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Abstract Extrusion-based sintering-assisted additive manufacturing (ES-AM) enables the fabrication of intricate metal structures, spanning from simple geometries to complex lattice structures. Sintering plays a vital role in metal densification that requires effective design and optimization of sintering processes for high-quality sintered parts. Notably, sintering behaviors in ES-AM differ from those in traditional methods, primarily due to the heterogeneous distribution of particles and pores induced by the anisotropic fabrication nature of additive manufacturing (AM). This review offers an overview of sintering processes and mechanisms fundamental to ES-AM. Theories governing solid-state sintering and liquid-phase sintering are summarized to advance a thorough comprehension of the associated sintering mechanisms. Computational studies on sintering processes at different length scales are also discussed, including atomic-level molecular dynamics, microlevel simulations (Monte Carlo, phase field, and discrete element method), and macroscopic continuum models. The distinctive anisotropic sintering behaviors in the ES-AM process are further elucidated across multiple levels. Ultimately, future directions for ES-AM, encompassing materials, sintering process, and sintering mechanisms, are outlined to guide research endeavors in this field. This review summarizes multiscale sintering behaviors in both traditional manufacturing and AM, contributing to a deeper understanding of sintering mechanisms and paving the way for innovations in the next generation of manufacturing.
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Comparing hydrothermal sintering and cold sintering process: Mechanisms, microstructure, kinetics and chemistry
- Award ID(s):
- 1728634
- PAR ID:
- 10149612
- Date Published:
- Journal Name:
- Journal of the European Ceramic Society
- Volume:
- 40
- Issue:
- 4
- ISSN:
- 0955-2219
- Page Range / eLocation ID:
- 1312 to 1324
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Cold sintering is an unusually low-temperature process that uses a transient transport phase, which is most often liquid, and an applied uniaxial force to assist in densification of a powder compact. By using this approach, many ceramic powders can be transformed to high-density monoliths at temperatures far below the melting point. In this article, we present a summary of cold sintering accomplishments and the current working models that describe the operative mechanisms in the context of other strategies for low-temperature ceramic densification. Current observations in several systems suggest a multiple-stage densification process that bears similarity to models that describe liquid phase sintering. We find that grain growth trends are consistent with classical behavior, but with activation energy values that are lower than observed for thermally driven processes. Densification behavior in these low-temperature systems is rich, and there is much to be investigated regarding mass transport within and across the liquid-solid interfaces that populate these ceramics during densification. Irrespective of mechanisms, these low temperatures create a new opportunity spectrum to design grain boundaries and create new types of nanocomposites among material combinations that previously had incompatible processing windows. Future directions are discussed in terms of both the fundamental science and engineering of cold sintering.more » « less
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The sintering behavior of nanoparticles (NPs), which determines the quality of additively nanomanufactured products, differs from conventional understanding established for microparticles. As NPs have a high surface-to-volume ratio, they are subjected to a higher influence from surface tension and a lower melting point than microparticles, resulting in variations in both crystallographic defect-mediated and surface diffusion mechanisms. Meanwhile, the interplay between these controlling mechanisms in NPs has not been well understood, primarily because sintering occurs on the nanosecond timescale, making it an exceptionally transient process. In this work, sintering of both equal and unequal sized Ag and Cu NP doublets with and without misorientation (both tilt and twist) is modeled through molecular dynamics (MD) simulations. The formation and evolution of crystallographic defects, such as vacancies, dislocations, stacking faults, twin boundaries, and grain boundaries, during sintering are investigated. The influence of these defects on plastic deformation and diffusion mechanisms, such as volume diffusion and grain boundary (GB) diffusion, is discussed to elucidate the responsible sintering mechanisms. The surface diffusion mechanism is visualized by using detailed atomic trajectories generated during the sintering process. Finally, the overall effectiveness of all diffusion sintering mechanisms is quantified. This study provides first insights into the complexity and dynamics of NP sintering mechanisms which can aid in the development of accurate predictive models.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.jeurceramsoc.2019.11.049
