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A wide variety of industrial applications require Al-Zn-Mg-Cu alloys with high strength and ductility. However, Zn-rich Al-Zn-Mg-Cu alloys prepared by rapid solidification methods usually show excellent strength but poor formability, which restricts their wide application in complex forming. In this study, we developed a new deformation method for the spray-deposited Zn-rich Al-Zn-Mg-Cu alloy to avoid crack formation and achieve isotropic properties. The microstructure evolution and crystallographic textures were analyzed and compared with the results of a normal deformation process. Crack-free forgings with the ultimate tensile strength (UTS), yield strength (YS) and elongation of 727 ± 5 MPa, 690 ± 3 MPa, 5.0 ± 0.7% along the radial direction and 735 ± 2 MPa, 693 ± 3 MPa, 6.3 ± 0.2% along the tangential direction were finally obtained. The improvement in the mechanical properties can be attributed to the larger amount of subgrains and substructures generated in the canned deformed alloy. The results of this study show excellent advantages and potential application prospects of the canned deformation to hard-deformed Al-Zn-Mg-Cu alloys. [ABSTRACT FROM AUTHOR]

Process and rate of the crater wear development on the rake face of uncoated cemented carbide inserts were investigated when Ti-6Al-4V alloy was turned under dry cutting conditions. Contour maps were outlined to study the relationship between the area of the contour region and its wear depth. An effectively predictive method was proposed to predict wear-related quantities of the crater, including the crater depth, wear area, and wear volume. The predictive method was verified by the experiments with different cutting parameters. The development rate of the crater with the wear depth was acquired by analyzing the relationship between the area of the contour boundary region and its wear depth, and reasons on a sharp increase of the development rate were discussed at the wear depth of ( KT-1) or ( KT-2). The relationship between the area of the contour region and cutting time at a certain wear depth was proposed and could be used to predict the wear-related quantities of the crater. [ABSTRACT FROM AUTHOR]

Developing light structure materials that work stably at elevated temperatures is a long-standing challenge for many application fields, particularly in the development of aerospace equipment. Zn/Cd alloying elements were prospected to improve the stability of the lightest Mg-Li based alloys; however, little is known about the intermediate-temperature mechanical properties of such alloys. The present work investigated the tensile behaviors of a cold-rolled Mg-Li-Al-Cd-Zn alloy in a temperature range of 30–150 °C. The results indicate that the alloy can host a tensile strength σUTS of 108~121 MPa, a yield strength σYP of 97~109 MPa and elongation εB of 14–15 % at 150 °C, dependent on the tensile direction. The mechanical properties intensively are modulated by temperature through the competition between work hardening and softening. Work hardening due to dislocation blocking by the precipitated MgLi2X phase dominated the deformation at low temperatures, while softening that resulted from dynamic recrystallization was the main effect at high temperatures. Correspondingly, a quasi-cleavage mechanism dominated the fracture at temperatures near room temperature, and microvoid coalescence worked at high temperatures above 100 °C. Our results offer a new experimental understanding of the elevated-temperature mechanical behaviors of Mg-Li alloys and will advance the development of new light magnesium alloys with high stability. [ABSTRACT FROM AUTHOR]

morphous CoFeSiB wires with smooth surface and circular cross section were fabricated by melt extraction technology using a copper wheel with a knife-edge cross section angle of 60 deg. The effect of some process parameters such as wheel circumference velocity, molten alloy feed rate, and temperature on the geometry and weight, i.e., melt extracted layer thickness, of wire was examined carefully. An optimum process parameter to produce high-quality circular wires was presented. A high resolution CCD video camera recorder was used to monitor the changing of the surface shape of molten alloy contacting the wheel tip under different conditions. It was found that the mechanism of the wire formation during the optimum process condition was controlled by the momentum mechanism, while in the low wheel speed region, heat transfer turned out to be a dominant factor. Some characteristics of the circular wires such as amorphous nature and tensile strength were also studied. [ABSTRACT FROM AUTHOR]

In this paper, we report the results obtained from the hot compression behaviour of co-spray-formed Al-Si/7075 bimetallic gradient alloys by investigating the five selected layers divided evenly from top to bottom. It was found that with a decrease in the strain rate and an increase in temperature, the hot compression flow stress of deposited alloys decreases gradually, as expected. The relationship between flow stress, temperature and strain rate follows the Arrhenius relationship. The deformation activation energy of the co-spray formed gradient alloy gradually increases from bottom to top in the height direction, which are 100.15, 167.35, 185.54, 208.78 and 220.83 KJ/mol, indicating that the degree of difficulty in the deformation of the alloy is affected by changes in the silicon content of the alloy. Finally, the flow stress constitutive equation is calculated for each layer of alloy material, which is instructive for the subsequent study of the densification process of co-spray-formed gradient alloys. [ABSTRACT FROM AUTHOR]

Bimetallic gradient alloys have attracted research attention recently due to their potential applications in the aerospace and automobile industries. In this study, Al-20Si/7075 bimetallic gradient alloys were successfully manufactured by co-spray forming and the roll process. We investigated the thermal expansion behavior of the gradient alloy. It was found that the coefficients of thermal expansion increased with silicon content and increased temperature, reaching the highest point at 573 K, after which they decreased on account of the relaxation of residual thermal stress and the silicon desolvation from the supersaturated aluminum phase. The measured thermal expansion coefficient can be roughly predicted through the traditional theoretical models. Our results revealed the thermal expansion behavior of Al-20Si/7075 bimetallic gradient alloys and would improve the development of new type aluminum–silicon alloy for electronic packaging. [ABSTRACT FROM AUTHOR]

It has been well documented that the maximum thickness of as-cast glassy samples attainable through conventional metallurgical routes is the decisive criteria for measuring the glass-forming ability (GFA) of bulk metallic glasses (BMGs). Here we report the exceptionally high GFA of an FeCoCrMoCBY alloy which can be fabricated in the form of glassy rods with a maximum sample thickness of at least 16 mm. It is demonstrated that, by substituting Fe with a proper amount of Co in a previously reported Fe-based BMG alloy, the glass formation of the resultant new alloy can be extensively favored both thermodynamically and kinetically. The new ferrous BMG alloy also exhibits a high fracture strength of 3500 MPa and Vickers hardness of 1253 kg mm-2. [ABSTRACT FROM AUTHOR]

Metallic additive manufacturing (AM) offers near net-shape fabrication but often results in insufficient strength and/or ductility due to voids or cracks, coarse initial crystalline microstructure, insufficient volume fraction of precipitates and yet post-AM strengthening/toughening methods non-destructive to shape are generally lacking. Here, we report a laser-directed energy deposited (L-DED) medium entropy alloy (MEA) with a heterostructure (HS) comprising alternate layers of solid-solution and intermetallic-dispersed MEA that possess ultimate tensile strength of 1132.8 MPa and elongation of 50.6 %, corresponding to strength-ductility synergy higher than other medium- or high-entropy alloys reported. The multilayers were produced from a dual source of CoCrNi MEA powder and a powder mixture of the same MEA, Al and Ti with stoichiometry (CoCrNi) 86 Al 7 Ti 7 , and the remarkable strength-ductility synergy is achieved only after post-L-DED heat treatment, which causes Al and Ti to diffuse across the layers to form a low-gradient HS. The significant back stress due to the HS contributes to the high strength, while the high ductility results from a high strain-hardening rate suppressing necking. This study demonstrates the concept of using AM not just as a near net-shape fabrication method but also a unique tool to produce low-gradient HSs with superb mechanical properties, via the use of multiple powder sources combined with suitable shape-preserving post-fabrication heat treatment. [Display omitted] • A layered heterostructure medium entropy alloy was fabricated by laser directed energy deposition. • The gradient distribution of L1 2 and σ phases at the layer interface is realized by heat treatment. • The synchronous improvement of strength and ductility results from precipitation hardening and back stress strengthening. [ABSTRACT FROM AUTHOR]

• Laser shock peening is an effective way to introduce gradient structures that improve the mechanical properties of high entropy alloy (HEA). • A hardened layer of several hundred micrometers is produced on the surface of HEA via laser shock peening. • Twin boundaries, dense dislocations, and grain refinement in the laser affected layer result in enhanced yield strength of HEA. • Excellent plasticity during loading of the laser-treated HEA is mainly accommodated by dislocations in the laser unaffected core region. For most metallic materials, surface hardening via modifying the near-surface microstructure is an effective method for improving mechanical properties. Among these processes, laser shock peening (LSP), which is versatile and nondestructive to the fabricated product shape, has received much attention. The present work has shown that the mechanical properties of CrFeCoNiMn 0.75 Cu 0.25 high entropy alloy (HEA) have a significant improvement after LSP treatment. Yield strength more than two times of as-cast alloys is achieved in HEA samples treated by LSP for 4 cycles, due to the introduction of a gradient microstructure comprising subgrains, dense dislocations and nano-twins near the treated surface. The combination of dislocation hardening and mechanical twinning improves the strain hardening ability for the LSP-treated HEA, leading to excellent plasticity during tensile loading. Grain refinement also takes place via a faulting process of dislocation dissociation on nearly every {111} plane. Then, TEM observations and finite simulation of the LSP processed HEA samples after different levels of accumulated strain demonstrate that further tensile deformation is mainly accommodated by dislocations in the core region of the sample unaffected by the LSP, while the top LSP-affected layer accommodates little further plasticity as it is sufficiently hardened by the LSP. The present results indicate the possibility to develop gradient-structured HEAs with excellent mechanical properties using laser shock peening. [ABSTRACT FROM AUTHOR]

• A β-solidifying TiAl alloy reinforced with ultra-fine yttrium-rich precipitates was consolidated by spark plasma sintering. • This TiAl alloy with refined duplex microstructure exhibited excellent tensile properties at room temperature. • Two types of yttrium-rich precipitates were detected, and the crystallographic relationship between them and γ-TiAl matrix were determined. A β-solidifying TiAl alloy with a refined microstructure and ultra-fine yttrium-rich precipitates that was consolidated by spark plasma sintering was investigated by scanning and transmission electron microscopies. Two categories of yttrium-rich precipitates, Y 2 O 3 and YAl 2 , with sizes ranging from tens to hundreds of nanometers were found to be dispersed within the matrix uniformly. The crystallographic relationship between the two precipitates and the γ-TiAl matrix was determined by the selected area electron diffraction and high-resolution transmission electron microscopy. This spark plasma sintered TiAl alloy was characterized by a uniform duplex microstructure, and it exhibited excellent tensile properties at room temperature. Typically, specimen sintered at 1150°C has an ultimate tensile strength of 1113.1 MPa, yield strength of 881MPa, and a moderate plastic elongation of 1.41%. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Bifilm defects have been proposed to be critical for the generation of various metallurgical defects in castings and have been reported to exist in various composition-based alloys. However, the geometry structure of bifilm defects has not yet been well understood. This present work reconstructed the bifilm defects in a nickel-aluminium bronze alloy casting in three-dimensional (3D) space through the use of computer tomography technology. It was shown that the shape of the bifilm defects is very complex and different from a spherical defect in 3D space. The bifilm defects were experimentally extracted successfully by an electrolysis method and were imaged, which confirmed the folded double-layer structure of the bifilm defects. These results will shed new light on the understanding of bifilm defects and improve the defect control engineering of castings. Image, graphical abstract [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel high-entropy alloy CoCrFeNi microfibers with heterogeneous gradient structures was developed. • The CoCrFeNi microfibers displays an excellent strength–ductility combination both at 293 K and 150 K. • The deformation mechanisms of the microfibers at ambient and cryogenic temperatures are revealed. Exploring metallic microfibers with an excellent combination of high strength and ductility is a challenge for structural applications under extreme conditions. In this work, a heterogeneous gradient structure was introduced into CoCrFeNi high-entropy alloy (HEA) microfibers via thermomechanical processing. The annealed CoCrFeNi microfiber displays an ultrahigh yield strength of ∼ 1 GPa, an ultimate tensile strength of 1.45 GPa, and an outstanding uniform elongation of 75% at 150 K. These excellent properties originate from the ultrafine grains and heterogeneous gradient structure, as well as the activation of multiple deformation mechanisms including deformation twins, dense dislocations, stacking faults, Lomer-Cottrell locks, phase transformation and 9R phase. Our work not only suggests that HEA microfibers have great potential for structural applications in cryogenic environments, but also sheds light on the design of advanced multi-component metallic microfibers with superior mechanical properties. [ABSTRACT FROM AUTHOR]

Here, a new strategy, i.e., laser shock peening (LSP) followed by cyclic deep cryogenic treatment (DCT), is proposed to generate the gradient hierarchical structures and thus promote strength-ductility synergy of a high entropy alloy (HEA). We show that the non-equiatomic CrFeCoNiMn 0.75 Cu 0.25 HEA sample treated by this new strategy possesses an excellent combination of high strength (∼1100 MPa) and high plasticity (30%). Higher yield strength is achieved in HEA samples treated by LSP, due to the introduction of a gradient microstructure comprising sub-grains, dense dislocations and nano-twins (NTs) near the treated surface. Then, the following cyclic DCT processing can further introduce various types of reinforcing defect microstructures in core region of LSP-treated HEA, including dense intersecting NTs and stacking faults, thus effectively improving the tensile strength and plasticity. These results obtained here can shed new insights into develop high performance HEAs by tailoring residual stress and generating optimized microstructures. [Display omitted] [ABSTRACT FROM AUTHOR]

• The formation mechanism of bifilm defect in Mg-Gd-Y-Zr alloy is revealed as surface Y 2 O 3 oxide film shrinkage. • The bifilm in Mg-Gd-Y-Zr alloy contains Zr-cores. • Microcracks resulted by the shrinkage of bifilm is elucidated responsible for the generation of Zr-core. Mg-Gd-Y-Zr alloy has excellent mechanical properties at room and high temperatures, but its high oxidation properties can also result in a significant number of bifilm defects. However, its formation mechanism was not revealed so far, which was explored in the present work. The results showed that the surface oxide film folds into a grid-like double layer structure defect during solidification, due to the difference of thermal expansion coefficient between surface oxide film and matrix. In addition, the oxide film produces microcracks. As the magnesium alloy melt fills the crack, Zr precipitates into crystal nucleus with peritectic reaction and Y 2 O 3 accumulates. These results would shed new lights on the understanding of shrinkage formation of bifilm defects and improving the defects control of magnesium alloy castings. [ABSTRACT FROM AUTHOR]

Abstract: The effect of cooling rate on the mechanical behaviors of a Ti-based bulk metallic glass has been studied using nanoindentation technique. It is found that the hardness increases, while the plastic deformation capacity gradually decreases from the edge to the center of the sample. The variation of the structural uniformity within the as-cast glassy sample may account for the cooling rate dependence of mechanical performance. [Copyright &y& Elsevier]

• The relationship between the relative clearance and the fractured morphologies of the punched-out HEA was established. • The fractured surfaces of punched-out disc are composed generally of deformation zone, fracture zone, and burr zone. • The relative clearance affects the distribution of stress states of HEA plate during shear punching process. In this paper, the deformation and fracture behaviors of Co 20 Cr 20 Fe 20 Ni 20 Mn 15 Cu 5 high entropy alloy plates in the shear punching tests were studied. The fractured surfaces of the punched-out high entropy alloy discs consist of three parts, i.e., the deformation zone, the fracture zone, and the burr zone. As the ratio of clearance to the plate thickness, i.e., the relative clearance, gradually increases, the percentages of both deformation zone height and burr zone height increase. This phenomenon was attributed to the changes of stress states during shear punching process. Meanwhile, a larger relative clearance favors more plastic deformation, generating numerous slip bands and some elongated dimples on the fractured surface. [ABSTRACT FROM AUTHOR]

• CrMnFeCoNi HEA exhibits excellent mechanical properties at cryogenic temperatures. • Enhanced yield strength of the alloy stems from the larger lattice distortion. • High dislocation density and nano-twins lead to the high SHR. • Lower deformation temperature pronouncedly decreased SFE. Here, the evolution of the deformation mechanism of the well-known CrMnFeCoNi high entropy alloy (HEA) under a cryogenic temperature was investigated via using transmission electron microscopy characterization after compressive experiments. It is found that, in contrast to the dominate mechanism of dislocation slip at 298 K, the deformation mode of the studied HEA at 123 K can be divided into two stages: (i) at the initial plastic stage, the plasticity is mainly induced by the planar dislocation glide; and (ii) at the late plastic stage, the combination of dislocation hardening and mechanical twinning facilitates high strength for the studied alloy. These findings are helpful to understand the temperature dependent deformation mechanism of high entropy alloys. [ABSTRACT FROM AUTHOR]

• The novel medium-entropy alloys were fabricated by melt-extraction and exhibit excellent magnetic entropy change. • The microwires show typical amorphous characteristics and second-order phase transition. • The microstructure of microwires near room temperature is studied by in-situ HEXRD. A melt-extracted HoErCo medium-entropy alloy (MEA) with large magnetic entropy change and excellent magnetic refrigerant capacity is successfully designed in this study. The microstructure evolution of these microwires near room temperature is studied by an in-situ high energy synchrotron X-ray diffraction (HEXRD). The wires show typical amorphous characteristics during room temperature to 250 K. For a field change of 5 T, the maximum magnetic entropy change (-Δ S M max) of the microwires reaches a maximum value of 15.0 J•kg−1 K−1. Magnetization measurements revealed a paramagnetic to ferromagnetic phase transition at T C ~16 K. The refrigerant capacity (RC) and relative cooling power (RCP) are 527 J•kg−1 and 600 J•kg−1, respectively. This investigation highlights the potential of HoErCo MEA microwires as promising magnetocaloric effect materials for cryogenic applications of magnetic cooling. [ABSTRACT FROM AUTHOR]

• The oxide bifilm defects were separated from the casting matrix through electrolysis method for the first time. • The composition, phase structure and morphology of individual bifilm defects were measured directly. • The mechanical properties of amorphous alumina bifilm were tested. • The formation reasons of bifilm with different crystal types were analyzed. Bifilm defects are proposed to be critical among the metallurgical defects generated in castings. However, direct investigations of individual bifilm defects separated from the casting matrix were absent to date. In this study, separated bifilm defects in nickel-aluminium bronze were investigated systematically. The results showed that an electrolysis method can successfully separate the bifilms from the casting matrix. Al 2 O 3 with an amorphous state, a γ-phase structure, and an α-phase structure were observed in the separated bifilms, respectively, violating the conventional prediction of only α-Al 2 O 3 existing in the final casting. The thickness of the bifilm defects was not uniform and varied in a wide range from several nanometres to several hundred nanometres. Upon analysis, the thinner bifilm presented a much smaller Young's modulus in comparison to the crystallised Al 2 O 3. The thicker bifilm was intergrown with several single crystals and covered by smooth and faceted faces. These results suggest the complex bifilms form in cast nickel-aluminium bronze alloys and more investigations are therefore required in future. [ABSTRACT FROM AUTHOR]

Here, a single-track CoCrFeMnNi high entropy alloy（HEA） was prepared by laser melting deposition. The microstructural evolution of columnar to equiaxed transition was experimentally observed across the molten pool. The temperature gradient and solidification rate were theoretically calculated by a finite element model via numerical simulation. Combining experimental observations and numerical simulations, a solidification map was established to quantitatively reveal the underlying correlation between solidification parameters and microstructural morphology. A decrease in the ratio of gradient temperature to solidification rate corresponding to an increasing constitutional undercooling induced columnar to equation transition during the laser melting deposition process. It was expected that the fundamental understanding of microstructural prediction of single-track as-deposited HEA parts via the solidification map would have implications on the production of bulk components with the desired microstructure and high performance. Unlabelled Image • Single-track CoCrFeMnNi high entropy alloy was fabricated by laser melting deposition. • Columnar to equiaxed transition (CET) was systematically investigated combining experimental observations and numerical simulations. • A solidification map was established to quantitatively reveal the underlying correlation between temperature gradient (G) and solidification rate (R) and microstructural morphology. [ABSTRACT FROM AUTHOR]

The CrMnFeCoNi high-entropy alloy (HEA) exhibits higher yield strength, ultimate strength and ductility at lower temperature. To further clarify the effect of the testing temperature on microstructure evolution, in-situ synchrotron-based high-energy X-ray diffraction tensile tests were carried out from 298 K down to 123 K. The enhanced yield strength of the alloy at cryogenic temperatures can be attributed to the greater lattice distortion prior to plastic deformation. Higher strain hardening rate leads to the simultaneously enhanced strength and ductility of the studied HEA below room temperature. Both dynamic Hall-Petch hardening (twinning) and dislocation hardening provide high work hardening capacity for this alloy during the plastic deformation at cryogenic temperatures. The increased dislocation density and nano-twins at cryogenic temperatures can be attributed to the decrease in the stacking fault energy as the deformation temperature decreases. These studies could provide an in-depth understanding for the strengthening mechanisms of the HEA in different temperature conditions and guide the exploration of HEAs with superb mechanical properties at cryogenic environments. • CrMnFeCoNi HEA exhibits good mechanical properties at cryogenic temperatures. • Enhanced yield strength of the alloy stems from the larger lattice distortion. • High dislocation density and nano-twins lead to the high SHR. • Lower deformation temperature pronouncedly decreased SFE. [ABSTRACT FROM AUTHOR]

This study deals with the densification of a pre-alloyed TiAl powder with excessive yttrium addition by spark plasma sintering (SPS) technique. The gas-atomized Ti–43Al–5Nb–2V–1Y (at. %) powders were sintered at various temperatures between 1100 and 1250 °C, applying a uniaxial pressure of 40 MPa. The microstructures of pre-alloyed powders and SPSed TiAl alloy samples were analyzed by scanning and transmission electron microscopies. In addition, the compression tests of SPSed alloys was carried out at room temperature (RT). Attention is focused on the existing form and distribution of excess yttrium in the initial powders and the SPSed samples. The initial powder exhibits a dendrite structure, and yttrium-rich phases (YAl 2) are segregated along the interdendritic zone. After sintering, duplex, nearly lamellar (NL) and fully lamellar (FL) microstructures were obtained as a function of the sintering temperature. For duplex and NL microstructures, the YAl 2 phases are fine granular precipitates in homogeneous dispersion state. Conversely, stripe-like YAl 2 precipitates, which surround the α 2 /γ lamellar colonies, emerged in the FL microstructures. Excessive sintering temperature leads to grain growth and serious segregation of the YAl 2 phases, and it deteriorates the mechanical properties of this alloy eventually. Image 1 • TiAl alloy with excessive yttrium addition was prepared by spark plasma sintering. • Fine YAl 2 particles are dispersed in samples sintered at relatively low temperature. • Strip-like YAl 2 phases with network structure formed in FL microstructure. • The SPSed alloys with fine YAl 2 particles own better compression properties. [ABSTRACT FROM AUTHOR]

Ti–48Al–2Cr–2Nb alloy reinforced with ceramic particle Y 2 O 3 was fabricated by induction skull melting (ISM) technique in a vacuum environment. The thermodynamic feasibility of the reactions between nano Y 2 O 3 and molten alloy has been considered. The as-cast microstructure of Ti–48Al–2Cr–2Nb adding nanoY 2 O 3 during melting was analyzed by OM, SEM, EDS and TEM. It is concluded that multiple reinforcements are synthesized and they show different shapes. Y 2 O 3 grows in regular geometry shapes when the content of Y 2 O 3 is about 0.1 at. % and grows in dendritic shapes when the content of Y 2 O 3 is below 0.05 at.%. The work shows that adding nano Y 2 O 3 could refine microstructure of TiAl and improve strength and elongation of TiAl alloy effectively within a certain range. • The evolution of nanoY 2 O 3 in molten TiAl has been studied. • Diffused micron regular geometry particle was formed in the TiAl microstructure. • The TiAl has excellent room temperature strength(752 MPa) and elongation (0.75%). [ABSTRACT FROM AUTHOR]