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Laser powder bed fusion (LPBF) is a rapid prototyping technology with high forming accuracy, which can print complex metallic components applied in the aerospace field. The aluminum alloy parts manufactured by LPBF can better achieve lightweight structures than other metallic materials due to the combination of materials and structure. However, many metallurgical defects such as spherification, porosity, coarse grain, and crack are more likely formed inside the printed components during the LPBF process, resulting in the decline of properties of the aluminum alloy. In order to solve the above-mentioned problems, researchers have conducted in-depth exploration to improve the mechanical properties of LPBF fabricated Al parts. In this paper, the methods to improve the forming quality of aluminum alloy are explored from the direction of regulation strategies for microstructure and properties. The current research status of LPBF-processed aluminum alloy is discussed from the aspects of process parameter optimization, alloying element modification, reinforcing phase addition, and post-treatment. Furthermore, the microstructure and properties of LPBF-processed aluminum alloy are systematically reviewed. [ABSTRACT FROM AUTHOR]

Activating fluxes (AF) can be applied in the welding process to improve the morphology, microstructure, and mechanical properties, such as hardness, tensile strength, and yield strength. Regarding the published research on AF application in Tungsten Inert Gas (TIG) welding, there are limited studies concerning the Gas Metal Arc Welding (GMAW) process. This gap in research has prompted investigations aimed at determining the influence of AF during the GMAW process. The purpose of this paper is to apply three types of AF (SiO2, TiO2, and CaCO3) in 316L stainless steel GMAW processing and analyze their influence on the weld bead geometry, hardness, and microstructure. The results showed that the highest penetration and the smallest width can be obtained using TiO2 as AF while the highest reinforcement can be obtained by CaCO3 as AF. This also indicated a possible significant increase in AF addition after-welding hardness, which may be caused due to the microstructure changes. The microstructure observation revealed that the welding area without AF was mainly composed of austenite and the addition of AF increased the welding temperature, which caused the martensite structure to be found in these samples. The heat treatment was introduced to reduce the hardness since large and uneven hardness would bring negative consequences such as brittleness. The after-HT analysis showed that HT can reduce the hardness effectively and improve the uniformity of the whole weld bead. Additionally, it was found that samples with AF were more sensitive to HT. This study concludes that AF can be applied in the GMAW welding process and influence the weld bead significantly. [ABSTRACT FROM AUTHOR]

Analysis of publications has shown that the use of the exothermic addition with a combined oxidizer (xCuO + (x-1)Fe2O3-Al) as components of filler materials will reduce energy consumption and increase the efficiency of the welding/hardfacing process. However, in the literature, there are no studies of exothermic addition with combined oxidizers, which allow to vary the chemical composition of the deposited metal within a wide range. In this paper, the use of exothermic addition with combined oxidizer (xCuO + (x-1)Fe2O3-Al) was considered. To study the characteristics, standard methods were used to determine the arc stability, melting characteristics, weld bead morphology, melting-energy characteristics, and efficiency parameters, and mechanical properties were made. The structural characteristics were analyzed by optical microscope (OM), X-ray diffractometer (XRD). Microhardness values of the hardfaced samples were obtained using a Vickers hardness tester. The greater stability of arc voltage was shown by the processes performed with flux-cored wires in which oxidizing agents of exothermic addition Al-CuO-Fe2O3 in the core filler were taken with an equal content of oxidizing agents or with a slight excess of oxidizing agent CuO/(CuO + Fe2O3) = 0.5–0.6, whereas the greater stability of the welding current was shown by the processes carried out with the use of flux-cored wire with the exothermic addition with an equal or greater proportion of Fe2O3 oxidizer in the combined oxidizer CuO/(CuO + Fe2O3) ≤ 0.5. Further studies of melting characteristics (deposition rate, spattering factor, etc.), melting-energy characteristics (melt-off coefficient CM and deposition rate coefficient Cd), and efficiency showed the efficiency of using exothermic addition with combined oxidizer of Al-CuO-Fe2O3 system. The study showed high arc stability of the hardfacing process, an increase in deposition efficiency (De), and a decrease in spattering loss, which increased deposition rate from 4.73 kg·h−1 to 6.42 kg·h−1 compared to exothermic addition with simple Al-Fe2O3 system. Analysis of weld bead morphology showed improvement in weld bead parameters. The results showed high energy efficiency and productivity of the welding/hardfacing process with the introduction of exothermic addition with combined oxidizer of CuO-Fe2O3-Al system at the following share of copper oxide in combined oxidizer CuO/(CuO + Fe2O3) = 0.5–0.6. [ABSTRACT FROM AUTHOR]

Lightweight bent aluminum profiles are widely utilized in transportation fields. In this paper, the torsional channel self-bending extrusion process (TCSE) was adopted to machine AA6063 bent aluminum profiles in a single operation to verify the process's feasibility. Effects of extrusion parameters on the curvature, microstructure, and mechanical properties of the profiles were researched, and the extrusion process was simulated. The results show that the extruded profiles had good curvature stability. The grains were equiaxed in the cross longitudinal section, and the grain size at the outside diameter (OD) position was smaller than the inside diameter (ID) position. When the difference in deformation temperature at the OD edge was above 31 K, a smaller peripheral coarse grain (PCG) layer was formed at the OD edge with a thickness of about 400 μm, resulting in reduced hardness. The Mg2Si particles served as the main strengthening phase, which increased in number and decreased in size with increasing billet temperature and extrusion speed. Increasing the billet temperature and speed improved the mechanical properties of the material, with an increase in average hardness of 55.9% and 19.5%, and ultimate tensile strength (UTS) of 12.5% and 7.1%, respectively. By comprehensively considering the factors of extrusion load, microstructure, and mechanical properties, the optimum bent profile for different curvatures was determined. When a large curvature (≥328.67 mm) was required, it was preferred to increase the billet temperature. When a smaller curvature (≤328.67 mm) was required, it was advisable to increase extrusion speed. [ABSTRACT FROM AUTHOR]

This paper considers the applicability of high-velocity forming by investigating the compound explosion process of electrical and chemical energy in electric-pulse-triggered energetic materials loading (ETEL). The deformation behavior of DP600 steel sheets during ETEL and wire explosion loading (WEL) is studied by experiments, numerical simulation, and microstructure analysis. The increment of quantized energetic materials (EMs) (0.5 g) on the deformation volume of the sheet is reduced during ETEL, indicating that triggering more EMs at the same discharge energy reduces its energy utilization. The percentage contribution of different discharge energies triggering the same mass of EMs to the deformation volume of the sheet has no effect, with 1.0 g EMs contributing about 35.5%. Compared with WEL specimens of a similar bulging height, an appropriate increase in discharge energy in ETEL is beneficial to improve the energy utilization. The relationships between the kinetic energy, plastic strain energy, stress, and strain of the sheets during ETEL/1.5 g and WEL/5472 J are analyzed by numerical simulation. The results show that ETEL has a smaller stress gradient difference than WEL, indicating that ETEL changes the stress distribution in the deformation zone and expands the strain distribution range. Compared with WEL/5472 J, the low angle grain boundary (LAGB) fraction of ETEL/1.5 g increases, and dislocations are uniformly distributed in the grains and disperse the strain concentration at the grain boundaries. The fracture specimens of ETEL also show multiple necking bands, large and deep dimples, and thicker tear ridges, indicating a significantly higher degree of deformation. [ABSTRACT FROM AUTHOR]

TiAl-based alloys represent a novel class of lightweight, high-temperature structural materials that exhibit exceptional properties, including low densities, high specific strength, and remarkable thermal resistance. These properties make them exceedingly promising for supplanting nickel-based superalloy in the production of pivotal components for aerospace, marine, and automotive engines. Regrettably, like most intermetallic compounds, TiAl-based alloys are subject to certain shortcomings, such as room-temperature brittleness, deformation difficulties, and susceptibility to cracking, which present challenges for shaping these materials into intricate forms using traditional processing methods. In this regard, additive manufacturing (AM), with its high processing freedom and energy, has emerged as a revolutionary technology for the fabrication of complex structural components of TiAl-based alloys. However, AM TiAl-based alloys are still plagued by issues such as cracking, porosity, and uneven microstructure. Therefore, various post-processing techniques were employed to tune the microstructure, and thus enhance the performance of AM TiAl-based alloys. This paper reviews the research progress of AM TiAl-based alloys, summarizing the effects of process parameters, alloying, heat treatment, and surface treatment on the microstructure and mechanical properties of these alloys. Additionally, it discusses the challenges and prospects for the future development of AM TiAl-based alloys. [ABSTRACT FROM AUTHOR]

This paper presents a thorough manufacturability study of 2507 super duplex stainless steel (SDSS) produced by the Laser Powder-Directed Energy Deposition (LP-DED) process. First, experimental observations on single-track surface morphology and geometrical characteristics are described. Then, dimensional and porosity analyses of thin walls and bulk samples are presented and discussed in order to identify the optimal process parameter combinations, from a process point of view, for further characterizations to determine the general properties of LP-DED-printed samples. Finally, the results obtained on wrought steel of the same grade are compared to those of the printed material in terms of microstructure, texture, and ferrite/austenite ratio. A set of meticulously chosen process parameters with regard to the process and the machine (nozzle size, maximum power deliverable) gives the optimal results for the as-built LP-DED material in terms of porosity and microstructure quality but with smaller grains (irrespective of the phase studied) and a higher proportion of ferrite (about 75%). [ABSTRACT FROM AUTHOR]

Developing hollow components that integrate a large number of complex coolant channels for thermonuclear reactors remains a challenging task, owing to potential technical problems such as dissimilar metal connections, over-aging, and large welding areas (meter-scale). In this paper, CuCrZr/316L hollow components were manufactured using an improved explosive welding technique, where theoretical calculations and composite filling mold were used to achieve ideal welding conditions. Microstructure analysis showed that irregular waves of continuous and complete metallurgical bonding were detected at the bonding interface, and the defects at the corner of the flow channel were controlled at the hundred-micron level. The joint exhibited high shear strength (~ 292 MPa) under the given high-temperature conditions (200 ℃), whose peak strength, stress–distance curve, and failure mode were almost consistent with the experimental results at room temperature (25 ℃). Finally, under all conditions of the helium-leak test, the leak tightness of the CuCrZr/316L hollow component met the standard requirement. [ABSTRACT FROM AUTHOR]

Gear shafts are commonly manufactured by machining of gear teeth and shaft separately. This kind of approach entails quite some problems, such as long processing time, large die, and low production efficiency. To tackle these problems, this paper innovatively proposes a new process of cross wedge rolling (CWR) that is specifically tailored to the manufacturing of gear shafts, with which the shaft and teeth are formed at one go. The finite element model of CWR forming of gear shaft is established to simulate and analyze the CWR forming process. A three-factor and three-level response surface test is designed to optimize the processing parameters, where the friction coefficient, rolling temperature, and die movement speed are chosen as three factors, and inhomogeneous deformation is set as the response. The optimal parameters are obtained as follows: the rolling temperature is 1240 ℃, the speed of the die movement is 336 mm/s, and the friction coefficient is 0.8. This result is subsequently verified by experiments. Further on, the microstructure evolution of the characteristic points of the CWR forming process of gear shaft is analyzed. It is found that the grains at the gear teeth section are continuously refined and grown from the boundary at the early section of deformation, and the final grains grown are much smaller than the original ones. In addition, the grains appear to grow in a short range of time in the process of deformation, but the overall trend is towards refinement. In the shaft section, the evolutions of the grains in the two stepped shaft segments are almost the same; the grain deformation shows cyclic changes; the degree of grain refinement in the shaft is higher than that in the teeth; and the degree of grain refinement in the shaft center is higher than that in the shaft edge. The results of the study provide a theoretical basis for short-process forming of high-performance gear shafts by cross wedge rolling. [ABSTRACT FROM AUTHOR]

Laser-based powder bed fusion (LPBF) is a widely utilized technique for additive manufacturing (AM) of metal components. The size of LPBF-produced parts is restricted by machine dimensions. Welding emerges as a feasible solution for connecting smaller parts generated via PBF. Nevertheless, the weldability of PBF parts differs from conventional ones due to the unique thermal history of PBF components. This paper investigated the weldability of stainless steel 316L and tensile behavior of welded samples, comparing samples produced through LPBF and the conventional wrought method. Tensile testing, grain size analysis, microhardness test, and assessment of secondary dendrite arm spacing were conducted on every welded combination of materials (AM-AM, wrought-wrought, and AM-wrought) using gas tungsten arc welding (GTAW). The findings indicate that the wrought material demonstrates a higher maximum strength (577.5 MPa) and a lower yield strength (231.7 MPa) compared to the AM material (with a maximum strength of 548.2 MPa and a yield strength of 399.9 MPa). This difference may be attributed to the annealing process applied to the wrought material, which has not been applied on the AM material. Additionally, welded wrought samples have a significantly lower tensile strength compared to non-welded samples. The wrought samples exhibit a larger average grain size (11.14 to 31.12 μ m ) in the heat affected zone (HAZ) compared to non-heat affected regions (8.13 μ m ). In contrast, it is found that grain coarsening does not occur in PBF samples, which exhibit a similar grain size in the HAZ (15.04 μ m ) vs 13.97 μ m outside of the HAZ. Larger grain sizes within the HAZ correspond to a larger reduction in tensile strength for the wrought samples, compared to PBF samples. Similar secondary dendrite arm spacing has been observed in the weld regions of both PBF and wrought materials. Microhardness test results indicated that the AM base material has the highest microhardness and gradually decreases as transitioning to the HAZ and weld region. In summary, the PBF samples exhibit less reduction of strength and ductility after welding than wrought samples. Therefore, it is determined that additively manufactured 316L stainless steel has a higher weldability than traditionally manufactured wrought 316 stainless steel. [ABSTRACT FROM AUTHOR]

The direction in which wire and powder feedstock are fed influences deposit quality of as-built parts produced using laser-direct energy deposition (L-DED). While lateral wire feed has been explored in existing L-DED investigations, limitations like process instability persist, especially in achieving the required connection between the wire and the melt pool. Co-axial feedstock deposition offers a potential solution, enabling higher manufacturing flexibility and efficiency by co-axially feeding wire or powder. However, the full potential of L-DED using co-axial feeding for metal components remains underexplored due to equipment limitations. This study systematically evaluates the printability of stainless steel (SS) 316L and compares the microstructures and microhardness properties between co-axial powder-fed and wire-fed L-DED specimens. Utilizing the MELTIO M450 L-DED system in an argon environment, single-layer three-track specimens are produced with different combinations of process parameters. Comprehensive characterization, employing optical and scanning electron microscopy alongside microhardness testing, reveals powder-fed specimens exhibit greater melt pool depth and cooling rates, while wire-fed counterparts display fewer oxide inclusions and smoother surfaces. Microstructural differences include higher δ-ferrite content in wire-fed specimens. Microhardness values between powder-fed and wire-fed specimens are comparable. These findings hold implications for sequential powder and wire deposition, enabling the production of diverse mechanical structures with distinct characteristics. Overall, this paper provides an insight into feedstock selection for efficient metallic part production via co-axial feedstock deposition and recommends a range of process parameters suitable for fabricating SS316L parts using co-axial deposition in L-DED. [ABSTRACT FROM AUTHOR]

To reveal the influence mechanism of linear heat input (LHI) on the mechanical properties and corrosion behaviors of SUS304 weldments manufactured by local dry underwater pulsed metal inert-gas welding (LDU-PMIG), phase structure, grain structure, grain preferred orientation, and grain type of weld metal (WM) were investigated in this paper. With LHI increasing, ferrite phase morphology transformed from lath to skeleton, and grain size was enlarged. The content of equiaxed grains was increased, and that of columnar grains was reduced remarkably. The mechanical performance ascended first and then reduced with the increase of LHI. The increase of equiaxed grain content and the diversification of grain preferred orientation were beneficial to the improvement of mechanical performance, then, grain coarsening led to mechanical performance decreasing. Besides, the corrosion potential, corrosion current and pitting potential of WM were detected through electrochemical corrosion tests. The results illustrated that the corrosion resistance of WM was lower than that of base metal (BM), and the corrosion rate was enlarged with LHI enhancing, which meant the corrosion resistance declining. The corrosion resistance was mainly determined by Cr precipitates, ferrite phase and grain size. The microhardness, tensile strength, and elongation reached their maxima in the LHI of 336.7 J/mm. The greatest corrosion resistance of WM was obtained in the LHI of 256.2 J/mm and reached 69.9% of BM. This study is meaningful to promote the further development and application of LDU-PMIG in marine underwater welding field. [ABSTRACT FROM AUTHOR]

Steel matrix composites are widely used in automotive, aerospace, wear, and cutting applications due to their superior mechanical properties, ease of manufacture, and low cost. However, there are still some limitations in the strength, reinforcement dispersion, and interface control of steel matrix composites, which are mainly achieved through different preparation processes and the addition of reinforced particles with mixed metal powders. Previous studies have demonstrated the enhanced ability of various reinforcing particles such as titanium carbide, silicon carbide, and alumina to enhance the wear performance of steel substrates, but there are still some challenges, such as uneven particle distribution, interface cracks, and unsatisfactory wettability. In this paper, the preparation methods of ceramic-reinforced metal matrix, ceramic reinforcement, steel matrix composition, microstructure, mechanical properties, and wear properties, as well as the parameters affecting their properties, are reviewed. The preparation processes of different ceramic-reinforced steel matrix composites are introduced, which are very suitable for overcoming challenges such as insufficient strength, poor dispersion, uneven distribution, and poor interfacial wettability. The influence of the morphology distribution and volume fraction of reinforcement on the wear rate of steel matrix composites was discussed. The importance of the microstructure of ceramic reinforcement in steel matrix and the interface between ceramic and matrix to improve the mechanical properties of steel matrix composites were emphasized. This review identifies the development trends in the field of research to fully illustrate the importance of more in-depth scientific research in steel matrix composites. [ABSTRACT FROM AUTHOR]

With the rapid development of industrial manufacturing, traditional WC–Co cemented carbides have exposed more and more problems. Therefore, the preparation of ultrafine/nanocrystalline-grained cemented carbides and the development of new binders have become a hot issue in the field of cemented carbides. Due to the unique design concept, the high-entropy alloys (HEA) binder not only has the unique properties of the HEA itself, but also can replace the traditional Co element as the binder of cemented carbide, which opens up the possibility for industrial manufacturing. The stable chemical properties of WC are coupled with the multi-principal element characteristics of HEA binder, which makes novel WC-HEA cemented carbides have the characteristics of grain refinement, compact structure, stable structure, and excellent capability. A multitude of studies have found that the new WC-HEA cemented carbide exhibits better service performance than WC–Co cemented carbide. In this paper, the main preparation processes of WC-HEA cemented carbide in recent years are summarized; the influence of the working principle, advantages, and defects of the two different preparation methods on the microstructure and properties of WC-HEA cemented carbide were described. The characteristics and influence mechanism of microstructure such as the composition of high-entropy alloy binder and the change behavior of phase structure of WC-HEA cemented carbide were discussed. The service performance characteristics of WC-HEA cemented carbides were discussed, including mechanical properties, wear resistance, oxidation resistance, and corrosion resistance. Finally, it summarizes the research challenges and prospects in the current research work, and provides an outlook on the research direction and application prospects of WC-HEA cemented carbide. [ABSTRACT FROM AUTHOR]

Additive manufacturing is a powerful process to build complex geometry. Besides the numerous process parameters influencing the mechanical part performances, other parameters related to the initial powder feedstock or component machining are of most importance. In this study, the combined effect of a wide particle size distribution, surface machining and stress-relief heat treatment on the microstructure and mechanical properties (tension and fatigue) of a stainless steel AISI 316L, produced by laser powder bed fusion, is investigated. In order to correctly investigate those parameters separately, the netshape/machined character of the sample, alongside with the heat treatment, is studied for two kinds of powder having different particle size distributions, i.e. narrow and widely spread. Results show that a large spread of particle size is only slightly detrimental to the fatigue life, in particular in high-cycle conditions due to a larger porosity related to a weakly more uneven particle spatial distribution in the bed. Nevertheless, this effect is of a second order compared to machining or heat treatments which greatly affect the mechanical behaviour. Surface machining and moderate heat treatment are then the best post-operational steps to increase the fatigue life in high-cycle fatigue conditions independently of the particle size distribution. Results are discussed in terms of defects, microstructural modifications, surface roughness, martensitic transformation and mechanical loading. [ABSTRACT FROM AUTHOR]