Coatings are used for improving the physical properties of drill bits.
Black oxide coated HSS drill bits have better corrosion resistance. They last longer than basic HSS bits and work well on a variety of materials, including metal, hardwood, softwood, PVC and fiberglass.
Titanium coated HSS drill bits produce less friction and have high heat limit. They’re tougher than basic HSS bits and stay sharp longer. These drill bits can cut a broad variety of materials such as steels, irons, wood and plastic.
Carbide tipped drill bits stay sharp much longer than steel, HSS or titanium bits. They’re effective for drilling tile and masonry.
Cobalt drill bits are extremely hard and dissipate heat quickly. Cobalt is used for materials that HSS cannot cut, they’re mostly used for drilling tough metals such as stainless steel. As a drawback cobalt coatings are excessively brittle.