The paper presents the adaptation of the modified pulse method for investigating temperature characteristics of thermal diffusivity in the vicinity of the second-order phase transition points. The principle of the adaptation consists in the modified in relation to the original method, development of the characteristics of temperature changes between boundary surfaces of a flat-parallel specimen after the laser shot onto its front surface. The application of this adaptation was illustrated with investigation into thermal diffusivity of nickel (99.9% wt) in the temperature range of 20-380◦C. In all cases the measurement error was less than 3%, and the averaging interval for the measured values of thermal diffusivity was not greater than 1.2 K.

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This paper presents the possibility of using a modified-pulse method (MPM) determining the temperature characteristics of thermal diffusivity in order to identify phase transformations in metals. The experiment and attempt of phase identification were conducted for the Fe65Ni35 alloy in the 20–500 °C temperature range during both sample heating and cooling. The estimated error of discrete thermal diffusivity measurements was less than 3%. The method allows us to narrow down the averaging of the interval of this value, as a function of temperature, in the range below 1 K. Recently published analysis of the phase diagrams of Fe–Ni alloys, and the results of the authors’ own research into the Fe65Ni35 alloy, showed very good correlation between changes occurring when heating the alloy and the equilibrium diagram provided by Cacciamani G., Dinsdale A., Palumbo M., and Pasturel A. (Intermetallics 18, 2010, 1148–1162) showing the position of phases with a crystal-lattice structure based on the face-centered cubic (FCC) cell.