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Laser additive manufacturing of biodegradable magnesium alloy WE43: a detailed microstructure analysis
摘要： WE43, a magnesium alloy containing yttrium and neodymium as main alloying elements, has become a well-established bioresorbable implant material. Implants made of WE43 are often fabricated by powder extrusion and subsequent machining, but for more complex geometries laser powder bed fusion (LPBF) appears to be a promising alternative. However, the extremely high cooling rates and subsequent heat treatment after solidification of the melt pool involved in this process induce a drastic change in microstructure, which governs mechanical properties and degradation behaviour in a way that is still unclear. In this study we investigated the changes in the microstructure of WE43 induced by LPBF in comparison to that of cast WE43. We did this mainly by electron microscopy imaging, and chemical mapping based on energy-dispersive X-ray spectroscopy in conjunction with electron diffraction for the identification of the various phases. We identified different types of microstructure: an equiaxed grain zone in the center of the laser-induced melt pool, and a lamellar zone and a partially melted zone at its border. The lamellar zone presents dendritic lamellae lying on the Mg basal plane and separated by aligned Nd-rich nanometric intermetallic phases. They appear as globular particles made of Mg3Nd and as platelets made of Mg41Nd5 occurring on Mg prismatic planes. Yttrium is found in solid solution and in oxide particles stemming from the powder particles’ shell. Due to the heat influence on the lamellar zone during subsequent laser passes, a strong texture developed in the bulk material after substantial grain growth.
关键词： Rapid solidification,Microstructure,Bone scaffolds,Electron microscopy,Biodegradable implants,WE43,Laser powder bed fusion,Magnesium
更新于2025-11-21 11:20:48
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In Situ and Ex Situ Characterization of the Microstructure Formation in Ni-Cr-Si Alloys during Rapid Solidificationa??Toward Alloy Design for Laser Additive Manufacturing
摘要： Laser beam-based deposition methods such as laser cladding or additive manufacturing of metals promises improved properties, performance, and reliability of the materials and therefore rely heavily on understanding the relationship between chemical composition, rapid solidification processing conditions, and resulting microstructural features. In this work, the phase formation of four Ni-Cr-Si alloys was studied as a function of cooling rate and chemical composition using a liquid droplet rapid solidification technique. Post mortem x-ray diffraction, scanning electron microscopy, and in situ synchrotron microbeam X-ray diffraction shows the present and evolution of the rapidly solidified microstructures. Furthermore, the obtained results were compared to standard laser deposition tests. In situ microbeam diffraction revealed that due to rapid cooling and an increasing amount of Cr and Si, metastable high-temperature silicides remain in the final microstructure. Due to more sluggish interface kinetics of intermetallic compounds than that of disorder solid solution, an anomalous eutectic structure becomes dominant over the regular lamellar microstructure at high cooling rates. The rapid solidification experiments produced a microstructure similar to the one generated in laser coating thus confirming that this rapid solidification test allows a rapid pre-screening of alloys suitable for laser beam-based processing techniques.
关键词： Ni-Cr-Si,laser coating,rapid solidification,anomalous eutectic
更新于2025-09-23 15:21:01
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Application of Atom Probe Tomography to Complex Microstructures of Laser Additively Manufactured Samples
摘要： Additive Manufacturing (AM) technologies have gained increasing interest across multiple industrial sectors ranging from biomedical to aerospace. AM is not only used for prototyping, but also for tooling as well as for final part production. The computer-controlled, layer-by-layer building up process allows for increased design freedom enabling to produce almost any shape. Additional benefits are potential resource efficiency, increased product customization and lightweight design. Two prominent metal-based laser AM (LAM) techniques are laser powder bed fusion (LPBF) and laser metal deposition (LMD). In LPBF, a focused laser beam is scanned over a bed filled with metal powder to locally melt and fuse the powder to produce fully dense metal parts. The next layer of powder is then distributed and the laser scans again. LMD is a nozzle-based AM process in which a focused laser beam creates a melt pool in the build’s surface. Metallic powder is then injected into the melt pool through a nozzle. The 3D part is built by moving the nozzle/laser assembly forward track by track and layer by layer. Material produced by LAM exhibits a unique thermal history: initially, the material is cooled rapidly from the liquid state in the meltpool. Subsequently, the material experiences a cyclic reheating, the so-called intrinsic heat treatment (IHT), as neighboring tracks and further layers are deposited during the LAM process. Consequences of this thermal history are very complex, sometimes hierarchical microstructures with inhomogeneities at scales ranging from nanometers up millimeters. Fully understanding and characterizing these microstructures is challenging and requires the combination of methods spanning a similar range: from light optical microscopy (LOM) to electron microscopy to atom probe tomography (APT). Here we present examples how APT can deliver valuable information on complex microstructures to better understand the IHT, rapid solidification as well as phase separation in different metallic alloys. Here I will discuss examples in steel, Al- and Ni-based superalloys, and high entropy alloys (HEA).
关键词： Laser Additive Manufacturing,Additive Manufacturing,Phase Separation,Microstructures,Atom Probe Tomography,Rapid Solidification,Intrinsic Heat Treatment
更新于2025-09-23 15:19:57
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A brief introduction to the selective laser melting of Ti6Al4V powders by supreme-speed plasma rotating electrode process
摘要： In the present study, Ti6Al4V spherical powders were prepared by supreme-speed plasma rotating electrode process and the particle size fit log-normal distribution. The average diameter of the powders was successfully determined by a model developed in this work, suggesting that the particle size distribution is mainly affected by the rotating speed. The log-normal distribution factor of the particle size distribution maintains stable as the rotating speed ω varies. The particle size distribution indicates that the main atomization mode of Ti6Al4V under supreme-speed plasma rotating electrode process is of the characteristics of direct drop formation. The mechanical properties of the samples prepared by selective laser melting of Ti6Al4V powders were characterized, indicating that such Ti6Al4V samples with isotropy structure exhibit high yield strength and good ductility.
关键词： Atomization,Ti6Al4V,Selective laser melting,Rapid solidification,Particle size distribution,Plasma rotating electrode process
更新于2025-09-16 10:30:52
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Effect of laser power and deposition environment on the microstructure and properties of direct laser metal-deposited 12CrNi2 steel
摘要： Direct laser metal deposition was used for preparing blocks of steel 12CrNi2 using four different laser powers under two different deposition environments including atmospheric environment and Ar-protected chamber. The results showed that microstructures and mechanical properties were significantly affected by different laser powers. Increasing laser power and deposition in Ar chamber will lead to a decrease in the quantity and size of the voids, which brings more elongation to the samples. Bainitic microstructure was replaced by Widmanstatten ferrite and pearlite, and the amount of proeutectoid ferrite increased with increasing laser power. Moreover, microstructures of previous layers were completely altered in high laser power. Excessive heat accumulation by using high heat input can produce equiaxed ferritic grains with the pearlites in previously deposited layers. Hardness of deposited samples increased from the bottom layer toward the top layer. By using a diode laser with a spot diameter size of 2 mm, the 900-W laser power is suitable for producing crack- and void-free samples. However, post-deposition heat treatment is necessary for obtaining homogeneous desired microstructure and grain size in the manufactured samples.
关键词： Rapid solidification,Microstructure,Mechanical properties,Equiaxed ferrite,Direct laser metal deposition,Void,Bainite,Steel
更新于2025-09-12 10:27:22