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Grain growth in IN718 superalloy fabricated by laser additive manufacturing
摘要： The grain growth mechanism of IN718 superalloy fabricated by selective laser melting (SLM) was studied. Epitaxial growth with the same crystallographic orientation or rotating by 90° across the melting pool boundary and competitive growth in the same melting pool were observed. Either of the two patterns of epitaxial growth can maintain the same grain across the melting pool boundary. Competitive growth is determined by both the heat flow direction and preferred crystallographic orientation. In SLM, the grains grow along the preferred crystallographic orientation owing to a high solidification rate. The smaller the deviation angles between the heat flow direction and the preferred crystallographic orientation, the faster the grain growth rate.
关键词： competitive growth,crystallographic orientation,selective laser melting,IN718,Epitaxial growth
更新于2025-09-23 15:19:57
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Secondary Grain Growth in Organica??Inorganic Perovskite Films with Ethylamine Hydrochloride Additives for Highly Efficient Solar Cells
摘要： The grain boundaries of perovskite polycrystalline are regarded as a defect region that not only provides carrier recombination sites but also introduces device degradation pathways. Efforts to enlarging the grain size of perovskite film and reducing its grain boundary are crucial for highly efficient and stable PSCs. Some effective methods that facilitate grain growth are post-deposition thermal annealing and solvent vapor annealing. However, a detailed understanding of grain growth mechanisms in perovskite films is lacking. In this study, perovskite films were prepared by adding ethylamine hydrochloride (EACl) to the precursor solution. This additive strategy promotes a new grain growth mode, secondary grain growth, in perovskite films. Secondary grain growth leads to much larger grains with high crystallographic orientation. These excellent properties lead to reduced grain boundaries and the densities of boundary defects. The improved film quality results in a prolonged charge–carrier lifetime and a significantly enhanced PCE. Compared with the PCE 18.42% of the control device, the PCE of the device with EACl additives reaches 21.07%.
关键词： Organic-inorganic perovskite,crystallographic orientation,grain growth,power conversion efficiency,solar cells
更新于2025-09-19 17:13:59
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Thermodynamics analysis and rapid solidification of laser polished Inconel 718 by selective laser melting
摘要： This paper presents thermodynamics analysis and rapid solidi?cation of laser polishing technology for selective laser melting (SLM) Inconel 718 superalloy. Signi?cant porosity reduction has been examined in the laser polished layer, where the surface porosity is reduced by 65.7% compared with that of the as-fabricated SLM surface. The results show that the temperature in the polished zone is over 1683 K, and the cooling rate is approximately up to 2.46 × 106 K/s. Besides, the polished layer consists of equiaxed grain and columnar grain with average grain size of 10 ± 2.4 μm and 5 ± 1.2 μm, respectively, and tiny cell grains with average size of 3.5 μm in the heat-a?ected zone (HAZ). Moreover, the transmission electron microscope (TEM) results show that the orientation relationship (OR) between the γ matrix and Laves phase is found to be Burgers OR [0 1 1] ‖[0 1 1ˉ 2] Laves on the as-received layer and [1ˉ 1 1] ‖[1 2ˉ 1 3ˉ] Laves on the polished layer.
关键词： Inconel 718 superalloy,Microstructural evolution,Crystallographic orientation,Selective laser melting,Laser polishing
更新于2025-09-16 10:30:52
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Construction of Cellular Substructure in Laser Powder Bed Fusion
摘要： Cellular substructure has been widely observed in the sample fabricated by laser powder bed fusion, while its growth direction and the crystallographic orientation have seldom been studied. This research tries to build a general model to construct the substructure from its two-dimensional morphology. All the three Bunge Euler angles to specify a unique growth direction are determined, and the crystallographic orientation corresponding to the growth direction is also obtained. Based on the crystallographic orientation, the substructure in the single track of austenitic stainless steel 316L is distinguished between the cell-like dendrite and the cell. It is found that, with the increase of scanning velocity, the substructure transits from cell-like dendrite to cell. When the power is 200 W, the critical growth rate of the transition in the single track can be around 0.31 ms?1.
关键词： cell,cell-like dendrite,crystallographic orientation,model,laser powder bed fusion,substructure,growth direction
更新于2025-09-12 10:27:22
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Effects of crystallographic orientation and negative rake angle on the brittle-ductile transition and subsurface deformation in machining of monocrystalline germanium
摘要： In this study, taper cutting experiments using a diamond tool were conducted to investigate the effects of negative rake angle and cutting orientation on the brittle-ductile transition and subsurface deformation of monocrystalline germanium cut on the (100), (101), and (111) planes. Confocal laser scanning microscopy and Raman spectroscopy were used to observe the three-dimensional surface topographies of the samples and characterize the subsurface deformation, respectively. The results showed that the negative rake angle and crystallographic orientation have a significant effect on the brittle-ductile transition and subsurface deformation mechanisms in ductile regime machining of monocrystalline germanium. A large negative rake angle alters the initial surface crack patterns, as well as anisotropic behavior of the ductile-brittle transition and subsurface deformation of monocrystalline germanium.
关键词： brittle-ductile transition,negative rake angle,crystallographic orientation,subsurface deformation,Germanium
更新于2025-09-10 09:29:36
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FABRICATION OF PYRAMIDAL CAVITY STRUCTURE WITH MICRON-SIZED TIP USING ANISOTROPIC KOH ETCHING OF SILICON (100)
摘要： Microelectromechanical System (MEMS) are systems of micron-sized structures and typically integrated with microelectronic components. Bulk micromachining using wet anisotropic etching is able to etch silicon substrates to a desired three-dimensional (3D) structure, depending on the silicon crystallographic orientation. To date, MEMS components i.e. thermal, pressure, mechanical, bio/chemical sensors have been fabricated with wet anisotropic etching of silicon. This paper presents the fabrication of a 3D pyramidal cavity structure with micron-sized tip of silicon (100) using anisotropic KOH etching of w/w 45 % at 80 oC temperature. Volume percent of 10 % IPA as a less polar diluent is added to the KOH etching solution in saturating the solution and controlling the etching selectivity and rate. Smooth etched silicon surface of hillock free is able to be achieved with IPA addition to the KOH etching solution. A characteristic V-shaped cavity with side angle of 54.8 degrees has successfully been formed and is almost identical to the theoretical structure model. Comparison of two different silicon nitride window masks on the micron-size tip formation is also investigated. Under etch, over etch and etching selectivity, as common problems effecting the micron-tip size variation, are also addressed in this work. In conclusion, anisotropic KOH etching as a simple, fast and inexpensive bulk micromachining technique, in fabricating 3D MEMS structure using silicon (100), is validated in this work.
关键词： pyramidal cavity structure,MEMS,KOH etching,anisotropic,crystallographic orientation
更新于2025-09-04 15:30:14