Cracking during sintering is a common problem in powder processing and is usually caused by constraint that prevents the sintering material from shrinking in one or more directions. Different factors influence sintering‐induced cracking, including temperature schedule, packing density, and specimen geometry. Here we use the discrete element method to directly observe the stress distribution and sinter‐cracking behavior in edge notched panels sintered under a uniaxial restraint. This geometry allows an easy comparison with traditional fracture mechanics parameters, facilitating analysis of sinter‐cracking behavior. We find that cracking caused by self‐stress during sintering resembles the growth of creep cracks in fully dense materials. By deriving the constrained densification rate from the appropriate constitutive equations, we discover that linear shrinkage transverse to the loading axis is accelerated by a contribution from the effective Poisson's ratio of a sintering solid. Simulation of different notch geometries and initial relative densities reveals conditions that favor densification and minimize crack growth, alluding to design methods for avoiding cracking in actual sintering processes. We combine the far‐field stress and crack length to compute the net section stress, finding that it characterizes the stress profile between the notches and correlates with the sinter‐crack growth rate, demonstrating its potential to quantitatively describe sinter‐cracking.
- Award ID(s):
- 1826064
- PAR ID:
- 10389165
- Editor(s):
- Shamsaei Nima, Seifi Mohsen
- Date Published:
- Journal Name:
- Progress in Additive Manufacturing 2020
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
more » « less
Abstract Nanoparticle 3D printing and sintering is a promising method to achieve freeform interconnects on compliant substrates for applications such as soft robotics and wearable healthcare devices. However, previous strategies to sinter metallic nanoparticles while preserving the soft polymer substrate are rife with problems such as cracking and low conductivity of the metallic features. In this paper, the mechanisms of cracking in nanoparticle‐based 3D printed and sintered stretchable interconnects are identified and architecture and processing strategies are demonstrated to achieve crack‐free interconnects fully embedded in thin (<100 μm in thickness) stretchable polydimethylsiloxane (PDMS) with external connectivity. Capillary forces between nanoparticles developed through rapid solvent evaporation in the colloidal ink is hypothesized to initiate cracking during drying. Additionally, the presence of oxygen promotes the removal of organic surfactants and binders in the nanoparticle ink which increases nanoparticle agglomeration, grain growth, and subsequently conductivity. An experimental step‐wise variation of the thermal/atmospheric process conditions supports this hypothesis and shows that the presence of air during a low temperature drying step reduces the capillary stress to produce crack‐free interconnects with high conductivities (up to 56% of bulk metal) while having an excellent compatibility with the underlying polymer materials. Finally, stretchable interconnects fully‐encapsulated in PDMS polymer, with 3D pillar architectures for external connectivity are demonstrated, thus also solving an important “last‐mile” problem in the packaging of stretchable electronics.
-
more » « less
Currently, bioresorbable electronic devices are predominantly fabricated by complex and expensive vacuum‐based integrated circuit (IC) processes. Here, a low‐cost manufacturing approach for bioresorbable conductors on bioresorbable polymer substrates by evaporation–condensation‐mediated laser printing and sintering of Zn nanoparticle is reported. Laser sintering of Zn nanoparticles has been technically difficult due to the surface oxide on nanoparticles. To circumvent the surface oxide, a novel approach is discovered to print and sinter Zn nanoparticle facilitated by evaporation–condensation in confined domains. The printing process can be performed on low‐temperature substrates in ambient environment allowing easy integration on a roll‐to‐roll platform for economical manufacturing of bioresorbable electronics. The fabricated Zn conductors show excellent electrical conductivity (≈1.124 × 106S m−1), mechanical durability, and water dissolvability. Successful demonstration of strain gauges confirms the potential application in various environmentally friendly sensors and circuits.
-
more » « less
Abstract Flexible thermoelectric (TE) devices hold great promise for energy harvesting and cooling applications, with increasing significance to serve as perpetual power sources for flexible electronics and wearable devices. Despite unique and superior TE properties widely reported in nanocrystals, transforming these nanocrystals into flexible and functional forms remains a major challenge. Herein, demonstrated is a transformative 3D conformal aerosol jet printing and rapid photonic sintering process to print and sinter solution‐processed Bi2Te2.7Se0.3nanoplate inks onto virtually any flexible substrates. Within seconds of photonic sintering, the electrical conductivity of the printed film is dramatically improved from nonconductive to 2.7 × 104S m−1. The films demonstrate a room temperature power factor of 730 µW m−1K−2, which is among the highest values reported in flexible TE films. Additionally, the film shows negligible performance changes after 500 bending cycles. The highly scalable and low‐cost fabrication process paves the way for large‐scale manufacturing of flexible devices using a variety of high‐performing nanoparticle inks.
-
more » « less
Abstract Three-dimensional (3D) printing of metal components through powder bed fusion, material extrusion, and vat photopolymerization, has attracted interest continuously. Particularly, extrusion-based and photopolymerization-based processes employ metal particle-reinforced polymer matrix composites (PMCs) as raw materials. However, the resolution for extrusion-based printing is limited by the speed-accuracy tradeoff. In contrast, photopolymerization-based processes can significantly improve the printing resolution, but the filler loading of the PMC is typically low due to the critical requirement on raw materials’ rheological properties. Herein, we develop a new metal 3D printing strategy by utilizing micro-continuous liquid interface printing (μCLIP) to print PMC resins comprising nanoporous copper (NP-Cu) powders. By balancing the need for higher filler loading and the requirements on rheological properties to enable printability for the μCLIP, the compositions of PMC resin were optimized. In detail, the concentration of the NP-Cu powders in the resins can reach up to 40 wt% without sacrificing the printability and printing speed (10 μm·s−1). After sintering, 3D copper structures with microscale features (470 ± 140 μm in diameter) manifesting an average resistivity of 150 kΩ·mm can be realized. In summary, this new strategy potentially benefits the rapid prototyping of metal components with higher resolution at faster speeds.
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Conference Paper:
- The DOI is not currently available.
