Physical properties of thermal barrier coatings using electron beam-physical vapor deposition

A method for applying thermal barrier coatings of variable thermal conductivity to a plurality of turbine airfoils using a physical vapor deposition apparatus that includes an evacuated vacuum chamber containing a pair of ingots and a pair of high energy sources to melt and vaporize the ingot material to disperse vapors therefrom, comprising the steps of:

• evacuating the vacuum chamber;
• placing a plurality of airfoils in the vacuum chamber for a preselected time over the ingots and at preselected distances from the ingots, the distances selected so that the thermal conductivity of applied coating decreases with increasing distance from the ingots;
• directing beams from the high energy sources onto the ingots so that melt pools are formed on top of the ingot substrates from which the ingot material is vaporized, at least a portion of the vapors from the ingots being deposited on each airfoil to form a coating;
• maintaining the vaporization of the ingot material until a predetermined thickness of coating is established on the surface of the airfoils, the thermal conductivity of the applied coating on each airfoil decreasing with increasing distance from the ingot and the thickness of the coating decreasing with increasing distance from the ingot so that the ratio of thermal conductivity to thickness of the coating on the airfoils is substantially constant.

Apparatus for depositing a coating having increased porosity on a workpiece using a physical vapor deposition process comprising:

• a vacuum chamber;
• means for removing gases from the vacuum chamber;
• a plurality of material sources positioned within the vacuum chamber;
• at least one high energy source for melting and vaporizing material from the material sources;
• and
• a zone for forming a low density coating, wherein the plurality of material sources are positioned at preselected distances from one another so that a zone is formed in which at least one workpiece placed within said zone is coated with material from the material sources upon evacuation of the vacuum chamber and upon directing the high energy source onto the material sources to melt and vaporize material from the material sources, the coating formed on the workpiece within said zone having increased porosity so that the thermal conductivity of the workpiece is at least 10% less than the thermal conductivity of workpieces positioned at preselected heights substantially above the material sources.