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Open Access Research Article Issue
Microstructural evolution and oxidation in α/β titanium alloy under fretting fatigue loading
Friction 2023, 11 (10): 1906-1921
Published: 18 April 2023
Downloads:16

Coupling effects of fretting wear and cyclic stress could result in significant fatigue strength degradation, thus potentially causing unanticipated catastrophic fractures. The underlying mechanism of microstructural evolutions caused by fretting wear is ambiguous, which obstructs the understanding of fretting fatigue issues, and is unable to guarantee the reliability of structures for long-term operation. Here, fretting wear studies were performed to understand the microstructural evolution and oxidation behavior of an α/β titanium alloy up to 108 cycles. Contact surface degradation is mainly caused by surface oxidation and the generation of wear debris during fretting wear within the slip zone. The grain size in the topmost nanostructured layer could be refined to ~40 nm. The grain refinement process involves the initial grain rotation, the formation of low angle grain boundary (LAGB; 2°–5°), the in-situ increments of the misorientation angle, and the final subdivision, which have been unraveled to feature the evolution in dislocation morphologies from slip lines to tangles and arrays. The formation of hetero microstructures regarding the nonequilibrium high angle grain boundary (HAGB) and dislocation arrays gives rise to more oxygen diffusion pathways in the topmost nanostructured layer, thus resulting in the formation of cracking interface to separate the oxidation zone and the adjoining nanostructured domain driven by tribological fatigue stress. Eventually, it facilitates surface degradation and the formation of catastrophic fractures.

Open Access Research Article Issue
An effective strategy for preparing transparent ceramics using nanorod powders based on pressure-assisted particle fracture and rearrangement
Journal of Advanced Ceramics 2022, 11 (12): 1976-1987
Published: 12 November 2022
Downloads:145

Achieving full densification of some ceramic materials, such as Y2O3, without sintering aids by spark plasma sintering (SPS) is a great challenge when plastic deformation contributes limitedly to the densification as the yield stress of the material at an elevated temperature is higher than the applied sintering pressure. Herein, we demonstrate that particle fracture and rearrangement is an effective strategy to promote the densification during the pressure-assisted sintering process. Specifically, Y2O3 nanocrystalline powders composed of nanorod and near-spherical particles were synthesized and sintered at various temperatures by the SPS. The results show that the relative density of the ceramics prepared by the nanorod powders is higher than the density of the ceramics from the near-spherical powders after 600 ℃ due to the fracture and rearrangement of the nanorods at low temperatures, which leads to the decrease of particle size and the increase of density and homogeneity. Based on this novel densification mechanism, ultrafine-grained Y2O3 transparent ceramics with good optical and mechanical properties were fabricated successfully from the nanorod powders.

Open Access Research Article Issue
A systematic analysis of the radial resonance frequency spectra of the PZT-based (Zr/Ti = 52/48) piezoceramic thin disks
Journal of Advanced Ceramics 2020, 9 (3): 380-392
Published: 05 June 2020
Downloads:64

In this paper, both the 1D radial mode and the equivalent circuit of a piezoceramic disk resonator were theoretically analyzed based on IEEE standards. And then, the radial resonance frequency spectra of the PZT-based (Nb/Ce co-doped Pb(Zr0.52Ti0.48)O3, abbreviated as PZT-NC) piezoceramic circular disks were measured by an impedance analyzer. A set of resonance frequency spectra including six electrical parameters: Z, R, X, Y, G, and B, were used for making a value distinction between three possible resonance frequencies, and between three possible antiresonance frequencies. A new-form Nyquist diagram was depicted to describe the position relations of these characteristic frequencies. Such a complete resonance frequency spectrum was used to perform the accurate calculation of some material constants and electromechanical coupling parameters for the PZT-NC piezoceramics. Further, the frequency dependence of the AC conductive behavior of the specimen was characterized by the complex impedance measurement. The values of AC conductivity at resonance/antiresonance were deduced from the equivalent circuit parameters. Moreover, the Van Dyke circuit model was assigned to each element contribution and the simulated curves showed a nice fitting with the experimental results. Finally, an additional impedance analysis associated with resonance frequency calculation revealed a complicated coupled vibration mode existing in the annular disk specimen.

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