查看更多>>摘要：? 2022A Y–Ti–O oxide-dispersion-strengthened (ODS) Cu alloy has been successfully fabricated by mechanical alloying (MA) and spark plasma sintering (SPS). Excessive cold-welding during high energy ball-milling was effectively suppressed by mixing TiO2 and pre-alloyed Cu(Y) powders as the raw powders. Microstructural evolutions during the MA and SPS processes and the subsequent annealing were investigated with a focus on the Y–Ti–O nano-oxides. The 12 h ball-milling failed to achieve super-saturations of Y, Ti, and O in Cu, which led to the in-situ formation of various types of oversized Y/Ti-rich oxides with very irregular morphologies during the SPS. With a prolonged ball-milling of 48 h, the subsequent SPS + annealing processes can promote a high density precipitation of ultra-fine Y–Ti–O nano-oxides. These nano-oxides were further identified as Y2Ti2O7 mostly, with a high degree of coherency in Cu. Fabricating Y–Ti–O ODS-Cu alloys via MA was thus confirmed to be technically feasible, although the dispersion of nano-oxides desires further improvement.
查看更多>>摘要：? 2022 Elsevier Inc.Two Nickel-based single crystal superalloys (one Ru-free and one containing 3 wt.% Ru) were comparatively investigated by the three-dimensional atom probe tomography and the nanoindentation atomic force microscope to reveal the effect of Ru addition on the microstructure and the mechanical properties of γ' phases after standard heat treatment. The results showed that the Ru addition neither altered the morphology and the volume fraction of γ' phases, nor changed the interface structure and the partition coefficients of alloying elements between γ and γ' phases, however, it enhanced the hardness and elastic modulus of γ' phases. First-principles calculation indicated that no matter whether the Ni site or Al site was occupied by Ru, the elastic modulus of γ' phases increased, which might be ascribed to the solution strengthening effect of Ru on γ' phases.
查看更多>>摘要：? 2022Basing on the systematical research of the powder properties of calcined dolomite mineral (CM) obtained from raw dolomite mineral (RDM), a novel Al2O3-CA6-MA/Ni multi-phase composite was developed using the in-situ generated strengthening-toughening phases of calcium hexaluminate (CA6) and magnesium aluminate spinel (MA) being introduced into an Al2O3-Ni system by regulating the reaction between CM and Al2O3. Under the anisotropic growth behaviour of CA6, the composite obtained a unique “ring” microstructure, while the mechanical properties were improved. In addition, the strengthening-toughening mechanisms related to this modification and improvement were studied in depth, that is, the pull out and fracture behaviours of CA6 and MA grains promoted crack deflection, bridging and branching, and the nano precipitation behaviour of metal Ni particles at the boundaries between CA6 and Al2O3 grains realized the bonding effect. This finding has important practical significance and economic value for the deep processing and application of RDM.
查看更多>>摘要：? 2022 Elsevier Inc.6-mm 6061-T6/SUS304 butt joints were obtained successfully with a breakthrough through a deep-penetration welding-brazing process using a laser hybrid metal inert gas (MIG). The laser powers were optimized to obtain a sound joint with good formation. The quality of joints was evaluated via tensile tests. Moreover, the morphology and thickness of the intermetallic compound (IMC) layer along Al/steel interface were also studied via Scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that the spreading degree on the steel side of the molten metal was improved with increasing laser power, and a sound joint without visible defects was obtained when the laser power was 4150 W. Double IMC layers consisting of η-Fe2(Al, Si)5 and θ-Fe(Al, Si)3 were formed at the three interface regions regardless of the laser power. A larger number of cracks appeared at the interface as the laser power increased to 4200 W. TEM analysis revealed that characterization and thickness of the IMC layer at the interface on the top and bottom were quite distinct. The maximum tensile strength (140.7 MPa) with reinforcement was significantly higher than that of the 6 mm Al/steel fusion welding joints using laser or laser-arc keyhole welding technology.
查看更多>>摘要：? 2022 Elsevier Inc.In the present paper, the wide miscibility gap in liquid phase in the Al-Fe-Sn system is well defined for the first time. A large miscibility gap extends from the Sn[sbnd]Fe side and dramatically extends upon addition of Al. The evolution of the microstructure during solidification was investigated experimentally in the entire concentration range in binary Sn[sbnd]Fe and ternary Al-Fe-Sn systems using SEM/EDS, XRD and DTA/DSC techniques. The existence of Fe3Sn phase in the Sn[sbnd]Fe system was confirmed. It was found that the FeAl2 phase in the ternary system participates in equilibrium with the liquid phase contrary to the binary Al[sbnd]Fe system where it is formed in a solid state. All the binary phases do not demonstrate any essential solubility of the third component. Liquidus and solidus projections, melting diagram, isothermal section at 850 °C, vertical sections on isoconcentrates 10, 20 and 35 at.% Sn and a Scheil reaction scheme for the Al-Fe-Sn system covering the whole concentration range were constructed for the first time.
查看更多>>摘要：? 2022 Elsevier Inc.Uniaxial (UC) and plane strain compression (PSC) tests were performed on the Cu-Cr-Zr-Ti alloy specimens to investigate the effect of the deformation mode on the stress-strain response, work hardening behaviour and microstructural evolution in the alloy. These tests were performed at a strain rate of 1 s?1 and in the temperature range of 700–800 °C to impart von Mises equivalent strains of 0.15, 0.45 and 0.69. The alloy showed a regime of constant work hardening rate in the recovery stage before transitioning to the steady state under UC as opposed to PSC in which the alloy exhibited a smooth transition from recovery stage to the steady state stage. The microstructures evolved under UC consisted of randomly oriented equiaxed grains delineated by high angle boundaries (HABs) with high fraction of Σ3 boundaries. On the other hand, under PSC a very strong {001}〈100〉 cube texture evolved with increase in strain. This strong cube texture was ascribed to the evolution of and the increased stability of cube-oriented elongated substructures observed in the deformed matrix. The difference in the work hardening behaviour was thus attributed to the higher evolved Σ3 fraction under UC and the cube-oriented elongated substructures evolved under PSC. The dynamically recrystallized grains fraction calculated from area of grain orientation spread (GOS) map with GOS < 2o was found to be lower in the alloy under PSC owing to the presence of high orientation gradients within the evolved cube-oriented elongated substructures.
查看更多>>摘要：? 2022 Elsevier Inc.To address the excessive formation of brittle compounds when brazing TiAl alloys, a TiZrHfCoNiCu high-entropy brazed filler was developed to realize the brazing of TiAl/Ti2AlNb couples. The TiAl/Ti2AlNb brazed joints can be divided into 4 zones, i.e., 2 diffusion zones at the TiAl/braze filler, Ti2AlNb/braze filler interfaces and 2 zones divided inside the brazed seam. α2 + γ-TiAl were the main reaction products formed at the TiAl/braze filler interface and α2+ Ti0.5Al0.12Nb0.38 were the main reaction products at the Ti2AlNb/braze filler interface. Effects of brazing temperatures on the interfacial microstructure and mechanical properties of the TiAl/Ti2AlNb brazed joints were investigated. When brazing at 1100°C/15 min, the highest shear strength can reach 157 MPa (room temperature), and 123 MPa (650°C) respectively. The relationship between the microstructure and the corresponding mechanical response were discussed in detail. This research can offer new insights on developing desirable brazing filler when joining TiAl and TiAl based alloys.
查看更多>>摘要：? 2021Fe-based amorphous nanocomposite with nominal composition Fe58.82Cr11.12Mo1.52Si4.16B15.12P8.88C0.39 (at%) has been processed through melt-spinning, melt-spinning followed by ball milling and thermal spray deposition of coating onto a mild steel substrate. X-ray diffraction and electron microscopy characterization of the processed alloy reveals that the melt-spun ribbon is mostly amorphous with uniform distribution of very fine crystals of α-Fe and oP30 (Fe2B7) phase. In the melt-spun followed by ball milled powder mainly cI58 (Fe18Cr6Mo5), tP30 (Fe62Cr34Mo4) and mI32 (Fe5C2) phases are obtained. However, the tP30 (Fe62Cr34Mo4) phase while ball milling undergoes distortive changes locally to produce oC68, tP60 and tP58 phases with similar composition. The interface between the two structures is considerably strained. In the coating, cF118 (Fe18Cr6Mo5) and oI92 (Fe62Cr34Mo4) are observed in the amorphous matrix. Essentially the cF118 and oI92 can be seen as a structural derivative of cI58 and tP30 phases respectively. Local composition fluctuation and availability of a suitable nucleation condition leads to the nucleation of crystalline phases in the amorphous matrix in the melt-spun ribbon. In the melt-spun followed by ball milled powder further distortive changes are observed locally, which leads to the formation of polymorphically related phases to tP30 phase. Even though all the phases are crystallographically quite complicated, they are all derived from either the tP30 (Fe62Cr34Mo4) phase or cI58 (Fe18Cr6Mo5) phases. Thermodynamic calculations through Miedema's model indicates that the nominal composition of the alloy lies at the boundary of glass forming composition. The crystal compositions, although different from the nominal composition of the alloy, lies in the crystal forming composition range. Local composition fluctuation, favorable thermodynamic conditions for nucleation and growth leads to the crystal nucleation. Although all the phases are crystallographically different, they have similar polyhedral order in them. The polyhedral structures cannot be correlated with Frank-Kasper or Bernal deltahedral phases. This is a significant difference between metal-metalloid glasses with its metal-metal counterpart.
查看更多>>摘要：? 2022 Elsevier Inc.Oxide dispersion strengthened (ODS)-CrFeNi medium entropy alloys (MEAs) with different addition amounts of Y2O3/Zr were prepared by mechanical alloying (MA) and spark plasma sintering (SPS) to reveal the influence of Y2O3/Zr amounts on microstructure and mechanical properties. The microstructure was characterized by XRD, BSE, EBSD, HRTEM, and the micro-hardness was tested. The results show that ODS-CrFeNi MEA with 1 wt% Y2O3/Zr addition (1YZ alloy) mainly consists of face-centered cubic (FCC) matrix, body-centered cubic (BCC) phase and high-density nanoscale oxides Y4Zr3O12 while in ODS-CrFeNi MEA added 3 wt% Y2O3/Zr (3YZ alloy), additional [Ni, Zr] phase is formed except for FCC matrix, BCC phase and nanoscale Y4Zr3O12. The average size and number density of Y4Zr3O12 depend on the addition amount of Y2O3/Zr, which are 9.8 nm/3.9 × 1021/m3 and 24.6 nm/3.3 × 1021/m3 in 1YZ and 3YZ alloys, respectively. The average grain size of 1YZ and 3YZ alloy are 127 nm and 344 nm, respectively. The effective grain refinement in 1YZ alloy results in the higher hardness, which is 474 HV. The hardness of 3YZ alloy is 368 HV. The detailed strengthened mechanisms are discussed.
查看更多>>摘要：? 2022 Elsevier Inc.In the last two decades, grain boundary engineering (GBE) study has neglected the high stacking fault energy BCC materials. Researchers have tried many single or multi-step strain recrystallization routes for improving the grain boundary character distribution (GBCD) in BCC materials, but the results have not been satisfactory. So, in this study, a single-step low deformation (5%, 10%) strain annealing route is employed for obtaining optimized GBCD and triple junction distribution (TJD) in interstitial free steel. This low deformation (5%) and low temperature (923 K) short annealing (10 min) treatment led to the evolution of 48.2% of Σ3, 54.3% of low Σ CSL boundaries, and 31.1% of special triple junctions (J2 and J3 type) in the microstructure. To the best of the authors' knowledge, these are the highest values reported for BCC material in literature. A good correlation is found between {111}〈110〉, {111}〈112〉 gamma fiber texture components and low deviation Σ3 boundaries. Moreover, a thorough analysis of average grain size, residual strain, GBCD, TJD, and grain orientation spread indicates that the regeneration mechanism (due to strain-induced boundary migration (SIBM)) is responsible for establishing a GBE microstructure in the thermomechanically processed sample (5%, 923 K, 10 min). The present work also explains the role of abnormal grain growth (AGG) on the deterioration of GBCD and TJD in the highly deformed (10%) samples.
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