Non-destructive evaluation of ion implantation-induced microhardness by photothermal spectroscopy

Abstract High-flux N + implantation in steel is used to improve the hardness by a factor of two in a surface layer of ion range-determined thickness. This paper reports the results of non-destructive and contactless photothermal measurements and Knoop hardness testing of the N + -implanted X90CrMoV18 steel. Defect formation, precipitation and new phases considerably change the optical and thermal properties in the layer. The photothermal wave method sensitively probes these changes of structural material properties. Using modulated reflectivity for the thermal wave detection, in addition to the thermal wave analysis, information will be gained by modulated spectroscopy concerning the changes of the dielectric function of the material. The maximum of hardness is strongly correlated with the phase transition indicated by the thermomodulated dielectric function.