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In this paper, the microstructure and mechanical properties of Al-6.5Si-5.5Cu-0.2Zr-0.01Sr-0.06Ti-0.2Ce cast aluminum alloys were investigated in multistage solid solution systems. The microstructure of the alloy was characterized using an optical microscope (OM), scanning electron microscope (SEM), energy-dispersive spectrometer (EDS), x-ray diffraction (XRD) and transmission electron microscope (TEM), respectively. The hardness and conductivity of the alloy were measured using a Vickers hardness and eddy current conductivity testers, respectively, and the tensile properties were described by a drawing machine. The results showed that the mechanical properties of the alloy are the worst under the four-stage solid solution system (G1). With the increase in multistage solution temperature and holding time, θ phase (Al2Cu) was gradually dissolved into α-Al matrix to enhance the effect of dislocation strengthening. When the solution temperature reached 510 °C, the mechanical properties of the alloy were the best, and the tensile strength and elongation were increased to 354.90 MPa and 9.02%, respectively. With the increase in temperature, eutectic Si agglomeration and large area of insoluble phase between metals were found, resulting in the decrease in mechanical properties. [ABSTRACT FROM AUTHOR]

The paper reports on the atomic investigation about β phase in Mg 96 Gd 2 Y 1 Ni 1 alloy by using the first-principles study and the high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) corrected by atomic Cs. By using HAADF-STEM, the rectangular β phases were observed in the underage and peak aging stages in Mg 96 Gd 2 Y 1 Ni 1 alloy. The β phase could be precipitated from the previously precipitated β phase, and the β phase grew in steps when it was precipitated. A special transition structure of three atomic layer thicknesses was first observed at the edge of the β phase and the structure of this interface is probably as the β/Mg 1 interface for the analysis of thermodynamic characterization and electronic characterization. The β' phase and the β H structure were precipitated only at the edge of the length directions of the β phase. The β' phase continues to grow into a β phase directly without the formation of β 1 phase, resulting in an increase in the length of the β phase, which is discovered for the first time. [ABSTRACT FROM AUTHOR]

Cu additions notably strengthen Al-Mg-Si and Al-Si-Mg alloys due to the dense precipitation of quaternary nano precipitates during ageing. However, the chemical evolution and mechanical behaviors of the quaternary micro-scale Q constituent phase occurring in cast and homogenized states have rarely been studied. Meanwhile, there exists a type of AlCuMgSi cluster in the cast state, which has been regarded as Q particles. The accurate identification of phase constituents is the basis for the future design of alloys with better performance. In our work, this type of cluster was revealed to consist of α-Al, θ-Al2Cu, Q, and Si phases through micro-to-atomic scale studies using scanning and transmission electron microscopes. The skeleton of the dendrite was θ phase. The second phases in the dendritic eutectic cluster dissolved quickly during a 4 h homogenization at 550 °C. The Q phase was found to effectively absorb the Fe impurities during casting and homogenization. As a result, the formation of other harmful Fe-rich intermetallics was suppressed. These Q constituent particles were observed to break into separate pieces in an intermediately brittle manner when compressed in situ in a scanning electron microscope. These findings provide insights into the thermodynamic modeling of the Al-Mg-Si-Cu system and alloy design. [ABSTRACT FROM AUTHOR]

Mg-3Sn-1Mn-xLa alloy bars were prepared using backward extrusion, and the effects of the La content on the microstructures and mechanical properties of the alloy were systematically studied using an optical microscope (OM), X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), and tensile tests. The results of this research show that the Mg2Sn phases were mainly formed at the α-Mg grain boundaries and within the grains in the Mg-3Sn-1Mn alloy. After adding a certain amount of La, the plate-shaped MgSnLa compounds consisting of Mg17La2, Mg2Sn, and La5Sn3 gradually disappeared in the α-Mg matrix and grain boundaries. With an increase in La content, the Mg2Sn phase in the crystal was gradually refined and spheroidized. When the content of La reached 1.5%, the tensile strength of the alloy reached 300 Mpa and the elongation reached 12.6%, i.e., 25% and 85% increases, respectively, compared to the Mg-3Sn-1Mn alloy. The plate-shaped compound of Mg-3Sn-1Mn-1.5La had an average length of 3000 ± 50 nm, while the width was 350 ± 10 nm. Meanwhile, the extruded alloy's grain size was significantly refined, and there were many small cleavage steps and dimples in the fracture surface of the alloy. When the La content reached 2%, the alloy performance showed a downward trend due to the coarsening of the grains. The formed plate-shaped MgSnLa compounds and Mg2Sn phases were consistent with the α-Mg matrix. They effectively pinned the dislocations and grain boundaries, which is the main reason for strengthening the mechanical properties of extrusion alloys. [ABSTRACT FROM AUTHOR]

Novel HEAp-Ti/Al laminated composites embedded with particles of the high-entropy alloy Al0.5CoCrFeNi (HEA) were fabricated by vacuum hot-press sintering at 730 °C. The phase composition and microstructure of the composites were studied with X-ray diffractometer (XRD), scanning electron microscope SEM, energy dispersive spectrometer (EDS), transmission electron microscope (TEM), and electron backscattering diffraction (EBSD) techniques. At this temperature, it has been observed that Al3Ti intermetallic compound is the favored phase and the reaction results in the dispersion of Al3Ti in the original Al layer. A large number of interfaces are formed between Al3Ti and Al. The deformed Al3Ti grains are concentrated in the interface near the Ti side. The mechanical properties, including tensile and compressive properties at room temperature, were analyzed. The tensile test results indicate that the composite exhibited an average tensile strength of 258 MPa and an average yield strain of 9.86%. Compression test results show that when a load perpendicular to the layer is applied, the yield strain and yield stress of the material are 9.67% and 474.09 MPa, respectively. Moreover, under a load parallel to the layer, the material fails due to interfacial debonding. [ABSTRACT FROM AUTHOR]

In this paper, Fe-Cr-C-N-Al-Y wear-resistant surfacing alloy was prepared by open-arc surfacing with self-shielded flux-cored wire. The wear properties of the surfacing alloy were analyzed using an MLS-23 rubber wheel wet sand wear tester. The phase composition and microstructure of the surfacing alloy were analyzed using X-ray diffraction, scanning electron microscope, electron backscatter diffraction and transmission electron microscope; the strengthening mechanism and wear mechanism of the alloy were discussed. The results show that the microstructure of Fe-Cr-C-N-Al-Y surfacing alloy is composed of M + γ-Fe + M7C3 + AlN. When the content of nano-Y2O3 is 0.456 wt.%, the formability of the surfacing alloy is the best, and the wetting angle is the smallest, which is 50.8°; AlN and M7C3 precipitate the most, and the microstructure grain is the smallest. At this time, the hardness value of the surfacing alloy is up to 62.3 HRC, which is 11.8% higher than that of the unmodified surfacing alloy. The minimum wear weight loss is 0.125 g, and the wear resistance is increased by 41.86%. The wear mechanism of the surfacing alloy is mainly a plastic deformation mechanism, and the material removal processes are microcutting and furrow wear. This study provides theoretical guidance for refining primary carbides and improving the wear resistance of high chromium cast iron. [ABSTRACT FROM AUTHOR]

In this study, the effects of magnesium addition on the microstructure and comprehensive properties of Al-5Si-5.3Cu-0.3Sr-0.2Zr-0.2Y-0.06Ti alloys were investigated by optical microscope, scanning electron microscope, transmission electron microscope, hardness tester, and tensile testing machine. It is found that the addition of magnesium increases the number of undissolved particles in the alloy. However, on the one hand, magnesium addition refines the θ′ phase and increases its number density in the alloy. On the other hand, it generates a smaller Q′ phase. Both phases can enhance the precipitation strengthening and dislocation strengthening of the alloy. In addition, adding magnesium reduces the width of the precipitation-free zone (PFZ) and changes the distribution of grain boundary precipitates (GBPs). At 1% magnesium addition, the dislocation strengthening and precipitation strengthening effects of the θ′ and Q′ phases were the best, the width of PFZ was the smallest, and the GBPs were discontinuously arranged along the PFZ. Therefore, a high-strength, high-hardness, and intergranular corrosion-resistant cast aluminum alloy with dense structure, a tensile strength of 364.4 MPa, elongation of 4.87%, hardness of 145.4 HV, and intergranular corrosion grade of 3 was obtained. [ABSTRACT FROM AUTHOR]

In this study, the influence of the high-pressure torsion (HPT) processing parameters and solution treatment (ST) on the corrosion and tribocorrosion behavior of CoCrMo (CCM) alloys was investigated for possible usage in biomedical applications. The corrosion behavior of the CCM alloys was investigated by using potentiodynamic scanning (PDS) and electrochemical impedance spectroscopy (EIS) tests. Tribocorrosion tests were carried out in a reciprocating ball-on-plate tribometer at 1 Hz, 1 N load, and 3 mm stroke length for 2 h. All electrochemical measurements were performed using a potentiostat in standard phosphate-buffered saline (PBS) solution at body temperature (37 ± 2 °C). The samples were characterized by using a scanning electron microscope (SEM), transmission electron microscope (TEM), optical microscope (OM), and X-ray diffraction (XRD). The deepness and width of wear tracks were examined by using a profilometer. The results showed that HPT and ST processes did not affect significantly the corrosion resistance of samples. However, the ST-treated samples had a higher material loss during sliding in standard phosphate-buffered saline (PBS) at body temperature as compared to HPT-treated samples. [ABSTRACT FROM AUTHOR]

An amount of 100 dpa Si2+ irradiation was used to study the effect of transmutation rhenium content on irradiated microscopic defects and hardening in W-xRe (x = 0, 1, 3, 5 and 10 wt.%) alloys at 550 °C. The increase in Re content could significantly refine the grain in the W-xRe alloys, and no obvious surface topography change could be found after high-dose irradiation via the scanning electron microscope (SEM). The micro defects induced by high-dose irradiation in W and W-3Re alloys were observed using a transmission electron microscope (TEM). Dislocation loops with a size larger than 10 nm could be found in both W and W-3Re alloy, but the distribution of them was different. The distribution of the dislocation loops was more uniform in pure W, while they seemed to be clustered around some locations in W-3Re alloy. Voids (~2.4 nm) were observed in W-3Re alloy, while no void was investigated in W. High-dose irradiation induced obvious hardening with the hardening rate between 75% and 155% in all W-xRe alloys, but W-3Re alloy had the lowest hardening rate (75%). The main reasons might be related to the smallest grain size in W-3Re alloy, which suppressed the formation of defect clusters and induced smaller hardening than that in other samples. [ABSTRACT FROM AUTHOR]

High-cycle fatigue (HCF) is a critical property of metastable β Ti alloys in aerospace applications. In this work, the HCF behavior and corresponding microscale deformation mechanisms of a metastable Ti-5Al-5Mo-5V-1Cr-1Fe (Ti55511) alloy with a basket-weave structure were investigated. HCF and its deformation mechanisms of a Ti55511 alloy were systematically studied in the deformed condition by using a scanning electron microscope (SEM), a transmission electron microscope (TEM), and electron backscatter diffraction (EBSD). It was found that the Ti55511 alloy exhibited an excellent HCF strength (107 cycles, Kt = 1, R = 0.06) of 738 MPa. The fractographic investigation demonstrated that fatigue striations and secondary cracks were the main features in the crack initiation zone. Dislocation analyses indicated that the HCF deformation of the basket-weave microstructure was mainly affected by the dislocation slipping of the primary α (αp) phase. In addition, the dislocation pile-up at the αp/βtrans interface led to crack initiation. EBSD analyses indicated that the prismatic type slip system of the αp phase was preferentially activated during the HCF deformation process of the Ti55511 alloy, followed by the basal type and pyramid type systems. [ABSTRACT FROM AUTHOR]

In the process of directional solidification, the degree of element segregation can be changed by altering the drawing rate to affect the phase transformation behavior of the alloy. In this paper, four kinds of MnNi alloy specimens were prepared by directional solidification at different drawing rates. The phase transformation behavior of the alloy was studied by differential scanning calorimetry (DSC), X-ray diffraction (XRD), thermal expansion analysis and dynamic mechanical analysis (DMA). The microstructure of the alloy was observed by metallographic microscope, scanning electron microscope and transmission electron microscope. The results show that the microstructure of directionally solidified MnNi alloy has the characteristics of polymorphy. There are multi-scale twins from micron to nanometer in the alloy, and their coordinated movement makes the internal friction of twins 3-6 times than that of rolled alloy. It is found that during heating, the alloy undergoes fct1→fcc phase transformation in the interdendritic spacings of Mn-poor region while fct2→fco→fcc multi-stage phase transformation occurs in Mn-rich dendrite. This multiply phase transformation behavior makes the damping capacity of directionally solidified MnNi alloy 2-6 times than that of rolled MnNi alloy in a wide temperature range. [ABSTRACT FROM AUTHOR]

As promising substitutes for Cu-Be alloys, Cu-Ni-Si series alloys have been investigated intensively concerning their mechanical and electrical properties but without much attention on their corrosion performance. Herein corrosion behaviors and mechanisms of the supersaturated and peak-aged CuNiSiCr alloys are investigated using salt spray test, x-ray diffraction, scanning and transmission electron microscopes. The corrosion rate of the aged sample is lower than that of the supersaturated one due to forming a denser protective corrosion product, Cu2O. Theoretical analyses indicate that the Cu2O film grows by oxidization of the matrix and its granular size is greatly influenced by the precipitates. The second corrosion product Cu2(OH)3Cl/CuCl2·3Cu(OH)2 forms by consuming the oxide Cu2O, which will induce pitting and deteriorate the corrosion resistance. Based on the obtained results, guidance concerning the composition and treatment optimization is provided for enhancing the anti-corrosion capability of the CuNiSiCr alloys. [ABSTRACT FROM AUTHOR]

Device-related infection or inflammatory and stress shield are still the main problems faced by titanium alloy implants for long-term implantation application; therefore, it is of great significance to design an alloy with low elastic modulus and good antibacterial properties as well as good biocompatibility. In this paper, Ti-13Nb-13Zr-xCu(x = 3, 7 wt.%) alloys were designed and prepared to reveal the influence of Cu content on the elastic modulus and antibacterial property. X-ray diffractometer, metallographic microscope, scanning electron microscope, and transmission electron microscope were used to study the phase transformation, microstructure, mechanical properties, antibacterial properties, and cytotoxicity of the alloys. The experimental results have demonstrated that the antibacterial performance and the elastic modulus were significantly improved but the corrosion resistance deteriorated with the increase of the copper content. Ti-13Nb-13Zr-3Cu with a low modulus of 73 GPa and an antibacterial rate of over 90% against Staphylococcus aureus (S. aureus) exhibited great potential as a candidate for implant titanium in the future. [ABSTRACT FROM AUTHOR]

The topologically close-packed (TCP) μ phase is usually known as an undesirable precipitation in highly alloyed Ni-base superalloys and steels. However, the ultrastrong μ phase with micron/nano-scale distribution plays a key role in driving the emergence of self-sharpening in our recently developed WMoFeNi high-entropy alloy (HEA). Herein, a detailed study is carried out to understand the substructure and atomic occupation of the μphase by scanning electron microscope (SEM) and aberration-corrected transmission electron microscope (ACTEM). The Fe/Ni and W/Mo element pairs are equivalent in the μ phase structure. Moreover, the elements in μ phase exhibit a near-equiatomic ratio, and the μ phase can grow during annealing at 1150 °C. (0001)μ and ( 1 1 ¯ 02 )μ twins are the main substructures of the μ phase, and their atomic configurations and twinning mechanisms are investigated. The geometrical structural analysis of μ phase possesses a great significance for the design of self-sharpening HEAs. [ABSTRACT FROM AUTHOR]

With the development and wide application of nickel-based single-crystal superalloys, the effect of Ru on the microstructure stability and high-temperature properties of superalloys is becoming increasingly important. In this study, the effect of Ru on the evolution of the γ′ phase in Ni-Al-Ru ternary alloys during aging treatment was analyzed, using a scanning electron microscope and transmission electron microscope, combined with energy-dispersive spectroscopy. The relationship between chemical partition behavior and γ/γ′ lattice misfit was investigated in detail. During the aging process, Ru addition suppressed the growth rate and rafting process of γ′ precipitates, while the effect of Ru on hindering γ′ phase growth was reduced when the Ru content was over 3 at%. Ru preferentially partitioned to the γ phase, and its partitioning ratio to the γ phase increased with a variation in Ru content from 1 at% to 3 at% and decreased for the NiAl6Ru alloy. Additionally, the lattice misfit of all alloys was positive and reduced with the increase in Ru content, which hindered the Ru atoms to diffuse into the γ phase and promoted the shape of γ′ precipitates to change from cubic to spherical. [ABSTRACT FROM AUTHOR]

This study was conducted with a high level of thoroughness. X-ray diffraction (XRD), Scanning Electron Microscope (SEM), and Transmission Electron Microscope (TEM) were used to analyze the phase composition and microstructure of the AM-2024Al and the RO-2024Al. The hardness and porosity of the AM-2024Al, as well as the bonding strength between AM-2024Al and RO-2024Al, were also investigated. Furthermore, the corrosion and tribocorrosion properties and failure mechanisms of the AM-2024Al and the RO-2024Al were systematically and thoroughly compared and analyzed. The results of this comprehensive study revealed that the AM-2024Al displayed a similar phase structure and higher hardness in comparison to the RO-2024Al, and the AM-2024Al was compact and tightly bound to the RO-2024Al with a bonding strength of over 55.5 MPa. Furthermore, the AM-2024Al exhibited better corrosion resistance under PDP (potentiodynamic polarization) corrosion and similar wet sliding wear resistance under an approximate pure friction process (OCP corrosion, namely open circuit potential corrosion) and tribocorrosion compared with the RO-2024Al. These findings provide a high level of confidence in the potential of cold spraying additive manufacture 2024Al as a reliable way to repair damaged RO-2024Al. [Display omitted] • The tribocorrosion is first reported for the CS additive manufacturing 2024Al alloy. • The AM-2024Al exhibits superior anti-corrosion compared to the RO-2024Al. • The AM-2024Al has a comparable tribocorrosion resistance to the RO-2024Al. • Splats (AM-2024Al) and grains (RO-2024Al) are partly peeled during the tribocorrosion. • A plastic deformation layer was generated in the wear track surfaces of the two 2024Al. [ABSTRACT FROM AUTHOR]

The microstructure, phase composition, precipitates evaluation, casting, and mechanical properties of the novel cast Al-4Cu-2.1Er-1Mg-0.2Zr-0.2Cr-0.15Fe-0.15Si-0.1Ti alloy were analyzed using by optical microscope, scanning and transmission electron microscopes, differential scanning calorimetry, thermodynamic calculations, hot cracking and mechanical properties measurements. The positive effect of Cr as a substitution of Mn on plasticity and precipitation strengthening was demonstrated. The 0.2Zr, 0.2Cr and 0.1 Ti as a grain refiners provide a fine grain size of 25 μm in the as-cast state due to primary Al 75–80 Cu 10–12 Er 3–4 Cr 7 phase particles formation as a nucleation centers of Al. The hot cracking index (HCI) of the AlCuErMgCr alloy was 12–14 mm which is similar with HCI of the cast Al-Si-Cu-Mg alloys. The good casting properties in the AlCuErMgCr alloy achieved due to a fine grain structure and narrow solidification range. The contribution of the Al 3 (Zr,Er) (40 nm), Al 45 Cr 7 (6 nm), and S'(θ') (100/5 nm) precipitates is 38.5 MPa, 140.4 MPa, and 198.9 MPa and the calculated contribution from dislocation and precipitates is 262.3 MPa. The ultimate tensile strength (UTS) and elongation (El.) of the AlCuErMgCr alloy are 372 MPa and 6% which is higher in 16.6% and 150%, respectively, than in the Mn-containing alloy. Novel alloy has an excellent combination of yield strength (YS) and plasticity at 20–250°C. The YS and El. are 301 MPa and 6% and 225–250 MPa and 4.6–11.5% at 20 and 200–250°C, respectively. The rupture strength at 250°C after 100 h (σ 100 250) is 106 MPa. Mechanical and casting properties of the novel alloy are superior to the properties of commercial 201.0 (Al-Cu-Mn-Mg-Ag-Ti) alloy. • Cr, replacing Mn, had a positive impact on both plasticity and precipitation strengthening. • 0.2Zr, 0.2Cr, and 0.1Ti as grain refiners resulted in the formation of primary Al 75–80 Cu 10–12 Er 3–4 Cr 7 phase particles. • The AlCuErMgCr alloy displayed an ultimate tensile strength (UTS) of 372 MPa and an elongation (El.) of 6%. • The rupture strength at 250°C after 100 hours was determined to be 106 MPa. [ABSTRACT FROM AUTHOR]

The microstructure and properties of the aged Cu-Cr-Zr-Nb alloy were studied by means of hardness tester, universal tensile testing machine, conductivity meter, X-ray diffraction, scanning electron microscope, and transmission electron microscope. The results indicated that the hardness and TS (tensile strength) of the Cu-Cr-Zr-Nb alloy increased first and subsequently decreased with increasing the aging temperature. Nevertheless, the electrical conductivity is gradually increasing. The aged Cu-Cr-Zr-Nb alloy was mostly made up of Cu matrix, Cr particles, Cr 2 Nb, and CuZr compounds. Due to the effects of dislocations accumulated by cold drawing and twins produced during the aging process, the softening temperature of the alloy reached 590 ℃. When the Cu-Cr-Zr-Nb alloy was aged at 490 ℃, < 111 > replaced < 110 > in the optimal orientation of the alloy, and the KAM (kernel average misorientation) value inside the alloy was the largest. The alloy exhibited great comprehensive properties at 490 ℃ for 1 h, with a hardness of 144.4 HBW, a TS of 521 MPa, and an electrical conductivity of 78.3%IACS. The contribution value of YS (yield strength) at different aging temperatures was further calculated. The computational results showed that precipitation strengthening was the main strengthening mechanism of the Cu-Cr-Zr-Nb alloy, and fine-grained strengthening and dislocation strengthening simultaneously played a supplementary role. • Due to the effects of dislocations accumulated by cold drawing, precipitation strengthening of Cr and twins produced during the aging process, the softening temperature of the Cu-Cr-Zr-Nb alloy reaches 590 ℃. • The Cu-Cr-Zr-Nb alloy exhibits great comprehensive properties at 490 ℃ for 1 h, with a hardness of 144.4 HBW, a tensile strength of 521 MPa, and an electrical conductivity of 78.3 %IACS. • The computational results show that precipitation strengthening is the main strengthening mechanism of the Cu-Cr-Zr-Nb alloy. [ABSTRACT FROM AUTHOR]

Thermite reduction as one of the most promising methods for preparation of TiAl alloy, the metal-slag separation behavior in the whole process of chemical reaction, including both the alloy components and slags to be removed, is still ambiguous. In this paper, the two-step nucleation mechanism was applied to investigate the metal-slag separation behavior in the thermite reduction process for the preparation of TiAl alloy, which was confirmed by thermodynamic calculation based on density functional theory. Moreover, the component of products acquired from thermite reaction was characterized and analyzed by x-ray diffractometer, scanning electron microscope and transmission electron microscope, respectively. According to the results of the experiment and calculation, the formation and separation mechanism between alloy and slag in the process of preparing TiAl alloy via thermite reduction is visualized, which is universal in the whole metallurgical procedure involving redox and slag-making process. [ABSTRACT FROM AUTHOR]

In this paper, the hot deformation behavior of A357 alloy was investigated by hot compression tests. Isothermal hot compression simulation tests for A357 alloy were carried out at the conditions of deformation temperature of 350-470 °C, strain rate of 0.001-10 s−1 and engineering strain of 50%. Based on the Prasad instability criterion and dynamic material model, the hot processing maps of A357 alloy were constructed. The microstructure of compressed samples at different areas of the hot processing map was characterized by metallographic and scanning electron microscope and transmission electron microscope. The experimental results showed that the unstable processing zone of A357 alloy was mainly distributed in the high strain rate (10 s−1) and low-temperature (350, 380 °C) region. With an increase in the strain, the unstable zone expanded from low temperature to high temperature (470 °C). The ideal deformation conditions were deformation temperatures of 380-410 °C and strain rates of 0.001-0.01 s−1, and deformation temperatures of 440-470 °C and strain rates of 0.01-1 s−1. When the A357 alloy was extruded with the optimal hot processing parameters, the results suggested that hot extrusion could make the microstructure uniform and fine, thereby improving mechanical properties, especially when the elongation was up to 19.5% higher than the as-cast A357 alloy. [ABSTRACT FROM AUTHOR]

The Cu-Cr-Nb alloys were prepared by vacuum induction melting with different cooling methods. The effects of niobium contents and different cooling methods on the microstructures and properties of these alloys were investigated. The microstructures were characterized by optical microscope, scanning electron microscope and transmission electron microscope. The electrical conductivity, hardness and the tensile strength of Cu-Cr-Nb alloys were tested as well. The results showed that the as-cast microstructures of Cu-Cr-Nb alloys consist of primary α phase dendritic and eutectic phase. With the addition of element Nb, the microstructures were refined and the secondary dendritic arm spacing obviously decreased. Compared with the furnace cooling, the homogeneous and refined microstructures were obtained by the graphite mold, and the hardness of the alloys is enhanced greatly. After the heat treatment, two reinforcing phases of Cr and Cr2Nb are precipitated from the copper matrix. The comprehensive properties were obtained when the Nb content is 0.4%. The Cu-1.2Cr-0.4Nb alloy performed by direct aging treatment without solution treatment exhibits the higher performance, the hardness and electrical conductivity are 143HB and 84%IACS, respectively. In addition, the tensile strength and the elastic limit of the Cu-1.2Cr-0.4Nb alloy can reach up to 413.0 and 238 MPa. [ABSTRACT FROM AUTHOR]

There has been great attention on high-entropy alloys (HEAs) over the past decade. Unlike conventional alloy systems, HEAs commonly include at least five principal elements with equiatomic or near-equiatomic ratio. HEAs with their superior mechanical, magnetic, and thermal properties are promising materials for critical engineering applications. Medium-entropy alloys (MEAs), which consist of less than five principal elements, have very similar structural features with HEAs such as robust thermodynamic stability and exceptional mechanical performance. The insights of MEAs have not been fully revealed yet. In the present study, novel MEAs (Cu20Ni20Al30Ti30, Cu25Ni25Al25Ti25, Cu34Ni22Al22Ti22, and Cu35Ni25Al20Ti20) have been designed using thermo-physical calculations and Thermo-Calc software. These MEAs were then produced using copper heart arc melting and suction cast into cylindrical rods with 3 mm diameters. X-ray diffraction (XRD), optical microscope (OM), transmission electron microscope (TEM), scanning electron microscope (SEM), and energy-dispersive spectroscopy (EDS) were used for structural characterization. The corresponding results reveal that the Cu20Ni20Al30Ti30, MEA, consists of a body-centered cubic (BCC-B2) phase with intermetallic compounds (ICs), whereas Cu25Ni25Al25Ti25 has single BCC-B2 phase. When the amounts Cu and Ni are increased, system drives itself toward a face-centered cubic (FCC) structure. A dual BCC and FCC composite Cu35Ni25Al20Ti20 has been detected as the most promising MEA among the others with 820 and 1338 MPa measured yield and compressive strength, respectively. [ABSTRACT FROM AUTHOR]

Optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and tensile machine were used to characterize the microstructures and mechanical properties of as-forged and aged Mg-9.5Gd-3.8Y-0.6Zr alloys. The results show that a novel kind of dislocation arrays, comprising parallel arranged dislocations, were obtained in the forged alloy. The arrays tend to extend parallel and are heterogeneously distributed with adjacent distances varying from 0.3 µm to 1.4 µm. After aging the alloy at 265 °C, a large number of preferential-oriented β' phases were precipitated on the dislocation arrays, forming a structure of "precipitation chains" (PCs), which results in simultaneous increments of strength and ductility. [ABSTRACT FROM AUTHOR]

Al0.4FeCrNiCox (x = 0, 0.25, 0.5, 1.0 mol) high-entropy alloys are developed by arc melting route to investigate the effect of cobalt content on thermal, mechanical, and microstructural properties. The phase, microstructure, and chemical composition are analyzed using x-ray diffraction, transmission electron microscope, and scanning electron microscope with attached energy-dispersive x-ray spectrometer. The obtained results have shown that the Al0.4FeCrNiCox (x = 0-0.5 mol) high-entropy alloys form a simple FCC + BCC-type solid solution and Al0.4FeCrNiCox=1 HEA forms a single-phase FCC structure. The compressive yield strength, microhardness, and thermal conductivity are observed to decrease from 965.22 to 233.37 MPa, 253.6 to 155.6 HV, and from 4.87 to 2.674 W/mK, respectively, whereas the electrical resistivity is observed to increase from 150.30 to 273.74 µΩ-cm with the addition of cobalt from x = 0-1 mol. Differential scanning calorimetry analysis has indicated that the Al0.4FeCrNiCox (x = 0, 0.25, 0.5, 1.0 mol) high-entropy alloys are thermally stable up to 1000 °C. [ABSTRACT FROM AUTHOR]

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The aim of the present study was to assess the influence of the milling time (10 h, 15 h and 20 h) on the structure and properties of Ti-10Ta-8Mo (wt.%) and Ti-10Ta-8Mo-3Sn (wt.%) alloys for potential biomedical application. In addition, the influence of the addition of 3 wt% Sn on the structure and properties of the milled and sintered materials was investigated. X-ray diffraction confirmed the partial synthesis and formation of the β phase during the milling process. The transmission electron microscope analysis of the bright and dark field images and the diffraction image proved the nanocrystalline nature of the material after being subjected to 20h milling duration. The scanning electron microscope observation of the sintered samples confirmed the influence of the milling time and presence of Sn on the microstructure of the obtained material. Furthermore, a small addition of Sn led to better size homogenization by establishing a better balance between the cold-welding and agglomeration processes. At the same time yielding different structures of pores for the sintered samples. The dry sliding tests revealed the excellent friction properties and wear rate of the samples previously milled for 15 h, with the addition of Sn. • The milling and sintering enables the preparation of porous Ti-Ta-Mo-(Sn) alloys. • The presence of Sn led to the finer, flake-like particles after ball milling. • The α, β and Mo nanocrystalline phases were prepared by ball milling. • For the Sn15 + HT sample the friction process and a COF that was three times lower. • The sample Sn15 + HT sample was characterized by the lowest specific wear rate. [ABSTRACT FROM AUTHOR]

In the present study, the microstructure and elevated-temperature mechanical properties of Mg-6Al, Mg-6Al-4Ca, Mg-6Al-4Sm and Mg-6Al-2Ca-2Sm alloys were investigated. The experimental results showed that the microstructure and elevated-temperature mechanical property of Mg-6Al alloy changed obviously with the different elements addition. By analyzing the results of optical microscope, x-ray diffraction analysis, scanning electron microscope, and transmission electron microscope, it could be determined that there was only Mg17Al12 phase in Mg-6Al alloy, there were Al2Ca and (Mg, Al)2Ca phases in Mg-6Al-4Ca alloy, there were Al2Sm and Mg17Al12 phases in Mg-6Al-4Sm alloy, and there were (Mg, Al)2Ca, Al2Ca and Al2Sm phases in Mg-6Al-2Ca-2Sm alloy. In addition, the addition of alloying elements including Ca and Sm, especially the composite addition, could significantly improve the tensile properties of Mg-6Al alloy. Compared to Mg-6Al alloy, the tensile strengths of Mg-6Al-2Ca-2Sm alloy at 448, 473 and 498 K were enhanced by 50.32, 87.92, and 94.99%, respectively. Furthermore, when the stretching temperatures were 448 and 473 K, the fracture pattern of Mg-6Al-2Ca-2Sm alloy was the mixture of intergranular fracture and trans-crystalline fracture. However, when the stretching temperature was 498 K, the fracture pattern of Mg-6Al-2Ca-2Sm alloy was the intergranular fracture. [ABSTRACT FROM AUTHOR]

A cost-effective iron-rich non-equiatomic Fe 50 Mn 20 Al 15 Ni 10 Co 5 medium entropy alloy (MEA) was synthesized by vacuum induction melting. The as-cast alloy exhibits a multiphase microstructure with the ordered B2 (a= 2.90 ± 0.01 Å), disordered body-centred cubic (BCC) (a= 2.89 ± 0.01 Å) and face-centred cubic (FCC) (a= 3.61 ± 0.02 Å) phases. X-ray diffraction (XRD) and transmission electron microscope (TEM) were used to confirm the structure of the evolved phases. The columnar dendrites having a width in the range of 120–300 µm were observed in the as-cast structure. The formation of Ni-Al rich B2 precipitates in the BCC matrix was confirmed based on detailed microstructural characterization using scanning electron microscope (SEM) and TEM. The phase separation in the form of modulated structure of ordered B2 and disordered BCC phase was related to the spinodal decomposition. The formation of the FCC phase at and near the grain boundaries is linked to simultaneous nucleation and growth mechanisms, which occur during the solidification. The as-cast alloy has shown an average compressive yield strength of ∼1250 MPa and ultimate strength of ∼1675 MPa, along with a compressive strain of ∼42%. The optimum balance of strength and ductility is achieved due to the formation of the hard (B2, BCC) and soft (FCC) phases and their interplay during the deformation process. These encouraging results of the alloy in the as-cast state have provided the direction to design and develop such economically viable alloys, which could be produced at industrial scale. • A novel cost-effective Fe 50 Mn 20 Al 15 Ni 10 Co 5 MEA was synthesized by vacuum induction melting. • Alloys exhibits two phase structure of BCC and FCC in as-cast state. • The modulated structure of B2 and BCC was related to spinodal decomposition. • The optimum balance of strength and ductility is achieved in the alloy. [ABSTRACT FROM AUTHOR]

Oxide dispersion strengthened tungsten (ODS-W) alloys are promising plasma facing material in future fusion reactors. In this study, composite powders of W-Er 2 O 3 were prepared by co-deposition method and hydrogen reduction, and then consolidated by spark plasma sintering (SPS). Microstructure evolution during co-deposition process was investigated using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and Fourier transform infrared spectrometer (FTIR). Also, simulation using DMol3 module in Materials Studio was carried out to understand the co-deposition mechanism. The results showed that H+ of W-OH bond in white tungstic acid was replaced by Er3+ due to coordination reaction during co-deposition process, leading to formation of ring-like chelate of (WO) n Er. This indicates that doping of Er3+ was achieved at a molecular level. Consequently, Er 2 O 3 particles were relatively uniformly distributed in W-Er 2 O 3 alloy, and the hardness and compressive strength reached 627 ± 19 HV and 1640 ± 40 MPa, respectively. • Thermodynamic diagram of W-H 2 O was calculated to optimize co-deposition process. • Co-deposition mechanism was analyzed by simulation and experimental methods. • W-Er 2 O 3 alloy was prepared by co-deposition method and two-step SPS. • Er 2 O 3 particles were relatively uniformly distributed in alloy. • Hardness and compressive strength reached 627 HV and 1640 MPa, respectively. [ABSTRACT FROM AUTHOR]

Laser powder bed fusion (LPBF) is one of the most widely used additive manufacturing (AM) methods to produce metal parts with new functionalities, but it still suffers from a low built rate. Increasing the powder layer thickness is an efficient way to augment LPBF productivity. The objective of this study is to investigate the influence of the powder layer thickness during the LPBF of F357 alloy on the microstructure and age-hardening response during T5 heat treatment. Scanning electron microscope (SEM) and transmission electron microscope (TEM) observations show that microstructure differences are negligible between samples printed at 30 µm and 50 µm layer thicknesses in the as-built condition. Samples built with both layer thicknesses and subjected to T5 heat treatments at 150 °C, 160 °C, and 170 °C also show similar microstructures and their α-Al cells contain large Si precipitates and small Si clusters and no β"-Mg 2 Si precipitates. Therefore, β"-Mg 2 Si precipitation hardening is not the dominant mechanism, and strengthening appears to be mainly due to the small Si clusters. With the help of the Johnson-Mehl-Avrami (JMA) model, the activation energy of the precipitation process of the samples built at 30 and 50 µm layer thicknesses is calculated to be 142 kJ/mol and 139 kJ/mol, respectively. These comparable values suggest a similar evolution of the precipitation hardening for both layer thicknesses, which is consistent with the observed microstructures. Consequently, the production efficiency of LPBF-printed F357 alloys can be enhanced by using higher layer thickness and the T5 heat treatment. • The as-built 30 µm sample exhibits higher hardness than the 50 µm sample. • T5 HT can strengthen both 30 µm and 50 µm samples at 150 °C, 160 °C, and 170 °C. • Hardness difference between 30 µm and 50 µm sample is reduced after T5 peak aging. • Similar T5 precipitation evolution of 30 µm and 50 µm samples is shown by TEM. • The apparent activation energy for both 30 µm and 50 µm samples is ∼140 kJ/mol. [ABSTRACT FROM AUTHOR]

In this study, the porous carbon-based materials loaded with Fe, Co, and Cu nanoparticles were fabricated by chemical blow molding carbonization to ameliorate the hydrogen storage performances of as-milled Mg 91 Al 5 Y 4 alloy. The Sievert apparatus was utilized to test the isothermal hydrogen absorption/desorption curves and P-C-T (Pressure-composition-temperature) curves. The microstructure characterizations of the specimens were completed by using XRD (X-ray diffraction), SEM (scanning electron microscope), TEM (transmission electron microscope), etc. Besides, Raman spectrum and Nitrogen adsorption/desorption isotherms have been applied to characterize the defect density, specific surface area and dominant pore diameter of the catalysts. Based on the results, the catalysts Tm@C (Tm = Fe, Co, Cu) with porous lamellar structure have the specific surface area of 156.9, 190.9, 106.4 m2/g and the diffraction intensity ratio (I D /I G) of 1.06, 1.09, 0.96, respectively, showing great catalytic influence on hydrogen storage performances of as-milled Mg-Al-Y alloy Concretely, the composite Mg 91 Al 5 Y 4 + 5 wt% Co@C with the minimum dehydrogenation activation energy of 84.8 kJ/mol can absorb a small amount of H 2 at 323 K, besides, the initial hydrogen desorption temperature of it is about 521.5 K. The catalytic functions of Tm@C can be ascribed to the following aspects: the enhancement of milling efficiency and the following particle/grain refinement of alloy; the introduction of great number of defects (active sites); the loaded transition metals (with high electronegativity and multi-valence) or their derivative nanoparticles, etc. • Tm@C (Tm Fe, Co, Cu) are prepared to improve Mg-Al-Y hydrogen storage alloy. • The Mg 91 Al 5 Y 4 -5 wt%Co@C composite has the minimum E a de value of about 84.8 kJ/mol. • The Tm nanoparticles supported by the catalysts and inner defects play a catalytic role. [ABSTRACT FROM AUTHOR]

The interface between LPSO and β' in the Mg-Gd-Al alloys is investigated by the high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) imaging and first-principles calculation. The formation energies of interface structures with different rare-earth-depleted layers (REDL) indicate that the interface structure with three-layer REDL is the most stable. The interfacial phase diagram with the chemical potential of Gd is obtained by the first-principles molecular dynamics analysis of interface energies, indicating that the β'/Mg interface layer in the three-REDL structure is the most stable, and the REDL is not only the Mg atomic layer, but also part of the LPSO phase. Moreover, it is also indirectly proved that the β'/Mg interface layer with three-layer REDL in Mg-Gd-Al alloys will form strong covalent and metallic bonds, and the bond energy is larger and more stable. Therefore, the characterization and calculations of the LPSO and β' interfaces provide a theoretical basis for future interface property analysis and interface design. • The interface between long-period stacking-ordered (LPSO) and β' phases by HAADF-STEM and first-principles calculation. • The first-principles molecular dynamics analysis and bond relationship of the rare-earth-depleted layer (REDL). • The interface with three REDLs (partof the LPSO phase) is the most stable structure. [ABSTRACT FROM AUTHOR]

[Display omitted] The solidification behavior of a eutectic AlCu specimen is investigated via in situ scanning transmission electron microscope (STEM) experiments. Solidification conditions are varied by imposing various cooling conditions via a micro-electro-mechanical system (MEMS) based membrane. The methodology allows the use of material processed by a melting and casting route close to industrial metallurgically fabricated material for in situ STEM solidification studies. Different rapid solidification morphologies could be obtained solely on a single specimen by the demonstrated strategy. Additional post-solidification heat treatments are investigated in terms of observation of spheroidization of lamellas during annealing at elevated temperatures. [ABSTRACT FROM AUTHOR]

Formation of profuse I 2 -type solute-enriched stacking faults (SESFs) in fine grains and transformation of SESFs to 18R-long period stacking ordered (LPSO) phase are attained in Mg-Er-Zn-Zr alloys. It is first confirmed by scanning Kelvin probe force microscopy (SKPFM) that SESFs with nanostructure act as weak anodes and the 18R-LPSO phase serves as cathode, which are verified by the theoretical calculated electronic work function and observation of scanning transmission electron microscope. Furthermore, the preferential corrosion of uniformly dispersed SESFs is demonstrated to be conducive to forming effective passivation film. It provides a new insight for developing high-strength and anti-corrosion Mg alloys. [Display omitted] • The PD of weak anode SFs is measured at the nanoscale by SKPFM for the first time. • The reliability of SKPFM results is verified by the theoretical calculated WF. • Preferential corrosion of SFs is demonstrated using STEM-EDS for the first time. • Preferential corrosion of solute-enriched SFs is conducive to formation of passivation film. • A new insight for designing high-strength and anti-corrosion Mg alloys is proposed. [ABSTRACT FROM AUTHOR]

A novel as-cast Mg96.82Gd2Zn1Zr0.18 alloy was produced by conventional ingot metallurgy. By scanning electron microscope and transmission electron microscope observations, its as-cast microstructure is mainly composed of the α′-Mg solid solution, the coherent fine-lamellae and the eutectic. The β-phase ((Mg,Zn)3Gd) as the second phase in eutectic has a face-center cubic structure. While, the coherent lamellae consist of the 2H–Mg and the 14H-type long period stacking ordered (LPSO) structure. At present, the lamellar 14H-type LPSO structure has first been observed within α′-Mg matrix in the as-cast Mg–Gd–Zn–Zr alloys. It can be concluded that the lamellar 14H-type LPSO structure within α′-Mg matrix is a special structure obviously different from α-Mg matrix (2H-type structure) in structure, composition, and formation condition. [ABSTRACT FROM AUTHOR]

Cryogenic deformation can improve the strength and plasticity of Al–Li alloy, although the underlying mechanism is still not yet well understood. The effects of cryogenic temperature on the tensile properties and microstructure of an Al–Cu–Li alloy were investigated by means of tensile property test, roughness measurement, scanning electron microscope (SEM), optical microscope (OM), electron backscatter diffraction (EBSD), and transmission electron microscope (TEM). The results indicated that the strength and elongation of the as-annealed (O-state) and solution-treated (W-state) alloys increased with the decrease in deformation temperature, where the increasing trend of elongation of the W-state alloy was more significant than that of the O-state alloy. In addition, a temperature range was observed at approximately 178 K that caused the strength of the W-state alloy to slightly decrease. The decrease in temperature inhibited the dynamic recovery of the Al–Cu–Li alloy, which increased the dislocation density and the degree of work hardening, thus improving the strength of the alloy. At cryogenic temperatures, the internal grain structure was more involved in the deformation and the overall deformation was more uniform, which caused the alloy to have higher plasticity. This study provides a theoretical basis for the cryogenic forming of Al–Li alloy. [ABSTRACT FROM AUTHOR]

The present study demonstrates the direct observation of pore formation by rapid release of vacancies in ultrafine grain (UFG) Al-0.4at%Zr alloy during in-situ annealing in a scanning transmission electron microscope. The ultrafine grain structure was preliminary obtained by high pressure torsion processing at a hydrostatic pressure of 6 GPa up to 10 revolutions. In-situ annealing reveals the rapid formation of pores in triple junctions (TJs) of grain boundaries (GBs) during the first few minutes followed by their subsequent slow resorption with the complete disappearance of some of them. During annealing, no noticeable displacement of GBs is observed. By considering the evolution of non-equilibrium GBs inherited by the severe plastic deformation, a theoretical description is suggested which describes: (i) the pore formation at disclinated TJs as a thermodynamically driven process of free volume dissolution through generation of vacancies, which then migrate to the TJs and coagulate at them with growth of the pores diminishing the strain energy of the TJ disclinations, and (ii) further decrease of the TJ disclination strain energy through the climb of extrinsic GB dislocations towards the disclinated TJs, accompanied with dissolution of the TJ pores by emission of vacancies which provide the dislocation climb. The rapid release of excess vacancies during the early stage of heat treatment is consequently identified as a phenomenon responsible for accelerated atomic mobility. This work hence provides a new perspective for understanding the accelerated precipitation kinetics observed in severely deformed alloys. ga1 • It is demonstrated that grain structure of a severely deformed Al-alloy store large amounts of vacancies. • Vacancy release by the rearrangement of near equilibrium grain boundaries is followed by in-situ annealing in STEM. • The kinetics of pore formation and dissolution has been followed by in-situ STEM observations. • Theoretical models are provided that reproduce the formation and dissolution of pores formed by vacancy condensation. • A proportion of stored vacancies may be responsible for faster precipitation kinetics in severely deformed alloys. [ABSTRACT FROM AUTHOR]

The fracture behaviour of DO3 Fe3Al-based intermetallic alloys with and without Mn (1.5 at%) were investigated by tensile tests (TT), transmission electron microscope (TEM) and scanning electron microscope (SEM). The results show that the addition of Mn could improve mechanical properties of the alloy, including room temperature ductility and high temperature strength. DO3 Fe–28Al fractured in a transgranular cleavage mode at room temperature and it gradually changed to a ductile style with temperature increasing, whereas the sample with addition of Mn fractured mainly in a mixed intergranular–transgranular cleavage mode. Three major factors are considered to have effect of Mn on fracture behaviour of the alloys: reducing grain size, promoting slip and cross slip and enhancing cleavage strength. © 1998 Chapman & Hall [ABSTRACT FROM AUTHOR]

The effect of Zr and Er on the microstructure, electrical conductivity and mechanical properties of Al-0.4Fe alloy was investigated using optical microscope (OM), scanning electron microscope (SEM), electron back-scattered diffraction (EBSD), transmission electron microscope (TEM) and energy dispersive x-ray spectroscopy (EDS). It is revealed that both of the Zr and Er could inhibit the recrystallization process of Al-0.4 wt %Fe alloy due to the formation of Al 3 Zr or Al 3 Er particles. Zr is more recrystallization-resistant than Er due to the preferential precipitation of Al 3 Zr. Both of the Zr and Er could modify the morphology of Al 3 Fe particle from needle-like to sphere-like or rod-like, which reduce the negative effect of Al 3 Fe phase. Zr could significantly refine dendrites of the Al-0.4Fe alloy, while Er shows a negligible effect on dendrite refining due to the delayed formation of Al 3 Er during solidification. However, the low solubility of Er is beneficial for strength and electrical properties of Al-0.4Fe alloy. In consideration of strength and electrical conductivity, the Al-0.4Fe-0.2Er is selected as the best alloy among the four alloys, which shows a yield strength of 145 MPa, elongation at fracture of 8% and electrical conductivity of 61.2 %IACS after cold-rolling. The results provide an insight in design high strength, high conductive aluminum conductor material. • The coarse needle-like Al 3 Fe phases could be modified into sphere- and rod-like small particles by Zr and Er additions. • Synergetic improvement of strength and conductivity in Al-0.4Fe-0.2Er alloy is gained. • Co-adding Zr and Er improves recrystallization resistant capability of the Al-0.4Fe alloy better than the single one. [ABSTRACT FROM AUTHOR]

The thermal stability of magnetron-sputtered Zr-Cu-Ag thin films, presenting key-antibacterial properties against E. coli and S. aureus , is studied by using an in situ multiscale approach. This study is carried out to better understand the general evolution of these amorphous films under thermal constraint, and to determine their limit of use in aggressive conditions. The general crystallization behavior and structural stability are investigated by in situ X-ray diffraction (XRD) in heating mode, and completed at micro- and nano-scale by complementary electron microscopy characterizations. The global crystallization temperature of films, determined by XRD, is found between 200 °C and 400 °C depending on the composition. The in situ HT-ESEM (High Temperature – Environmental Scanning Electron Microscope) observations show that, for the composition with the lowest Zr/(Cu + Ag) ratio (Zr 33 Cu 35 Ag 32), the crystallization process is followed by a total dewetting of the thin film. The Zr 73 Cu 16 Ag 11 film is a thin film metallic glass (TFMG), and was also investigated at the nanoscale. In situ HT-TEM (High Temperature – Transmission Electron Microscope) allows observing the progressive crystallization of the TFMG, describing the different steps of transformation from the amorphous as-deposited structure, the individual formation of intermetallics and to the whole crystalline state. • Zr-Cu-Ag thin film metallic glasses, known for their biocide activity, were synthesized by PVD magnetron sputtering. • Their structural and microstructural thermal stability was characterized through an in situ multiscale approach. • Adopting in situ XRD, SEM and TEM technics, both films crystallization and dewetting processes were directly observed. • The Zr 73 Cu 16 Ag 11 film shows a thin film metallic glass character. • From a chemical viewpoint, the higher the Zr/(Cu + Ag) atomic ratio, the higher their thermal resistance. [ABSTRACT FROM AUTHOR]

• The secondary acicular β-phase appeared after a 650 °C–1000 h aged process and significantly increased in quantity for 3000 h. • The morphology and quantity of the primary β phase changed significantly with the prolonged aging time. Taking the GH783 alloy bolt of intermediate pressure main stop valve used in 1000 MW ultra-supercritical unit as the research object, the optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffractometer (XRD) and mechanical performance tests were carried out to study the microstructure transformation and mechanical properties of GH783 alloy bolts at different aging stages under 650 °C aging environment. The results showed that the secondary needle β phase began to appear in the bolts aged for 1000 h, and the density of secondary β-phases in bolts aged for 3000 h significantly increased. When the aging time reached up to 20,000 h, the secondary β phase coarsened significantly. At the same time, as the aging time prolonged, the morphology and quantity of the primary β phase changed significantly. In terms of mechanical properties, the tensile strength and impact toughness of the bolts gradually decreased. This was due to the growing γ' phase, the formation of Ni 5 Al 3 phase and the Nb-rich Laves phase in the structure during the aging process. [ABSTRACT FROM AUTHOR]

Serration behavior is a kind of plastic instability phenomenon of materials, which widely exists in the high-entropy alloys and has influence on microstructure and mechanical properties. In this work, the microstructure and mechanical properties of a NiCrFeCoMn high-entropy alloy (HEA) were studied under high-speed impact. The microstructure of a NiCrFeCoMn HEA were investigated by optical microscope (OM), scanning electron microscope (SEM), electron backscatter diffraction (EBSD), and transmission electron microscope (TEM). The dislocation density increased with the true strain at high-strain-rate deformation, and the dislocations can be hindered and released continually by the twin layers, resulting in serration on the true stress—true strain curve. When values of the strain rates are 1250, 2000 and 4800 s−1, the yield strength of the deformed NiCrFeCoMn HEA are 510, 525 and 680 MPa, respectively. Moreover, the fluctuation of the serration became more serious with the increasing of the strain rate. Compared with the as-cast NiCrFeCoMn HEA, the true stress—true strain curve of the deformed NiCrFeCoMn HEAwas smoother. [ABSTRACT FROM AUTHOR]

There are many means and mechanisms to strengthen alloys, but often at the cost of plasticity. Strength or plasticity? In practice, the two often appear as contradictory relationships. In the current work, the ZrSn 1.5 Al x (x = 6, 8, 10, 12, 14 at. %) alloy obtained by controlling the Al content was smelted and hot-rolled at 890 °C, and then immediately quenched to obtain an alloy containing α + β + AlZr3 multiphase structure. Compared with ZrSn 1.5 Al 6 alloy, ZrSn 1.5 Al 14 alloy reaches a high ultimate tensile strength (1080.84 MPa) and a large elongation at fracture (28.59%) at room temperature, an increase of 27.6% and 86.3%, respectively. The formation of AlZr3 particles pins dislocations, promotes cross-sliding of dislocations, and improves the dislocation nucleation rate by changing the dislocation sliding mode, which increases the dislocation density and promotes uniform plastic deformation, enhance the strain-hardening ability of the alloys, thereby improve its plasticity and strength simultaneously. Optical microscopy (OM) and scanning electron microscope (SEM) were used to observe the metallographic structure and tensile fracture morphology. The transmission electron microscope bright field (TEM-BF) image and scanning transmission electron microscope high-angle annular dark field (STEM-HAADF) image of the sample were observed for detailed analysis. The samples were taken in the rolling direction and the mechanical properties were evaluated by uniaxial tensile tests at room temperature. In summary, the machining process is simple, the cost is low, and it is suitable for large-scale industrial-grade applications. It may have reference significance to other alloy systems. • The strength and plasticity have been improved simultaneously. • ZSA14 shows high ultimate tensile strength (1080.84 MPa) and a large elongation at fracture (28.59%). • FCC AlZr3 phase formed when Al content is over 8 at. %. • AlZr3 particles hinder dislocations, dislocation nucleation rate was increased by changing the dislocation slip mode. • The strain-hardening ability of the alloy improved. [ABSTRACT FROM AUTHOR]

The VAlTiCrMo and (VAlTiCrMo)N x coatings were prepared by sputtering V–Al–Ti–Cr–Mo splicing targets. The microstructure and chemical composition were analyzed by means of X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and transmission electron microscope (TEM). The high-entropy alloy coating and the corresponding nitride coating have body-centered cubic (BCC) and face-centered cubic (FCC) structures respectively. Nitriding changes the phase structure and growth mode of the high-entropy coating, and the synthesized high-entropy nitride coatings are more compact. Meanwhile, the introduction of nitrogen leads to severe lattice distortion, which improves the mechanical properties of the high-entropy coating. As the nitriding degree increases, the corrosion resistance of the high-entropy nitride coatings in 3.5 wt% NaCl solution is improved. The synthesized (VAlTiCrMo)N x coating exhibits optimized mechanical properties and nobler corrosion resistance when the N 2 flow is 800 sccm. Corrosion inhibition by the microstructures of the VAlTiCrMo and its nitride coatings. Image 1 • VAlTiCrMo high-entropy alloy coating and its nitride coatings prepared by splicing targets. • The change of coating structure is more obvious with the increase of nitrogen flow rate. • The introduction of nitrogen changed the structure of the coating from BCC to FCC. [ABSTRACT FROM AUTHOR]

The effects of solute element content and cooling rate on the morphology of Al6Mn phase in suction casting Al–Mn alloys were investigated by transmission electron microscope, scanning electron microscope, and X-ray diffractometer. Results show that Al6Mn dendrite morphology with different degrees of development can occur in the microstructure of as-cast Al–Mn alloys. For the Al–4 wt.% Mn alloy, there are small amounts of block Al6Mn crystals at the center of sample, while we see a block Al6Mn phase and a feathery Al6Mn phase in the sample of Al–6 wt.% Mn alloy. Moreover, the block Al6Mn phases in the Al–8 wt.% Mn alloy disappear, and only snowflake-like Al6Mn phases play a dominant role in the microstructure. However, with an increase in Mn content to 10 wt.%, more dendritic trunks are formed, and secondary dendrite arms are degraded more seriously due to the formation of an icosahedral quasicrystal in suction casting. In addition to the effect of Mn content on Al6Mn morphology, with the increase in cooling rate from the center to the edge of samples, the outline diameter of equiaxed dendrite decreases. The evolution of Al6Mn dendrite morphology and the formation of quasicrystal are further discussed. [ABSTRACT FROM AUTHOR]

The microstructural evolutions and resulted mechanical responses during isothermal holding of multipass hot deformation are essential aspects in the processing of high performance titanium alloys. In this work, isothermal holding testing was performed on a Ti-5Al-3V alloy after hot compression at temperatures of 900 °C, 930 °C and 960 °C, respectively. Stress relaxation, dilatometer measurements, and microstructure examinations (i.e. scanning electron microscope, electron backscatter diffraction and transmission electron microscope) were employed to investigate the phase transformation behaviors. The results showed a flow stress hardening phenomenon during the interrupted isothermal holding in two phase region. The post-dynamic transformation from α to β phase took place first during the early stage of isothermal holding after hot deformation. With longer isothermal holding time, the reverse transformation of meta-stable β phase to α phase was then observed. Under TEM, the reverse transformed α phases were isolated from quenched α ' phases. The in-depth mechanisms of post-dynamic α to β phase transformation and reverse transformation were discussed as well. Unlabelled Image • Flow stress hardening is found during double-stage deformation in two phase region. • A post-dynamic transformation of α to β phase occurred during interrupted holding. • The reverse transformation of β phase to α phase occurred with further holding. • The reverse transformed α phases were distinguished from α ' phases by TEM. • The post-dynamic transformation should be driven by stored energy and stress. [ABSTRACT FROM AUTHOR]

Effects of Bi additions on age-hardening response and precipitation of Mg–2.31Zn–0.31Co (at.%) alloy have been investigated. The addition of Bi can substantially promote the age-hardening response at 200 °C. The precipitates microstructure is characterized using high-angle annular dark-field scanning transmission electron microscope, and the results show that the remarkable improvement is attributed to a much higher number density of β 1 ' rods and the formation of prismatic Mg 3 Bi 2 plates. At the early stage of ageing, Mg 3 Bi 2 precipitates out first and then Zn segregates to the Mg 3 Bi 2 /Mg interface, which could provide chemical environment and heterogeneous nucleation sites for the subsequent precipitation of the β 1 ' phase. Image 1 • The addition of Bi can substantially enhance the age-hardening response of Mg–2.31Zn–0.31Co alloy. • Bi additions result in a higher number density of β 1 ' rods and the formation of prismatic Mg 3 Bi 2 plates. • Zn atoms segregate at Mg 3 Bi 2 /Mg interface. • Rod-like β 1 ' phase heterogeneously nucleates at Mg 3 Bi 2 /Mg interfaces. [ABSTRACT FROM AUTHOR]

In this study, friction and wear behaviors of an amorphous Zr 20 Ti 20 Cu 20 Ni 20 Be 20 high-entropy alloy (a-HEA) were characterized using a nanoscratch method. Scratch tests were carried out under both ramping and constant loading conditions to measure the coefficient of friction (COF) and wear resistance of the amorphous alloy. The morphology of scratched surface and subsurface was further examined using scanning and transmission electron microscopes. It was found that friction behavior of the a-HEA can be divided into two regions: elastic and plastic. In the elastic region, the COF dramatically decreases with increasing normal force, however, it monotonically increases in the plastic region. Morphological observation indicated that brittle fracture dominated in the plastic region, which was consistent with the result that a series of load serrations were accompanied by the formation of brittle cracks along the scratched track. Wear performance of the a-HEA was also evaluated and compared with "conventional" metallic glasses and crystalline high-entropy alloys. As a result of high hardness and large elastic recovery, the current a-HEA exhibited good wear resistance and low COF, behaved more like brittle amorphous alloys rather than ductile high-entropy alloys. Image 1 • Friction and wear behaviors of an amorphous high-entropy alloy (a-HEA) were studied using a nanoscratch technique. • Friction of the a -HEA can generally be divided into two regions: elastic and plastic. • Brittle fracture dominates the plastic deformation, as manifested by load serrations and scratched surface morphology. • As a result of high hardness and large elastic recovery, the a-HEA exhibited good wear resistance and low COF. [ABSTRACT FROM AUTHOR]