In some instances, a metallic undercoat such as nickel or nickel alumide is applied between the base metal and the hardface coating. Metallic undercoats are applied to increase the coating system’s resistance to thermal shock and to improve bond strength. Bonding of the metallic undercoat to the base metal is stronger than the bond between coating and base metal. In addition, the as-sprayed undercoat provides a good surface for the coating to mechanically bond. Undercoating is most frequently used with the weaker bond strength metal and plasma spray processes.