Performance Assessment of Protective Thermal Spray Coatings for Lightweight Al Brake Rotor Disks

This paper presents the results of a study to evaluate stainless steel thermal spray coatings on aluminum-based substrates. Coating wear, corrosion, and thermal cycling resistance were evaluated using pin-on-disk, cyclic corrosion, and a custom laser-based heating system, respectively, for 300-series stainless steel coatings deposited by arc-sprayed and cold-sprayed systems. Arc spray coatings were found to have equivalent wear and frictional performance as compared to gray cast iron (wear rates of 0.730-1.524 versus 1.294x10(-5)mm(3)/m, COF of 0.35-0.36 versus 0.36). However, arc spray coating exhibited low adhesion (30MPa) and early spalling under thermal cycling conditions, i.e., <600 cycles, as well as corrosion and delamination. The cold-sprayed coatings were found to have high corrosion and thermal cycling resistance, i.e., above 10,000 cycles. However, cold-sprayed coatings exhibited wear rates higher than those of the cast iron (cold spray wear rates of 4.774x10(-5)mm(3)/m). A duplex coating composed of a cold-sprayed bond coat and an arc-sprayed top coat was created and showed good wear properties under simulated extreme braking conditions. The results from this study show that stainless steel coatings on aluminum substrates could be viable substitute for the cast iron in future brake rotors.