55. The purpose of the metal spray rub coating on the rotor and stator casing of an axial-type compressor is which of the following?

The metal spray rub coating enables close clearances between rotor/stator blades and the casing, minimizing leakage and improving compressor efficiency. This coating is an abradable surface that allows blade tips to 'rub in' without damage, reducing the gap and enhancing performance; it does not protect gearbox components, control airflow, or seal dovetails.