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Intermetallics
Elsevier Science
Intermetallics

Elsevier Science

0966-9795

Intermetallics/Journal IntermetallicsSCIISTPEI
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    Oxidation behaviors of CrNb, CrNbTi, and CrNbTaTi concentrated refractory alloys

    Butler T.M.Senkov O.N.Daboiku T.I.Velez M.A....
    17页
    查看更多>>摘要：? 2021The 1200 °C oxidation behaviors of CrNb, CrNbTi and CrNbTaTi are reported. All alloys formed some combination of BCC and Laves phases. However, additions of Ti produced a unique inflection point where the microstructure inverts to a Ti-rich BCC matrix with Laves phase precipitates. Further additions of Ta to CrNbTi were found to increase the overall phase fraction of BCC phase. The oxidation kinetics for CrNb and CrNbTi were similar and nearly parabolic throughout the duration of exposure. CrNbTaTi exhibited inferior oxidation kinetics and mixed mode behavior throughout oxidation testing. All alloys formed intricate multi-phase oxide structures, consisting of a combination of both simple and complex oxides. The resulting microstructures are characterized using a variety of analytical techniques and the results are discussed relative to modeling predictions using ab initio density functional theory (DFT).
      原文链接:
    • NSTL
    • Elsevier

    Shear band evolution related with thermal annealing revealing ductile-brittle transition of Zr35Ti30Be27.5Cu7.5 metallic glass under complex stress state

    Liu X.Wang T.Wang Q.Song X....
    12页
    查看更多>>摘要：? 2021 Elsevier LtdThe ductile-brittle transition (DBT) caused by thermal annealing was systematically investigated by means of small punch test (SPT), accompanied by finite element simulation, uniaxial compression and nanoindentation in Zr-based metallic glasses (MGs) annealed for 1 h in a wide temperature range, i.e., sub-Tg, Tg ～ Tx and above-Tx. In multiaxial loading mode, three deformation mechanisms, i.e., (ⅰ) circumferential shear bands (CSBs) + radial shear bands (RSBs), (ⅱ) RSBs and (ⅲ) radial cracks (RCs), can be found separately on MGs annealed sub-Tg, Tg ～ Tx and above-Tx, leading to a transition in deformation mode from ductility to brittleness. First, for MGs with sub-Tg, Tg ～ Tx annealing, the reduction in the number of CSBs and RSBs, as well as the disappearance of CSBs, are responsible for the ductile-brittle transition, which is attributed to the annihilation of free volume caused by structural relaxation and the reduction of released elastic energy. Based on simulation results, the decrease in plasticity of MGs is accompanied by the reduction in stress distribution area, which is in agreement with the change in the number and distribution area of shear bands. The initiation of multiple shear bands and their strong interaction dramatically improve the plasticity of MGs under the synergistic effect of large stress distribution area and high content of free volume. Second, the embrittlement of MGs with above-Tx annealing is mainly attributed to the rapid formation and extension of RCs induced by the occurrence of crystallization. Meeanwhile, simulation results indicate that stress distribution area decreases gradually and facilitate the formation of stress concentration, leading to the rapid extension of RCs and the occurrence of catastrophic fracture of MGs. In addition, MGs with sub-Tg, Tg ～ Tx and above-Tx annealing not only exhibit such DBT in uniaxial compression, but also show a soft-hard transition in nanoindentation test.
      原文链接:
    • NSTL
    • Elsevier

    Highly sensitive elastocaloric response in a directionally solidified Ni50Mn33In15.5Cu1.5 alloy with strong <001>A preferred orientation

    Wang H.Li D.Zhang G.Li Z....
    8页
    查看更多>>摘要：? 2021 Elsevier LtdSolid-state elastocaloric cooling based on elastocaloric effect resulting from superelastic martensitic transformation has been conceived as a very competitive alternative to the conventional vapor-compression refrigeration. Reducing the driving stress of elastocaloric effect is very beneficial to the miniaturization and compactness of refrigeration devices. Here, we demonstrate large elastocaloric effect driven by low stress in a directionally solidified Ni50Mn33In15.5Cu1.5 alloy. Owing to the coarse columnar shaped grains with strong <001>A preferred orientation, large adiabatic temperature change (ΔTad) values up to ?9.5 K and ?11.4 K can be achieved on removing the relatively low compressive stress of 113 MPa and 150 MPa, respectively, showing the high sensitivity of elastocaloric response with the specific adiabatic temperature change (|ΔTad/σmax|) up to 83.5 K/GPa. Such value is much higher than those in other Ni–Mn-X based alloys reported previously.
      原文链接:
    • NSTL
    • Elsevier

    Magnetocaloric effect, heat capacity and exchange interactions in nonstoichiometric Er0.65Gd0.35Co2Mnx compounds

    Gerasimov E.G.Inishev A.A.Mushnikov N.V.Terentev P.B....
    7页
    查看更多>>摘要：? 2021 Elsevier LtdThe crystal structure, magnetic and magnetothermal properties of nonstoichiometric Er0.35Gd0.65Co2Mnx (0 ≤ x ≤ 0.4) compounds have been investigated. It is observed a considerable increase in the Curie temperature from TC = 170 K up to above room temperature TC = 324 K with increasing the Mn content. The exchange interactions in nonstoichiometric alloys of the RCo2Mnx - type (R is Er, Er0.35Gd0.65 and Tb) are determined within a two-sublattice mean field model. It is shown that increase in the Curie temperature of the RCo2Mnx-type nonstoichiometric alloys is associated with increasing of the magnetic moment and strengthening exchange interactions in the 3d-sublattice. The magnetization and heat capacity measurements were used to estimate the magnetocaloric effect in the compounds for the magnetic field change ΔH ≈ 20 kOe. It was found that compounds exhibit plateau-like temperature dependence of the field induced magnetic entropy change ΔSm over a wide temperature range from 50 to 350 K and high values of Relative Cooling Power (up to 235 J/kg), the full width at half maximum of ΔSm (ΔTFWHM up to 310 K) and refrigerant capacity (RC up to 196 J/kg). The calculated and directly measured temperature variation of the adiabatic temperature change ΔТ are found to be similar.
      原文链接:
    • NSTL
    • Elsevier

    Understanding roles of Zr and W on hot/warm deformation behavior of FeCrAl alloy: Grain boundary features and dynamic precipitation of Laves phase

    Liu W.Liu Z.Luo W.Liu H....
    12页
    查看更多>>摘要：? 2021The present work investigated the hot (800–1100 °C) and warm (600 °C) deformation behavior of Fe–13.5%Cr–4.7%Al–2.0%Mo–1.0%Nb (wt.%) (FeCrAl), Fe–13.5%Cr–4.7%Al–2.0%Mo–0.9%Nb–0.11%Zr (wt.%) (FeCrAl–Zr) and Fe–13.5%Cr–4.7%Al–1.4%Mo–1.0%Nb–1.32 W (wt.%) (FeCrAl–W) ferritic stainless steels using a thermal simulation machine at strain rates of 0.01–10 s?1. Before deformation, all the samples were solution-treated at 1150 °C, 1250 °C, and 1200 °C for FeCrAl, FeCrAl–Zr, and FeCrAl–W alloys, respectively. The stress–strain curves showed dynamic softening in FeCrAl, FeCrAl–Zr, and FeCrAl–W alloys, and processing maps were also constructed. A large number of low-angle grain boundaries (LAGBs) could be created by hot (800 °C) and warm (600 °C) deformation, and Zr/W slightly increased the proportion of LAGBs in the samples deformed at 800 °C and 1100 °C. In addition, both lower deformation temperature (800 °C), higher strain rate (1 s?1), and Zr/W addition could significantly increase the size of the precipitate-free zone and the content of grain boundary precipitates during hot deformation, which could result in the hysteresis phenomenon of the softening behavior. These results can be expected to provide guidance for the subsequent determination of possible hot and warm processing of FeCrAl alloys.
      原文链接:
    • NSTL
    • Elsevier

    Effect of defects on the phase transition of Al0.1CoCrFeNi high-entropy alloy under high pressure

    Li R.Ma Y.Liu X.Lu Y....
    6页
    查看更多>>摘要：? 2021 Elsevier LtdKnowledge pressure-driven phase transition in condensed physics requires an understanding of how phase-transition-pressure in a substance is affected by defect concentration and type. The effect of defects on phase transition was investigated in this paper by comparing structure evolutions in Al0.1CoCrFeNi high-entropy alloy (HEA) prepared by mechanical alloying with as-cast one using in situ synchrotron radiation X-ray diffraction technique and high-resolution transmission electron microscope (HRTEM), as well as the calculated dislocation density. Pressure-induced partial irreversible phase transitions from face-centered cubic (fcc) to hexagonal close-packed (hcp) phase has been observed in both ball-milled and as-cast Al0.1CoCrFeNi HEAs. In comparison to the as-cast Al0.1CoCrFeNi HEA, the ball-milled HEA has a large number of defects, especially higher density dislocations, and a low nucleation energy barrier, resulting in a lower phase-transition-pressure of 7.0 GPa and a higher fraction of hcp phase of 32.12% at pressure ～30 GPa. The HRTEM result confirms that hcp and fcc phases coexist after pressure releasing. The investigation of the link between defects and phase transition process might lead to a potential approach for customizing the percentage of fcc and hcp phases in HEAs, allowing them to improve their structure and characteristics as a novel engineering material.
      原文链接:
    • NSTL
    • Elsevier

    Microstructure refinement and improvement of mechanical properties of Ti46Al8Nb0.9B alloys by electromagnetic cold crucible continuous solidification

    Wang Y.Li W.Yuan H.Ding H....
    8页
    查看更多>>摘要：? 2021Microalloying with boron is effective and economical for refining microstructures of as-cast TiAl alloy. However, microstructural refinement is easily affected by the alloy composition and cooling rate, leading to inhomogeneous grain size in different areas of the ingot. In this study, the Ti46Al8Nb0.9B alloys are continuously solidified by the electromagnetic cold crucible, aiming to obtain homogeneous and fine microstructure. After electromagnetic cold crucible continuous solidification (EMCS), the obtained ingot shows finer and more homogeneous microstructure with lamellar colony size of about 50 μm. The results of tensile test show that the EMCS ingot exhibited improved properties with yield strength (σ0.2) of 548 MPa and plastic elongation of 0.6%.
      原文链接:
    • NSTL
    • Elsevier

    First-principles calculations to investigate structural, elastic, electronic and magnetic properties of novel d0 half metallic half Heusler alloys XSrB (X=Be, Mg)

    Abada A.Marbouh N.Bentayeb A.
    10页
    查看更多>>摘要：? 2021The structural, elastic, electronic properties and magnetism of new d0 half Heusler alloys XSrB (X = Be, Mg) were investigated by means of first-principles calculation based on the density functional theory (DFT). The exchange-correlation functional is treated by the generalized gradient approximation proposed by Perdew–Burke–Ernzerhof (GGA-PBE). The Tran-Blaha modified Becke-Johnson (TB-mBJ) exchange potential, which can compute accurately the band gap of solids, is adopted to improve the calculations of the electronic structure and magnetic properties. We found that the two alloys are energetically and mechanically stable in the α phase presenting ductile nature with negative cohesive energies. It was found that MgSrB compound can be experimentally synthesized because of its negative formation energy. The two compounds are half-metallic ferromagnets with total magnetic moment of 1.000 μB per formula unit, in well agreement with Slater-Pauling rule (Mtot = (8 – Ztot) μB). Our calculations show that BeSrB and MgSrB have majority band gaps of 1.024 eV (1.387 eV) and 0.831 eV (1.277 eV) with half-metallic gaps of 0.165 eV (0.613 eV) and 0.311 eV (0.626 eV), respectively, by GGA-PBE (TB-mBJ). The origin of these gaps is well discussed. It was also found that BeSrB and MgSrB are robust half-metallic alloys with respect to the variation of lattice constants. They kept their half-metallicity in relatively wide range of lattice constants of 5.90–7.00 ? and 6.18–7.28 ?, respectively. The obtained results reveal also that BeSrB and MgSrB compounds are considered as nearly gapless half-metallic ferromagnets for lattice parameters range of 7.03–7.88 ? and 7.50–8.40 ?, respectively, which makes them promising candidates for potential applications.
      原文链接:
    • NSTL
    • Elsevier

    Microstructural evolution and mechanical properties in Zr–Cu–Al–Nb bulk metallic glass composites prepared by laser metal deposition

    Luo N.Galgon F.Morales L.A.Zenk C.H....
    12页
    查看更多>>摘要：? 2021 Elsevier LtdIn this work, laser metal deposition (LMD), a direct energy deposition (DED) additive manufacturing technology, is used to prepare Zr59.3Cu28.8Al10.4Nb1.5 bulk metallic glass composites (BMGCs). Phase constitutions and thermal behavior of LMD-processed Zr–Cu–Al–Nb samples are examined using X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The microstructure evolution parallel to the build direction is characterized in detail utilizing scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), electron probe microscopy analysis (EPMA) and electron backscatter diffraction (EBSD). Young's modulus and hardness in typical microstructures are evaluated employing nanoindentation. Within each deposited layer, a periodic microstructure, exhibiting crystalline features of three distinctly different morphologies, is observed, depending on the location within that layer. Along the build direction, the dominating microstructure of the melt pool evolves from a nearly featureless amorphous state over fine nanocrystals to coarse nanocrystals while the morphology of most micro-scale dendritic crystals changes from flower-shaped to columnar, simultaneously a coarse microstructure appearing in upper layers. The fine Al-rich phases gradually coarsen directionally parallel to the build direction. Furthermore, the correlation between microstructure and mechanical properties is investigated. This work enhances our knowledge about microstructural characteristics and mechanical properties of BMGCs in-situ fabricated by DED additive manufacturing.
      原文链接:
    • NSTL
    • Elsevier

    Pressure effects on electronic structure and electrical conductivity of TiZrHfNb high-entropy alloy

    Uporov S.A.Ryltsev R.E.Estemirova S.K.Sterkhov E.V....
    9页
    查看更多>>摘要：? 2021 Elsevier LtdDue to specific highly distorted crystalline structure, high-entropy alloys (HEAs) are expected to demonstrate interesting behavior under high pressures. However, this issue is not yet well studied. Here we address pressure effects on electronic structure and electrical conductivity of TiZrHfNb alloy. Among the multiplicity of single-phase HEAs explored so far, the TiZrHfNb one is an exemplar of thermally stable metallic material that crystallizes into body-centered cubic (BCC) structure and demonstrates excellent mechanical, corrosion, and friction properties compared to conventional alloys. We synthesize this material with BCC structure and analyze its electrical, superconducting, and magnetic properties. The alloy is a Curie-Weiss paramagnet and a type-II superconductor with the critical temperature of about 6.3 K. The estimated upper critical field and critical current density in the HEA are rather moderate compared to those observed in the superconductors based on Ti–Nb alloys. In the normal state, the alloy demonstrates high electrical resistance that practically independent of temperature but significantly dependent on pressure; it decreases linearly by 12.5% as the pressure increases up to 5.5 GPa. By analyzing the experimental data, we suggest that alloy resistance is mainly determined by two contributions: the residual resistance and Mott's s-d scattering. We show that a cooperative effect from changes in both the Debye temperature and electronic band structure near the Fermi level are the main factors responsible for the electrical resistance behavior of the HEA under pressure. Ab initio calculations performed at different pressures support this conclusion. The results show that TiZrHfNb alloy is a promising material for designing resistance pressure gauges.
      原文链接:
    • NSTL
    • Elsevier