ABSTRACT
Yttria-stabilized zirconia (YSZ) and Al2O3 multilayer coatings were fabricated by plasma spraying. Thermal conductivity and thermal shock test were investigated to find out the thermal properties of the coating layer and the surface of the crack. Thermal conductivity was investigated using laser flash method and thermal shock were measured by water quenching method. Furthermore, the factors influencing thermal properties of these coatings were analyzed in detail. Multilayer coatings have imperfect interfaces. At an imperfect interface, the heat transfer coefficient was close to zero, indicating a low thermal conductivity. Multilayer coatings increase thermal shock resistance. This is because ZrO2 phases transformation from tetragonal to monoclinic occurring to the cooling process, resulting in microcracks due to volume expansion. The crack generated at this time dispersed and absorbed the thermal shock, so that it exhibited excellent thermal shock resistance.
ABSTRACT
Optimum processing conditions were obtained by evaluating the hot working behavior of commercially pure Ti using hot torsion tests. Hot torsion tests were conducted at temperatures ranging from 800 °C-1000 °C and strain rates ranging from 0.1-10 s-1. The flow curves show that the peak stress increases as the temperature decreases and the strain rate increases. The optimum processing conditions were derived by comparing the processing and activation energy maps. The microstructure was characterized based on various regions of the processing map. The activation energy for plastic deformation was obtained using the constitutive equation. The activation energy differs depending on the constituent phases.
