Cooperative material transport during the early stage of sintering

Abstract

The complex transport processes contributing to sintering are not yet fully understood, partially because in-situ observations of sintering in three dimensions (3D) are very difficult. Here we report a novel experiment in which monocrystalline copper spheres are first marked with microscopic boreholes drilled using a focused ion beam, after which high-resolution synchrotron X-ray tomography is carried out to measure translational, rolling and intrinsic rotation movements of some hundred spheres during sintering. unlike in 1D and 2D systems, we show that, in 3D, intrinsic rotations are more pronounced than angular rolling rearrangements of the particle centres and become the dominant mechanism of particle movement. We conclude that in addition to the well-known neck growth and centre approach mechanisms, grain boundary sliding caused by the different crystallographic orientations of the individual spheres occurs.

Direct observation of grain rotations during coarsening of a semisolid Al–Cu alloy

“…1), as captured under laboratory conditions by so-called ball-on-plate experiments (14)(15)(16)(17). Indeed, Grupp et al (12) proposed that the particle rotations in their experiment resulted primarily from a misorientation-based driving force, but experimental evidence for the validity of this assertion was lacking, as the measurement technique they usedabsorption-contrast X-ray computed tomography-is insensitive to the crystal orientation of sintering particles.…”

“…Of particular interest in this regard is the 3D rearrangement of particles that occurs during early-stage sintering (8,13), which can significantly affect subsequent densification but is hardly accessible from 2D cross-sections. In a recent experiment, Grupp et al (12) observed individual particle rotations as large as 8°during the sintering of loosely packed…”

“…With recent advances in 3D imaging, however, researchers can now perform time-resolved measurements of the true size, shape, and interconnectivity of particles and pores (9)(10)(11)(12), from which it may be possible to pin down the atomic-level mechanism(s) underlying each stage of sintering. Of particular interest in this regard is the 3D rearrangement of particles that occurs during early-stage sintering (8,13), which can significantly affect subsequent densification but is hardly accessible from 2D cross-sections.…”

Three-Dimensional Copper Foil-Powder Sintering Current Collector for a Silicon-Based Anode Lithium-Ion Battery

“…Some researchers studied the mechanics of the sintering process. Grupp et al [10] reveals that particles in early stages of sintering not only roll with respect to their interparticle contacts, but also revolve at a greater angle around their own centers, even if they are firmly bonded to adjacent particles. Thus, during the sintering process, the kinetic energy of copper molecular is high, whereas the surface energy of the interface is low.…”

In situ Investigation of Titanium Powder Microwave Sintering by Synchrotron Radiation Computed Tomography

“…However, studies adopting conventional testing techniques have yet to observe microwave sintering in situ because of the experimental limitations of conventional testing techniques, such as optical microscopy, transmission electron microscopy, and scanning electron microscopy. Therefore, in situ and non-destructive testing techniques [8], such as synchrotron radiation computed tomography (SR-CT) [9], should be developed.…”