FRICTION-INDUCED SOLID STATE AMORPHIZATION FROM NON-EQUILIBRIUM SOLID SOLUTION PHASE IN Fe-Cr-B-Ni-Mo SPRAY COATINGS

摘要

Experimental evidence of friction-induced amorphization is presented from cross-sectional TEM investigations. Rapid quenching of Fe-Cr-B-Ni-Mo alloys resulted in the non-equilibrium microstructure composed of micro-crystalline (Cr, Fe)_2B borides and nano-crystalline α-(Fe, Cr) solid solution phase supersaturated with B and Si. Cross-sectional TEM observations revealed that the crystalline-to-amorphous phase transition occurred in the outer surface layer of the α-(Fe, Cr) phase. The spray coatings exhibited significantly enhanced wear resistance with a significantly low friction coefficient (～0.04) with a presence of thin (～150nm) amorphous surface layer. Theoretical calculations based on thermodynamic instability of crystalline phase suggest that the super-saturation of the α-(Fe, Cr) solid solution phase and the introduction of lattice defects due to frictional work are the major factors to trigger the amorphization reaction.