Study of melting and crystallization of Cu – P alloy using a universal vacuum viscometer and thermal analysis

Methods of differential thermal analysis (DTA) and measurement of the melt viscosity are widely used in studying the properties of alloys at high temperatures. We have made an attempt to combine those two complementary methods of research. In contrast to the single-stranded Shvidkovskii viscometer, a bifilar suspension on two thermocouple wires is used in the proposed construction of the installation. The system based on the bifilar suspension provides using thermocouple in contact with the crucible with a sample, thus ensuring measurements of the crucible temperature like the measuring cell in DTA. The adjusting thermocouple located near the coil of a bifilar heater is used as a reference thermocouple. Since thermal analysis requires linear heating at a constant rate, and the viscosity is usually measured in a steady-state (steady-state) regime with long exposures at each measurement temperature, a series of dynamic viscosity determinations with a heating rate of 1, 2, 3 and 5 °C/min is carried out, the heating rates of 1 and 2 °C/min being approximately equal to the average heating rate under steady-state conditions. It is shown that when measuring in a dynamic mode at a heating rate up to 3 °C/min, the viscosity curves coincide with the measurement data in a steady-state mode, and the results of the thermal analysis (experimental setup) are consistent with the data of DTA (STA 409 setup). Results of measuring the logarithmic decrement of vibrations for Cu – 7.3% P alloy and data of thermal analysis are presented. Data of thermal analysis obtained on our experimental setup coincide completely with the DTA results obtained on a STA 409 unit. A model experiment carried out to explain the delay of growth of the logarithmic damping decrement at the beginning of melting and sharp decrease at the beginning of crystallization indicates to the effect of blocking free flow of the liquid melt component by the solid skeleton having a higher melting point.

1. Morokhov P. V., Anan’in V. M., Ivannikov A. A., Sevryukov O. N., Suchkov A. N. Gravity-induced macro-segregation of melt and its effect on viscosity and differential thermal analysis / Tsvet. Met. 2014. N 12. P. 38 – 43 [in Russian].

2. Shvidkovsky E. G. Some questions of viscosity of the fused metals. — Moscow: Gostechizdat, 1955. — 206 p. [in Russian].

3. RF Pat. N 158198, MPK GOIN 11/00 (2006.01). Vacuum high-temperature viscometer / Anan’in V. M., Morokhov P. V., Sevryukov O. N., et al; applicant and owner LLC «MEPhI-AMETO», National Research Nuclear University — MEPhi. — N 2015142136; appl. 05.10.2015; publ. 20.12.2015. Bull. N 35 [in Russian].

4. Korchagin O. N., Kalin B. A., Anan’in V. M. Hardware-software complex for measurement of characteristics of fading fluctuations / Zavod. Lab. Diagn. Mater. 2011. Vol. 77. N 12. P. 38 – 42 [in Russian].

5. Boettinger W. J., Kattner U. R., Moon K. W., Perepezko J. H. DTA and heat-flux DSC measurements of alloy melting and freezing. — Washington, 2001. — 90 p.