-hardness and tensile strength analysis. Results indicated that fabrication of samples in an air atmosphere without proper protection leads to 2.5% spherical porosities, TiO2 and TiN formation in top layers, changing the c/a ratio from 1.59 to 1.61, absorption of 1870 and 500 ppm oxygen and nitrogen and 155 HV increment in micro-hardness value. Also, uncommon semi-globular microstructure in different locations of samples has been observed. The special protective atmosphere provided by argon shower led to 6.3% spherical porosities, negligible lattice parameter variation and martensite microstructure formation. It was found that in the optimal protection condition that was provided by a closed box, the typical basketweave microstructure with less than 1% porosity and 960 and 140 ppm oxygen and nitrogen absorption were achieved, which did not exceed the standard limits. In addition, the mechanical properties of UTS tensile strength, yield strength and elongation, were obtained 1042, 893 MPa and 13.2% respectively.

During the direct laser deposition (DLD) manufacturing process, complicated cladding process, and multiple thermal cycles lead to changeable transport phenomena and solidification behavior in the melt pool, which significantly affect the evolution of the structure and properties of part. Clarifying the process mechanism of the DLD process is of great value for further promoting its application service, and the development of an accurate and robust layer cladding model is obviously the key point. In this study, a three-dimensional numerical layer cladding model consisting of coupled heat transport and fluid flow, layer cladding and interface capture is developed and validated. Then, the heat and mass transfer characteristics, as well as its formation mechanism in multilayer cladding process are investigated in depth. Results show that a smooth, continuous, equal height, and common width cladding layer is formed in any cladding layer. Under the effect of the asymmetric evolution in scanning direction, the sub-layer reverse scanning strategy can effectively improve the surface roughness reducing at the end of previous layer. Besides, the front layer residual heat has significant influence on the multilayer cladding process. When the melt pool expands, the maximum temperature and velocity increase sharply, but the average energy decreases. Furthermore, the layer evolution will enter quasi-steady state as the heat input and dissipation reach dynamic balance. A 3-D model incorporated "interface growth" method is developed for multilayer cladding process. Sub-layer reverse scanning strategy can effectively reduce the layer roughness. The average energy in melt pool continuously decreases as the residual heat in front layer increases. The layer evolution will enter quasi-steady state as the heat input and dissipation reach dynamic balance. [ABSTRACT FROM AUTHOR]

Despite strong interest from many industrial sectors driving demand and advancements in laser additive manufacturing (LAM) of steels, some issues remain as barriers limiting the current industrial applications, such as defects, residual stress, scattered, inadequate or/and anisotropic properties. To overcome these problems, several effective approaches have been developed to control and/or enhance the properties of LAM produced steel components. To help researchers and engineers attain up-to-date information and knowledge in this rapidly growing area, the present work provides an overview of current research in LAM of steels, in particular austenitic steels, ferritic steels, duplex steels and martensitic steels, with a focus on understanding the interrelation between process, microstructure and mechanical properties. This review also includes substantive discussions on the effects of processing parameters, their interactions and post-LAM treatments on the metallurgy, microstructure and properties. In addition, the advances, ongoing challenges and outlooks in LAM of steels are highlighted. [ABSTRACT FROM AUTHOR]

By recording and analyzing complete wave profiles using the VISAR laser interferometer, measurements of the Hugoniot elastic limit and critical fracture stresses were carried out under the spalling conditions of the heat-resistant Inconel 718 alloy, additively manufactured by direct laser deposition, at shockwave loading up to ~6.5 GPa using a light-gas gun. For comparison, similar experiments were performed with the Inconel 718 alloy made by the traditional method of vacuum induction melting. The process of the delay of an elastic compression wave during its propagation through the sample and the dependence of the spall strength on the strain before fracture in the range 105–106 s−1 were investigated. To identify the anisotropy of the strength properties of the material under study, two series of experiments were carried out on loading additively manufactured samples along and perpendicular to the direction of the deposition. The measurements performed showed that the additively manufactured Inconel 718 alloy demonstrates weak anisotropy of strength properties for both the initial and thermal-treated samples. The thermal treatment leads to a noticeable increase in the Hugoniot elastic limit and the spall strength of the samples at low strain rates. For all types of samples, there is an increase in the spall strength with an increase in the strain rate. The spall strength measured for the cast alloy practically coincides with the strength of the as-received additive alloy and is noticeably lower than the strength of the thermal-treated additive alloy over the entire range of the strain rates. The process of the decay of the elastic precursor in the cast alloy occurs much faster than in the additive one, and the minimum values of the Hugoniot elastic limit are measured for thick samples in the cast alloy. [ABSTRACT FROM AUTHOR]

In the present work, we have extensively examined the alternative-band microstructure of a Ti-47Al-2Cr-2Nb alloy fabricated via direct laser deposition by means of high resolution transmission electron microscopy and selected area electron diffraction. The studied samples exhibit two types of long-periodic stacking ordered phase with 6H and 18R structures, which were never reported for those obtained by traditional approaches. Moreover, the ordered phases possess stacking sequences of ABCBACA and ABCABCBCABCACABCABA, being analogous to the periodically arranged stacking faults in α2 and γ phases, respectively. With the presence of these unusual structures, the as-deposited sample tends to have superior mechanical properties. IMPACT STATEMENT Unusual ordered phases with long periodic stacking structures, seldom reported in the TiAl alloys obtained by traditional approaches, were comprehensively characterized, and demonstrated to possess excellent mechanical properties.

In this paper, the corrosion-wear-resistant alloy steel gradient material for camshaft was successfully prepared by direct laser deposition (DLD). The phase evolution, microstructure characteristics, microhardness, wear behaviors and corrosion resistance of alloy steel gradient material were studied using X-ray diffraction (XRD), electron backscatter diffraction (EBSD), hardness tester, wear tester and electrochemical workstation, respectively. The results showed that phase evolutions with the increase of stainless steel powders from α-Fe + Cr23C6 to α-Fe + Cr23C6 + (Cr, Fe)7C3. The microstructure of the alloy steel gradient material was refined with increasing the stainless steel powders. The preferred texture was weak with the increase of gradient due to the each layer experiencing a variety of complex thermal cycle effects. Meanwhile, the content of high-angle grain boundaries (HAGBs) and the volume fraction of Cr23C6 and (Cr, Fe)7C3 increased with gradient increasing, which promoted the toughness and enhanced the wear reaiatance of the material. In addition, the microhardness distribution of alloy steel gradient material showed a gradient increase from 281 HV to 795 HV along with deposition direction. The wear resistance and corrosion resistance of alloy steel gradient material were extremely improved. The average specific wear rate and corrosion current density of alloy steel gradient material specimen were 0.30 × 10−5 mm3/Nm and 1.3 × 10-7 A cm-2, respectively.

Recent studies have shown the benefits of utilizing ceramic particles as reinforcement in metal alloys; nevertheless, certain drawbacks, including loss of ductility, embrittlement, and decreases in toughness, have been noted. For the objective of obtaining balanced performance, experts have suggested the addition of metal particles as supplement to the ceramic reinforcement. Consequently, high-performance metal hybrid composites have been developed. However, achieving the optimal mix for the reinforcement combination with regards to the optimal performance of developed composite remains a challenge. This research aimed to determine the optimal mixture of Al50Cu10Sn5Mg20Zn10Ti5 lightweight high-entropy alloy (LHEA), B4C, and ZrO2 for the fabrication of trihybrid titanium composites via direct laser deposition. A mixture design was involved in the experimental design, and experimental data were modeled and optimized to achieve the optimal performance of the trihybrid composite. The ANOVA, response surface plots, and ternary maps analyses of the experimental results revealed that various combinations of reinforcement particles displayed a variety of response trends. Moreover, the analysis showed that these reinforcements significantly contributed to the magnitudes and trends of the responses. The generated models were competent for predicting response, and the best formulation consisted of 8.4% LHEA, 1.2% B4C, and 2.4% ZrO2.

The direct laser deposition (DLD) process has seen rigorous research in the past two decades due to its ability to directly manufacture products followed by minimal machining. The process input variables play a vital role in determining the properties achieved in the products manufactured by the DLD method. Inconel 625, a nickel-based superalloy with exceptional mechanical performance and corrosion resistance, has been used in critical applications within the aerospace, process, and marine industry. However, its poor machinability and higher load requirements for plastic deformation have been challenging for manufacturers. Therefore, many studies have explored the additive manufacturing of Inconel 625 to overcome these problems. This article focuses on the DLD of Inconel 625 and its composites, presenting the state-of-the-art, drawing a relation among laser processing parameters and resulting material properties, microstructure and phase evolution, and the high-temperature performance of DLD Inconel 625. The paper highlights the areas on which further studies may focus.

Pores are some of the most common defects that form during direct laser deposition of ceramic materials. A mathematical model of pore formation for Al 2 O 3 -ZrO 2 ceramic was developed. The pore formation model, which was developed from the bubble escape factor, reveals the relationship between the movement of the solid-liquid interface of the molten pool and that of the bubbles. In the frontier region of the molten pool, with increasing laser power, the proportion of bubbles that escaped and the area from which bubbles escaped increased. With increasing laser power, the actual and theoretical porosity decreased from 80 % to 40 %. At the central region of the molten pool, the bubble escape factor increased with increasing bubble diameter under the same laser power. The theoretical porosity and the actual porosity decreased with increasing laser power. The pore formation model provides a basis for fabricating high-quality Al 2 O 3 -ZrO 2 ceramics by direct laser deposition. [ABSTRACT FROM AUTHOR]

The Hugoniot elastic limit and spall strength were measured for a heat-resistant metal-matrix composite Inconel 625–5%NiTi–TiB2 alloy additive manufactured (AM) by direct laser deposition. The strength characteristics of the alloy were obtained from the analysis of the complete wave profiles recorded with a VISAR laser Doppler velocimeter during shock-wave loading of the samples. The samples were loaded using a PP50 pneumatic gun or ad hoc explosive devices along and across the material deposition direction in order to determine the strength anisotropy of the AM alloy under study. The maximum shock compression pressure was ~7 GPa, and the strain rate under tension before spalling varied in the range of 105–106 s–1. Kinetic dependencies of elastic/plastic transition and critical fracture stresses vs. loading conditions were plotted. It was shown that the Hugoniot elastic limit of the alloy under study decreases as the shock wave travels into the sample, while the spall strength increases as the material’s strain rate increases at the moment of spall fracture. A comparison of the strength characteristics of the Inconel 625–NiTi–TiB2 composite alloy with the original Inconel 625 alloy has shown that an addition of 5% of powder based on NiTi-TiB2 leads to a decrease in its elastic limit and critical fracture stresses upon spalling by more than 10%. The alloy under study demonstrates anisotropy of strength properties relative to the material deposition direction.

CM247LC is classified as a non-weldable Ni alloy due to the high Ti + Al content, which makes it susceptible to cracking. It is particularly prone to microcracking when processed by direct laser deposition (DLD). In this work, multiple single walls were manufactured by DLD in CM247LC using two different laser modes: continuous wave and pulse wave (PW). The manufactured walls were studied during processing and post-processing, and characterised by scanning electron microscopy, electron backscattered diffraction, thermal analysis and X-ray diffraction. The results indicate that crack-free conditions during the deposition process and the subsequent thermal processing can be achieved using the PW laser mode and that this can also lead to outstanding mechanical properties.

This study investigates the feasibility of in-situ manufacturing of a functionally graded metallic-regolith. To fabricate the gradient, digital light processing, an additive manufacturing technique, and spark plasma sintering were selected due to their compatibility with metallic-ceramic processing in a space environment. The chosen methods were first assessed for their ability to effectively consolidate regolith alone, before progressing regolith directly onto metallic substrates. Optimized processing conditions based on the sintering temperature, initial powder particle size, and different compositions of the lunar regolith powders were identified. Experiments have successfully proven the consolidation of lunar regolith simulants at 1050°C under 80 MPa with digital light processing and spark plasma sintering, while the metallic powders can be fully densified at relatively low temperatures and a pressure of 50 MPa with spark plasma sintering. Furthermore, the lunar regolith and Ti6Al4V gradient was proven to be the most promising combination. While the current study showed that it is feasible to manufacture a functionally graded metallic-regolith, further developments of a fully optimized method have the potential to produce tailored, high-performance materials in an off-earth manufacturing setting for the production of aerospace, robotic, or architectural components.

With the rapid development of aviation industry, the key components of hypersonic vehicles will face more severe service environment. The development of high-temperature-resistant and high-strength materials has become an important research focus. Titanium matrix composites (TMCs) have higher specific strength, specific modulus and service temperatures than traditional titanium alloys, have greater development potential. Tungsten(W) can be applied as a potential reinforcing phase for TMCs due to its higher melting point, strength and thermal conductivity, and the fact that it does not produce intermetallic compounds with titanium. Therefore, in this work, W particles reinforced Ti6Al4V composites (10 wt%、20 wt%、30 wt%、40 wt%W/Ti6Al4V composites) were prepared by direct laser deposition(DLD), and the correlation mechanism between microstructure and mechanical properties of W/Ti6Al4V composites was revealed in detail. As the W mass fraction increasing from 10 % to 40 %, owing to the fact that W as a β-stabilising element could reduce the allotropic transformation temperature of titanium, and W particles could provide heterogeneous nucleation points for α-laths, the content and width of α-Ti decreased significantly, while the content of metastable β-Ti gradually rised and β-Ti tended to grow rapidly to form coarse grains and continuous solid solutions with W. Since W bonded well with Ti6Al4V matrix, the solid solution strengthening induced by dissolved W and α-Ti grain refinement in the Ti6Al4V matrix directly increased the microhardness of TMCs, resulting in an excellent wear resistance of composites. Moreover, the tensile strength of 10 % TMCs was 1327.0 ± 10.2 MPa, which was nearly 39.7 % higher than that of Ti6Al4V prepared by DLD. Fine grain strengthening was the dominant strengthening mechanism, which contributed 66.3 % of the total strength increments. [ABSTRACT FROM AUTHOR]

Direct laser deposition (DLD), as a popular metal additive manufacturing process, shows advantages of technical flexibility and high efficiency to gain a high-performance alloy steel component. However, during the processing of DLD, the deposited steel layer is affected by the subsequent layer depositing. The DLD block shows different microstructure and mechanical properties at the bottom, middle and top of the deposited parts. To date, there are few research works about the effects of inter-layer interval time and laser power on the microstructure evolution and mechanical properties of the deposited layers. In this study, the idle time and laser power layer by layer during DLD of 12CrNi2 steel were controlled to cause the deposited layers to maintain a high cooling rate, while the bottom deposited layer was subjected to a weak tempering effect. Results show that a high proportion of martensite is produced, which improves the strength of the deposited layer. Under the laser scanning strategy of laser power 2,500 W, scanning velocity 5 mm·s−1, powder feeding rate 11 g·min−1, overlap rate 50%, and a laser power difference of 50 W and a 2 min interval, the tensile strength of the deposited layer of 12CrNi2 steel is in the range of 873–1,022 MPa, and the elongation is in the range of 16.2%–18.9%. This study provides a method to reduce the tempering effect of the subsequent deposition layers on the bottom layers, which can increase the proportion of martensite in the low-alloy high-strength steel, so as to improve the yield strength of the alloy steel. [ABSTRACT FROM AUTHOR]