Additive manufacturing letters最新文献

This work aims to fully characterise the Nb-Ti-Si based alloy (Nb-26Ti-16Si-2.2Al-2Cr), processed by the electron-beam powder-bed-fusion in both as-built and heat-treated conditions, to elucidate the microstructure-property relationships. The as-built condition has [001]-oriented columnar grains of the Nb₃Si phase with the Nbss phase dispersed throughout the microstructure. The microhardness is 645.2 ± 6.7 HV_0.5, and the indentation fracture toughness shows distinct directionality: 7.7 MPa·m^1/2 in the horizontal direction compared to 5.3 MPa·m^1/2 in the vertical direction. Both properties are comparable to the cast version. The directionality is attributed to the underlying mechanisms such as crack bridging, arrest, and micro-crack formation. By contrast, in the heat-treated condition, the alloy exhibits a dual-phase microstructure (Nbss and Nb₅Si₃ phases) with near-equiaxed grain shape due to the Nb₃Si phase decomposition. The fracture toughness increases to 12.1 MPa·m^1/2, at the expense of a reduced microhardness of 564.4 ± 15.0 HV_0.5.

This study proposes a novel deep learning technique for efficient powder morphology characterization, crucial for successful additive manufacturing. The method segments powder particles in microscopy images using Pix2Pix image translation model, enabling precise quantification of size distribution and extraction of critical morphology parameters like circularity and aspect ratio. The proposed approach achieves high accuracy (Structural Similarity Index of 0.8) and closely matches established methods like laser diffraction in measuring particle size distribution (within a deviation of ∼7 %) and allows determination of additional particle attributes of aspect ratio and circualarity in a reliable, repeated, and automated way. These findings highlight the potential of deep learning for automated powder characterization, offering significant benefits for optimizing additive manufacturing processes.

Electron beam melting (EBM), also known as electron beam powder bed fusion (EB-PBF), is a metal additive manufacturing (AM) technology that can make metal parts that are difficult, inefficient, or unachievable through conventional manufacturing routes and other AM technologies. However, a comprehensive understanding of the dynamics of electron beam-matter interactions in EBM remains elusive, which is a barrier for the development and adoption of EBM technology. Here, we report the dynamics and mechanisms of pore formation, pore elimination, and crack elimination in EBM. Three mechanisms of pore formation are observed: (1) pore formation from feedstock powders, (2) pore formation from pre-existing defects, and (3) pore captured by solidification front. One pore elimination mechanism is discovered: pore elimination due to metal vapor condensation, which is unique to EBM. One crack elimination mechanism is uncovered: crack elimination through remelting. These results will enhance the understanding of defect formation and evolution mechanisms in EBM and may inspire the invention of effective approaches to mitigate and control defects (porosity and cracks) in EBM.

Developing high-performance β-Ti alloys is a persistent and long-term demand for the advancement of next-generation biomaterials. In this study, a strategy of leveraging the unique characteristics of laser powder bed fusion (L-PBF) technique and nanocarbon materials was proposed to design a novel carbon-supersaturated β-Ti alloy. Ultrathin graphene oxide (GO) sheets were closely covering onto spherical Ti-15Mo-5Zr-3Al (Ti1553) powders, enhancing laser absorptivity while maintaining good flowability. Consequently, the GO-added Ti1553 builds tended to be denser than the initial ones, indicating an improved additive manufacturability. During L-PBF, GO sheets were completely dissolved into the Ti1553 matrix, generating fully carbon-supersaturated β-Ti structures with a reduced grain size. Thanks to the exceptional strengthening effects of high-concentration solid-solution carbon (∼0.05 wt%), the GO/Ti1553 builds achieved a high ultimate tensile strength of 1166 MPa. Moreover, as revealed by the immunofluorescence staining experiments, the GO/Ti1553 builds demonstrated a retained cytocompatibility. This study provides new insight into composition and processing design of high-performance Ti components for biomedical applications.