Briefly describe the plasma spray process.

• A. It is accomplished by applying a metallic spray material, in an atomized state, to the base metal at high velocity and heat
• B. It uses a cold deposition of metal onto the surface
• C. It relies on mechanical brushing to apply a coating
• D. It involves dipping the blade in molten metal

Answer: (A)

Plasma spray coatings are made by feeding a coating material into a plasma torch, where it is heated to a molten or semi-molten state and ejected as fine droplets toward the base metal at high velocity. On hitting the surface, the droplets rapidly flatten and solidify, bonding through mechanical interlocking and some metallurgical bonding to form a durable coating. This method can apply metallic or ceramic materials and is commonly used on turbine blades for wear resistance, corrosion protection, and thermal barriers. The other described methods don’t match plasma spray: cold deposition involves little or no heat, brushing is a mechanical method without spraying, and dipping in molten metal is a bath process rather than an atomized spray approach.