Microstructure and Abrasive Wear of Cobalt-Based Laser Coatings

Cobalt-based alloys are used as wear-resistant materials for hardfacing cheap steel substrates. A substantial enhancement in mechanical properties of cobalt-based superalloys is attributed to the martensitic fcc → hcp phase transformation. Alloying elements can be classified as phase modifiers (Ni and Fe stabilize fcc whereas W and Cr stabilize hcp), solid-solution strengtheners (W and MO), which affect only the matrix, and elements that form carbides (Cr-rich M7C3 and M23C6 M = metal). Of the different depositing techniques such as plasma spray, tungsten inert gas, oxyacetylene flame and laser cladding, the latter delivers coatings with a low dilution with the substrate material and no pores. Moreover the laser cladding process has the advantage of being well controllable. This paper reports on the deposition of five different cobalt-based Stellite alloys on steel substrates by laser cladding.