Thermal barrier coating protected by alumina and method for preparing same

A method for preparing a thermal barrier coating for an underlying metal substrate, the method comprising the steps of:

• 1. forming over the underlying metal substrate an inner layer comprising a non-alumina ceramic thermal barrier coating material in an amount up to 100% by weight;
• and
• 2. codepositing on the inner layer a non-alumina ceramic thermal barrier coating material and alumina so as to form an outer layer of different composition than the inner layer having an exposed surface by separately plasma spraying the non-alumina ceramic thermal barrier coating material and the alumina on the inner layer in a manner such that the non-alumina ceramic thermal barrier coating material and the alumina blend together to form a substantially homogeneous mixture, the outer layer comprising at least about 50% by weight non-alumina ceramic thermal barrier coating material and up to about 50% by weight alumina and in an amount sufficient to protect the thermal barrier coating at least partially against environmental contaminants that become deposited on the exposed surface, wherein the non-alumina ceramic thermal barrier coating material and the alumina are separately deposited on the inner layer in a manner such that the non-alumina ceramic thermal barrier coating material and the alumina combine together to form a substantially homogeneous mixture.