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Grain size evolution under different cooling rate in laser additive manufacturing of superalloy
摘要： The processing parameters in laser additive manufacturing have a crucial impact on solidification microstructure especially grain size, thus influencing the properties of the final products. In this paper, experiments were conducted to investigate the effects of processing parameters including scanning speed, laser power and powder feeding rate on grain size of the solidified track during laser metal deposition. A three-dimensional model considering heat transfer, phase change and Marangoni convection flow had also been developed to simulate the solidification parameters especially cooling rate (G × R) to illustrate the underlying mechanisms. The experimental and simulated results indicated that cooling rate increased and grain size decreased from 8.7 μm to 4.7 μm with the increase of scanning speed from 2 mm/s to 10 mm/s. Contrarily, cooling rate decreased and grain size increased with the increase of laser power and powder feeding rate. The numerical and experimental results provide the additive manufacturing process with the potential of microstructure control and performance optimization.
关键词： Grain size,Laser additive manufacturing,Superalloy,Solidification,Cooling rate
更新于2025-11-21 11:18:25
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Suppression of crystallization in ZBLAN glass by rapid heating and cooling processing
摘要： ZBLAN glass is a heavy metal fluoride glass that tends to undergo heavy devitrification, resulting in a crystalline material. It has many applications, including its use as an optical waveguide for fibre optic technology. However, when the glass is processed with traditional casting techniques, crystallites form readily that act as scattering centres, which results in large attenuation losses. In this study, it has been experimentally demonstrated that processing ZBLAN rapidly with a heating rate of 25,000 K/min and cooling rate of 4,000 K/min yields test samples that are fully amorphous and retain a disordered molecular arrangement characteristic of its molten state. This novel method was developed using a specifically designed equipment named a Rapid Electro-thermal Processing Device, or “REPD”. The REPD applies ohmic heating and thermal conduction to a heat sink to rapidly process the ZBLAN material. The absence of crystallites in the rapidly processed ZBLAN test samples were verified using transmission electron microscopy (TEM) analysis. Applying a theoretical algorithm, the critical cooling rate for yielding fully amorphous ZBLAN glass was determined to be 1081 K/min for a sample volume of 9.4 x 10-8 m3.
关键词： rapid cooling,microscopy,crystallization,ohmic heating,cooling rate,Joule heating,rapid heating,diffraction experiment,ZBLAN
更新于2025-09-23 15:23:52
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Formation of Cobalt Impurity Microinclusions in Silicon Single Crystals
摘要： The structure and chemical composition of cobalt impurity microinclusions in silicon have been studied by electron probe microanalysis using n- and p-type Si?Co? samples prepared by diffusion doping and cooled at different rates after diffusion annealing. The cooling rate after diffusion annealing has been shown to have a significant effect on the structural parameters of the samples and the size of the forming impurity microinclusions. The size and shape of the impurity microinclusions determine their distribution over the bulk of the samples.
关键词： cobalt microinclusions,cobalt silicide,cooling rate,electron probe microanalysis
更新于2025-09-23 15:23:52
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Numerical simulation of temperature field of B1500HS steel/Q235 laser tailored blanks by external thermal action
摘要： Taking high-strength B1500HS steel/Q235 laser tailored blanks as the research object, this paper established the finite element model of the laser welding process of high-strength B1500HS steel /Q235 laser tailored blanks based on the theoretical model of laser welding temperature field. The temperature field of laser tailored blanks was numerically simulated under the conventional condition and External Thermal Action (ETA). The thermal cycle curve of welded joints was compared and analyzed, and the influence of welding power and welding speed on the welding width was analyzed. The results show that, under ETA condition, the cooling rate of weld and heat affected zone decreases greatly, and the residence time above the phase transition temperature becomes longer. And it is conducive to the homogenization of austenite structure at high temperature and the coordination of mechanical properties of welded joints. In addition, under the same welding power, the welding width of ETA is wider than that of conventional welding, and the larger the welding speed is, the smaller the welding width is. In order to ensure the penetration of welding, the welding speed should between 2mm/s and 7mm/s.
关键词： laser welding,external thermal action,cooling rate,numerical simulation,temperature field
更新于2025-09-23 15:21:01
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Study on mechanical and metallurgical properties of fiber laser welded Nb-1% Zr-0.1% C alloy
摘要： Laser welding of Nb-1% Zr-0.1% C was attempted in butt-welding configuration using top and bottom sided inert gas shielding. The precautionary measure during welding was to limit the reactivity of niobium alloy in ambient atmosphere. The ranges of input parameters, that is, laser power (P), welding speed (V) and beam diameter (D) for full penetration welding were attempted by carrying out bead-on-plate (BOP) experiments. The selection of the combination of process parameters was such that the formed weld area could be minimized without hampering the depth of penetration. Bead-geometry, hardness and tensile strength were quantified to study the influence of input process parameters during laser welding. Base metal had an average hardness of 108 VHN and the average hardness of fusion zone (FZ) was found to lie between 278 and 546 VHN. The steeper increment in microhardness value of the FZ could be due to the grain refinement, dissolution of precipitates and formation of brittle intermetallic phases of carbide and oxides, which were evident by the result of energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) phase analysis. The weld joint that failed in the weld zone exhibited the brittle failure, and ductile mode was achieved in the joint, where failure occurs at base metal. The range of elongation in laser welded joints varied in between 1.97 and 5.73 mm. The reduction of tensile strength and ductility of the joints could be due to marginal enhancement of microhardness and increment of brittle phase density in fusion zone, as were evident from XRD phase analysis. The main focus of the present work was intended towards the establishment of laser welding as an alternative technique for fabrication of reactive niobium alloy in ambient atmosphere.
关键词： Cooling rate,Laser welding,Grain refinement,Niobium alloy,Mechanical properties,Nb-1% Zr-0.1% C
更新于2025-09-23 15:19:57
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[The Minerals, Metals & Materials Series] TMS 2020 149th Annual Meeting & Exhibition Supplemental Proceedings || Critical Quenching Rates After Solution Annealing: Peculiarities of Aluminuma??Silicon Alloys Fabricated by Laser Powder-Bed Fusion
摘要： Hot isostatic pressing is commonly used to reduce the porosity of (sand-)cast age-hardenable Al-alloys in order to meet the high quality requirements defined by aircraft and automotive industries. In order to establish additive manufacturing methods, such as laser powder-bed fusion (L-PBF), hot isostatic pressing can be utilized to reduce the anisotropic mechanical properties in as-built condition and at the same time eliminate porosity. For the cast aluminum alloy A356, a gas pressure of 75 MPa during hot isostatic pressing lowers the critical cooling rate required to achieve an oversaturated solid solution to about 1 K/s, which is significantly lower than the required quenching rate at atmospheric pressure (2–4 K/s). Thus, an oversaturated state of dissolved magnesium and silicon atoms within the aluminum matrix of cast alloys can easily be achieved in modern hot isostatic presses, thereby avoiding the necessity of a separate solution annealing step. In this work, we applied hot isostatic pressing followed by rapid quenching and direct aging to age-hardenable aluminum alloys processed by both sand casting and laser powder-bed fusion. It was shown that the proposed process of direct aging could be utilized for post-heat treatment of additively manufactured age-hardenable aluminum alloys to open up new fields of applications, for which components have to possess a high fatigue resistance.
关键词： Hot isostatic pressing,Critical cooling rate,Additive manufacturing,Fatigue resistance,Laser powder-bed fusion,Selective laser melting
更新于2025-09-23 15:19:57
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The effect of temperature distribution and cooling rate on microstructure and microhardness of laser re-melted and laser-borided carbon steels with various carbon concentrations
摘要： Laser heat treatment was arranged as a laser remelting and laser boriding. Materials with different carbon concentration were used. Three zones characterized the microstructure after laser treatment: re-melted zone (MZ), heat-affected zone (HAZ) and substrate material. The differences in carbon content and physical properties of used materials influenced the obtained microstructure, temperature distribution and hardness. In case of laser re-melted specimens, the limited martensite transformation proceeded only in C20, C45 and C90 steels. As a result of laser boriding the microstructure of MZ contained additionally iron borides. The specimens with higher dilution ratio value was characterized by higher hardness of re-melted zone. The aim of this study was to indicate the possibility of predicting the microstructure and depths of MZ and HAZ with the usage of Ashby and Esterling model. The influence of carbon concentration in steel on the thickness, dilution ratio and hardness of laser-borided layers was determined.
关键词： microhardness,laser remelting,temperature distribution,laser boriding,cooling rate,microstructure
更新于2025-09-19 17:13:59
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Influence of Solidification Conditions on the Microstructure of Laser-Surface-Melted Ductile Cast Iron
摘要： The thermal conditions in the molten pool during the laser surface melting of ductile cast iron EN-GJS-700-2 were estimated by using infrared thermography and thermocouple measurements. The thermal data were then correlated with the microstructure of the melted zone. Additionally, the thermodynamic calculations of a Fe-C-Si alloy system were performed to predict the solidification path of the melted zone. It was found that increasing the cooling rate during solidification of the refined ledeburite eutectic but also suppressed the martensitic transformation. A continuous network of plate-like secondary cementite precipitates and nanometric spherical precipitates of tertiary cementite were observed in regions of primary and eutectic austenite. The solidification of the melted zone terminated with the Liquid → γ-Fe + Fe3C + Fe8Si2C reaction. The hardness of the melted zone was affected by both the fraction of the retained austenite and the morphology of the ledeburite eutectic.
关键词： laser surface melting,ductile cast iron,cooling rate,thermography,tertiary cementite,secondary cementite
更新于2025-09-19 17:13:59
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The cooling rate controlled (040) facets of BiVO<sub>4</sub> particles and its characterization
摘要： The photogenerated carriers of BiVO4 are easily recombined and desired to be improved effectively. In this paper, the separation degree was improved by prolonging the cooling time in the process of BiVO4 synthesis. When the cooling rate was 50℃/h, the performance of BiVO4 particles was significantly optimized, including the highest peak of (040) facets, the improvement of morphology, the increase of carriers separation and the optimum degradation of doxycycline. When the degradation time was only 15min, doxycycline in water could be effectively removed with a removal rate of 63%. These studies are valuable for improving the chemical properties of BiVO4 and broadening its application.
关键词： degradation,(040) facets,BiVO4,cooling rate
更新于2025-09-16 10:30:52
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In-Fiber Production of Laser-Structured Stress-Mediated Semiconductor Particles
摘要： The ability to generate stressed semiconductor particles is of great importance in the development of tunable semiconductor and photonic devices. However, existing methods including both bottom-up synthesis and top-down fabrication for producing semiconductor particles are inherently free of stress effects. Here, we report a simple approach to generate controllable stress effects on both encapsulated and free-standing semiconductor particles using laser-structured in-fiber materials engineering. The physical mechanism of the thermally induced in-fiber built-in stress is investigated, and the feasibility of precisely tuning the stress state during the particle formation is experimentally demonstrated by controlling the laser treatment. Gigapascal-level built-in stress, which is a sufficiently strong stimulus to enable inelastic deformations on the fabricated semiconductor particles, has been achieved via this approach. Both encapsulated and free-standing stressed semiconductor particles are generated for a wide range of in-fiber and out-fiber optoelectronic and biomedical applications.
关键词： Built-in stress control,Laser cooling rate,Residual stress,Stressed semiconductor particles,In-fiber material engineering
更新于2025-09-12 10:27:22