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

Abstract

For a lot of applications in the mechanical industry, materials combining both attractive mechanical properties and enhanced wear resistance are required. Usually such a combination is achieved only by performing surface treatments, especially by manufacturing coatings with the appropriate composition and microstructure. Laser cladding is an innovative and attractive manufacturing 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 injection of powder into the laser beam) and then characterised by metallurgical, tribological and mechanical analysis. Directly after manufacturing, Hadfield steel coatings are sound, metallurgically bonded to the substrate and with an austenitic structure. Their mechanical features are fairly good: hardness HV = 350, Young modulus: E = 210 GPa, yield strength: σ_E = 1200 MPa. However, the most attractive features are as follows:

--they are very ductile: relative deformations higher than 80% are achieved without ntermediate annealing and without deleterious damages. This deformation yields to a large work-hardening phenomenon, since hardness values higher than 800 HV are measured.

--wear observed during fretting tests is limited and delayed, whatever the nature 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