Microstructure and wear behaviour of powder and suspension hybrid Al2O3–YSZ coatings

Suspension based plasma sprayed coatings can yield superior microstructural and tribological properties compared to conventional powder based plasma sprayed coatings. This study investigates a new hybrid method, using simultaneous spraying from powder and suspension, to produce composite coatings using alumina and yttria stabilised zirconia (YSZ), with potentially excellent wear and thermal properties. Dry sliding wear showed the alumina suspension-YSZ suspension coating yielded half the specific wear rate of the alumina powder-YSZ suspension, explained by preferential gamma alumina formation and increased porosity in the latter. Both YSZ-containing samples showed superior toughness and wear rate than simple alumina powder and suspension coatings

Microstructure and mechanical properties of MgO-stabilized ZrO2-Al2O3 dental composites

The aim of the present study was to investigate the production of tetragonal zirconia (t-ZrO2) particles (experimental t-ZrO2) from monoclinic zirconia (m-ZrO2) and to evaluate the effect of the t-ZrO2 content on the fracture toughness of alumina-zirconia composites by conducting ASTM astm:E399 standard test. In the laboratory study, t-ZrO2 powder was produced by heat treating m-ZrO2 containing 10 wt.\% MgO. Alumina and alumina-zirconia composite powders containing various types and amounts of m-ZrO2 and t-ZrO2 were prepared (0-20 wt.\%), shaped by slip casting to achieve a uniform distribution and homogeneous microstructure in accordance with the dimensions of ASTM astm:E399 standards, dried, sintered at three different temperatures: 1400, 1500 and 1600 degrees C for two hours, and characterized. The results of the XRD analysis showed that t-ZrO2 was produced at 1400 degrees C. In t-ZrO2-doped alumina composites, t-ZrO2 partially transformed to m-ZrO2 after sintering, whereas commercial t-ZrO2 (Tosoh TZ-3Y) remained intact. SEM studies on samples sintered at 1600 degrees C revealed that the addition of zirconia inhibited abnormal grain growth of alumina, leading to a homogeneous and equiaxed grain structure, especially at high concentrations of zirconia. ZrO2-doping enhanced the fracture toughness of the composites, which increased with an increase in the t-ZrO2 content. The maximum fracture toughness was 11.5 MPa m(1/2) and was observed when the t-ZrO2 content was equal to 20 wt.\%. Alternatively, the maximum fracture toughness for pure alumina was 5.9 MPa m(1/2). (C) 2012 Elsevier Ltd. All rights reserved