HEAT TREATMENT AND P EFFECT ON Ni-P/SiC COATINGS HARDNESS

Ni-P/SiC coatings electrolytically deposed on mild steel having P contents up to 20at.% in the Ni matrix and a constant content of SiC reinforcing particles have been investigated in three heat treatment conditions. Having in view the small thickness of the coatings (a few tens of microns) a series of small loads F in the range 15 up to 300 g have been applied on the indenter during the Vickers microhardness testing. On account of the hardness dependence on load (ISE effect) not a unique hardness value but sets of H-V -F curves have been considered to have a meaning for revealing the composition, structure and heat treatment influence on the coating hardness. The precipitation hardening heat treatment at 420 degrees C was shown to have a far larger influence in increasing the coating hardness than the increase of the P content in the Ni supersaturated solid solution.