Additive manufacturing letters最新文献

The present work systematically investigates the effects of BN nanopowder functionalization on the processability, microstructure and tensile response of the custom Powder Bed Fusion Laser Beam (PBF-LB) Al alloy ‘AMALLOY3D’. The results show that a minor addition of BN (0.3 % by weight) not only produces near fully dense parts (99.91 %), but is also paired with improved flowability, enhancing the overall processability. Electron backscatter diffraction (EBSD) analysis revealed the transformation to a fully equiaxed grain structure in the BN-functionalized material, resulting in a 40 % increase in yield strength. Energy dispersive spectroscopy using a scanning transmission electron microscope (STEM-EDS) was employed to reveal the intricate secondary phases’ arrangements. These observations coupled with the help of the CALPHAD approach led to the reconstruction of the solidification history of AMALLOY3D and the BN-functionalized material. The present study unravels the complex dynamics leading to the columnar-to-equiaxed transition in BN-reinforced AMCs, proving that such unique microstructures and exceptional tensile properties can be achieved without compromising PBF-LB processability.

This study reports an anomalous temperature-dependent tensile behavior of laser-beam powder bed fusion (PBF-LB) processed Cu–Cr–Zr alloy. The yield strength of the alloy initially decreases as the temperature increases to 200±5 MPa and then increases to 350±11 MPa at 500°C before reducing to 234±6 MPa at 600°C. The microstructure consists of elongated Cu grains with a high concentration of Cr solute (∼1 mass%), resulting from rapid solidification during the PBF-LB process. Transmission electron microscopy for the specimens deformed at 500°C revealed the presence of numerous nanoscale Cr-rich particles embedded inside the supersaturated solid solution of the Cu matrix. Nanoscale particles can act as barriers to dislocation motion, leading to an increase in internal stress during plastic deformation at elevated temperatures. This work provides the high potential of post heat treatments for achieving superior mechanical performance using high solute supersaturation formed by the PBF-LB process.

Generalized large language models (LLMs) such as GPT-4 may not provide specific answers to queries formulated by materials science researchers. These models may produce a high-level outline but lack the capacity to return detailed instructions on manufacturing and material properties of novel alloys. We introduce “AMGPT”, a specialized LLM text generator designed for metal AM queries. The goal of AMGPT is to assist researchers and users in navigating a curated corpus of literature. Instead of training from scratch, we employ a pre-trained Llama2-7B model from Hugging Face in a Retrieval-Augmented Generation (RAG) setup, utilizing it to dynamically incorporate information from $\sim$50 AM papers and textbooks in PDF format. Mathpix is used to convert these PDF documents into TeX format, facilitating their integration into the RAG pipeline managed by LlamaIndex. A query retrieval function has also been added, enabling the system to fetch relevant literature from Elsevier journals based on the context of the query. Expert evaluations of this project highlight that specific embeddings from the RAG setup accelerate response times and maintain coherence in the generated text.

Single element detection, spatial frequency modulation imaging (SPIFI) is deployed in a laser processing environment. SPIFI images are used to monitor a laser melting process, like that encountered during additive manufacturing, with an exposure time of $120\mu s$, which enables real-time, in-situ monitoring of melt track formation coaxial with the processing laser. SPIFI images from a single photodiode are shown to be comparable to or better than white light camera images taken at the same numerical aperture. SPIFI deployed in this manner represents a disruptive new sensor metrology system that, when coupled with developing process models, can ultimately be used to validate statistically significant process parameter-signature-quality relationships with quantified uncertainty.

Additively manufactured (AM) Al alloys have widespread applications. Their high-temperature mechanical behaviors are also of significant interest. In this study, we investigated the microstructure and mechanical behavior of Al-2Ti-2Fe-2Co-2Ni (at%) alloy processed by laser powder bed fusion. The as-printed alloy contains a distinctive heterogeneous microstructure characterized by nanoscale intermetallic lamellae arranged in rosette patterns in the Al matrix. Notably, this alloy exhibits high tensile strength and thermal stability up to 500 °C as revealed by in-situ tension studies in a scanning electron microscope. The enhanced high temperature performance can be attributed to a substantial volume fraction of well-dispersed, nanoscale stable intermetallic particles.

Laser powder bed fusion (LPBF) is a well-established additive manufacturing process for producing high-quality metal components with unparallelled design freedom. However, LPBF also has its limitations, including a limited materials palette, low productivity and high costs, mainly due to the expensive feedstock powders. These powders must meet highly stringent requirements regarding particle size (15–$45\mu m$), particle size distribution (mono-modal) and morphology (spherical), which is achievable only through expensive gas- and plasma-atomised powders. This paper investigates slurry-LPBF as an alternative to conventional dry powder LPBF. The use of slurry removes some of the stringent powder requirements by allowing deposition of smaller particles with a variety of particle morphologies. Slurry-LPBF can therefore increase the useful yield of the atomisation process and expand the materials palette for LPBF, by enabling the use of powders for which atomised variants are not commercially available. This study used 316L stainless steel powder with an average particle size $<18\mu m$. An existing slurry-LPBF machine was re-designed and re-built, allowing successful slurry processing. Two optimal parameter sets were obtained, resulting in component density of 99.4%. Tensile testing revealed an ultimate tensile strength (UTS) of 622 ± 2 MPa and an elongation at break of 66 ± 2%. These results are consistent, and fall within the range of reported values in literature for dry-powder LPBF, with the UTS being on the lower side of the range, whilst elongation at break being on the higher side.

Recent supply chain issues affecting the airfoil casting industry have renewed interest in industrial-scale 3D printing of ceramic cores. Ceramic cores are conventionally manufactured through injection molding. However, injection molding of low-volume production runs can be challenging because of the long lead times and high costs associated with mold tooling. 3D printing can mitigate up-front tooling costs, but there are other trade-offs, e.g., higher material costs of 3D printing feedstocks. Here, we develop a techno-economic model that accounts for costs (materials, tooling, equipment), core size, experience curve effects, and other important variables to determine threshold production volumes for which 3D printing is less expensive than conventional processing techniques. Using market data from 2019, our analysis shows that 3D printing a single dedicated core design with typical dimensions for aeroengine applications is less expensive than injection molding below ∼1,800 units. By simultaneously printing multiple core designs, this threshold increases to 120,000 units, or approximately 2 % of the 2019 aeroengine market demand. This threshold value decreases with increasing core size, indicating 3D printing is less favorable for large castings used in industrial gas turbines. These results are compared against the demand for ceramic cores in engine development, engine sustainment, and new engine manufacturing.

Pulsed laser assisted additive manufacturing has been demonstrated as a promising technology for controlling grain structure in 3D-printing processes. The integration of a nanosecond laser onto a wire arc additive manufacturing tool has enabled the localized printing of Inconel 718 with grain sizes meeting ASTM 9 standards (average measured grain size of $13.7\mu m$) for wrought material within a single bead under solidification conditions that would otherwise produce $340\mu m$ columnar grains. The observed grain refinement holds promise, provided scale up is possible, for overcoming the highly anisotropic mechanical properties and microcracking associated with large columnar grains of Inconel 718 that have long stood in the way of leveraging the advantages of direct energy deposition printing techniques of difficult to machine alloys. Experiments on large bead sizes allowed for decoupling surface versus bulk nanosecond laser/liquid metal interaction mechanisms to determine that the source of the observed grain refinement is the collapse of cavitation bubbles originating from acoustic waves generated by momentum transfer into the melt of an ablation plasma. Additionally, experiments that increased the cavitation bubble density within the mushy zone during solidification by tuning the nanosecond laser scan path went beyond the 25 times reduction in grain size to a 70 times factor of refinement with a minimum average grain diameter approaching $4\mu m$.

Additive manufactured (AM) 94 % alumina was successfully 3D printed using the Lithography Ceramic Manufacturing (LCM) technique. Each 3D printed sample was exposed to a different stage of the thermal post-process to identify changes in chemical composition at each stage. The thermal phases studied were the as printed green state, preconditioning at 120 °C, debinding at 600 °C, debinding at 1100 °C, and sintering at 1650 °C. Fourier Transform Infrared Spectroscopy (FTIR), Raman Spectroscopy, Thermogravimetric Analysis (TGA), and X-Ray Fluorescence (XRF) were used to evaluate the changes in composition at each stage of the thermal post-process. Cross-sectional images of 3D printed alumina samples after thermal exposure were captured using scanning electron microscopy (SEM).

In-situ microstructural control is desirable in additively manufactured metal parts due to limited post-processing options for net-shaped components. Here, we introduce a novel selective rescanning approach to control the local solidification conditions and the microstructure in metal parts produced by laser powder-bed fusion (LPBF). We show that the melt pool dimensions, grain size, and sub-grain cell structure can be selectively varied in three dimensions to engineer the mechanical response of LPBF parts. The lattice-based rescanning strategy enables the formation of an interpenetrating microstructure comprised of fine and coarse grains. The localized heating and cooling-induced thermal stresses increase the hardness and tensile strength of rescanned specimens. The study shows the potential of selective rescanning strategy as a promising avenue for achieving precise control of microstructure and properties in as-printed LPBF parts without subsequent processing.