Mechanical and tribological properties of Hadfield steel coatings manufactured by laser processing

For a lot of applications in the mechanical industry, materials combining b oth attractive mechanical properties and enhanced wear resistance are requi red. Usually such a combination is achieved only by performing surface trea tments, especially by manufacturing coatings with the appropriate compositi on and microstructure. Laser cladding is an innovative and attractive manuf acturing route. Ceramic or metal-matrix composites are possible candidates in some circumstances. However their low plastic deformation ability limits their use. The present works reports on metallic coatings (Fe-Mn-C steels, known as Hadfield steels). They are obtained by laser cladding (direct inj ection of powder into the laser beam) and then characterised by metallurgic al, tribological and mechanical analysis. Directly after manufacturing, Had field steel coatings are sound, metallurgically bonded to the substrate and with an austenitic structure. Their mechanical features are fairly good: h ardness HV = 350, Young modulus: E = 210 GPa, yield strength: sigma(E) = 12 00 MPa. However, the most attractive features are as follows: -they are very ductile: relative deformations higher than 80% are achieved without intermediate annealing and without deleterious damages. This deform ation yields to a large work-hardening phenomenon, since hardness values hi gher than 800 HV are measured. -wear observed during fretting tests is limited and delayed, whatever the n ature of the regime: elastic or plastic. A metallurgical analysis indicates that this behaviour is due to a twinning phenomenon, at least in a particular deformation range. (C) 1999 Kluwer Ac ademic Publishers.