Mechanical spectroscopy of the high-temperature brittle-to-ductile transition in ceramics and cermets

Theoretical and experimental determination of the major thermo-mechanical properties of RE 2 SiO 5 (RE = Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y) for environmental and thermal barrier coating applications

“…7(c). Schaller [27] suggested that brittle-to-ductile transition can be decomposed into two stages namely, brittle-to-tough transition and tough-to-ductile transition. As the cracks propagating along the grain boundary can dissipate more energy, fracture toughness must be enhanced at elevated temperatures.…”

How do the grains slide in fine-grained zirconia polycrystals at high temperature?

“…Indeed, a few percent of sintering aids in Si 3 N 4 ceramics, in particular, instigates large amorphous-phase agglomerates (amorphous pockets) at multiple junctions and thin or even thick amorphous film at grain boundaries. 14,16,17 By contrast, doping of 3Y-TZP ceramics with SiO 2 phases does not manifest any amorphous films at grain boundaries. This is attested in Fig.…”

“…The exponential background is a manifestation of the deformation of the rigid skeleton around the pockets. 17 It dominates over the peaks in SiO 2 doped 3YS-TZP at high temperature, as well as tanφ of high-purity 3YS-TZP above 1300 K at 1 Hz, where the mechanical loss occurs by deformation of grains in the skeleton. During mechanical spectroscopy at 1 Hz frequency range the experimental conditions are close to transient creep, and therefore only local motions of grains in the skeleton can take place, the easiest ones are the relative displacements of neighboring grains.…”

“…5,[14][15][16][17] The sintering aids added to the powder compacts for improving the powder compressibility and densification during the processing, together with powder impurity, result in the formation of amorphous phases at triple junctions and grain boundaries. Indeed, a few percent of sintering aids in Si 3 N 4 ceramics, in particular, instigates large amorphous-phase agglomerates (amorphous pockets) at multiple junctions and thin or even thick amorphous film at grain boundaries.…”

Dislocation Forces on an Edge Dislocation Near Crack Tip in Ferroelectric Materials

“…A lot of physicists and mechanists made numerous researches and discussions revolving around this challenging problem since 1990s, and discovered that the dislocation emission from the crack tip may be one of the critical performances of brittle-ductile transition of materials (Rice and Thomson, 1974;Beltz, and Rice, 1992). Although the ferroelectric materials present brittleness at low and room temperature due to high bond energy of electrovalent bond and covalent bond, their applications are usually under high temperature in aerospace and petroleum industry, this can intensify atom thermal vibration and activate dislocation emission to overcome the lattice resistance (Hartmaier, 2005;Sen et al, 2010;Schaller, 2000;Friedel, 1980). The brittle-ductile transition arising from the thermally activated dislocation slip can strongly influence the degradation mechanism such as fatigue, fracture and plastic deformation in high-temperature ferroelectric ceramics.…”