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In the present study, ZrO 2 based composites were synthesized in-situ and sintered by the novel RSPS-assisted carbothermal reduction of ZrSiO 4 (Z) in the presence of graphite (G) and Activated Carbon (AC). The RSPS process was performed using a vacuum furnace at different temperatures of 1400–1600°C for 5–15 min under an external pressure of 30 MPa. The thermodynamic analysis was conducted on the synthesis process by FactSage software. The microstructure development and mechanical properties of RSPS-ed ZrO 2 -based composites were investigated. The Phase evolution and phase content, as functions of temperature, were characterized using x-ray diffraction and FESEM/EDS analysis. The XRD studies showed that all primary ZrSiO 4 was decomposed into ZrO 2 , ZrC, SiC, and SiO 2 phases. The unreacted graphite or activated carbon was also identified in the samples. Finally, the hardness and flexural strength of the composites were examined by Vickers hardness and 3-point bending strength tests. The results indicate that the SPS-ed ZrSiO 4 + Activated Carbon composite (ZAS-3) has the best mechanical properties. A density of 2.87 ± 0.05 g/Cm3, an open porosity of 0.02%, a bending strength of 132.4 ± 11.2 MPa and a hardness of 9.86 ± 1.1 GPa were estimated for the SPS-ed ZrSiO 4 + Activated Carbon mixture of powders at 1600°C. [ABSTRACT FROM AUTHOR]

ZrO2-based composites reinforced with 6.5 vol.% of carbon foam, carbon fiber, and graphite were fabricated using spark plasma sintering, and characterized using scanning electron microscopy and X-ray diffractometry. Their thermal properties were also investigated. The microstructures of the reinforced composites showed that carbon fiber fully reacted with ZrO2, whereas carbon foam and graphite did not. The carbothermal reaction of carbon fiber had a negative effect on the thermal properties of the reinforced ZrO2 composites because of the formation of zirconium oxycarbide. Meanwhile, the addition of carbon foam had a positive effect, increasing the thermal conductivity from 2.86 to 3.38 W m−1 K−1 at 1,100°C. These findings suggest that the homogenous distribution and chemical stability of reinforcement material affect the thermal properties of ZrO2-based composites.

Abstract The oxidation induced crack healing behavior of pre-cracked Nb 2 AlC particle loaded ZrO 2 -matrix composites was explored by annealing in air at 1200 °C for short periods of 10 and 20 min. Composites loaded with 0, 6.5, 13, and 19.5 vol% Nb 2 AlC powder dispersed in 3Y-TZP matrix powder were manufactured by spark plasma sintering (SPS) at 1300 °C. Semi-elliptical artificial surface cracks with a length exceeding 220 µm were produced by Vickers indentation. The modulus of rupture of virgin, indented and annealed samples was measured in three-point bending mode. Compared to single phase 3Y-TZP strength recovery of the Nb 2 AlC loaded composite upon annealing at 1200 °C in air is accelerated and reaches > 60% of the initial strength after a short healing period of 10 min only. A semi-empirical oxidation cohesive zone healing model was derived which describes the crack microstructure evolution as a combined effect of 3Y-TZP-matrix healing superimposed by Nb 2 AlC particle oxidation induced healing. [ABSTRACT FROM AUTHOR]

Abstract: Linearly reciprocating sliding wear experiments on WC-Co and WC-Ni cemented carbides and ZrO2-WC, ZrO2–TiCN and ZrO2–TiN composites with different surface finishes corresponding to sequential wire-EDM or grinding/polishing have been performed using an ASTM G133 system with WC-6wt%Co cemented carbide as counter body. The WC-based alloys contained 6 up to 12wt% of binder, whereas the amount of secondary phase for the ZrO2-based composites was 40vol.% pin-on-plate testing was carried out in unlubricated circumstances at constant oscillating frequency with fixed displacement amplitude and normal contact loads ranging between 15 and 35N. 3D topography mapping and volumetric quantification of the wear tracks was obtained by surface profilometry. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy were employed to observe morphological and chemical features of worn surfaces and wear debris. The identified wear mechanisms are discussed. The highest wear resistance was encountered with the WC-Ni alloy, whereas the ZrO2–TiN composite displayed the lowest wear resistance. Wire-EDM surfaces displayed higher friction and wear compared to their ground/polished equivalents, especially during running-in. The inferior wear resistance of wire-EDM’ed samples could be correlated to 3-point bending tests, revealing a considerable decrease in flexural strength compared to ground samples. [Copyright &y& Elsevier]