In this communication, Al2O3‐20 wt% ZrO2 composites (ZTA) were prepared by a novel oscillatory pressure sintering (OPS) process. An almost perfectly full density of 99.94% and a relatively high ...flexural strength of 1145 MPa can be achieved for the OPS‐fabricated specimen, which were higher than those prepared by pressureless sintering (98.24% and 682 MPa) and hot pressing (99.53% and 990 MPa). The enhancement of flexural strength of the OPS‐fabricated specimen was correlated with its smaller flaw size and higher fracture surface energy. It was suggested that OPS was an effective approach to fabricate ZTA composites with ultrahigh density and high strength.
The cement-bonded corundum castables are often subjected to great temperature gradient in the service process of purging plugs for refining ladle. The mechanical properties of such castables are of ...particular interest in the serviceability and the safety of purging plug, which are significantly influenced by the microstructures including the amount, size and morphology of materials. The reported cement contents in compounds of purging plugs are generally low or ultralow, which inevitably limits the adjustable range of the mechanical properties enhancement by regulating their microstructures. In the present research, a serial of comprehensive experiments have been carried out, including the high cement contents (10–15 wt%), so as to further understand the role of cement content on the microstructural evolution and mechanical properties of castables. It is found that the phase compositions and microstructure can be optimized through adjusting the cement content in corundum castables. When the cement content is below 10 wt%, the hexagonal flake CA6 grains are platelet-shaped both in the matrix and at the border of the aggregates, their amount and size increase and distributions are more uniformly with cement content. When the cement content is above 10 wt%, small amount of granular crystals CA2 are detected in matrix, and CA6 crystals transform to equiaxial morphologies after cement content of 10 wt%. This research also provides quantitative relationship between the mechanical properties of the castables and the cement content. Castables with cement content of 10 wt% contain most hexagonal flake CA6 crystals, so that they have the highest CMOR and HMOR after heating at 1600 °C. However, CMOR decreases after cement content of 10 wt% due to the porosity and volumetric expansion from the formation of in-situ CA6 and CA2.
In this work, we prepared Al2O3 ceramic green parts with complex geometry and architecture using an additive manufacturing process based on stereolithography. The rheological and thermal behavior of ...Al2O3 slurry was firstly examined and used to establish the conditions for molding and debinding. As opposed to previous researches that only focused on manufacture techniques, the sintering behavior and densification process were systematically investigated. In addition, special attentions were paid to the evolution of microstructure between green bodies and sintered parts. The results showed that debound parts were equipped with uniform particle packing and narrow pore size distribution. The dimensions of the Al2O3 parts changed anisotropically with the different processing steps. The densification process was greatly accelerated by the decrease in pore size and annihilating of interconnected pores in which significant grain growth was observed above 1450°C. The sintered part also had a homogeneous microstructure and no interface between adjacent layers. High densification (relative density of 99.1%) and much desirable Vickers hardness (17.9 GPa) of Al2O3 parts were achieved at the sintering temperature of 1650°C.
A cheap and environmental friendly non-aqueous tape casting process for preparing high density ZrO2 ceramic substrates was explored. A binary solvent mixture of ethanol and ethyl acetate -based ...formula was developed by using castor oil, polyvinyl butyral and dibutyl phthalate as the dispersant, binder and plasticizer, respectively. The influence of dispersant content, binder content and solid loading on the rheological properties of ZrO2 slurries was firstly investigated. It was found that the optimized formulation for dispersant, binder and solid loading was 1wt%, 4wt% and 60wt%, respectively. The flat, flexible and uniform green tapes with a thickness of 200–280µm and high-quality including high bulk density, uniform pore distribution and low porosity were obtained. After drying and debinding, the green sheets were sintered at 1480℃ for 1h, where ZrO2 ceramics with a relative density of 98% and a dielectric constant being 32 can be achieved. The sintered samples could satisfy the use requirement of the fingerprint identification cover plate.
A study of microstructural evolution, mechanical and thermo-mechanical properties of MgO–C refractories, based on graphite oxide nanosheets (GONs), carbon nanotubes (CNTs) and carbon black (CB), was ...carried out by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS), three-point bending and thermal shock tests. Meanwhile, these results were compared to the conventional MgO–C refractory containing 10wt% flaky graphite prepared under the same conditions. The results showed that higher cold modulus of rupture was obtained for the composition containing GONs, and the composition containing CNTs exhibited larger displacement after coking at 1000°C and 1400°C. Also, the addition of nanocarbons led to an improvement of the thermal shock resistance; in particular, both compositions containing CNTs and CB had higher residual strength ratio, approaching the thermal shock resistance of the reference composition containing 10wt% flaky graphite, as it was associated with the presence of nanocarbons and in-situ formation of ceramic phases in the matrix.
We report the preparation of a category of ultrastrong tough zirconia ceramics by engineering defects using an oscillatory pressure during pressure assisted sintering. The introduced oscillatory ...pressure enhances the dynamic grain rearrangement, plastic deformation, mass transportation, and pore removal, leading to the formation of pore‐free ceramics characterized by the rich coherent grain boundaries among individual mesocrystalline grains with intragranular quasi‐interfaces. As a proof of concept, the pressure required by oscillatory pressure sintering (OPS) for preparing fully dense 3Y‐TZP ceramics is significantly reduced, which is just ∼1/5 of that required by hot isostatic pressing. The OPS‐prepared 3Y‐TZP ceramics reached a record‐breaking high bending strength and fracture toughness, being up to 1.8 GPa and 16 MPa·m1/2, respectively. This success illustrates a universal principle of engineering defects for making breakthrough in exploring other ultrastrong tough ceramics.
Alumina-calcium hexaluminate refractories experience crack development under severe conditions, leading to a significant reduction in mechanical strength. The external finite element method and ...Paris' law were employed to investigate the effects of external load and in-situ crack length on stress intensity factor. Fatigue life and crack propagation process of refractories were simulated for varying CAx contents under Model I failure. The findings revealed a linear correlation between the stress intensity factor and external load for a fixed in-situ crack length (a≤16 mm). The ultimate strength of alumina-calcium hexaluminate refractories is inversely proportional to the in-situ crack length. The material's microstructure significantly influences the ultimate strength of refractories, whereas the crack propagation ratio at the interface-to-the aggregate level strongly affects fatigue life. Refractories with a CAx content of 29.78% exhibit the longest fatigue life, attributed to the favorable formation of CA6/CA2 and the highest interface-to-aggregate crack propagation ratio.
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Mullite reticulated porous ceramics (RPC) are one of the key components for porous media burner, the mechanical properties of mullite RPC decided the service life of the burner. However, the ...irregularities of cellular structure made it difficult to reveal the fracture behavior of mullite RPCs. In this study, the three-dimensional (3-D) structures of mullite RPCs were analyzed by X-ray computed tomography. The strength and damage behavior of mullite RPCs were respectively investigated via the compression tests and finite element modeling based on the actual 3-D model, also the corresponding strengthening mechanism was proposed. The results indicated that the reconstructed 3-D model exhibited the real microstructure of mullite RPCs, containing the hollow struts and strut defects. The Young's modulus calculated from actual 3-D structures was lower than that from Gibson-Ashby theory. In addition, the surface defects preceded triangular tips to generate the area of stress concentration, leading to the fracture behavior first occurred at the strut defects. With the formation of dense strut in mullite RPCs, the stress uniformly distributed in the whole solid skeleton, thus significantly improving the damage resistance of mullite RPCs.
The in-situ catalytic formation of nanocarbons and ceramic bonding phases in low–carbon magnesia–graphite refractories is one of the significant strategies for heightening their mechanical properties ...and thermal shock resistance. Here, effect of aluminum content and nickel–containing catalyst addition on microstructural evolution, mechanical and thermo-mechanical behavior of such refractories was explored. Under the function of the catalyst, addition of aluminum powders allowed the newly growth of plenty of nanocarbons (e.g., carbon nanotubes and carbon onions), and also accelerated the in–situ formation of more ceramic bonding phases (e.g., magnesia whiskers and spinel whiskers/particles, etc.) in samples. This occurrence optimized significantly the microstructure of samples, correspondingly giving rise to their superior mechanical properties and thermal shock resistance. This work might provide a path for exploring low–carbon magnesia–graphite refractories with high performances.
•Catalytic formation of nanocarbons and ceramic bonding phases was discussed.•Effect of Al contents on mechanical properties of MgO-C refractories was studied.•MgO-C refractories with catalyst exhibited improved thermal shock resistance.
Magnesia-carbon (MgO–C) refractory is considered as the most crucial lining material in steelmaking furnaces. To provide reference for producing high performance MgO–C refractory containing different ...carbon contents, the microstructure, mechanical strength, thermal shock resistance and thermal properties of this material with 1–18 wt% flake graphite were studied systematically in this work. The results showed that carbon content had small effect on microstructural evolution of MgO–C refractory after high temperature treatment, mainly MgAl2O4 particles, Al4C3 whiskers and plate-/whisker-shaped AlN formed in the matrix of all specimens. As carbon content added increased gradually, fracture strength of specimens exhibited a reduced tendency whereas the corresponding fracture displacements became higher and higher owing mainly to good sliding ability of flake graphite. Furthermore, the increase in carbon content reduced thermal expansion rate of specimens and correspondingly increased thermal conductivity, consequently contributing to enhanced resistance to thermal shock of MgO–C refractory.
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