| 1. |
- Chen, Xu, et al.
(author)
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Ductility deterioration induced by L21 phase in ferritic alloy through Ti addition
- 2023
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In: Journal of Materials Research and Technology. - : Elsevier Editora Ltda. - 2238-7854. ; 25, s. 3273-3284
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Journal article (peer-reviewed)abstract
- Ductility deterioration induced by L21-Ni2AlTi precipitates in the aged ferritic alloys was examined systematically by using a combination of scanning transmission electron microscope (STEM), mechanical tests and first-principles thermodynamic calculations. The experimental studies revealed that the strength and hardness of the aged Fe–10Cr–5Ni–1Al–1Ti ferritic alloy containing B2–NiAl and L21-Ni2AlTi precipitates were higher than that of the aged Fe–10Cr–5Ni–1Al ferritic alloy containing NiAl precipitates, whereas the elongation-to-failure decreased dramatically from 9.3% to 0.3% indicating an obvious ductility deterioration due to the formation of L21-Ni2AlTi precipitates. This was also confirmed by the observation of fracture transition mode from dimpled failure to cleavage failure. The first-principles calculations, concerning the precipitate/matrix interface, were carried out to provide a theoretical analysis for the ductile–brittle transition by means of empirical ductility criteria ratios G/B and (C12–C44)/B as well as cleavage energy. The cleavage energy results indicated an intrinsic brittleness of the L21-Ni2AlTi phase and the L21-Ni2AlTi/BCC-Fe interface. Our analysis revealed that the intrinsic brittleness of L21-Ni2AlTi phase and L21-Ni2AlTi/BCC-Fe interface plays a vital role in determining the deformation behavior of the aged Fe–10Cr–5Ni–1Al–1Ti alloy.
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| 2. |
- Du, Xueli, et al.
(author)
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Study of rare-earth oxide sintering aid systems for AlN ceramics
- 2007
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In: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 460-461, s. 471-474
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Journal article (peer-reviewed)abstract
- In the present work, effects of Y2O3 and Dy2O3 sintering aid systems on density and thermal conductivity of AlN ceramics sintered at low temperature were investigated. The AlN powder synthesized by self-propagating high-temperature synthesis (SHS) was mixed individually with six different sintering aids, which were Y2O3, Dy2O3, CaF2–Y2O3, CaF2–Dy2O3, CaF2–Li2CO3–Y2O3 and CaF2–Li2CO3–Dy2O3, and then fabricated by employing press forming technique. The specimens were sintered at 1650 °C in nitrogen atmosphere at atmospheric pressure for 4 h. X-ray diffraction (XRD) was used to identify the secondary phases. The microstructure of the specimen was observed by scanning electron microscopy (SEM). The thermal diffusivity at room temperature was measured by a laser flash technique. Density of sintered specimen was measured by Archimedes displacement method. The result reveals that the density and thermal conductivity of AlN ceramics sintered with one component sintering aids were lower than those of sintered with multiple components sintering aids. The thermal conductivity of AlN ceramics sintered with CaF2–Li2CO3–Y2O3 and CaF2–Dy2O3 were 141 W m−1 K−1 and 142 W m−1 K−1, which were higher than that of any others.
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| 3. |
- Feng, Peizhong, et al.
(author)
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Effect of the composition of starting materials of Mo--Si on the mechanically induced self-propagating reaction
- 2008
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In: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 456:1-2, s. 304-307
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Journal article (peer-reviewed)abstract
- The effect of the raw materials composition of Mo–Si powders mixture on mechanical alloying has been investigated using a high-energy vibratory type ball-milling machine. The phase transformation of powders mixture is characterized by means of X-ray diffractometer. The results show that the molybdenum silicide is formed by the mechanically induced self-propagating reaction in relatively broad composition range from the molar ratio of Mo:1.5Si to Mo:2.5Si. As the content of silicon increases, the amount of critical stored energy for mechanically induced self-propagating reaction is increased, whereas the favorable Mo–Si reactive interface is decreased, and the difficulty of formation of Mo(Si) supersaturated solid solution is enhanced. These factors prolong the incubation period of mechanically induced self-propagating reaction from 60 to 130 min. Compared to stoichiometry of MoSi2, the excess amount of Mo acts as accelerant, and the redundant Si acts as diluting agent.
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| 4. |
- Feng, Peizhong, et al.
(author)
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Mechanically activated reactive synthesis of refractory molybdenum and tungsten silicides
- 2008
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In: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 26:3, s. 173-178
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Journal article (peer-reviewed)abstract
- In this study, processing of elemental powders mixtures was carried out by mechanical alloying (MA) and heat treatment in vacuum at 700–1000 °C for 1 h. The phase transformation of the powders was investigated by X-ray diffractometer (XRD). The results showed that mechanical alloying promoted the formation of a solid solution of elemental powders. The energy stored in the powders was increased as a result of exterior energy and the barrier energy of the formation of the compound could be exceeded easily. Intermetallics of MoSi2, WSi2, Mo5Si3, Mo3Si and SiC/MoSi2 composite powders were synthesized by mechanically activated reactive synthesis (MARS). The mechanically induced self-sustaining reaction was observed in MoSi2 and MoSi2 + 10 wt%SiC stoichiometry system. It has concluded that mechanically activated reactive synthesis is an effective method for the preparation of high melting-point refractory compounds.
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| 5. |
- Feng, Peizhong, et al.
(author)
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Self-propagating high temperature synthesis of MoSi 2 matrix composites
- 2006
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In: Rare Metals. - 1001-0521 .- 1867-7185. ; 25:3, s. 225-230
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Journal article (peer-reviewed)abstract
- MoSi2 is presently regarded as the most important material for electrical heating and as one with huge potential for high temperature structural uses. MoSi2 and MoSi2 matrix composites were prepared by self-propagating high temperature synthesis (SHS). Pure MoSi2 was obtained and a compound of MoSi2 and WSi2 was synthesized in the form of predominant solid solution (Mo, W)Si2. By adding aluminum of 5.5 at.% to Mo-Si, the crystal structure of MoSi2 changed into a mixture of tetragonal CIIb MoSi2 and hexagonal C40 Mo(Si, Al)2. The (Mo, W)Si2-Mo(Si, Al)2-W(Si, Al)2 composite materials were synthesized by adding aluminum of 5.5 at.% to Mo-W-Si. However, if the amount of the added aluminum was not larger than 2.5 at.%, it did not have any significant effect. SHS is an effective technology for synthesis of MoSi2 and MoSi2 matrix composites.
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| 6. |
- Humail, Islam S, et al.
(author)
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Tensile behavior change depending on the varying tungsten content of W--Ni--Fe alloys
- 2007
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In: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 25:5-6, s. 380-385
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Journal article (peer-reviewed)abstract
- Tungsten heavy alloys (WHAs) are metal–metal composites consisting of nearly pure spherical tungsten particles embedded in a Ni–Fe–W or Ni–Co–W or Ni–Cu–W ductile matrix. In this dual phase alloy, there are several complicated relations between the ductile matrix and hard tungsten particles. The aim of this research was to examine the effect of varying tungsten content on the microstructure and mechanical properties of tungsten heavy alloys. The microstructural parameters (grain size, connectivity, contiguity and solid volume fraction) were measured and were found to have a significant effect on the mechanical properties of tungsten-based heavy alloys. The result shows that the binding strength between the W and the matrix phase has a major influence on the ductility of tungsten-based alloys. The larger this binding force is, the better the ductility is.
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| 7. |
- Li, Bo, et al.
(author)
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Constructing water-resistant CH3NH3PbI3 perovskite films : Via coordination interaction
- 2016
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In: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 4:43, s. 17018-17024
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Journal article (peer-reviewed)abstract
- Organic-inorganic halide CH3NH3PbI3 (MAPbI3) perovskite solar cells (PSCs) have attracted intensive attention due to their high power conversion efficiency and low fabrication cost. However, MAPbI3 is known to be very sensitive to humidity, and the intrinsic long-term stability of the MAPbI3 film remains a critical challenge. 2-Aminoethanethiol (2-AET) was used as a ligand to bridge the organic compound (MAI) and inorganic compound (PbI2), which restricted the fast growth of PbI2 to realize the synchronous growth environment of MAI and PbI2 crystals, resulting in the formation of a compact MAPbI3 film with polygonal grains. Due to the compact (PbI2)-2-AET-(MAI) molecule barrier layers in the MAPbI3 structure, the resulting perovskite films showed excellent intrinsic water-resistance, with the MAPbI3 perovskite crystal structure retained for a long time (>10 minutes) after immersion in water. This work makes a step towards obtaining long-term stable MAPbI3 perovskite devices.
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| 8. |
- Liu, Ye, et al.
(author)
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First-principles investigation on the thermodynamic and mechanical properties of Y4Zr3O12 and Y2Ti2O7 oxides in ferritic alloy under helium environment
- 2024
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In: Journal of Materials Research and Technology. - : Elsevier. - 2238-7854. ; 29, s. 1872-1886
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Journal article (peer-reviewed)abstract
- This study investigates the thermodynamic and mechanical properties of Y4Zr3O12 and Y2Ti2O7 oxides in ferritic alloys with and without Helium utilizing a systematic first-principles approach. Firstly, the atomic arrangement of Y and Zr atoms at cation 18f sites in δ-(Y–Zr–O) oxide is identified, while it is found that Y4Zr3O12 exhibits a more robust formation tendency than Y2Ti2O7. Furthermore, it is noted that both Y4Zr3O12 and Y2Ti2O7 oxides demonstrate a prior ability to trap Helium compared to the bcc-Fe matrix, which leads to a substantial enhancement on the stiffness of both oxides. The elastic moduli of both Y4Zr3O12 and Y2Ti2O7 oxide exhibit a gradual increase with the growing Helium concentration. As a result, the enhanced shear modulus of oxides and sustained shear modulus of the bcc-Fe matrix collectively contribute to the overall strength of ferritic alloys under Helium environments. The findings in this work propose valuable insights for guiding critical strategies in the design of high-performance oxide-dispersion-strengthened ferritic alloys, particularly for applications in Helium environments.
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| 9. |
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| 10. |
- Tian, Jianjun, et al.
(author)
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Behavior of residual carbon in Sm(Co, Fe, Cu, Zr)z permanent magnets
- 2007
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In: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 440:1-2, s. 89-93
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Journal article (peer-reviewed)abstract
- When sintered Sm(Co, Fe, Cu, Zr)z permanent magnets are prepared by metal injection molding, some organic binders are added in alloy powder, which leads to much residual carbon in the magnets. The residual carbon decreases magnetic properties and destroys the microstructure of the magnets. In this paper, the behavior of carbon in Sm(Co, Fe, Cu, Zr)z permanent magnets has been studied. The results indicate that Sm(Co, Fe, Cu, Zr)z magnets can keep excellent magnetic properties when the carbon content is below 0.1 wt.%: Br ≥ 10 kGs, Hcj ≥ 22 kOe, BHmax ≥ 25 MGOe. When the carbon content is above 0.1 wt.%, Br, Hcj and BHmax decrease with increasing carbon content evidently. Carbon consumes Zr content and forms ZrC, which reduces the volume fraction of the lamella and Sm(Co, Cu)5 phases. Thus, the cell size increases and the cellular microstructure deteriorates. When the carbon content reaches 0.43 wt.%, there is not enough Sm(Co, Cu)5 phase to form a uniform cellular microstructure. Br, Hcj and BHmax are approximate to zero. Since carbon has little influence on the content of Sm2(Co, Fe)17 phase, Ms can keep a high value (≥100 emu/g). ZrC has high melting point (3420 °C) and acts as dispersion particle in the magnets, which prevents the grains of SEM structure growing and reduces the liquid content of green compacts during sintering. Therefore, the density of the magnets decreases
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