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This study explores the use of silicon carbide to strengthen CoCrFeNi high-entropy alloys (HEAs) with face-centered cubic structure. CoCrFeNi(SiC)x (x = 0, 0.1, 0.2, and 0.3) HEAs were prepared through laser metal deposition. The effects of different contents of SiC particles on the microstructure and mechanical properties of CoCrFeNi HEA were investigated. The results indicate that the addition of SiC particles led to the formation of the Cr7C3 phase, which refined the grain size and shifted the grain orientation from to . With the further addition of SiC, the amount of Cr7C3 phase increased, and β-SiC particles appeared. The Cr7C3 phase increased the average hardness of specimens from 191.71 HV to 403.86 HV. Tensile tests showed that the 10 at.% SiC specimens exhibited a yield strength of 534.00 MPa, an ultimate tensile strength of 799.67 MPa, and an elongation of 8.17%, hence optimizing the combination of ultimate tensile strength and elongation. The improvement in mechanical properties is mainly attributed to the refinement of grain boundaries and enhancement of dislocation density.

Powder Plasma Arc Additive Manufacturing (PPA-AM) technique has tremendous potential for the practical application in medium-entropy alloys (MEAs). In this study, we investigated the effect of heat treatment on microstructural evolution, mechanical properties, and the work hardening behavior in the PPA-AM processed (CoCrNi)90Al5Ti5 MEA. The results show that the As-built specimen is a single-phase FCC structure, displaying strong FCC texture in the deposition direction. The stacking faults (SFs) and dislocations were observed in the alloy, which formed the stacking fault networks and the Lomer-Cottrell locks structure. The plasticity of the alloy increased significantly after the high-temperature heat treatment, which can be attributed to the modifications of the microstructure, such as the weakening of the texture strength and the reduction of the stresses. Low-temperature heat treatment decreases the density of dislocations in the alloy, but promotes the generation of the co-lattice phase. The evolution of the dislocation density, texture strength, and precipitates significantly influenced the strain hardening behavior and mechanical properties. The tensile results showed that the strength and plasticity of the samples were increased after two-step heat treatment. The yield strength, ultimate tensile strength, and elongation to failure were 733 MPa, 1080 MPa, and 22.3%, respectively, which were 16.2%, 20.3%, and 15.5% higher than the As-built samples. This work elucidates the underlying mechanisms of heat treatment on the microstructure and mechanical properties of the alloy.

This paper is the first attempt to fabricate eutectic high entropy alloy (EHEA) using dual-wire arc additive manufacturing (D-WAAM) technology with twisted wire + single wire. Using CoFeNi twisted wire and Al single wire as raw materials, the eutectic point was determined by adjusting the Al content over a wide range by adjusting the speed of the Al single wire. We designed and fabricated Al19Co25Fe25Ni31 hypo-eutectic, Al20Co22Fe30Ni28 eutectic, and Al21Co22Fe29Ni28 hyper-eutectic high entropy alloys, and conducted in-depth research on their mechanical properties and microstructure. With increasing Al content, the microstructural changes from hypo-eutectic to hyper-eutectic, the strength of the alloy increases, and the plasticity of the alloy decreases. The fabricated Al20Co22Fe30Ni28 EHEA shows the best strength-plastic balance. This characteristic is mainly attributed to the eutectic alloy exhibiting a dual-phase lamellar microstructure consisting of an ordered face-centered cubic (FCC) L12 phase with a volume fraction of 56.9% and an ordered body-centered cubic (BCC) B2 phase with a volume fraction of 43.1%. Because the alloy contains both the hard B2 phase and the tough L12 phase, the room temperature tensile strength reaches 1041 MPa, and the plasticity reaches 14.9%, which is higher than those of other EHEAs fabricated by casting and arc melting. The excellent strength and plasticity of these materials show great potential in engineering applications. This approach not only expands the existing additive manufacturing technology but also provides new ideas for the additive manufacturing of EHEAs.

Graded materials are promising alloys due to their improved strength and ductility. In this study, a functionally graded Alx-Co-Cr-Fe-Ni high entropy alloy with a variation of Al concentration along the building direction was produced in-situ by dual wire arc additive manufacturing for the first time, and the microstructure and mechanical properties of the deposited alloy were investigated. The results showed that the FCC + BCC dual-phase gradually transformed to a single BCC phase with increasing Al content, the precipitation temperature of the ordered B2 phase became high, and the precipitation temperature range of the disordered BCC phase became wider, which promoted the formation of the disordered BCC phase. With the change in phase ratio, the hardness gradually increased from 342 HV to 397 HV, and the bottom deposited alloy had an optimal combination with a compressive strength of 827.4 MPa and elongation of 42.3%. Compared to the bottom region, the top region shows much higher sliding wear resistance. The high-density dislocations and grain refinement result in better toughness and strength in the bottom region, while the segregation of Cr elements at the grain boundaries changes the properties of the grain boundaries and makes them more brittle in the top region. This investigation realizes a novel method to fabricate GHEAs, which can produce a more convenient and cost-effective gradient material with a complex composition.

Macroscopic deformation and microscopic pores are the main defects affecting the comprehensive performance of laser powder bed fusion (LPBF) parts. The LPBF process involves highly coupled multiple physical mechanisms over a wide time scale, making it difficult to obtain strongly correlated defect characteristics and achieve online monitoring. Thus, this study proposes an acoustic-based macro–micro defect synchronous monitoring technology. It enables monitoring by analysing process information progressively from intra-layer to inter-layer. The research identifies that high energy density leads to deformation defects, with helical scan strategy energy fluctuations exacerbating deformation. A correlation between keyhole pores and high-frequency signal components allows quantitative pore analysis directly from acoustic signals. Furthermore, an intelligent diagnosis model (gn-Res_SC) is proposed, incorporating high-order information interaction and residual structure for in-depth process analysis. The model demonstrates superior performance with accuracy (90.70%), recall (90.70%) and F1-score (90.40%) in LPBF acoustic monitoring signal evaluation.

Additive Manufacturing (AM) can rapidly fabricate and produce customized, large-scale components, thereby fully exploiting High-Entropy Alloys (HEAs)' performance and industrial value—their broad potential for application in extreme service environments such as nuclear energy and aerospace. Because HEAs have a vast composition space, researchers can accurately map their mechanical properties by HEAs phases to reduce time-consuming and intensive experimental work. However, it is still a considerable challenge to predict HEAs phases accurately. And machine learning (ML) can predict the phases to accelerate the study of HEAs.To accurately predict the HEAs phases, the study propose deep learning (DL) algorithms that rely on AM process parameters and data augmentation and do the following: (i) This study developed a more detailed phase classification strategy for HEAs to enable the model to predict the complex multiphase of HEAs; (ii) The process parameters of AM affect the formation of the HEAs phase. In this study, the process parameters of AM are added to the model features to improve the model's accuracy in predicting the HEAs phase; (iii) To alleviate the data scarcity dilemma of HEAs, this study use data augmentation to improve DL's performance further. The results show that after adding AM process parameters to the model and performing data augmentation, the DL model's accuracy to 91.23%. In addition, this study manufactured four new HEAs through AM experiments to verify the robustness and practicality of their algorithms.

To enhance the strength and toughness of metallic materials simultaneously over a wide range of temperatures and strain rates, a eutectic high-entropy FCC/Laves composite with a heterogeneous initial microstructure was fabricated by powder plasma arc additive manufacturing. The mechanical behavior of the composite over a wide range of temperatures and strain rates was tested with the aid of an electronic universal testing machine and an improved Split Hopkinson pressure bar. The high-entropy FCC/Laves composite possesses a unique combination of strength and ductility over the selected temperature and strain rate ranges due to the in situ composite nature with both soft high-entropy FCC phase and hard high-entropy Laves phase. Complicated thermal viscoplastic behavior is presented. To reveal the mechanisms of the complicated thermal viscoplastic behavior, microstructure evolution was characterized. The high-entropy Laves phase, as a kind of multi-component intermetallic, defies convention by displaying plastic deformation at room temperature and different strain rates. Superior damage tolerance of the high-entropy FCC/Laves composite can be achieved over the selected temperature and strain rate ranges with the contribution of deformation twin in FCC phase, as well as dynamic recrystallization over high temperature range. Finally, a constitutive description was developed, which is shown to be able to accurately describe the complicated plastic behavior over a wide range of temperatures and strain rates. These findings suggest promising prospects for advanced material design, opening a new avenue to achieve a fine balance between strength and ductility across different conditions.

In laser shock processing (LSP) of aero-engine blades, overlap marks due to spot overlapping cause irregular surface morphology that becomes a source of cracks under fatigue behaviors. This reduces the beneficial effect of compressive residual stress induced by LSP and undermines fatigue performance of blades. In this paper, laser shock imprinting (LSI) is proposed to improve fatigue performance of aero-engine blades. In this process, a layer of contact film with micro-grooves is placed between the absorption layer and the workpiece (blade) of the LSP. By using the double action of laser shock wave and micro-grooves in contact film, blade surface morphology is transformed towards the direction conducive to improve its fatigue performance. Using ABAQUS software, Johnson-Cook model and Fabbro model were considered to study the plastic rheological behavior of blade surface material induced by LSI. Effect of process parameters namely, peak pressure, impact number and spot overlapping ratio on residual stress and micro-plastic deformation of blade surface were studied. Simulation results showed that under the action of laser shock wave, blade surface material flowed into micro-grooves in contact film via extrusion plastic deformation. This resulted in micro-bulge morphology having geometrically specific arrangement on blade surface, which achieved accurate control of micro-plastic deformation on blade surface. Increase in peak pressure and impact number increase the surface micro-bulges height. However, increase in peak pressure lowers the stress difference between bulging edge and non-bulge zones. It was found that 33% spot overlapping impact resulted in more uniform surface micro-bulge morphology on blade surface.

Functionally graded materials (FGMs) are novel composite materials characterized by gradual changes in compositions and/or microstructures along at least one direction and hence locally tailored properties. In this paper, an innovative twin-wire plasma arc additive manufacturing (TW-PAAM) process was used to fabricate the thin-walled stainless steel 304 L/Inconel625 compositionally graded materials. The chemical composition, microstructure, phases, and microhardness of the as-fabricated FGMs were investigated. The results reveal that sharp changes in composition between 304 L and In625 in non-graded sample resulted in large variations in microstructural morphology and hardness around the interface between these two materials. With the increase of the gradient layers, the microstructural morphology displayed a smooth transition from 304 L to In625. However, cracks were found in the 25%In625 region due to MC carbides distributed at the grain boundary and A solidification mode. The grain growth at the interfaces between adjacent layers with different compositions follows a typical epitaxial growth. As the mixing ratio of In625 increased, the secondary phases changed from MC carbide to Laves phase and their content increased. Furthermore, the microhardness decreased in the 21%In625 region, then increased with the increase in mixing ratio of In625. The absence of δ-ferrite and low content of secondary phases were the main factors contributing to the decrease in microhardness in the 21%625 region. The study provides a guideline for the wire arc additive manufacturing of 304 L/In625 FGMs with the consideration of gradient composition to avoid cracks and weakening of properties.

The microstructure and texture evolution during thermo-mechanical processing (TMP) and their relationship with the mechanical properties in the non-equiatomic CoCrFeNiAl0.4 high-entropy alloy (HEA) were investigated. In this work, a combination of cold rolling and annealing technology was used to investigate the HEA which has been fabricated by powder plasma arc additive manufacturing (PPA-AM) in the deformed and recrystallized states. Microstructure and texture analysis were performed by electron backscatter diffraction. The mechanical properties were evaluated using static tensile testing. It was substantiated that annealing twins facilitates the transition from the cube texture to the shear texture and has a great influence on the evolution of texture after TMP. Based on the research of CoCrFeNiAl0.4 high-entropy alloy, thermo-mechanical processing under appropriate conditions can increase the work hardening rate, but the work hardening rate is relatively stable under 30%–45% plastic deformation. The correlation during TMP between mechanical properties and work hardening, texture evolution, and recrystallization was discussed.

The present work investigates the possibility of modifying the surface of the Ti-based alloy Ti-6.5Al-1Mo-1V-2Zr by deposition of a coating by selective laser melting of Ni-based superalloy Ni-16Co-11Cr powder. Scanning electron microscopy, field emission transmission electron microscopy and X-ray structural analysis were applied to investigate the structural-phase state of the material. Nano-hardness and tribological tests were selected to study mechanical and wear properties. The thickness of the coating ranges from 70 to 130 μm. SLM coating deposition results in multiple titanium and nickel enrichment of the surface layer. The coating consists of several phases; the main ones contain titanium TiCo0.5Ni0.5, Ti0.25Al0.75, TiNi, TiCrAl. Nanohardness of the coating reaches its maximum of 10.5 GPa at the distance of 50 μm from the surface that is 2 times higher than that of the Ti-based substrate. Young's modulus of the coating varies similarly, reaching its maximum of 140 GPa at 50 μm from the surface and a minimum of 120 GPa in the substrate. The specific wear rate of the coating is 2.7 times lower than that of the substrate. To sum up, our work was the first to perform a detailed characterization of Ni-based coatings deposited on the Ti-based substrate via selective laser melting additive technology.

Elliptical elements are essential optical surfaces for modifying optical systems. For polishing the whole elliptical surface using doughnut-shaped MCF polishing tool with variable tilt angle, an experimental investigation was conducted in this work. Firstly, a flat workpiece was polished to determine the polishing feasibility. It was found that the middle portion of the polishing tool had optimal ability to remove materials, and the surface roughness Sa at the material removal peak was changed from 134 nm to 17.5 nm within 50 min of polishing. A smoother surface could be obtained using MCF2 slurry and MCF3 slurry, but the use of MCF1 slurry resulted in a rough surface. Then, the effects of working gap h, revolution speed of MCF polishing tool and polishing time on the polishing results were tested to study the polishing characteristics. Sa 9.6 nm and glossiness 278 Gu were obtained, and form error improved from 2.3 μm to 1.3 μm. Finally, the MCF polishing tool was dried to observe the microstructure of the MCF polishing tool after polishing. Abrasive particles were distributed evenly after polishing. It was seen that the abrasive particles were grabbed by the ferric clusters, and the α-celluloses were interleaved between the clusters.

Laser shock peening (LSP) induces an irregular topography on the treated metal surface, thereby reducing the gain effect of the metal fatigue property caused by compressive residual stress. A technique named laser shock imprinting (LSI) is proposed in this paper to guide plastic deformation on a titanium surface. An FEM simulation and experiment were conducted to explore the embossment forming process and residual stress distribution of TA2 pure titanium. The simulated results show that the embossment on the sample surface went through five stages, namely, static, growth, rebound, fluctuation and stabilization, under a single LSI. With an increase in loading pressure, the contact pressure between the sample and contact foil increased along with increasing embossment height. Sufficient loading pressure could induce a difference in residual stress between the zones with and without embossment. The experimental results show that the height and clarity of embossment increased with increasing laser energy, a result similar to that of the simulation. In addition, compared with LSP, the sample treated by LSI had a lower surface roughness and flatter surface profile.

The paper discusses the complex effect of melt overheating with subsequent fast cooling down to the pouring temperature on the crystallization process, microstructure and mechanical properties of Al-Mg-Si aluminum alloy. The results obtained facilitated the establishment of rational modes of melt overheating, leading to a significant change in the dispersion and morphology of structural components. In particular, with an increase in the melt overheating temperature to 900 °C with holding and subsequent rapid cooling to the casting temperature, a decrease in the average size of dendritic cells of the aluminum solid solution from 39 μm to 13 μm was observed. We also noticed the refinement of eutectic inclusions of the Mg2Si phase with compact morphology. An increased level of mechanical properties was noted; the maximum values of tensile strength and elongation reached 228 MPa and 5.24%, respectively, which exceeded the initial values by 22.5% and 52.3%, correspondingly. The microhardness of the aluminum solid solution sequentially increased from 38.21 to 56.5 HV with an increase in the temperature during melt overheating. According to the EDS linear scanning, an increase in the superheat temperature of the melt is accompanied by an increase in the degree of saturation of the solid solution with magnesium.

In high entropy alloys (HEAs), the addition of large-size atoms results in lattice distortion and further leads to solid solution strengthening or precipitation strengthening. However, the relationship between atomic radius, solid solution strengthening and precipitation strengthening has not been discerned yet. In this work, CoCrFeNiX0.4 (X = Al, Nb, Ta, with an equi-atomic radius) HEAs were prepared by powder plasma arc additive manufacturing (PPA-AM) and evaluated for their mechanical properties. Compression and nano-indentation hardness tests showed that the HEA with Ta showed the best properties. The influence of atomic radius and solid solubility on solid solution strengthening was investigated and the main strengthening mechanism that determines the mechanical properties of the developed HEAs was analyzed. The results showed that (i) the CoCrFeNiAl0.4 alloy did not show any solid solution strengthening effect and that a clear relation between solid solution strengthening and atomic size was not observed; (ii) in both CoCrFeNiTa0.4 and CoCrFeNiNb0.4 HEAs, precipitation strengthening and grain boundary strengthening effects are observed, wherein the difference in mechanical properties between both the alloys can be mainly attributed to the formation of fine eutectic structure in CoCrFeNiTa0.4; and (iii) from the microstructural analyses, it was identified that, in the CoCrFeNiTa0.4 HEA, the location containing a fine eutectic structure is accompanied by the formation of low-angle grain boundaries (LAGBs), which is also the region where deformed grains gather, giving rise to improved mechanical strengthening.

In this work, a welding solidification crack sensitivity test platform was established to study the effect of wire feeding speed (WFS) on solidification crack sensitivity during cold metal transfer (CMT) welding for AA6061 aluminum alloy. The test results show that as the WFS increased from 4 m/min to 5.5 m/min, the sensitivity of the solidification cracks also increased. With a further increase in the value of the WFS, the crack sensitivity decreased and eventually ceased to exist. A new perspective of the microstructure and crack propagation mechanics model was applied to understand the effect of WFS on solidification cracks. With the use of scanning electron microscopy (SEM) and a high-speed camera, it was found that as the WFS increased from 4 m/min to 5.5 m/min, the microstructure of the grain size changed from bigger to smaller, and the stability of the crystal microstructure was reduced. The crack propagation mechanics model was changed, which promotes crack propagation, increasing by 233%. When the WFS continued to increase beyond 5.5 m/min, the size of the crystal structure changed from small to big, the stability of the crystal microstructure was increased, the crack generation was suppressed, and the cracking rate was significantly reduced.

The current study focusses on the phase composition, solidification path, and microstructure evaluation of gravity cast Al-4Mg-0.5Si-xLa aluminum alloy, where x = 0, 0.1, 0.25, 0.5, 0.75, and 1 wt.% La. A computational CalPhaD approach implemented in Thermo-Calc software and scanning electron microscopy technique equipped with electron microprobe analysis (EMPA) was employed to assess its above-mentioned characteristics. The thermodynamic analysis showed that the equilibrium solidification path of La-containing Al-Mg-Si alloys consists of only binary phases LaSi2 and Mg2Si precipitation along with α-Al from the liquid and further solid-state transformation of this mixture into α-Al + Al11La3 + Mg2Si + Al3Mg2 composition. Scheil–Gulliver simulation showed a similar solidification pathway but was accompanied by an increase in the solidification range (from ~55 °C to 210 °C). Furthermore, microstructural observations were congruent with the calculated fraction of phases at 560 °C and related to α-Al + LaSi2 + Mg2Si three-phase region in terms of formation of La-rich phase having both eliminating effect on the eutectic Mg2Si phase. Quantitative EMPA analysis and elemental mapping revealed that the La-rich phase included Al, La, and Si and may be described as Al2LaSi2 phase. This phase shows a visible modifying effect on the eutectic Mg2Si phase, likely due to absorbing on the liquid/solid interface.

The application of low transformation temperature (LTT) wire can effectively reduce residual stress, without the need for preheating before welding and heat treatment after welding. The mechanism reduces the martensitic transformation temperature, allowing the martensite volume expansion to offset some or all of the heat-shrinking, resulting in reduced residual stress during the welding process. In this paper, commercial ER110S-G welding wire and LTT wire with chemical composition Cr10Ni8MnMoCuTiVB were developed to solve the problem of stress concentration. The microstructure of the LTT joint is mainly composed of martensite and a small amount of residual austenite, while the microstructure of the ER110S-G joint is mainly composed of ferrite and a small amount of granular bainite. The micro-hardness and tensile strength of the LTT joint is higher than that of ER110S-G joint; however, the impact toughness of the LTT joint is not as good as that of the ER110S-G joint. The martensitic phase transformation of LTT starts at 212 °C and finishes at around 50 °C, and the expansion caused by phase transition is about 0.48%, which is much higher than that of the base metal (0.15%) and ER110S-G (0.18%). The residual tensile stress at the weld zone of the ER110S-G joint is 175.5 MPa, while the residual compressive stress at the weld zone of LTT joint is −257.6 MPa.

Numerous processes take place in materials under the action of concentrated energy flows. The most important ones include heating together with the temperature misdistribution throughout the depth, probable vaporization on the surface layer, melting to a definite depth, and hydrodynamic flotation; generation of thermo-elastic waves; dissolution of heterogeneous matrix particles; and formation of nanolayers. The heat-based model is presented in an enthalpy statement involving changes in the boundary conditions, which makes it possible to consider melting and vaporization on the material surface. As a result, a linear dependence of penetration depth vs. energy density has been derived. The model of thermo-elastic wave generation is based on the system of equations on the uncoupled one-dimensional problem of dynamic thermo-elasticity for a layer with the finite thickness. This problem was solved analytically by the symbolic method. It has been revealed for the first time that the generated stress pulse comprises tension and compression zones, which are caused by increases and decreases in temperature on the boundary. The dissolution of alloying elements is modeled on the example of a titanium-carbon system in the process of electron beam action. The mathematical model is proposed to describe it, and a procedure is suggested to solve the problem of carbon distribution in titanium carbide and liquid titanium-carbide solution in terms of the state diagram and temperature changes caused by phase transitions. Carbon concentration vs. spatial values were calculated for various points of time at diverse initial temperatures of the cell. The dependence of carbon particle dissolution on initial temperature and radius of the particle were derived. A hydrodynamic model based on the evolution of Kelvin-Helmholtz instability in shear viscous flows has been proposed to specify the formation of nanostructures in materials subjected to the action of concentrated energy flows. It has been pointed out for the first time that, for certain parameters of the problem, that there are two micro- and nanoscale peaks in the relation of the decrement to the wavelength of the interface disturbance.