Papers by Keyword: Single Crystal

Abstract: The nickel base alloy IN718 was manufactured by Laser Powder Bed Fusion (LPBF) using a laser spot size of 1024 μm and a laser power of 1.3 kW at a layer thickness of 160μm. The resulting porosity, microstructure and mechanical properties are presented. Very coarse and in build direction elongated grains are stacked to form a polycrystalline material with sharp single-crystal-like texture. The appearance of ∑5 grain boundaries between coincidence side lattices is recognized. Tensile testing shows highly anisotropic mechanical properties according to the revealed texture. Increasing the hatch distance reduces the severity of the texture.

Abstract: Kink-strengthening for mille-feuille structures has attracted many attentions in recent years. This study aims at identifying the kink formation/strengthening mechanisms via numerical reproductions of emerging kink-like morphologies based on FTMP (Field Theory of Multiscale Plasticity)-incorporated FE simulations, considering the Rank1 connection, where the incompatibility-based relevant underlying microscopic degrees of freedom for kinking are introduced. The targeted phenomena here include an experimentally-observed unique feature recently reported based on the combined ND–AE (neutron diffraction - acoustic emission) technique, i.e., scale-free-like energy release before (precursor) and during kink formations. This study uses a Mg single crystal model with alternatingly aligned soft and hard layers in parallel to the basal plane under c-axis plane-strain compression, where the soft/hard regions are controlled by the values of the hardening ratio. Also, we assume that the kink mode is only active, while the basal, prismatic and pyramidal slip and the twin systems are not operative associated with the layered structure. From the simulated results, we confirm kink-like morphologies and the attendant significant misorientation in the basal plane angles. Also, the simulated results are demonstrated to exhibit power-law type distributions in the strain energy fluctuation from the early stage of deformation even before the massive emergence of kink-like regions, which are analogous to the above-mentioned ND–AE observations.

Abstract: The features of the structure of single crystals LiNbO₃:B³⁺ (0.12 and 0.18 wt %) grown by the Czochralski method from the mixture of different genesis were studied. It was found that boron is able to incorporate into the crystal structure of lithium niobate in a trace amounts (~ 10^–4–10^–5 wt %), decreasing the concentration of structural defects Nb_Li. Thus, ordering of structural units of the cation sublattice of lithium niobate crystals grown from a congruent composition melt approach in that of stoichiometric crystals.

Abstract: Large diameter aluminum nitride (AlN) substrates, up to 50 mm, were manufactured from single crystal boules grown by physical vapor transport (PVT). Synchrotron-based x-ray topography (XRT) was used to characterize the density, distribution, and type of dislocations. White beam topography images acquired in transmission geometry were used to analyze basal plane dislocations (BPDs) and low angle grain boundaries (LAGBs), while monochromatic beam, grazing incidence images were used to analyze threading dislocations. Boule diameter expansion, without the introduction of LAGBs around the periphery, was shown. A 48 mm substrate with a uniform threading dislocation density below 7.0 x 10² cm^-2 and a BPD of 0 cm^-2, the lowest dislocation densities reported to date for an AlN single crystal this size, was demonstrated.

Abstract: LYSO:Ce single crystal was widely manufactured by Czochralski method. Considering its high cost and the pollution of the crucible, we tried to prepare the crystal by Verneuil method. Unlike Czochralski method, the Verneuil method need the powders with excellent fluidity and high purity. By comparing the powders annealed at 1100°C,1200°C,1300°C,1400°C and 1500°C, we can obtained the needed powders at 1500°C. We also increased the content of silica to satisfy the volatilization in crystal growth process. The single crystal was prepared by changing the growth parameter. We investigated the phase and the microstructure of the powders and observed the microstucture of the crystal fracture. We discussed the improved method of the process of crystal growth.

Abstract: A novel heterocyclic compound, 1-(4-methoxy phenyl)-2-((5-(1-(naphthalen-1-yloxy) ethyl) -[1,3,4]-oxadiazol-2-yl) sulfanyl) ethanone was synthesized using standard method and chemical structure of the synthesized compound was identified using FTIR spectrum. Needle shaped single crystals have been grown using solution growth technique. The grown crystals were characterized using single crystal XRD, UV-visible and Thermal analysis. The crystal structure study shows that the compound crystallizes in Monoclinic crystal system with a space group of P21/a and cell parameters are determined. UV-Visible study shows that the crystal is transparent in the entire visible region. The thermal stability of the material was determined by TG and DTA analysis.

Abstract: A novel NLO compound (E)-1-(5-chlorothiophene-2-yl)-3-(4-dimethylamino) phenyl) prop-2-en-1-one has been synthesized by adopting claisen schmidt condensation reaction method and the single crystals are grown using slow solvent evaporation technique. The FT-IR spectrum confirms the various functional groups present in the compound. The crystal structure was studied by XRD method, which reveals that the compound crystallizes in Monoclinic crystal system with a space group P21/n and the corresponding lattice parameters are a = 7.595 (2) Å, b = 17.441 (4) Å, c = 10.917 (3) Å, α = 90^o, β = 102.500 (12)^o, γ = 90^o. UV-Visible spectrum shows that the crystal is transparent in the entire visible region. Refractive index of the crystal was determined using Brewster’s angle method. Thermal stability of the material was determined from TG/DTA test. The Second harmonic generation efficiency of the crystal was estimated using NLO test and the efficiency was found to be 0.84 times that of UREA.

Abstract: Experimental data on thermionic current density and electron work function of YB₁₂ (100) at T = 1218 – 1978 K in high vacuum (p < 10^-4 Pa) are first introduced. Temperature dependences of the thermionic current density and effective electron work function are presented without extrapolation to the zero-field currents because of the anomalous Schottky effect. The temperature dependences of theYB₁₂ electron work function can be described by linear functions at certain temperature intervals. Preferential boron evaporation and additional ion bombardment by the residual gases ions and evaporated boron ions results in appearance of new phases depleted of boron on the YB₁₂ surface. As a result, an YB₄ – YB₆ double layer on the YB₁₂ single crystal surface has formed. The appearance of the new boride phases, depleted of boron, on the emitting surface causes an increase of thermionic current density compared with individual YB₁₂.

Abstract: In this study, to investigate effects of yttrium and other elements for non-basal slips, magnesium alloy single crystals were stretched parallel to basal plane in various temperatures, and polycrystalline magnesium alloys were also tested to estimate contribution of non-basal slips to their tensile deformation behaviour. In pure magnesium single crystals, second order pyramidal (c+a) slip (SPCS) was observed at 298K. Above room temperature, first order pyramidal (c+a) slip (FPCS) was active. In the Mg - (0.6-0.9) Y alloy single crystals, FPCS was observed at 77K to 298K, while yield stress of the Mg-Y alloy single crystals was higher than that of pure magnesium. In tensile test of polycrystalline specimen, slips lines of non-basal slip systems such as SPCS, FPCS and prismatic slip were observed even at yielding in addition to basal slip lines. Among the non-basal slips, activities of FPCS and prismatic slips were increased with increasing strain in Mg - Y alloy polycrystals. Our study suggested that active non-basal slip system in tension parallel to basal plane is (c+a) pyramidal slip and enhanced ductility of magnesium - yttrium alloy would be caused from increased activity of FPCS by yttrium addition.

Abstract: The stress-induced martensitic transformation and slip deformation behavior were investigated by the compression test with an in-situ observation in a Ti-6Mo-10Al (mol %) alloy single crystal. Owing to the stress-induced martensitic transformation from the parent β phase to the α′′ martensite phase, the single crystal of α′′ martensite without internal twinnings was successfully obtained at room temperature. By further compression, the slip deformation occurred in the single crystal of α′′ martensite. The operated slip system in the α′′ martensite was analyzed by the two face trace analyses, and the slip direction was determined to be []_o.