Nano-structured Alumina-ZrO2 ceramic laminates

In the last years many efforts have been expended to develop colloidal process that uses water instead of organicsolvents in the tape casting process. In present work, alumina/zirconia laminated nanocomposites were fabricatedby layer-by-layer method and using water-based tape casting process. Physical and mechanical properties as wellas the fracture mode were investigated. The laminates consisted of stacked alumina and zirconia green sheetsproduced by thermopressing. The ceramic laminates were first heated at 450°C (organic elimination) andsubsequently sintered in air at 1500°C during 1 h. The ceramic laminates showed a mechanical strength ofapproximately 103 MPa (AZAZA) and 44 MPa (ZAZAZ), respectively and an intergranular-transgranular mixedfracture mode.Keywords: nanocomposites, laminates, tape casting

Mechanical performance and healing process improvement of cement-coir pith particle composites by accelerated carbonation

The accelerated carbonation during the early cure age is a process used to improve the physical and mechanical properties of cement-based composites. In this work, cement-based composites with coir pith particles addition were subjected to the accelerated carbonation process during the first 48 hours of cure in a rich CO2 environment. After curing, the samples were dried and subjected to curing conditions until saturated at 28 days. Thermogravimetric analyses, scanning electron microscopy (SEM) and X-ray diffraction patterns were used to analyze the impact of accelerated carbonation during the early cure age in cement-coir pith composite. The results of the physical properties show an increase in bulk density and surface density of the carbonated samples, as well as reduced water absorption. The reduction of the Ca(OH)2 resulting in the increasing of CaCO3 content was observed by thermogravimetric analysis. The carbonated samples had a 41% increase in compression strength and 28% in the modulus of rupture as compared to non-carbonate samples. The results showed the potential of the accelerated carbonation cure process in cement-based composites with vegetable coconut waste addition. Keywords: Accelerated carbonation, mechanical properties, thermal analysis, cement-based composites, coir pith particle

Surface softening in metal-ceramic sliding contacts: An experimental and numerical investigation

This study investigates the tribolayer properties at the interface of ceramic/metal (i.e., WC/W) sliding contacts using various experimental approaches and classical atomistic simulations. Experimentally, nanoindentation and micropillar compression tests, as well as adhesion mapping by means of atomic force microscopy, are used to evaluate the strength of tungsten?carbon tribolayers. To capture the influence of environmental conditions, a detailed chemical and structural analysis is performed on the worn surfaces by means of XPS mapping and depth profiling along with transmission electron microscopy of the debris particles. Experimentally, the results indicate a decrease in hardness and modulus of the worn surface compared to the unworn one. Atomistic simulations of nanoindentation on deformed and undeformed specimens are used to probe the strength of the WC tribolayer and despite the fact that the simulations do not include oxygen, the simulations correlate well with the experiments on deformed and undeformed surfaces, where the difference in behavior is attributed to the bonding and structural differences of amorphous and crystalline W-C. Adhesion mapping indicates a decrease in surface adhesion, which based on chemical analysis is attributed to surface passivation