Browsing by Author "Liu, T"

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    Effect of grain size on Hertzian contact damage in 9 mol% Ce-TZP ceramics
    (Elsevier, 2002-05-15) Latella, BA; Liu, T; Atanacio, AJ
    The Hertzian contact damage in 9 mol% Ce-TZP ceramics with different grain sizes has been investigated. Single-cycle tests were conducted on materials of four grain sizes, 1.1, 1.6, 2.2 and 3 μm. The indentation stress–strain curves for all materials show striking nonlinearity and deviation from the Hertzian elastic response, illustrating a significant quasi-plastic component in the contact damage response. Subsurface damage patterns for these four materials are compared and contrasted using a bonded-interface sectioning technique. The transformation and deformation behaviour, characterised using optical and scanning electron microscopy, of the surface and subsurface regions revealed extensive deformation and compression-driven subsurface damage in the materials. Acoustic emission was used as a complementary technique in order to identify the damage processes during a load–unload cycle. Contact deformation and radial bands extending from the indent impressions due to autocatalytic tetragonal–monoclinic transformation are evident in all except the finest grained (1.1 μm) material. Irrespective of grain size there is no evidence of ring or cone cracking with all material showing hemispherical subsurface damage or yield zones resulting from the stress-induced tetragonal–monoclinic (t–m) transformation with extensive distributed microcracking within these areas for the 1.6, 2.2 and 3 μm grain-size materials. © 2002 Elsevier Science Ltd
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    Fatigue damage mechanisms in CeO2 stabilized tetragonal ZrO2
    (Springer Nature, 2002-06-01) Latella, BA; Atanacio, AJ; Liu, T
    Hertzian indentation studies, where an indenting sphere is subjected to single-cycle or repeated loading on a flat ceramic specimen surface, have provided useful insights into contact damage accumulation and fatigue processes at the scale of the microstructure (short-crack region) in numerous ceramic-based systems [1–3]. The nature of the degradation has been shown to be strongly dependent on the material microstructure. In homogeneous, fine-grained ceramic microstructures conical cracks form in the region of limited tension around the contact circle whereas in heterogeneous, coarse-grained microstructures, distributed shear faults develop within a subsurface zone of compression-shear beneath the contact [4]. Cyclic loading of toughened heterogeneous ceramics readily exhibit cumulative damage events at the microscale, leading to strength degradation and material removal [2, 5, 6]. Consequently, the Hertzian test is relevant to assessing fatigue damage mechanisms and evolution on a localized level in ceramics. © 2002 Springer Nature Switzerland AG.
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    Unravelling the nature of the intrinsic complex structure of binary‐phase Na‐layered oxides
    (Wiley, 2022-07) Paidi, AK; Park, WB; Ramakrishnan, P; Lee, SH; Lee, JW; Lee, KS; Ahn, H; Liu, T; Gim, J; Avdeev, M; Pyo, M; Sohn, JI; Amine, K; Sohn, KS; Shin, TJ; Ahn, D; Lu, J
    The layered sodium transition metal oxide, NaTMO2 (TM = transition metal), with a binary or ternary phases has displayed outstanding electrochemical performance as a new class of strategy cathode materials for sodium‐ion batteries (SIBs). Herein, an in‐depth phase analysis of developed Na1−xTMO2 cathode materials, Na0.76Ni0.20Fe0.40Mn0.40O2 with P2‐ and O3‐type phases (NFMO‐P2/O3) is offered. Structural visualization on an atomic scale is also provided and the following findings are unveiled: i) the existence of a mixed‐phase intergrowth layer distribution and unequal distribution of P2 and O3 phases along two different crystal plane indices and ii) a complete reversible charge/discharge process for the initial two cycles that displays a simple phase transformation, which is unprecedented. Moreover, first‐principles calculations support the evidence of the formation of a binary NFMO‐P2/O3 compound, over the proposed hypothetical monophasic structures (O3, P3, O′3, and P2 phases). As a result, the synergetic effect of the simultaneous existence of P‐ and O‐type phases with their unique structures allows an extraordinary level of capacity retention in a wide range of voltage (1.5–4.5 V). It is believed that the insightful understanding of the proposed materials can introduce new perspectives for the development of high‐voltage cathode materials for SIBs. © 1999-2024 John Wiley & Sons