Residual stress distribution in a functionally graded alumina-silicon carbide material

Functionally graded ceramic structures have a range of potential applications as they enable the exploitation of two ceramic materials with very different properties, such as coefficient of thermal expansion. We report the microstructural investigation of a novel functionally graded structure for alumina and silicon carbide with systematically varied composition. Stresses in the structure have been modelled analytically and by finite element modelling, and are consistent with fluorescence microscopy measurements of residual stress in the structure

Effect of residual compressive surface stress on severe wear of alumina-silicon carbide two-layered composites

Ceramics consisting of Al2O3 with a surface layer of Al2O3-10 vol% SiC have been fabricated by hot pressing. The residual compressive stress at the composite surface due to the difference in thermal expansion between the two layers has been measured experimentally by Cr3+ fluorescence microspectroscopy. The wear resistance in the severe wear regime of the two-layered samples was higher than those of a reference single-layer Al2O3-10 vol% SiC sample. The improvement in the wear resistance was due to a decrease in the amount of surface pullout which was attributed to the presence of the biaxial residual compressive stress in the surface layer of the specimens

IR laser line scanning treatments to improve levitation forces in MgTi0.06B2 bulk materials

Infrared (IR) laser-line scanning has been widely used to induce different surface microstructures in a broad range of materials. In this work, this laser configuration was applied on the surface of MgTi0.06B2 bulk samples in order to ascertain its effects on their superconducting properties, particularly on the magnetic levitation forces. The microstructural changes produced by this type of laser treatment were investigated by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). It was observed that the thermal treatment induced by the laser improves grain connectivity in a layer of material just below the irradiated surface, in agreement with the observed improvement in critical current density values, Jc, which were estimated from isothermal magnetic hysteresis loops. A significant increment of both vertical (Fz) and lateral (Fx) magnetic levitation forces was achieved. Numerical calculations were performed to understand the experimental behaviour and to clarify how an improvement of Jc near the surface can improve the magnetic levitation force of these materials. In addition, the same studies were carried out in similar bulk samples but with nano-sized silver particle additions of 3 and 6 wt %, in the outer ring of the bulk, observing also an improvement of the levitation forces, albeit less than in samples without Ag because of the better performance of the original samples after laser treatment. These results are relevant to those studying superconductor fabrication and material fabrication modelling, essential for the development of technological applications of superconductors, and are based on microstructure control via application of a recently developed laser-line scan method.As authors, we would like to thank the Scientific and Technological Research Council of Turkey (TUBITAK with program code 2219), the Spanish Agencia Estatal de Investigación and the European FEDER Program (project ENE2017-83669-C4-1-R), and the Gobierno de Aragón “Construyendo Europa desde Aragón” (research group T54_17R). Authors also would like to acknowledge the use of Servicio General de Apoyo a la Investigación-SAI, Universidad de Zaragoza and Erzincan University in Turkey for microstructural characterization.Peer reviewe