In the present study, hot isostatic pressing (HIP) subjected to high intermediate cooling rate is exploited to seal keyholes and tune the microstructure of equiatomic CoCrNi and (CoCrNi)94Al3Ti3 medium entropy alloys (MEAs) prepared by spark plasma sintering (SPS). For equiatomic CoCrNi, fracture toughness (KIC) is significantly increased but the yield strength (σ0.2) is almost constant when the relative density is increased from 98.9% to 99.7% by HIP. By contrast, σ0.2 and KIC of (CoCrNi)94Al3Ti3 are considerably advanced by 27.3% and 38.6%, respectively. Meanwhile, the change of grain size introduced by HIP treatment is very inconspicuous in present study. Obvious plastic deformation traces are observed near the crack in the samples subjected to HIP treatment. Systematic microstructure observations indicate that the nano-precipitates and the concurrent of the long split 9R structure and nanotwins in (CoCrNi)94Al3Ti3 formed during HIP treatment are responsible for the enhancement of σ0.2. The formation mechanisms of 9R phase in terms of the hierarchical architecture twins and dislocations activity are explored. Our findings offer new insights on design and processing of MEAs parts by the powder metallurgy.

An industrially-cast high entropy alloy with a nominal composition of Al0.65CoCrFe2Ni, having FCC and BCC phases, was compressed at high strain rates using a split Hopkinson pressure bar under a range of test temperatures. The strain rate sensitivity and strain hardening behaviour of the alloy were analyzed. The alloy exhibited high strain hardening and excellent strain rate sensitivity owing to its large solid solution strengthening and low athermal strength contributors. The alloy also displayed outstanding dynamic strain rate sensitivity compared to similar dual-phase high entropy alloys of the AlCoCrFeNi alloy system. The alloy exhibited excellent resistance to thermal softening at high strain rate loading due to higher phonon drag associated with an increase in the operating temperature. The substructures formed in the alloy during high strain rate deformation at room temperature comprised of Lomer-Cottrell (L-C) locks, deformation twins, planar deformation bands, and high dislocation pile-ups at interphase boundaries and subgrain boundaries. The high strain rate deformation at high temperatures resulted in the formation of dislocation cells, kinks and jogs, enabling the alloy to retain strain hardening behavior. The Johnson-Cook (J-C) model accurately predicted the plasticity behavior of the alloy under high strain rate loading.

The effect of adding N on the thermodynamics and corrosion resistance of as-cast Zr55Cu30Ni5Al10 bulk metallic glass (BMG) is clarified using electrochemical measurements, microstructure characterization and surface analyses. Compared with Zr55Cu30Ni5Al10 BMG, Nitrogen-doped (Zr55Cu30Ni5Al10)98.5N1.5 BMG is easier to nucleate during heating, but the nucleation growth process becomes more difficult. The corrosion potential (Ecorr) of (Zr55Cu30Ni5Al10)98.5N1.5 BMG and Zr55Cu30Ni5Al10 BMG is −0.32 V and −0.39 V respectively, and the corrosion current density (Icorr) of (Zr55Cu30Ni5Al10)98.5N1.5 BMG and Zr55Cu30Ni5Al10 BMG is 7.90 × 10−8 A/cm2 and 9.13 × 10−5 A/cm2, respectively. I.e., after nitrogen doping the corrosion potential increased slightly, but the corrosion current density decreased by about three orders of magnitude. Meanwhile the oxide film resistance increased significantly, and the surface corrosion diffusion effect weakened. Nitrogen reduces the H+ concentration in the pitting pits, slows down the pitting rate, and improves the corrosion resistance. Proper nitrogen can improve the thermal-stability and surface corrosion resistance of Zr-based BMGs.

Porous TiNi intermetallic compounds have a promising future as biomaterials, with some challenges for their corrosion resistance. In this work, TiNi intermetallic compound was prepared by reactive synthesis of elemental powders. The evolution of the microstructure and phase composition of TiNi at different temperatures was studied. And the electrochemical corrosion behavior of TiNi intermetallic compound in NaCl solution was investigated by electrochemical tests. The results show the formation of a core-shell structure during the sintering process, where Ni is the core and Ti2Ni, TiNi and TiNi3 are the shells. With uniform diffusion, a large pore replaces the Ni core due to the Kirkendall effect. TiNi intermetallic compound has a well-developed open pore structure with an open pore ratio of 50.98%. TiNi intermetallic compound exhibits better corrosion resistance compared to Ni and Ti, which can be attributed to the generation of passivation film on the surface.

Through mechanical alloying, the high entropy alloy AlCrFeNiTiZn (HEA) is produced. After 120 h, the milled powder shows uniform morphology and homogeneous composition, with an average size of 190 nm. Solid solution phases with BCC (A = 2.88 ± 0.02 Å) and FCC (a = 3.57 ± 0.02 Å) crystalline structures were confirmed by XRD and TEM in prepared high entropy alloy. There is only one exothermic peak at 290 °C on DSC thermogram of the 120 h milled powder. During milling, Johnson Mehl Avrami model effectively explained the kinetics of AlCrFeNiTiZn HEA formation and characterized its type as diffusion-controlled nucleation. In a tube furnace at 800 °C, similar phases were also observed after cold pressing and sintering HEA powder. The alloy had a porosity of 14% and a density of 86%.

The current research on the corrosion resistance of high entropy alloys (HEAs), mainly focuses on the influence of element composition and percentage difference. Considering the almost consistent passivation range with different corrosion resistance contributed by element addition, it inevitably exists obvious differences the passive film properties. The effect of passive film on corrosion behavior of HEA is worthy to be investigated in detail. Considering the microstructure transformation detected by electron probe X-ray microanalysis (EPMA) and surface feedback effect measured by approach curve of scanning electrochemical microscopy (SECM), the passivity of Alx(CoCrFeNi)100-x (x = 0–20) HEAs in 0.5 M H2SO4 solution has been investigated by cyclic potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), Mott-Schottky analysis and X-ray photoelectron spectroscopy (XPS). The results demonstrate that the passive film is thick and dense at low Al content (5%), which shows excellent corrosion resistance. However, with the increase of Al content, the corrosion resistance of passive film deteriorates gradually. XPS are adopted to detect film composition to explain the reason of film property change. The results suggest that there are more oxidized states of Al and less oxidized states of Cr in the passive film of HEAs with Al addition. The dominate semiconductor characteristics of Alx(CoCrFeNi)100-x with Al addition change from p-type to n-type. All results indicate that the addition of Al has a significantly influence on the composition and properties of passive film on the Alx(CoCrFeNi)100-x alloys surface.

The yield strength (YS) of single crystal Ni-based superalloys is a critical factor for low temperature low cycle fatigue and Out-of-phase thermomechanical fatigue durability of turbine blades. The chemical composition of this class of alloys appears to have a major role in their low temperature tensile behavior. Indeed, alloying elements modify the antiphase boundary (APB) energy of the γ′ phase and so its resistance to shearing. To investigate the influence of the chemical composition on the YS, 18 superalloys of different generations were tensile tested at 650 °C. The results show a significant YS evolution of up to 250 MPa between the first generation and the following generations. The YS differences are mainly attributed to the contributions of γʹ which in turn is dependent on the γʹ phase composition. An EDNNB model was adapted to estimate the APB energies for the aforementioned set of alloys using Thermo-Calc data. Ta and Ti elements appear to be the most efficient γ′ strengtheners. The higher their content is, the higher the APB energy is and the stronger the alloy is in terms of tensile YS. Several alloys also exhibit an important strain hardening.

The phase structure and composition of the Cu/Cu3Sn interface were investigated during aging at 150 °C via transmission electron microscopy. The newly formed Cu3Sn phase was hexagonal, and the Cu substrate was cubic. However, the fine Cu grains that formed at the Cu/Cu3Sn interface were monoclinic. The structure of the Cu3Sn/Cu interface exhibited special crystallographic relationships after aging, that is [21‾1‾6]Cu3Sn//[1‾01]Cu and (02‾20)Cu3Sn//(404)Cu. The mismatch of the crystal plane spacing between the (02‾20)Cu3Sn and (404)Cu crystal planes was 0.959%. In this study, monoclinic Cu precipitated at the Cu/Cu3Sn interface in the form of particles but did not produce a layered structure.

The γ/γ′ interface has an important influence on the nanoscale deformation of nickel-based single crystal superalloy. In this paper, nano-cutting simulations of nickel-based single crystal superalloy are performed by molecular dynamics methods, and the mechanical properties, atomic displacements, dislocation evolution, temperature, surface quality and Al atom precipitation behavior of the workpiece are analyzed in depth. We found that: the γ/γ′ interface will hinder the force conduction and dislocation development, resulting in fluctuation of processing force and dislocation density. In addition, the special two-phase structure will affect the deformation of the material, and the dislocation motion will stay in the γ phase for a long time and occur dislocation accumulation and work hardening, meanwhile, there are more displacement atoms in the γ phase than in the γ′ phase, and the degree of plastic deformation in the γ phase will be more drastic. It is also found that there is always a difference in the temperature distribution of the two phases of the material, and the uneven cutting surface always appears at the junction of the two phases, and the Al atoms on the subsurface will precipitate and form an Al film covering the surface after being influenced by the cutting temperature.

The non-isothermal thermal behavior of Fe74B20Nb2Hf2Si2 bulk metallic glass (BMG) was studied utilizing various thermal analytical methods. The obtained results showed that the viscosity behavior of this alloy in the supercooled region was strong due to the high kinetic fragility parameter (D* = 49.5) and low fragility parameter (m = 20.2). Also, the apparent activation energy (Ep) values for crystallization process were calculated in the range of 188.7–394.6 kJ/mol using the Gao-Wang method. Additionally, the Avrami's exponent (n) values increased from 2 to 4 with the progress of the crystallization process. The two-parameter Šesták-Berggren (SB) model was used to demonstrate the autocatalytic behavior of crystallization. Furthermore, the kinetic analysis revealed that all crystallization stages were controlled by the interface. The phase analysis showed that the Fe23B6, α-Fe, Fe2(Hf, Nb), and Fe2B phases were formed during the crystallization process. As obtained by the microstructural characterization, it was founded that the low dimensional growth (m = 2) is due to the complex structure of the main phase of Fe23B6 in the first crystallization stage. Moreover, the high dimensional growth (m = 3) during the second and third crystallization stages attributed to the Fe2B phase as the heterogeneous nucleation, as well as a significant increase in the volume fraction of the α-Fe phase, and the preferential orientation of the various crystalline phases. Hence, the values of Avrami's exponent (n) in the second and third crystallization stages were calculated equal to 3 and 4, respectively.

A single-phase FeCrNi medium-entropy alloy (MEA) with a face-centered cubic structure was successfully fabricated by selected laser melting (SLM). The SLMed FeCrNi MEA exhibits hierarchical microstructures, including molten pools, coarse columnar grains, submicron cellular structures and high-density dislocations, and shows an excellent strength-ductility combination. Notably, the SLMed FeCrNi MEA has ultra-high yield strength and ultimate tensile strength of 1.1 GPa and 1.5 GPa, respectively, at 77 K, which are almost 1.5 times higher than those at room temperature, while still maintaining a high fracture elongation of 49%. It was also found that the SLMed FeCrNi MEA deformed at 77 K could produce more nanotwins compared with that deformed at room temperature. The twinning-prone matrix can produce more significant twinning-induced plasticity effects, which contributes to a high plasticity. Additionally, the high-density cellular substructure can effectively hinder dislocation motion, which is the main reason for the high strength.

In the zinc electrowinning process, lead anodes have been the main cause of lead pollution, resulting in environmental and ecological imbalances. To address this issue, this study prepared high purity bulk and porous TiMn2 intermetallic compound lead-free anodes through elemental reaction synthesis and investigated their electrochemical properties and electrolytic performance. The Tafel slopes of the bulk and porous TiMn2 anodes were found to be 351.85 and 741.9 mV·dec−1, respectively, with oxygen evolution overpotentials of 0.952 and 0.704 V in 160 g L−1 H2SO4 solutions. Both bulk and porous TiMn2 anodes exhibited long-time stability of 4210 and 960 h, respectively, during simulated electrolysis at 500 A m−2. Additionally, porous TiMn2 anodes exhibited lower potential than lead in simulated electrowinning experiments, while maintaining the quality of the deposited Zn conforming to the Zn-1 standard according to ISO 752–2004, with higher electrowinning efficiency than lead anode. Therefore, this study proposes a new intermetallic compound anode system that shows great potential and application in electrowinning, while reducing lead pollution and promoting environmental and ecological balance.

Novel Fe52Co20-xB20Si4Nb4Mox (x = 0–5) bulk metallic glasses with a diameter of 2 mm are successfully prepared by vacuum suction casting and the effect of Mo addition on their nanoindentation creep behavior is studied. Through a differential scanning calorimetry and creep compliance spectral analysis, it is found that the addition of a small amount of Mo increases the enthalpies (ΔH) and free volumes of the alloys. These factors stimulate the rearrangement of the atomic structures of the alloys and induce the adjustment of their internal structure, resulting in a relatively loose atomic packing state that allows the alloys to provide a continuous response to stress during creep deformation. By analyzing the unloading and load holding sections on the load-displacement curves, it is shown that the hysteresis of deformation induces the displacement jump phenomenon and the amplitude of the jump is inversely proportional to the equivalent stress. The larger the equivalent stress, the less obvious the displacement pop-out phenomenon. The changes in strain rate sensitivity exponent (m) and hardness are also studied. Combined with a delay spectral analysis, it is found that a 5% Mo addition significantly improves the creep resistance of the alloys.

The effect of Si micro-alloying on the microstructure and mechanical properties of (Ti28Zr40Al20Nb12)100-xSix (x = 0, 0.1, 0.2, 0.5) high entropy alloys are studied. Coarse grains mainly composed of two ordered B2 phases are obtained during solidification, while the hcp-Zr5Al3 type precipitate formed after annealing at 1200 °C for 24h. As the Si content increases, the phase morphology at the grain boundaries gradually changes from a completely continuous structure to a partially continuous structure, and finally transfers to a necklace-type structure. The phase morphology inside the grains simultaneously transforms into merely randomly distributed particles. The changes in phase morphology are attributed to the stronger chemical affinity between Zr and Si. Owing to the severe inhomogeneity caused by the Si addition, a dramatic decrease of the fracture strain is observed in compression tests for as-cast samples. For Si micro-alloyed alloys, the annealed samples show an improvement of both compression strength and fracture strain. The obtained results suggest that Si micro-alloying has less impact on phase composition, but significantly affects elemental segregation, phase morphology and thus the mechanical properties.

In recent years, nickel–titanium (NiTi) coatings have shown excellent tribological performance due to their unique phase transition characteristics. However, in the laser cladding of NiTi coatings in a semi-open environment, there are still issues with nitrogen and oxygen impurities arising in the coatings due to their exposure to air. In this study, three rare earth (RE) compounds were used to modify NiTi coatings in a semi-open environment to obtain coatings without any impurities. The effect of different RE compounds (Y2O3, YF3 and YCl3) on phase composition, surface oxidation and mechanical properties were studied. NiTi, NiTi2 and the impurity phase titanium nitride (TiN) were observed in the original and Y2O3 modified coating. In addition, incompletely melted Y2O3 exists in the Y2O3-modified coating. The coatings with YCl3 and YF3 were composed of NiTi and NiTi2 phase and the TiN impurity phase was not observed in either coating. In addition, the oxidation phenomenon at the top of the coating gradually weakened in the original, Y2O3, YCl3 and YF3-modified coatings. Furthermore, the R-phase was characterised in the YF3-modified coatings. The average microhardness values of the original, Y2O3, YCl3 and YF3-modified coatings were 669.68 HV0.3, 755.1 HV0.3, 579.1 HV0.3 and 390.47 HV0.3, respectively, of which the microhardness of the YF3-modified coating was the lowest. Although RE compounds did not significantly change the tribological properties, the Y2O3-modified coating exhibited the best tribological properties (∼0.886 mm, 2.6 mg). The results show that YF3 can isolate pollutants from the air in the coating and protect the coating in a semi-open environment.

The present work aimed to develop a novel medium entropy alloy (MEA) with superior mechanical properties and biocompatibility for the metallic-bioimplant application. A series of (TiZrNb0.7)100-xOx (x = 0, 0.5, 0.75 at. %) MEAs were carefully designed and prepared. The microstructure, mechanical properties, corrosion resistance, and biocompatibility were investigated in detail. Single-phase body-centered cubic (BCC) structural (TiZrNb0.7)100-xOx MEAs consisted of as-cast dendritic morphology. Interestingly, the yield strength and ductility of (TiZrNb0.7)100-xOx MEAs were improved simultaneously with their O concentration. The (TiZrNb0.7)99.25O0.75 MEA had optimal mechanical properties, exhibiting a yield strength of 911 ± 11 MPa, a fracture elongation of 16.1 ± 0.7%, and an elastic modulus of 70.5 ± 1.2 GPa. According to the potentiodynamic polarization and cell culture experiment, the (TiZrNb0.7)99.25O0.75 MEA exhibited superior corrosion resistance and biocompatibility, equivalent to the commercially pure titanium (CP-Ti). These findings provide a paradigm for achieving outstanding comprehensive properties in MEA via O doping.

In this work, we report an elaborate study on the structural, magnetic and thermoelectric properties of two Ru-based Heusler alloys, viz., Ru2VAl and Ru2VGa, having valence electron count 24. While Ru2VGa exhibits a nonmagnetic ground state, in Ru2VAl a short range ferromagnetic interaction is developed below 10 K due to the structural antisite defects and disorder, that also manifests its signature in the specific heat and electrical resistivity measurements at low temperatures. Both the Seebeck coefficient (S) and Hall measurements suggest the dominance of hole-type carrier for electronic transport in Ru2VAl whereas Ru2VGa is found to be a n-type material. The linear nature and small absolute values of S, as well as non-zero values of electronic contribution to specific heat γS (γSRu2VAl = 4.9 mJ/mol-K2 and γSRu2VGa = 5.5 mJ/mol-K2) point towards a metallic ground state for both these alloys. Both the compounds exhibit lower thermal conductivity at room temperature in comparison to Fe-based Heusler alloys due to the presence of heavier element Ru.

Intrinsic brittleness and cold cracking sensitivity of Fe–Al intermetallic compounds make their fabrication and processing difficult. In recent years, an innovative additive manufacturing (AM) technology, twin-wire directed energy deposition-arc (TW-DED-arc), has been developed to prepare defect-free Fe–Al alloys via in-situ alloying of Fe and Al elements in a gas tungsten arc welding (GTAW) generated molten pool. However, unconstrained plasma of regular tungsten arc leads to excessive heating area and residual stress during AM buildup. And relatively weak arc pressure of GTAW makes composition inhomogeneity a concern in the in-situ alloying molten pool. To solve the two potential drawbacks, plasma arc welding (PAW) possessing higher energy density and arc pressure is used to power the TW-DED-arc process and fabricate Fe–30Al alloy. In the present research, a special wire-feeding strategy for stable twin-wire feeding of Fe and Al wires is successfully developed to overcome the droplet transfer difficulty induced by constrained arc of PAW and large thermophysical properties difference of heterogeneous filler wires. And according to microscopy characterization results, the innovative PAW powered TW-DED-arc process is capable of fabricating defect-free Fe–30Al bulk sample with homogeneous Al content and epitaxial columnar grain structures. The successful application of PAW-powered TW-DED-arc technique in fabrication of iron aluminide provides stabler and more efficient route for iron aluminide component.

Induction hot-pressing sintering, as an effective sintering technique, has been rarely investigated and reported in the sintering of TiAl alloys. In this paper, in-situ nano/micron Ti2AlC reinforced high-Nb TiAl composites were fabricated via induction hot-pressing sintering, and the effect of nano-C addition on the microstructure and tensile properties was investigated. With 0.75 at% nano-C addition, the lamellar colony size decreased from 406 ± 151 μm to 141 ± 62 μm, and the Ti2AlC particles were mainly distributed at the γ/α2 lamellar interface. At 800 °C and 900 °C, the ultimate tensile strength and the elongation of the TiAl alloy were 436 MPa and 437 MPa, 0.84%, and 1.12%, respectively. However, with 0.75 at% addition (after heat treatment 900 °C/48 h), the ultimate tensile strength increases by 129 MPa and 78 MPa, and the elongation increases by 0.27% and 0.64%, respectively. The significant improvement in tensile property is mainly attributed to the precipitation phase enhancement and grain refinement.

The Cu20Ni20Mn alloy possesses both high strength and excellent elastic modulus, which has the potential to work in some extreme environments. In our study, by adding Ga into the Cu-Ni-Mn alloy, a new kind of Cu20Ni20Mn-xGa (x = 0, 1, 5 wt%) alloys were produced. After undergoing different thermal-mechanical treatments, these alloys were comprehensively investigated particularly for their mechanical properties and microstructures. While at the peak aging condition, the ultimate tensile strength and total elongation of the Cu20Ni20Mn-1Ga alloy are 1476 MPa and 7.9% respectively, both are higher than that of the Ga-free case (1391 MPa and 3.9%). The Ga added in small amount facilitates the nucleation of NiMn nanoprecipitates inside the grain instead of on the grain boundary, which provides enormous precipitation strengthening and greatly enhances the alloy. However, with addition of excessive Ga (e. g. 5 wt%), discontinuous Ni2MnGa precipitates are observed at grain boundaries, which greatly reduce the ductility of the alloy. Based on our research, we believe that adding appropriate amount of Ga is beneficial for the mechanical properties of the Cu-Ni-Mn alloys, which will become a potential strengthening method for Cu alloys in the future.