3D multiscale-imaging of processing-induced defects formed during sintering of hierarchical powder packings

Abstract

The characterization of the processing-induced defects is an essential step for developing defect-free processing, which is important to the assurance of structural reliability of brittle ceramics. The multiscale X-ray computed tomography, consisting of micro-CT as a wide-field and low-resolution system and nano-CT as a narrow-field and high-resolution system, is suitable for observing crack-like defects with small length and with very small crack opening displacement. Here we applied this powerful imaging tool in order to reveal the complicated three-dimensional morphology of defects evolved during sintering of alumina. The hierarchical packing structure of granules was the origin of several types of strength-limiting defects, which could not be eliminated due to the differential sintering of heterogeneous microstructures. This imaging technique of internal defects provides a link between the processing and the fracture strength for the development of structural materials.

Electrophoretic deposition of coatings and bulk compacts using magnesium-doped aluminum oxide nanopowders

“…Various pressing technologies such as isostatic and magnetic-pulse pressing were applied to com-pact powdered materials [10][11][12]. However, the features of these methods include the difficulty to obtain uniform density and the presence of internal stresses in the material [13].…”

In Situ Evolution of Pores in Lithium Hydride at Elevated Temperatures Characterized by X-ray Computed Tomography

“…From the shape of pores, three kinds of pores are divided: roundshaped (Type I) pores, long strip (Type II) pores and branched crack-like (Type III) pores. Long strip pores and branched crack-like pores are formed at the boundaries among granules at sintering [23]. The length of Type II pores and Type III pores is the maximum of the 3D Feret Diameters, which is defined as the distance between two parallel tangents of the particle at an arbitrary angle.…”

“…Recently, the resolution of X-ray computed tomography (XCT) has reached the µm level [17]. XCT, such as micro-focus X-ray computed tomography (micro-CT), synchrotron radiation X-ray computed tomography (SR-CT) and multiscale X-ray computed tomography, has been used to investigate the pore evolution of some other ceramic materials in sintering, such as boron carbide, silicon nitride, alumina and silicon carbide [18][19][20][21][22][23][24][25][26][27]. Nevertheless, it was difficult to characterize the in situ changes of defects in sintered ceramics with an increasing temperature.…”

Characterization of ceramics based on laser speckle photometry

“…The static algorithm focuses on the image analysis, which uses the gray-value-related parameters in combination with statistical properties of speckle images. Parameters calculated from the gray level co-occurrence matrix (GLCM), such as mean intensity, speckle contrast, speckle size, and texture properties (Haralick, 1979;Rabal and Braga, 2008), can be used to numerically represent speckle signals of the LSP technique. Quasi-static algorithms are focused on the analysis of differences in the gray value distributions of a single pixel in the time sequence.…”

“…Traditional techniques such as the X-ray diffraction method (Gao et al, 2017;Xi et al, 2017), Raman spectroscopy (Jan-notti et al, 2017), and the hole-drilling method (Mainjot et al, 2011) are time-consuming, expensive, and sometimes destructive. In addition, speckle photography is a full-field optical method and, by combining it with the digital image correlation technique, can be used to measure in-plane deformations and strains in opaque materials (Blug et al, 2019;Schenuit et al, 2008;Tausendfreund et al, 2018). It records the speckle patterns before and after the deformation of the inspected workpiece.…”