Anti-
oxidation properties,carbon structures and related
phase transition in laser quenched
layer of 45~#
steel and in laser clad-Ni02 alloy layers are studied by Raman spectroscopy.It is shown that laser quenching elevates the anti-oxidation capacity greatly for the surface of 45~# steel and refines the particle sizes of carbon,which appears mainly as amorphous graphite in 45~# steel.With increasing excitation laser power,the Raman spectra of the surface and sub-surface layer remain unchanged,whereas those of the uniformly phase transition layer and the
substrate changes enormously. Intense Raman signals of α-Fe_2O_3 appear for the latter.These indicate that the laser quenched surface layer has unique high-temperature anti-oxidation capacity,which is much superior to that of the laser-quenched inner layer as well as the original material.It is found that a phase transition from amorphous carbon to diamond occurs around the interface between the substrate and
laser cladding layer of Ni02 alloy.This is explained by the high-temperature gradient at the bottom of the melt pool and the transient pressure produced during cooling process at the interface between the clad layer and the substrate.