| Plasma spraying is a well established technique for producing a wide range of metal alloy and ceramic coatings. Among these, cordierite (2MgO-2Al;Phase transformation occurred for as-sprayed cordierite and forsterite at elevated temperatures. Differential thermal analysis has shown that transition temperatures depend on heating rate and sample size.;The excellent thermal shock resistance of cordierite deposits is a consequence of its overall low thermal expansivity. The thermal shock resistance of the cordierite, spinel and forsterite deposits obtained experimentally were significantly greater than that obtained by calculation. This is attributed to the existence of porosity introduced by air plasma spraying. The pores can relieve thermal stress, thereby improving the thermal shock resistance.;Thermal fatigue testing has been performed on oxide coatings-on-bond coat/substrate using a flame rig apparatus. The longest thermal cycling lifetime belongs to an oxide coating with the least thermal mismatch between the top coating and the alloy bond coat/steel substrate, leading to a low level of thermal stress during thermal cycling.;In this study, phase analysis of the as-plasma-sprayed oxides were carried out using X-ray diffractometry and transmission electron microscopy. At cooling rates of the same order of magnitude, as-sprayed cordierite was found to be completely amorphous; as-sprayed forsterite contained a mixture of amorphous and crystalline phases; as-sprayed spinel was completely crystalline.;The dielectric behavior has been studied as a function of temperature at a frequency of 10 kHz utilizing a capacitance bridge. The dielectric constant of as-sprayed deposits is less temperature dependent than that of deposits annealed at 1100... |
