Heat Conduction in PVD Nanocoatings

Abstract

The model of heat conduction in nonisostructural multilayered coatings is presented in this paper. It is based on well known phonon and electron heat transfer mechanisms. The volume of heat conduction coefficient depends on the mean free path, which plays a significant role when the sublayer thickness becomes lower than the critical one. The value of the mean free path of the heat carriers was determined by means of Monte Carlo numerical experiment and on this base, the analytical model describing the coating modulation parameter influence on the heat conduction coefficient was elaborated. The same amorphisation degree of the structure was taken into account, what is connected with the electron role limitation in heat transfer process, on the one side and very strong mean free path decrement of the phonons on the other side, so the results are very low values of heat conduction coefficients of the interlayer boundaries. The modified equations describing effective heat and temperature conduction coefficient were introduced to connect the single sublayer properties and interlayer boundaries. Experimental verification was realized with use of the variable-temperature camera method. This method is based on the indirect temperature change measurement of the coating and the substrate during specified heat flux flow with use of the X-ray diffraction. The changes in thermal expansion of substrate in temperature function were used as a reference base.