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Analytical and numerical analyses for predicting the mechanical responses of BCC and FCC lattice structures under compressive loading were performed and verified by comparing them to experimental data. The analytical and numerical results are in excellent correlation, while the error between the experimental and numerical results is about 5.8 ~ 15.3 %, which was caused by the inconsistent lattice strut diameter and the material elastic modulus. The measured lattice strut diameter is smaller than the designed diameter by thermal shrinkage, so the thermal shrinkage should be taken into the lattice structure design in additive manufacturing processes. Based on the same analytical and numerical techniques, a parametric investigation of the elastic moduli of BCC and FCC lattice unit cells with respect to the strut aspect ratio, specific density and strut angle was performed. Finally, the elastic moduli of multi-cell BCC and FCC lattice structures with the same density were investigated by varying the number of rows and columns of lattice unit cells in both unconstrained and constrained boundary conditions. As the strut aspect ratio, density and angle increase, the elastic moduli of both BCC and FCC lattice increase. FCC elastic modulus is higher than that of BCC lattice with respect to the strut aspect ratio, density and angle, while BCC elastic modulus could be found to be higher than of FCC lattice for a constrained boundary condition.

A FeCrCuMnNi high-entropy alloy was produced using vacuum induction melting, starting from high-purity raw materials. The microstructure and mechanical properties of the as-cast FeCrCuMnNi alloy were studied, considering x-ray diffraction (XRD), scanning electron microscopy, and hardness and tensile tests. XRD results revealed the existence of two FCC phases and one BCC phase. Microstructural evaluation illustrated that the as-cast alloy has a typical cast dendritic structure, where dendrite regions (BCC) were enriched in Cr and Fe. Interdendritic regions were saturated with Cu and Ni and revealed G/B(T) {110} 〈111〉 and Brass {110} 〈112〉 as the major texture components. The produced alloy revealed an excellent compromise in mechanical properties due to the mixture of solid solution phases with different structures: 300 HV hardness, 950 MPa ultimate tensile strength and 14% elongation. Microhardness test results also revealed that the BCC phase was the hardest phase. The fracture surface evidenced a typical ductile failure. Furthermore, heat treatment results revealed that phase composition remained stable after annealing up to 650 °C. Phase transformation occurred at higher temperatures in order to form more stable phases; therefore, FCC2 phase grew at the expense of the BCC phase.

High-entropy alloys (HEAs), a novel class of metal alloys, have been receiving increasing attention from the scientific community. HEAs have the potential to be used in critical load-bearing applications in replacement of conventional alloys such as stainless steel and nickel-base superalloys. Tensile experiments at quasi-static to dynamic strain rates (10 −4 -10 3  s −1 ) were performed on two single-phase face-centered cubic HEAs, CoCrFeNi and CoCrFeMnNi. Electron backscatter diffraction was used to study the microstructure of the samples before the experiments, and transmission electron microscopy was performed postmortem. The dominant deformation mechanisms were dislocation slip at quasi-static strain rates with the addition of deformation nano-twins at dynamic strain rates. Ultimate dynamic tensile strength and ductility improved with the increase in strain rate, which can be attributed to the activation of deformation nano-twins in HEAs. CoCrFeNi and CoCrFeMnNi both have low stacking fault energies, which could promote twinning at high strain rates to accommodate plastic deformation. The strain rate sensitivity of the flow stress increased with increasing strain rate, beginning with negligible strain rate sensitivity in the quasi-static range to high strain rate sensitivity in the dynamic range. CoCrFeMnNi showed greater strain rate sensitivity of flow stress. CoCrFeNi, with less configurational entropy, had higher mechanical properties and strain-hardening rates compared to CoCrFeMnNi, which was attributed to the weakening effect of the addition of Mn on the solid solution hardening.

In this paper, the effect of applied multi-variant heat treatment on microstructure, phase composition and mechanical response of Haynes 282 nickel-based superalloy was investigated. For this reason, temperatures of both stages of standard two-stage aging treatment (i.e., 1010 °C/2 h + 780 °C/8 h) were extended to 900-1100 °C/2 h and 680-880 °C/8 h ranges, respectively. Consequently, 30 different variants of heat treatment were applied. The microstructural features of heat-treated samples were investigated by means of light microscopy and SEM/EDS methods, while mechanical properties were examined via microhardness measurements. It was found that by using various combinations of temperatures of the first and second stage of aging, the room temperature hardness of Haynes 282 alloy can be decreased by ~ 100 HV units or increased by up to 25 HV units as compared to that of the alloy subjected to the standard heat treatment schedule. The mechanical response of the alloy is determined by a complex structural evolution involving the secondary precipitation of γ′, M 23 C 6 and M 6 C phases, as well as their interaction with the fcc γ matrix.

In this paper, the microstructure, mechanical properties, and corrosion resistance of the dental Co-Cr-Mo-W alloys fabricated by selective laser melting (SLM) were systematically investigated and correlated. The microstructure of the SLM group (SG) specimens is composed of extremely fine columnar crystals, exhibiting supersaturated and homogeneous character. The matrix mainly consists of face-centered-cubic (FCC) cobalt solid solutions, and minimal hexagonal-close-packed (HCP) cobalt solid solutions. Mechanical test results showed that the 0.2% yield strength of SG was 775 ± 7 MPa, and the ultimate tensile strength was 1118 ± 25 MPa. The elongation of SG was 8.28 ± 0.4%, and the microhardness of SG was 476 ± 10 HV. All of these values largely exceeded the cast group (CG) specimens. The high strength is attributed to their fine columnar crystals and supersaturated matrices. The fewer content from the HCP phase and a lack of intermetallic compounds or eutectic contribute to the high ductility. Furthermore, a higher Ecorr, lower Icorr were acquired for better corrosion resistance compared to cast specimens, due to even less composition segregation and more microstructural homogeneity.

V element had positive effect in improving the strength of many alloys, so it was possible that V had potential to strengthen CoCrCuFeNi high-entropy alloys (HEAs) with face-centered cubic (FCC) crystal structure, which was relatively weak in strength and had outstanding ductility. In this paper, we studied the alloying effect of V on the phase evolution, microstructure and the mechanical properties of the (CoCrCuFeNi) 100− x V x ( x  = 0-16, atomic ratio, hereafter in at.%) HEAs systematically. The results showed that V element had capacity to induce sigma phase precipitation. The volume fraction of sigma phase increased from 0 to 12%; the compressive yield stress of (CoCrCuFeNi) 100− x V x HEAs increased from 300 to 613 MPa with V content increasing from 0 to 16% (atomic ratio, hereafter in at.%). However, the compression fracture strain decreased from 50 to 28%. V addition was beneficial in improving the strength of CoCrCuFeNi HEA, and the increase in sigma phase volume fraction was the key factor for the improvement of the (CoCrCuFeNi) 100− x V x HEAs in yield stress.

We report thickness-dependent thermal oxidation in Ni (t = 10–300 nm) thin films exposed to air annealing and the resulting vibrational, magnetic and electrical properties of Ni films deposited directly on thermally oxidized Si substrate using magnetron sputtering technique at ambient temperature. As-deposited Ni films exhibit face-centred cubic structure with fine crystals and large lattice constant (aNi) at lower t (< 50 nm). With increasing t, aNi decreases and approaches to bulk value. With increasing TA, aNi not only decreases to bulk Ni due to improved crystallization but also reduces below bulk Ni for t > 50 due to formation of NiO. The relative fraction of Ni and NiO in annealed films up to 400 ∘C strongly depends on t. Annealing Ni films at 500 ∘C results into complete oxidation of Ni into granular-type NiO. X-ray reflectivity studies reveal that oxidation process occurs from surface of the films converting Ni into NiO possibly through layer by layer process, which is subtle to t. Raman spectra show that intensity ratio between one-phonon longitudinal optical (LO) and two-phonon LO bands decreases and intensity of two-magnon band increases with increasing t for films annealed at particular TA. This confirms the growth of NiO not only with increasing TA, but also with t. As-deposited films exhibit ferromagnetism at room temperature. The presence of Ni and NiO in annealed films implies coexistence of ferromagnetic and antiferromagnetic interactions, leading to tunable exchange bias (HE), whose magnitude strongly depends on the ratio between Ni and NiO. Electrical resistance (R) of the as-deposited Ni films decreases with increasing t and follows the Namba’s model. Upon annealing, R increases largely due to oxidation of Ni. The observed results are explained on the basis of thickness dependent thermal oxidation process with increasing TA.

The migration of point defects, for example, crystal lattice vacancies and self-interstitial atoms (SIAs), typically occurs through three-dimensional random walk in crystalline solids. However, when vacancies and SIAs agglomerate to form planar clusters, the migration mode may change. We observed nanometer-sized clusters of vacancies exhibiting one-dimensional (1D) fast migration. The 1D migration transported a vacancy cluster containing several hundred vacancies with a mobility higher than that of a single vacancy random walk and a mobility comparable to a single SIA random walk. Moreover, we found that the 1D migration may be a key physical mechanism for self-organization of nanometer-sized sessile vacancy cluster (stacking fault tetrahedron) arrays. Harnessing this 1D migration mode may enable new control of defect microstructures such as effective defect removal and introduction of ordered nanostructures in materials, including semiconductors.

In this work, the mass transfer along an octahedral channel in an fcc copper single crystal is studied for the first time using the method of molecular dynamics. It is found that the initial position of the bombarding atom, outside or inside the crystal, does not noticeably affect the dynamics of its motion. The higher the initial velocity of the bombarding atom, the deeper its penetration into the material. It is found out how the place of entry of the bombarding atom into the channel affects its further dynamics. The greatest penetration depth and the smallest dissipation of kinetic energy occurs when the atom moves exactly in the center of the octahedral channel. The deviation of the bombarding atom from the center of the channel leads to the appearance of other velocity components perpendicular to the initial velocity vector and to an increase in its energy dissipation. Nevertheless, the motion of an atom along the channel is observed even when the entry point deviates from the center of the channel by up to 0.5 Å. The dissipated kinetic energy spent on the excitation of the atoms forming the octahedral channel is nearly proportional to the deviation from the center of the channel. At sufficiently high initial velocities of the bombarding atom, supersonic crowdions are formed, moving along the close-packed direction ⟨1¯10⟩, which is perpendicular to the direction of the channel. The results obtained are useful for understanding the mechanism of mass transfer during ion implantation and similar experimental techniques.

Strengthening mechanisms from thermomechanical processing treatments were explored in single-phase FCC high-entropy alloy Alsub 0.1CoCrFeNi. Cold work offers substantial strengthening in this low stacking fault energy material owing to the resultant high work hardening rates. An enormous increase in yield strength of 275% was obtained in 40% rolled material, but was accompanied by a steep drop in ductility. Recovery and recrystallization annealing treatments were investigated for improving elongation and obtaining better balance of strength–ductility combinations. Formation of novel microstructures from the different processing routes was examined. X-ray diffraction peak broadening and mechanical test results were coupled to estimate micro-strain in the different conditions and understand micro-strain’s correlation to strength. Retention of large-scale deformation twins formed during cold rolling is shown to play a key role in elevation of yield strength after heat treatments.