Method of measuring coating thickness using infrared light

A method of measuring a thickness of a thermal barrier coating on a metal substrate, the method comprising:

• emitting a first pulse of coherent light from a first laser toward the thermal barrier coating and the metal substrate, the first pulse of light having a predetermined first wavelength;
• emitting a second pulse of coherent light from a second laser toward the thermal barrier coating and the metal substrate, the second pulse of light having a predetermined second wavelength different than the first wavelength;
• measuring a first elapsed time from emission of the first pulse of light to reception of a reflection of the first pulse of light at a first detector from a surface of the metal substrate at an interface with the thermal barrier coating;
• measuring a second elapsed time from emission of the second pulse of light to reception of a reflection of the second pulse of light at a second detector from an outer surface of the thermal barrier coating;
• and
• determining a thickness of the thermal barrier coating as a function of a difference between the first and second elapsed times.

A method of measuring a thickness on a structure comprising a thermal barrier coating on a metal substrate, the method comprising:

• providing a structure comprising a metal substrate comprised substantially of nickel or cobalt and a thermal barrier coating on the metal substrate comprising 8 wt % yttria stabilized zirconia;
• emitting a first pulse of coherent light from a laser toward the thermal barrier coating and the metal substrate, the first pulse of light having a predetermined first wavelength and the thermal barrier being transmissive to the first wavelength;
• emitting a second pulse of coherent light from a laser toward the thermal barrier coating and the metal substrate, the second pulse of light having a predetermined second wavelength different than the first wavelength and the thermal barrier coating being reflective of the second wavelength;
• measuring a first elapsed time from emission of the first pulse of light to reception of a reflection of the first pulse of light from a surface of the metal substrate at an interface with the thermal barrier coating;
• measuring a second elapsed time from emission of the second pulse of light to reception of a reflection of the second pulse of light from an outer surface of the thermal barrier coating;
• and
• determining a thickness of the thermal barrier coating as a function of a difference between the first and second elapsed times.