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Surface nanocrystallization of Cu-Cr alloy by a high power density continuous laser beam
摘要： A nanostructured surface layer of (cid:1)300 lm thickness was fabricated on Cu-30Cr (wt%) hypereutectic alloy by a continuous laser beam with high power density (1.08 (cid:3) 107 W/cm2). The average grain size of Cr-rich particles was re?ned to (cid:1)40 nm, and the solid solubility limit of Cr in Cu was extended to 1.96 at. %. Experimental results show that the dispersion of nano-sized Cr-rich spheroids in Cu-rich matrix was attributed to the Brownian motion of Cr-rich spheroids, and the high cooling rate (5.75 (cid:3) 106 K/s) during liquid phase separation which inhibits the collisions between Cr-rich spheroids.
关键词： Solidi?cation,Surface nanocrystallization,Microstructure,Cu-Cr alloy,Laser surface melting
更新于2025-11-21 11:18:25
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Grain refinement in laser remelted Mg-3Nd-1Gd-0.5Zr alloy
摘要： Columnar grains are normally favoured with the high cooling rate and steep thermal gradient in laser-based additive manufacturing. Here, we demonstrate that ?ne, fully equiaxed grains can be achieved in Mg-3Nd-1Gd-0.5Zr (EV31) alloy by laser surface remelting. The grains in the melt pool are remarkably re?ned from 74 μm to 3.5 μm, which can be attributed to the growth restriction effect, i.e. the constitutional supercooling formed by Zr solute during solidi?cation in combination with the high cooling rate imposed by laser surface remelting. This novel ?nding could be applied for the control of grain morphology and alloy design for additive manufacturing applications.
关键词： Solidi?cation microstructure,Grain re?ning,Laser treatment,Magnesium alloys,Rapid solidi?cation
更新于2025-09-23 15:19:57
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Analysis of surface tension driven flow and solidification behavior in laser linear welding of stainless steel
摘要： A transient three-dimensional thermal-?uid-metallurgy model was proposed to study the surface tension driven ?ow and welding metallurgical behavior during laser linear welding of 304 stainless steel. Numerical simulation and experimental method were both used to investigate the thermal behavior, surface tension driven ?ow, driving mechanism and solidi?cation characteristics. The temperature related driving force was qualitatively analyzed, and surface tension and surface shear stress were quantitatively studied. Numerical method and dimensional analysis were also carried out to understand the importance of di?erent driving forces, respectively. The metallurgical model was sequentially coupled to the thermal-?uid model to calculate four solidi?cation parameters. Temperature gradient was observed to be much larger at the front of the melt pool due to the e?ect of thermal conductivity, and decreased from center to the periphery. Both the surface tension and surface tension driven ?ow were found smaller in the central area. The maximum shear stress may reach 2500 N/m2 and pushed an intense outward convection. The solidi?cation parameters were used to predict the solidi?ed morphology, and the prediction was well validated by experimental results. The obtained basic conclusions in this work demonstrated that this study of thermal-?uid-metallurgical behavior could provide an improved understanding of the surface tension driven ?ow and solidi?cation behavior inside the melt pool of welding and additive manufacturing process.
关键词： Solidi?cation behavior,Surface tension,Driving force,Additive manufacturing,Fluid ?ow
更新于2025-09-12 10:27:22
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Defect Prevention in Selective Laser Melting Components: Compositional and Process Effects
摘要： A model to predict the conditions for printability is presented. The model focuses on crack prevention, as well as on avoiding the formation of defects such as keyholes, balls and lack of fusion. Crack prevention is ensured by controlling the solidi?cation temperature range and path, as well as via quantifying its ability to resist thermal stresses upon solidi?cation. Defect formation prevention is ensured by controlling the melt pool geometry and by taking into consideration the melting properties. The model’s core relies on thermodynamics and physical analysis to ensure optimal printability, and in turn offers key information for alloy design and selective laser melting process control. The model is shown to describe accurately defect formation of 316L austenitic stainless steels reported in the literature.
关键词： additive manufacturing,solidi?cation cracking,austenitic stainless steel,porosity
更新于2025-09-11 14:15:04