Development of Protective Thermal Spray Coatings for Lightweight Al Brake Rotor Disks

This paper reports on the performance evaluation of stainless steel thermal spray coatings aimed at shielding lightweight aluminum brake rotor disks from excessive heat and providing an adequate tribological surface in contact with brake pads. Coating wear, corrosion and heat resistance performance were evaluated using pin-on-disk, cyclic corrosion tests and thermal cycling using a custom laser rig, respectively. Arc spray optimized coatings displayed lower or equivalent wear rates when compared with the baseline gray cast iron disks, with similar frictional behavior. However, arc spray coating exhibited low adhesion which limits the maximum coating thicknesses achievable and leads to early coating spalling after about 1000 thermal cycles. Arc sprayed coatings also corroded and delaminated under corrosion tests. Optimized cold spray coatings present high corrosion resistance and could resist above 10,000 thermal cycles without spalling. However, cold spray coatings exhibit wear rates at least 4 times those of the cast iron with a fluctuating coefficient of friction. Taking advantage both types of coatings, it was found that the production of a duplex coating made of a cold spray bond coat and an arc spray top coat could meet the requirements for protecting aluminum disks, with an expected disk weight reduction near half.