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Study on the element segregation and Laves phase formation in the laser metal deposited IN718 superalloy by flat top laser and gaussian distribution laser
摘要： The element segregation, Laves phase formation, and mechanical properties of the laser metal deposited IN718 superalloy by the flat top laser beam (FTLB) and gaussian distribution laser beam (GDLB) are studied. It is found that the Laves phase formation in the gaussian distribution laser deposited IN718 (GDLD-IN718) is substantially higher than that in the flat top laser deposited IN718 (FTLD-IN718). The higher production of the Laves phase in the GDLD-IN718 contributes to the higher microhardness and lower tensile strength (about 20% reduction) of the as-deposited IN718 than that of the FTLD-IN718. The element redistribution behavior in the laser rapid solidification under both of the lasers are also studied through the finite element simulation. The results show that the severe laser energy concentration in the center of the GDLB produces higher molten pool temperature, lower horizontal thermal gradient to vertical thermal gradient ratio (GX/GZ) of the solid-liquid interface. These typical thermal characteristic of the GDLB generated molten pool eventually results in a lower redistribution coefficient of the alloying elements and as a result, the interdendritic element segregation and Laves phase formation are dramatically improved in the GDLD-IN718. The present comparative study proves that the FTLB is more superior for the laser additive manufacturing than that of the GDLB.
关键词： Dendritic growth,Laser metal deposition,Element segregation,Redistribution coefficient,Laves phase
更新于2025-11-21 11:18:25
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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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Study of Inconel 718 Welded by Bead-On-Plate Laser Welding under High-Frequency Micro-Vibration Condition
摘要： Inconel 718 alloy laser-welded joints have poor mechanical properties due to the presence of Laves phases and liquation cracks. This paper intends to solve the above problems by high-frequency micro-vibration-coupled bead-on-plate laser welding. According to the shape of the weld beam, the upper part of the weld is defined as the nail head, and the lower part is the nail body. The results showed that high-frequency micro-vibration can achieve grain refinement. The micro-vibration could break the primary dendrite arm to form secondary dendrite and reduce epitaxial growth of the cellular crystal region. Micro-vibration exacerbated the flow of Niobium (Nb) elements surrounded by dendrites and reduced dendritic segregation, which decreased the formation of Laves phases. The combination of interdendritic Nickel (Ni), Titanium (Ti), and Nb and the precipitation of strengthening phases γ′ and γ′′ were promoted. When the vibration acceleration was 50.10 m/s2, it could inhibit the formation of Laves phases among dendrites and the size of the bulk Laves phase was effectively reduced. The cracks generated in the Inconel 718 alloy were distributed at three locations including the nail-head, the nail-body, and the junction of nail-head and nail-body. When the vibration frequency was 919 Hz, the length of the liquation crack reduced from 180 to 110 μm. While under 1331 Hz, the expansion of the liquation crack was extended, with the length of 200 μm.
关键词： Inconel 718,liquation crack,Laves phase,bead-on-plate laser welding,high-frequency micro-vibration
更新于2025-09-12 10:27:22
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Comparison of laser metal deposition of Inconel 718 from powder, hot and cold wire
摘要： The present paper details first results on laser metal deposition with a new direct diode laser head which allows for coaxial feed of powder, cold- and hot wire material in a single system. The three process variants are compared for laser metal deposition of Inconel 718. The surface appearance, integrity and microstructure of the specimens built with the LMD head are investigated. The presence and removal of the deleterious Laves phase which is detrimental to the mechanical properties is investigated. The results indicate that the new diode laser head allows for a direction-independent LMD process with low oxygen take-up and high surface quality.
关键词： nickel superalloy,Laves phase,direct diode laser,Laser metal deposition
更新于2025-09-12 10:27:22
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The δ Phase Precipitation of an Inconel 718 Superalloy Fabricated by Electromagnetic Stirring Assisted Laser Solid Forming
摘要： Fabricating an Inconel 718 superalloy using electromagnetic stirring assisted laser solid forming (EMS-LSF) is a novel method to modify its microstructure and mechanical properties by consuming the Nb element in the γ phase to alleviate interdendritic segregation. The precipitate C after EMS-LSF can help to achieve the uniform di?usion of Nb, and can also improve its mechanical properties. The precipitation behavior of the δ phase in an EMS-LSF Inconel 718 superalloy with di?erent heat treatment processes has been investigated. The results show that the morphology of the δ phase changes from rod-like to a long-needle shape and tends to grow from the inter dendrite to the core dendrite with electromagnetic ?eld intensity increasing, which is accompanied by the “cutting” and “dissolution” of the Laves phase. Through precipitation kinetics analysis, the precipitation rate of the δ phase is seen to increase with the electromagnetic ?eld intensity increasing. Under a combination of electromagnetic stirring and laser solid forming, the microhardness of the Inconel 718 samples increased slightly due to the fact that a higher content of Nb was distributed in the core dendrite resulting from the serious convection of liquid metal, which can strengthen the matrix.
关键词： electromagnetic stirring,laser solid forming,laves phase,δ phase,precipitation behavior
更新于2025-09-11 14:15:04
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Influence of Vanadium on the Microstructure of IN718 Alloy by Laser Cladding
摘要： A deleterious Laves phase forms in the solidi?ed structure of Inconel 718 (IN718) alloy during laser cladding. However, e?ective removal methods have not yet been identi?ed. In this study, we ?rst added the IN718 alloy cladding layers with a trace amount of vanadium (V, 0.066 wt.%). Then, we studied the solidi?cation structure of cladding layers using a confocal laser scanning microscope and scanning electron microscopy. The microstructure and Laves phase morphology were investigated. The distribution of niobium (Nb) was observed by experiment as well. We found that V is evenly distributed in dendrites and interdendritic zones. A more re?ned dendrite structure, reduced second dendrite arm spacing and lower volume fraction of Laves phase were observed in the solidi?cation structure. The results of linear energy-dispersive X-ray spectroscopy (EDS) indicate that the concentration of Nb decreases with an increasing of the distance from the Laves phase. The V-containing sample displayed a relatively slower decreasing tendency. The IN718 alloy sample was harder with the addition of V. In addition, the porosity of the sample decreased compared with the blank sample. The presented ?ndings outline a new method to inhibit the Nb segregation in IN718 alloy during laser cladding, providing reference signi?cance for improving the performance of IN718 alloy samples during actual processing.
关键词： laves phase,element segregation,vanadium,laser cladding,microstructure
更新于2025-09-11 14:15:04
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The Effects of Heat Treatment on Microstructure and Mechanical Properties of Tribaloy 400 Coatings Deposited by Laser Cladding
摘要： The effects of heat treatment on the microstructure, microhardness, nanohardness and wear resistance of Tribaloy 400 coatings prepared by laser cladding on 304 stainless steel were studied in this paper. The results show that the microstructures of Tribaloy 400 laser cladding layer are cobalt matrix dendrites and eutectic structure. After the heat treatment at 1250 °C for 1 h, the eutectic structure disappears and the strip-like Laves phase is formed on the Co matrix. Meanwhile, the hardness is obviously improved. After the heat treatment at 1250 °C for 1 h and then 900 °C for 4 h, a small amount of e-Co appears, the strip-like Laves phases become coarser and blunter, and some of the strip structures combine together to form blocky structures, and the hardness is decreased. The wear resistance of the samples at 600 °C is better than that at RT since the hardness of the Laves phase increases with the rise in temperature.
关键词： Laves phase,wear resistance,hardness,heat treatment,Tribaloy alloy
更新于2025-09-10 09:29:36