Thermal spraying of protective coatings has been in use since 1917 when the initial application was the spraying of zinc layers onto steel structures to prevent corrosion [1]. In the 1970’s plasma-spray technology was first used with the introduction of vacuum plasma-spraying [1]. Today, gases such as argon and nitrogen (sometimes with an additional gas such as helium or hydrogen) are often used in plasma-spray guns. In plasma-spraying an electric-arc discharge heats the gas stream to high temperature (≥ 10,000 K), turning it into a plasma. The gas exits the spray-gun at high speed (≈ 200 m/s to 600 m/s) towards the material to be coated. Material powder (often carried by a second gas stream) is injected into the plasma stream, where it melts into liquid droplets. These droplets are carried onto the target surface, where they rapidly cool (≈ 106 K/s) into solid, flat splats. A layer of material can be built up by repeated spraying of the same surface area. This high-temperature process allows for the spraying of virtually any material possessing a stable molten phase, including ceramics [2]. Further technical details and the history of plasma-spraying can be found in [1–2].