Quantitative analysis of the residual stress and dislocation density distributions around indentations in alumina and zirconia toughened alumina (ZTA) ceramics

This is an Open Access Article. It is published by Elsevier under the Creative Commons Attribution 3.0 Unported Licence (CC BY). Full details of this licence are available at: http://creativecommons.org/licenses/by/3.0/Alumina, 10% and 20% ZTA with 1.5mol% yttria stabiliser were subjected to Vickers indentation testing with loads from 1 to 20kg. Cr fluorescence and Raman spectroscopy were applied to the indent centre and around the indentation in order to investigate the origin of the signal, the effect of indentation loads and zirconia phase transformation on the residual stress and plastic deformation in the plastic zone. The results suggested that with very strong laser scattering, the depth resolution of ZTA materials was very poor, which lead to a very significant amount of the signal being collected from the subsurface regions below the plastic zone. It was also found that zirconia phase transformation reduced the compressive residual stress in the alumina matrix within the plastic zone, except at the indentation centre, due to the tensile residual microstress generated by the zirconia phase transformation. In addition, the dislocation density on the indent surface of the ZTA samples was significantly reduced due to the restriction of crack propagation and energy absorption during the phase transformation process. At the indent centre, the zirconia phase transformation was suppressed by the high compressive stress, therefore, no significant difference between alumina and ZTA in terms of their residual stress and dislocation density were observed. Using TEM observation, it was found that the plastic zone microstructure of pure alumina is different from that of ZTA, which is consistent with the Cr fluorescence results

Solvothermal nanoYAG synthesis: Mechanism and particle growth kinetics

This paper was accepted for publication in the journal Journal of Supercritical Fluids and the definitive published version is available at http://dx.doi.org/10.1016/j.supflu.2015.09.031NanoYAG particles with spherical morphology have been synthesised using a solvothermal method; a structure sensitive reaction, where the chemical reaction and the particle growth kinetics are interdependent. It has been observed that the primary YAG particles agglomerated into ∼30 nm clusters via a self-assembled Ostwald ripening process along (2 1 1) planes, separated by a distance of ∼0.49 nm, at 270 °C and 2.0 MPa for 2 h. These nanoclusters coalesced into single nanoparticles of ∼30 nm in size and exhibited a smaller inter planar distance of ∼0.26 nm, corresponding to the (4 2 0) planes, when synthesized at 300 °C and 8.5 MPa for 2 h. in addition, the solvent 1,4-butanediol transformed into 1,4-diacetoxybutane, this will have undergone esterification by reacting with the terminal acetate groups cleaved from the precursor, yttrium acetate. The proposed mechanism based on the analytical evidence suggests that a complete dissolution of precursors facilitated the structural re-arrangement of atoms within the planes and lead to a significantly higher degree of crystallinity. Moreover, once the particles with (4 2 0) planes had formed, they were no longer involved in facile coalescence along their preferential planes due to their lower interfacial energy compared to the (2 1 1) planes. This led to control of the particle morphology and with little agglomeration occurring in the final nanopowder

High pressure studies on AgI-Ag<SUB>2</SUB>O-MoO<SUB>3</SUB> glasses

The effect of pressure on the conductivity of AgI-Ag2O-MoO3 glasses has been reexamined. A conductivity maximum is observed around 0.7 GPa. No variation of the sample temperature is noted under pressure. The results are found to agree well with the cluster-tissue model

Biological evaluation of zirconia toughened apatitic composite implant

A biological study is reported where implants of β- TCP/ t- ZrO2 has been examined in rabbit mandibles. The composite is found to be fully biocompatible and evidence of good osteoconduction and tissue ingress has been noticed

Is copyright blind to the visual?

This article argues that, with respect to the copyright protection of works of visual art, the general uneasiness that has always pervaded the relationship between copyright law and concepts of creativity produces three anomalous results. One of these is that copyright lacks much in the way of a central concept of 'visual art' and, to the extent that it embraces any concept of the 'visual', it is rooted in the rhetorical discourse of the Renaissance. This means that copyright is poorly equipped to deal with modern developments in the visual arts. Secondly, the pervasive effect of rhetorical discourse appears to have made it particularly difficult for copyright law to strike a meaningful balance between protecting creativity and permitting its use in further creative works. Thirdly, just when rhetorical discourse might have been useful in identifying the significance and materiality of the unique one-off work of visual art, copyright law chooses to ignore its implications

Multi-material additive manufacture and microwave-assisted sintering of a metal/ceramic metamaterial antenna structure

Multi-material metal/ceramic 3D structures comprising of metallic silver and ultra-low sintering temperature silver molybdenum oxide ceramics, have been additively manufactured and hybrid densified using microwave-assisted sintering for the first time. Optimum densification conditions at 440 °C / 1 h, resulted in relative permittivity, εr = 10.99 ± 0.04, dielectric losses, tanδ = 0.005 ± 0.001 and microwave quality factor, Q × f = 2597 ± 540 GHz. Applying 2 kW microwave energy at 2.45 GHz for 60 min, was proven sufficient, to densify the metallic Ag infilling electrodes, without causing any macroscopic defects. A fully functional multi-layered antenna structure with a metamaterial artificial magnetic conductor was designed, dual-printed and densified, to showcase the potential of combining multi-material additive manufacturing with microwave-assisted sintering

Multi-material additive manufacturing of low sintering temperature Bi2Mo2O9 ceramics with Ag floating electrodes by selective laser burnout

Additive manufacturing (AM) of co-fired low temperature ceramics offers a unique route for fabrication of novel 3D radio frequency (RF) and microwave communication components, embedded electronics and sensors. This paper describes the first-ever direct 3D printing of low temperature co-fired ceramics/floating electrode 3D structures. Slurry-based AM and selective laser burnout (SLB) were used to fabricate bulk dielectric, Bi2Mo2O9 (BMO, sintering temperature = 620–650°C, εr = 38) with silver (Ag) internal floating electrodes. A printable BMO slurry was developed and the SLB optimised to improve edge definition and burn out the binder without damaging the ceramic. The SLB increased the green strength needed for shape retention, produced crack-free parts and prevented Ag leaching into the ceramic during co-firing. The green parts were sintered after SLB in a conventional furnace at 645°C for 4 h and achieved 94.5% density, compressive strength of 4097 MPa, a relative permittivity (εr) of 33.8 and a loss tangent (tan δ) of 0.0004 (8 GHz) for BMO. The feasibility of using SLB followed by a post-printing sintering step to create BMO/Ag 3D structures was thus demonstrated