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High-entropy alloys (HEAs) strengthened by dispersed oxide nanoparticles are considered potential structural materials used in advanced nuclear reactors. Herein, a novel Y-Si-O nanoparticle-strengthened near-equiatomic FeNiMnCr HEA was prepared via the powder metallurgy method. Microstructural characterizations revealed that the oxide dispersion-strengthened (ODS) FeNiMnCr HEA consisted of the face-centered cubic (FCC) matrix and high-density Y-Si-O nanoparticles (Y 2 SiO 5 and Y 2 Si 2 O 7). The average diameter and volume fraction of the nanoparticles were counted to be 21.3 nm and 1.02%, respectively. The grain size was reduced from 10.13 μm of the FeNiMnCr HEA to 0.79 μm of the ODS FeNiMnCr HEA. The ODS FeNiMnCr HEA showed a yield strength of 1125 MPa, an ultimate tensile strength of 1137 MPa, and a moderate elongation of 8.3% at room temperature. At 500°C, the ODS FeNiMnCr HEA also had a high yield strength of 662 MPa. Theoretical calculation showed that the high strength of the ODS FeNiMnCr HEA was mainly due to the grain boundary strengthening, dislocation strengthening, and precipitation strengthening. ● A newly designed ODS FeNiMnCr HEA with enhanced strength-ductility combination was fabricated by a powder metallurgy method. ● The alloy contained nano-sized grain structure and nano-oxide particles including Y 2 SiO 5 and Y 2 Si 2 O 7. ● The grain boundary strengthening, dislocation strengthening, and precipitation strengthening were the main reasons for the high mechanical strength of the ODS FeNiMnCr HEA. [ABSTRACT FROM AUTHOR]

The great variability of the additively manufactured quality is becoming a major challenge to limit its wide application. Here, we combine the high-throughput molecular dynamics simulations with the artificial neural network to search for the high surface quality and damage minimization of the selective laser melted (SLMed) FeCrNi multi-principal-element alloy (MPEA), based on the complex microstructure obtained from experiment characterization. By adjusting the laser scanning speed and laser power density, a large amount of data related to the surface roughness, dislocation characteristics, and residual stress in the SLMed MPEAs is obtained for optimizing the SLM process. Atomic simulation results show that there are various degrees of Cr segregation under different processing parameters, which leads to the uncertainty of residual stress distribution and dislocation characteristics. Thus, the surface roughness and subsurface damage is highly sensitive to the SLM parameters. According to the training results of the artificial neural network, the laser scanning speed plays a more key role in regulating the surface integrity and subsurface damage in the SLMed MPEAs. The overall prediction results exhibit that the relatively slow laser scanning speed effectively reduces the residual stress. Importantly, a complex relationship between the SLMed parameters and properties is built. The current work provides a predictive recommendation to optimize the quality and process design of the SLMed MPEAs with high surface integrity and low subsurface damage. • High-throughput molecular dynamics simulations and the artificial neural network are combined. • Effect of the scanning speed, and laser power density on surface integrity of the SLMed MEPA is systematically analyzed. • A extremely complex relationship between the SLMed parameters and surface quality is quantitatively built. • Considering different weight coefficients of performance, the selection strategy of processing parameters is determined. [ABSTRACT FROM AUTHOR]

Additive/subtractive hybrid manufacturing technology is a new technology that combines product design, software control, and additive manufacturing (AM) with subtractive technology, which can realize the metallurgical bonding of dissimilar materials. In this study, hybrid parts made of two materials were fabricated by depositing CuCrZr on a 316 L stainless steel substrate by selective laser melting (SLM) technology. The microstructure and mechanical properties of the SLM-ed CuCrZr, 316 L matrix components and the 316 L/CuCrZr interface were studied. The microstructure of SLM-ed CuCrZr consisted of elongated columnar crystals that developed along the building direction, and the 316 L matrix material was characterised by large equiaxed grains. After the 316 L substrate was polished, there were no macroscopic cracks and only a few pores at the interface of 316 L/CuCrZr, and good metallurgical bonding was achieved. The complex and uneven metal flow occurred inside the molten pool because of the Marangoni effect under the action of the laser, resulting in drastic changes in the grain size at the interface. • CuCrZr alloy was fabricated by SLM on the 316 L substrate to achieve hybrid manufacturing. • Substrate surface state can influence interface of 316 L/CuCrZr. • Dendritic microcracks and pores are the main defects at the interface. • Difference in physical properties of materials and stress caused cracks. [ABSTRACT FROM AUTHOR]

Abstract Recently, high-entropy alloys (HEAs) reinforced with ceramic particles have attracted increasing attentions due to their excellent hardness, strength and wear resistance. In this study, AlCoCrFeNi-xNbC high-entropy alloy (HEA) coatings (x = 10, 20, 30 wt%) were prepared by laser cladding. The phase constituents, microstructure and mechanical properties of the HEAs were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), electron back-scatter diffraction (EBSD), transmission electron microscope (TEM), microhardness and wear resistance tests. Due to the high entropy effect, the AlCoCrFeNi HEAs composites comprise only simple BCC and FCC structure phases. The addition of NbC particles results in a decrease in the fraction of the FCC phase. NbC particles are mainly distributed at the grain boundary in the HEAs with the addition of NbC. NbC particles have an advantage on the inhibition of HEA grain growth due to a strong pinning effect. The microhardness and the wear resistance of HEA composite improved significantly with the addition of NbC particles. A good comprehensive mechanical properties was obtained at the HEA with the addition of 20 wt% NbC particles. For the 20 wt% NbC-adding HEA, the average Vickers hardness is 525 HV, the average friction coefficient value is 1.023 and the mass loss is 1.05 mg. Highlights • AlCoCrFeNi-xNbC high-entropy alloys are prepared and researched. • The addition of NbC particles restrains the formation of FCC phase. • The addition of NbC particles plays a role of grain refinement. • The addition of NbC particles increases the mechanical properties of the alloys. [ABSTRACT FROM AUTHOR]

Refractory high-entropy alloys (RHEAs) usually have a high strength at elevate temperatures. However, their oxidation resistance is inferior for practical applications. Here we proposed a eutectic design of compositionally complex eutectic alloy (CCEA) by adding 10 at. % Ta to the Al 2 Co 28 Cr 20 Fe 25 Ni 25 , the resulting alloy shows a good combination of mechanical properties and oxidation resistance, e.g. a yield strength of 764 MPa and an oxidation resistance rate of 0.0031 mg cm−2h−1 at 800 °C, which outperforms those of RHEAs. The excellent oxidation resistance is attributable to the formation of protective Cr 2 O 3 and CrTaO 4 layer at the surface, which prevents the matrix from further contact with O 2. • A novel, non-equiatomic compositional complex alloy with eutectic structure was prepared by powder metallurgy. • The alloy exhibited an oxidation rate of only 0.0031 mg cm−2h−1 at 800 °C. • The protective Cr 2 O 3 and CrTaO 4 layers generated during oxidation prevents further contact with O 2. • The Laves phase transformed into the Co 0.6 Ta 0.4 phase near the surface of the alloys above 1000 °C. [ABSTRACT FROM AUTHOR]

Different contents of carbon element (0-3 at.%) was added into CoCrFeMnNi high entropy alloys (HEAs) to prepare carbide-reinforced CoCrFeMnNi matrix composites. The effects of carbon on microstructures and mechanical properties were systematically studied. The CoCrFeMnNi HEA sheet without carbon showed fine recrystallized grains with a grain size of approximately 5 μm and contained Cr-rich sigma phase. The CoCrFeMnNiC x HEA sheets with 1.0 at.% and 3.0 at.% C presented fine recrystallized grains and a small fraction of elongated grains. A large number of nano-scaled carbides were observed in the carbon-containing HEA sheets. With the carbon content increasing from 0 at.% to 3.0 at.%, the strengthening of the α-fiber texture is more obvious, and tensile yield strength increased from 371 MPa to 792 MPa, however, the elongation decreased from 54% to 11%, respectively. The CoCrFeMnNiC 1 HEA sheet with a volume fraction of 2.9% nano carbides showed excellent balanced mechanical property, with tensile yield strength of 634 MPa and elongation of 38%. The increase of yield strength for the CoCrFeMnNiC 1 HEA was mainly ascribed to the combined effects of precipitation Orowan strengthening and dislocations strengthening. Precipitation Orowan strengthening is the primary strength contributor, with a value of approximate 157 MPa. • Cr-rich sigma phase was observed in C-free CoCrFeMnNi HEA sheet. • Nano-scaled M 23 C 6 carbides were found in C-containing CoCrFeMnNi HEA sheets. • The CoCrFeMnNiC 1 HEA sheet showed an excellent balance of strength and ductility. • Nano-scaled M 23 C 6 carbides provided the largest contribution to the increase of YS. [ABSTRACT FROM AUTHOR]

Abstract In this study, the effect of hot extrusion on the microstructure and anti-corrosion performance of LDHs (layered double hydroxides) conversion coating on AZ91D magnesium alloy was investigated by means of microscopic observation and electrochemical measurement. After hot extrusion, the refinement and rearrangement of the β-Mg 17 Al 12 phase promotes the microgalvanic effect in the formation process, and the increase of dislocation density, twin, grain boundary and texture accelerates the dissolution rate of the Mg matrix. Due to microstructural differences, the electrochemical activity of various specimens in the formation process can be ranked as the increasing series: as-cast < transverse < longitude. Therefore, a thicker and more compact LDH conversion coating is formed on the longitudinal section of the extruded alloy, indicating the highest anti-corrosion performance. Highlights • The CO 2 pressurization method is the most environmentally friendly method. • The microstructure of the alloy was combined with the formation mechanism. • The formation mechanism of effect for β-Mg 17 Al 12 phases was found. • The role of microgalvanic and electrochemical activity was confirmed. [ABSTRACT FROM AUTHOR]

Abstract Inconel 718 (IN718) superalloy has been fabricated by selective laser melting (SLM) technology, and the effects of the solution and double aging treatment on the microstructures and mechanical properties of the alloy have been studied. Under the same aging condition, the hardness of the IN718 superalloy first increased and then decreased with the increasing of the solution temperature. When the solution temperature was 980 °C, the average microhardness of the alloy was increased to 502 HV 0.2 , with 17.56% increase. With the solution temperature increasing, more short-rod δ phase (Ni 3 Nb) was precipitated at the grain boundaries and distributed homogeneously, and the γ′′ phase (Ni 3 Nb) and the γ′ phase (Ni 3 (Al, Ti)) were formed. The δ phase (Ni 3 Nb) can pin grain boundary, inhibit the grain growth and improve the mechanical properties. In addition, the corrosion resistance of the alloy decreased after heat treatment. After heat treatments, the formation of the second phase subsequently increased the number of corrosion microbatteries and reduced the anticorrosive ability of the alloy. Highlights • The anticorrosive ability of IN718 alloys decreased after heat treament. • The second phase improve the property, but decrease the anticorrosive ability. • Giving good comprehensive mechanical properties after heat treament. [ABSTRACT FROM AUTHOR]

Hot processing is extremely effective in optimizing the microstructure of γ-TiAl alloy, and hot deformation mechanism is the decisive factor in the microstructure evolution. In this paper, hot compression tests under different conditions were carried out to investigate the characteristics of hot deformation behavior and deformation mechanism of Ti-48Al-2 Nb-2Cr alloy with near-γ microstructure. The Arrhenius constitutive model was established, and the predicted flow stress agreed well with the experimental value. Hot processing maps at different strains were constructed. High power dissipation efficiency (η) region which was suitable for hot working appeared in the temperature range of 1180–1210 ℃ and the strain rate range of 0.001–0.01 s−1. At the strain rates from 0.001 to 0.1 s−1, dynamic recrystallization (DRX) served as the primary softening mechanism of the alloy, which was closely related to the disordered transformation of α 2 →α. At the temperature above T α 2 → α and the strain rate of 1 s−1, flow softening of the alloy was mainly controlled by dynamic recovery (DRV). The occurrence of DRX in the lamellar structure can be promoted by the elevated temperatures and reduced strain rates. Discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) appeared in the γ and α/α 2 phases of the alloy deformed at the conditions corresponding to high η region. With the decrease of η value, DRX nucleation of the alloy under the relevant conditions was chiefly dominated by DDRX. • Hot working window is optimized based on hot processing map and DRX mechanism. • Deformation mechanisms under different conditions are discussed. • Phase transformations of α 2 → α and γ → α play significant roles in the DRX behavior. • Relationship between DRX nucleation mechanism and η value is explored. [ABSTRACT FROM AUTHOR]

A novel non-equiatomic Al 15.85 Fe 11.15 Co 32.11 Cr 10.76 Ni 30.13 high entropy alloy (HEA) was fabricated via powder metallurgy (P/M) method. The Al 15.85 Fe 11.15 Co 32.11 Cr 10.76 Ni 30.13 HEA exhibits dual-phase microstructure consisting of face-centered-cubic (FCC) and body-center cubic (BCC) phases. The Al 15.85 Fe 11.15 Co 32.11 Cr 10.76 Ni 30.13 HEA has high compressive yield strength of 938 MPa and fracture strength of 3360 MPa, and still maintains moderate fracture strain higher than 40%. Also, the Al 15.85 Fe 11.15 Co 32.11 Cr 10.76 Ni 30.13 HEA has high strength of 518 MPa at the temperature of 600 °C. Microstructural characterization shows that a large number of L1 2 and B2 nanoprecipitates are uniformly dispersed in the FCC and BCC phases, respectively, contributing to the enhancement of the strength of the two phases. The effective combination of FCC and BCC phases eventually leads to the high strength of the Al 15.85 Fe 11.15 Co 32.11 Cr 10.76 Ni 30.13 HEA. This finding provides novel guidance for the development of high-performance structural materials with superior balance of strength and ductility for future industrial applications. • Novel Al 15.85 Fe 11.15 Co 32.11 Cr 10.76 Ni 30.13 HEA was prepared through powder metallurgy method. • The HEA exhibits dual-phase (FCC + BCC) microstructure. • Massive L1 2 and B 2 nanoprecipitates are embedded in the FCC and BCC phases, respectively. • The HEA exhibits high compressive yield strength of 938 MPa at room temperature. • The high strength is attributed to the hierarchically heterogeneous microstructure. [ABSTRACT FROM AUTHOR]

High temperature compressive deformation behaviors of a carbon-containing FeCoCrNiMn high entropy alloy (HEA) was investigated at temperatures ranging from 700 °C to 1000 °C, and strain rates from 0.001s −1 to 1s −1 . The microstructure mainly consists of fcc solid solution. The data obtained from the flow curves was employed to develop the constitutive equation, and the apparent activation energy (Q) was determined to be 385.43 kJ/mol. The size of the dynamically recrystallized grains decreased with the increasing value of Zener-Hollomon ( Z ) parameter. At high Z condition, dislocation cross slip can act as the main deformation mechanism. At intermediate Z condition, dislocation cross slip accompanied by discontinuous dynamic recrystallization (dDRX) becomes the main deformation mechanisms. At low Z condition, continuous dynamic recrystallization (cDRX) becomes the dominant softening mechanism. Nano carbides can be precipitated at intermediate Z and low Z condition, which prevent grain from growing up and promote the nucleation of DRX. [ABSTRACT FROM AUTHOR]

TiC reinforced titanium matrix composites are promising for advanced applications. Generally, the relative density of the composites and the interfacial bonding between the matrix and reinforced particles may have a great influence on the mechanical properties. This study presented the fabrication of the full-densified Ti-15Mo-xTiC (x = 1.5, 3.0, 4.5 wt%) composites through in-situ reactive sintering of Ti, Mo, and MoC powders and hot swaging process. Experimental results show the formation of TiC and the absence of MoC in the fabricated composites. After hot swaging, the TiC particles showed aligned distribution along the swaging direction, and exhibited well bonding with the β-Ti matrix. Increasing the TiC content leads to increase tensile strength and Young's modulus but decrease elongation. Ti-15Mo-4.5TiC offers and outstanding combination: ultimate tensile strength = 1290 MPa, yield strength = 1075 MPa, Young's modulus = 89 GPa, and tensile elongation = 3.1%. The strengthening effect is attributed to Mo solid solution in Ti matrix, β-Ti grain refinement, and TiC particle reinforcement. The specific contribution of each mechanism is quantitatively calculated, showing good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

Numerous theoretical and experimental studies suggest that the chemical ordering microstructure plays an important role for the strength and plastic deformation in the multi-principal-element alloy (MPEA). Despite the importance of this fact has been well confirmed, little is known about the influence of chemical ordering degree from the atomic scale to nano scale for the nanocrystal MPEA over a wide grain size range. In the present work, considering the abnormal local stacking fault energy originated from the heterogeneous chemical element concentration, the modified Hall-Petch relationship is elaborately established in MPEA, quite different from the traditional alloys. Additionally, the effects of the solid solution, local chemical ordering, and precipitation on the strengthening contribution and strain partition are evaluated. The increase of the chemical ordering degree improves the stacking fault energy and deformation gradient, as well as microrotation field. This trend leads to the yield strength owing to the formation of the slender shear bands. The geometry of the ordered structure is deformed and twisted to a certain extent, for the compatible plastic deformation. This work gives the atomic understanding of chemical-ordering-degree dominated strengthening mechanisms, to develop the strong and ductile MPEAs with desired properties. The data that support the findings of this study are available from the corresponding author upon reasonable request. • Influence of chemical ordering degree on strength is studied in MPEA over a wide grain size range. • Modified Hall-Petch relationship dependent upon stacking fault energy from heterogeneous chemical element is established. • Reasonable regulation of chemical ordering degree mediated deformation/strain partitioning could obtain high strength. [ABSTRACT FROM AUTHOR]

To improve the dynamic mechanical properties of the selective laser melting (SLM)-NiCrFeCoMo 0.2 high entropy alloy (HEA), dynamic impact experiments were carried out on this alloy with different characteristic molten pools. Melt pool structures of different special sizes can be obtained by adjusting the laser power and scanning speed during the SLM process. In this work, the split-Hopkinson pressure bar (SHPB) is used to conduct dynamic impact on the SLM-NiCrFeCoMo 0.2 HEA samples with different molten pool size. The X-ray diffractometer (XRD), the scanning electron microscope (SEM), the electron probes micro-analyzer (EPMA) and the transmission electron microscope (TEM) were used to characterize the microstructure and deformation characteristics of the of the molten pool. The SLM-NiCrFeCoMo 0.2 HEA shows high impact energy absorption density and compressive strength at high strain rate. Volume energy density (VED) refers to the power delivered by the laser per unit volume of material during a SLM process, which can affect the size of the molten pool formed. Mo-rich σ phase precipitations are distributed near the molten pool boundary. In the cooling stage of the SLM process, the center of the molten pool has a faster cooling rate than the molten pool boundary, so area near the boundary stays in the temperature range where the precipitation occurs for a longer time, which is the reason why the precipitates are concentrated near the boundary. The precipitation strengthening in the SLM-NiCrFeCoMo 0.2 HEA is considered by measuring the relationship between the molten pool structure and the precipitation distribution, considering the material as a composite of the precipitation dense region (PDR) and the precipitation free region (PFR), and the strength contribution of precipitation is estimated by mixing rules. [Display omitted] • Control the size of molten pool by adjusting the input volume energy density. • Mo-rich precipitates are concentrated near the molten pool boundary. • The uneven cooling rate causes the concentrated distribution of precipitates. • The precipitate around molten pool boundary improves the dynamic mechanical property. [ABSTRACT FROM AUTHOR]

In this study, AlCrFeNiMn x high-entropy alloy coatings (x = 0, 0.5, and 1) were successfully prepared on a copper substrate by laser cladding. The influence of Mn addition was investigated on the phase constituent, microstructure, and mechanical properties of the HEA coatings. Due to the high-entropy effect, the AlCrFeNiMn x HEA coatings comprised only simple BCC and FCC structure phases. Moreover, the addition of Mn elements inhibited the formation of FCC phases due to the variation of ΔG mix , ΔH mix , δ, ∆x and VEC value. The addition of Mn leads to solute effect, so the grains were significantly refined with an increase in Mn content. When the Mn content was 0.5, good comprehensive mechanical properties were obtained with an average Vickers hardness of 625 HV, average friction coefficient value of 0.42, and a mass loss of 1.02 mg. • AlCrFeNiMn x HEA coatings are prepared on a copper substrate by laser cladding. • The addition of Mn inhibited the formation of FCC phase of the AlCrFeNiMn x HEAs. • The addition of Mn can significantly refine grains of the AlCrFeNiMn x HEAs. • The addition of Mn can improve the mechanical properties of the AlCrFeNiMn x HEAs. [ABSTRACT FROM AUTHOR]

• Seven AlSi10Mg alloys with different construction angles were prepared and researched. • The grains in vertical planes change from columnar grains to irregularly arranged grains, and then to equiaxed grains. • The AlSi10Mg exhibites mechanical property anisotropy that is a result of grain structure, dispersed Si, and residual stress. In this study, seven AlSi10Mg bulks with different construction angles (0°, 15°, 30°, 45°, 60°, 75°, and 90°) were fabricated by selective laser melting (SLM). The effects of different construction angles on the microstructure and mechanical properties of AlSi10Mg alloys were investigated. Increasing the construction angle changed the laser track segments from an ellipse to a semi-ellipse and then to fish-scale, specifically again from a semi-ellipse to an ellipse, due to the decrease of the laser radiation area. Meanwhile, the grains in the vertical planes changed from columnar grains to irregularly arranged grains, and then to equiaxed grains. The 45° sample exhibited the highest hardness of 154.44 HV 0.1. The 60° sample had a good combination of strength and plasticity with a tensile strength of 463.54 MPa, yield strength of 283.37 MPa, and elongation of 9.25%. The observed mechanical property anisotropy of the current AlSi10Mg alloy was a result of the pores, equiaxed grain structure, ultra-fine equiaxed sub-grains, and working hardening. In addition, the difference in the sample microstructures was attributed to the construction angles and deposited layer area. [ABSTRACT FROM AUTHOR]