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Dependence of h-BN film thickness as grown on nickel single crystal substrates of different orientation
摘要： Chemical vapor deposition of 2D materials has been an active area of research in recent years because it is a scalable process for obtaining thin films that can be used to fabricate devices. The growth mechanism for hexagonal boron nitride (h-BN) on metal catalyst substrates has been described to be either surface energy driven or diffusion driven. In this work, h-BN is grown in a CVD system on Ni single crystal substrates as a function of Ni crystallographic orientation to clarify the competing forces acting on the growth mechanism. We observed that the thickness of the h-BN film depends on the Ni substrate orientation, with the growth rate increasing from the (100) surface to the (111) surface, and the highest on the (110) surface. We associate the observed results with surface reactivity and diffusivity differences for different Ni orientations. Boron and nitrogen diffuse and precipitate from the Ni bulk to form thin multilayer h-BN. Our results serve to clarify the h-BN CVD growth mechanism which has been previously ascribed to a surface energy-driven growth mechanism.
关键词： surface diffusion,electron backscatter diffraction,growth mechanism,hexagonal boron nitride
更新于2025-09-23 15:21:01
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Characterization and correlation of microstructure and hardness of Tia??6Ala??4V sheet surface-treated by pulsed laser
摘要： A hot-rolled Tie6Ale4V (Ti-64) sheet was surface-treated by pulsed laser at two different powers (100 and 200 W), with microstructural features and hardness before and after the laser surface treatment (LST) systematically investigated. Results show that after the LST at both powers there are two modi?cation zones with distinct microstructural characteristics: melted zone (MZ) near the laser beam center, completely composed of ?ne martensitic plates with dense {10e11} nanotwins inside them; heat-affected zone (HAZ) far away from the laser beam center, comprised of mixed structures of short-rod b particles, martensitic plates and untransformed bulk a grains. Hardness measurements reveal that the hardness of the Ti-64 sheet can be markedly increased (especially in the MZ) after the LST. In-depth analyses suggest that the hardness increase in the MZ can be ascribed to combined contributions from grain re?nement, presence of nanotwins and solid solution of alloying elements, while only the structural re?nement by ?ne plate structures contributes to hardening in the HAZ. Comparisons between both the LSTed specimens reveal that increasing the laser power from 100 W to 200 W can effectively enlarge the laser-modi?ed zones (both the MZ and the HAZ) and simultaneously re?ne plate structures, leading to further hardness increase.
关键词： Ti-6Ale4V,Hall-petch relation,Hardness,Electron backscatter diffraction,Pulsed laser
更新于2025-09-23 15:19:57
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Surface microstructural characteristics and hardness of Cr-coated Zr702 sheet processed by pulsed laser
摘要： Microstructural characteristics and hardness of Cr-coated Zr702 sheet after the laser surface treatment (LST) were characterized and investigated by combined use of electron backscatter diffraction, electron channeling contrast imaging, energy dispersive spectrometry and hardness measurement. Results show that after the LST processing at 100 W, three zones with different microstructural characteristics are presented from the surface to the matrix: melted zone (MZ), solid-state phase transformation zone (SSPTZ) and matrix. Surface alloying with Cr occurs in the MZ, leading to the formation of a large number of discontinuous netlike ZrCr2 Laves phases. The SSPTZ is comprised of untransformed bulk α grains with internal substructures and fine martensitic plates. The appearance of such substructures can be attributed to dislocation movements induced by thermal stresses while the martensitic plates result from rapid β→α transformation induced by the pulsed laser. Hardness measurements show that the LST can remarkably increase surface hardness (by ~110%) of the Cr-coated Zr702 sheet, which can be ascribed to strengthening/hardening effects by solid solution of Cr, the formation of dense second phases and significant grain refinement.
关键词： Electron backscatter diffraction,Microstructure,Hardness,Laves phase,Zr702 sheet,Laser surface processing
更新于2025-09-19 17:13:59
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Microstructural characterization of Inconel 718 alloy after pulsed laser surface treatment at different powers
摘要： An annealed Inconel 718 alloy was surface-treated by pulsed laser at three different powers (100, 50 and 25 W). Microstructural changes induced by the laser treatments were characterized by use of electron backscatter diffraction and electron channeling contrast imaging techniques. Results show that both annealing twins and strengthening precipitates profusely existing in the as-received specimen are dissolved at elevated temperatures during the laser irradiation. Meanwhile, in the melting zone (MZ), densities of low angle boundaries (LABs) are greatly increased with a large number of Laves phases preferentially distributed along such LABs. For different specimens, widths and depths of their MZs are found to be gradually reduced with decreasing the laser powers. Orientation analyses reveal that the columnar grains in the MZ of the 100 W specimen could inherit orientations existing in the matrix while lower laser powers promote the formation of more nuclei with scattered orientations to grow to be granular grains in the MZ. Hardness tests reveal that the MZs of all laser-treated specimens are softer than the matrix probably due to both precipitate dissolution and grain coarsening.
关键词： pulsed laser surface treatment,hardness,grain boundaries,Inconel 718 alloy,electron backscatter diffraction
更新于2025-09-16 10:30:52