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Effects of phase transition temperature and preheating on residual stress in multi-pass & multi-layer laser metal deposition
摘要： To investigate the influences of phase transition temperature and preheating on the residual stress of multi-layer and multi-pass laser metal deposition (LMD), the multi-layer and multi-pass LMD, with and without preheating, were performed using five kinds of alloy with different phase transition features, and their residual stresses were measured using the hole drilling method. A finite-element (FE) model incorporating the phase transition was developed based on experimentally obtained physical property data. The results demonstrated that the low-temperature solid phase transition has a tensile stress relaxation effect, which leads to the formation of a compressive stress area. This relaxation effect was observed to decrease with the increase of the phase transition temperature. The high-temperature solid phase transition has no significant tensile stress relaxation effect during the multi-layer and multi-pass LMD process, which is different from the single track LMD. when the solid phase transition temperature is low, the preheating can improve the uniformity of the stress field only to a certain extent. However, when the preheating increases the lowest temperature of the thermal cycle and makes it higher than the starting point temperature of the solid phase transition, the tensile stress relaxation effect of the solid phase transition can be brought into full play.
关键词： Finite element analysis,Preheating,phase transition temperature,Residual stress,Laser metal deposition
更新于2025-11-28 14:24:20
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Optimized thermochromic properties of VO2/CoFe2O4 nanocomposite films via band gap engineering
摘要： VO2/CoFe2O4 nanoparticle composites were synthesized by hydrothermal method combined with annealing treatment. The nanocomposites consist of quasi-spherical nanoparticles with an average size of about 70 nm. The thermochromic properties of the nanocomposite films can be modulated by changing film thickness and the content of CoFe2O4 in the nanocomposites. The band gap of the VO2/CoFe2O4 nanocomposites increases with increasing CoFe2O4 additive content. The introduction of CoFe2O4 into VO2 matrix can not only lower the phase transition temperature, but also optimize the luminous transmittance and solar modulation ability of the VO2/CoFe2O4 nanocomposites as well. Our findings demonstrate a promising avenue in constructing VO2-based smart films with excellent thermochromic performance.
关键词： Solar modulation ability,VO2/CoFe2O4 nanocomposite,Luminous transmittance,Phase transition temperature
更新于2025-09-23 15:21:21
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Study of materials structure physics of isomorphic LiNbO <sub/>3</sub> and LiTaO <sub/>3</sub> ferroelectrics by synchrotron radiation X-ray diffraction
摘要： Electron charge density studies of stoichiometric LiNbO3 and LiTaO3 ferroelectrics have been carried out by analyzing the synchrotron radiation X-ray powder di?raction data using a combination of the Rietveld and maximum entropy methods. The clear relationships between the Nb(Ta)–O bond length, the electron charge density on the Nb(Ta)–O bond, and the phase transition temperature TC are revealed for isomorphic structures. Nb(Ta)–O bonding plays an important role in the elevation of TC. The TC in LiNbO3 being higher than that in LiTaO3 is attributed to the larger lattice distortion of the Nb–O oxygen octahedron in LiNbO3. The validity of estimating TC for LiNbO3 family crystals from the degree of lattice distortion in the ferroelectric structure is discussed.
关键词： ferroelectric,LiTaO3,X-ray diffraction,synchrotron radiation,LiNbO3,phase transition temperature,electron charge density
更新于2025-09-23 15:21:21
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Polarization-dependent phase transition temperature in plasmonic thin films
摘要： Nano-engineering the effective, macroscopic properties of composite materials is becoming increasingly important in material sciences and device development. Here, we report on using embedded plasmonic nanorods to modify the effective, as opposed to the intrinsic, phase transition temperature of vanadium oxide, a phase change material vital for infrared imaging and thermochromics. The nanorods function as controllable, nano-sized thermal sources through the excitation and dissipation of surface plasmons. The polarization dependence in the excitation efficiency modifies the effective phase transition temperature by up to 4.2 °C under broadband illumination of 5.0 W. This work constitutes a proof-of-principle demonstration of tunable and reversible plasmonic modulation of the phase transition temperature in a phase change material. It also represents a new strategy of thermo-plasmonic engineering at the nanoscale.
关键词： vanadium oxide,phase transition temperature,plasmonic thin films,thermo-plasmonic engineering
更新于2025-09-23 15:21:01
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Effect of Zr Doping on the Magnetic and Phase Transition Properties of VO2 Powder
摘要： In this work, V1?xZrxO2 powder (x = 0, 0.01, 0.02, 0.04) was synthesized by two step hydrothermal method. The micro-topography, magnetic and phase transition properties have been investigated using various measurement techniques. All prepared V1?xZrxO2 powder samples exhibit monoclinic structure at room temperature. With the Zr4+ ions doping concentration increased, the shapes of VO2 particles change from spherical to rectangular slice. Besides, the saturation magnetic moment of the samples decrease with the increase of doped Zr4+ ions concentration, while their phase transition temperature increase gradually with Zr ions doping at a rate of around 2 ?C/at% on average. We investigated the Zr doping effects on V-V dimers and con?rmed the role of V-V dimers in phase transition. We speculate that more V-V dimers form with Zr doping by magnetic measurements, which result in the monoclinic phase of Zr-doped VO2 sample is more stable than rutile phase. Therefore the phase transition temperature is elevated by Zr doping in our experiment. We further consider that the VO2 phase transition should be ascribed to Peierls transition caused by the changing of V-V dimers.
关键词： V-V dimer,magnetic properties,Zr-doped,phase transition temperature
更新于2025-09-19 17:15:36
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Tungsten doped M-phase VO2 mesoporous nanocrystals with enhanced comprehensive thermochromic properties for smart windows
摘要： The phase transition temperature (~ 68 oC) of M-VO2 film can be lowered significantly by tungsten (W) doping into the crystal lattice of VO2 due to the reduction of the strength of V-V pair interaction. However, W doping was always coupled with a serious weakening of luminous transmittance and solar modulation efficiency because W dopants can increase the electron concentration of VO2 film. Herein, the simultaneous introduction of W dopants and mesopores into M-VO2 nanocrystals was employed to prepare VO2 film. Interestingly, the obtained 0.4 at% W-doped mesoporous VO2 nanocrystals based composite films exhibited enhanced comprehensive thermochromic performance with excellent solar modulation efficiency (ΔTsol = 11.4%), suitable luminous transmittance (Tlum = 61.6%) and low phase transition temperature around 43 oC, much lower than 65.3 oC of undoped VO2. It was demonstrated that the lower phase transition temperature of VO2 can be primarily attributed to abundant lattice distortion after W doping, whereas the mesoporous structure can facilitate the uniform distribution of W dopants in VO2 nanocrystals, enhance the luminous transmittance and guarantee enough VO2 nanocrystals in the composite film to keep relatively high solar modulation efficiency. Therefore, this work can provide a new way to balance the three important parameters for the thermochromic performance of VO2 film (ΔTsol, Tlum and Tc) and probably promote the application of VO2 nanocrystals in the energy efficient windows.
关键词： thermochromic performance,phase transition temperature,mesoporous structure,W-doped VO2
更新于2025-09-09 09:28:46