RADIOMETRIC DEPTH PROFILING OF THERMAL-PROPERTIES IN METALS

Photothermal measurements at varied modulation frequencies allow for t he estimation of depth profiles of thermal diffusivity or thermal cond uctivity in case of known thermal density. Knowledge of thermal conduc tivity k is important because of its correlation to relevant microstru ctural properties of the samples under test as for instance mechanical hardness of steel. We suggest an inversion algorithm performing a seq uence of one-parameter fits in order to estimate k profiles. Surface p roblems in photothermal depth profiling and a approach to overcome the m are discussed. Experimental results of thermal conductivity depth pr ofiling of laser-hardened steel, based on this inversion algorithm are presented. The photothermally obtained k-profiles are interpreted and compared with results from conventional destructive measuring techniq ues.