Abstract
The influence of the microstructural constituents and of the microstructure itself on the wear resistance of cobalt based hardfacing alloys is reviewed. To a first approximation, the hard carbide particles provide resistance to abrasion, whereas the matrix confers cohesion and toughness. Carbide size relative to the width of the abrasive grooves is of great importance: if these dimensions are similar, carbides can be removed completely in the wear debris. The strength of the bonding at the carbide/matrix interface also strongly influences wear. During low stress abrasion, an increase of carbide volume fraction produces a corresponding improvement in wear resistance. The ability of the matrix to work harden and the related fcc → hcp phase transformation strongly affect wear resistance. Alloying elements which reduce the stacking fault energy of the matrix (hcp stabilisers) increase the work hardening rate and thus the resistance to galling and the erosion resistance. Silicon and manganese have been found to be most effective in stabilising topologically close packed hard intermetallic second phases, which provide good metal-metal wear resistance. These principles have been applied in the development of alternative iron based alloys with matrixes similar in composition to duplex stainless steels. Initial trials have indicated a good potential to replace the more expensive cobalt based alloys in some wear and corrosion resistant applications.
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