SUMMARY
Agraval P.G. Thermodynamics and phase transformations in multicomponent glass-forming systems of transition metals. – Qualification scientific thesis as the manuscript.
The thesis for the degree of Doctor of chemical sciences by specialty 02.00.04 – physical chemistry. – I. M. Frantsevich Institute for Problems of Materials Sciences, NAS of Ukraine, Kiev, 2021.
The thesis is devoted to the investigation of thermodynamic properties of multicomponent melts of glass-forming systems of transition metals. Their dependence on the composition determination, temperature and number of system components was determined and factors that determine their ability to form an amorphous phase in nonequilibrium synthesis were identified. The research was also pointed to modeling of equilibrium and metastable phase diagrams with participation of supercooled melts and predicting of their concentration regions of amorphization.
The enthalpies of mixing of the components in the binary Fe–Ti, Fe–Zr, Fe–Hf and in the ternary Co–Cu–Ti, Co–Cu–Zr, Cu–Fe–Ti, Cu–Fe–Zr, Cu–Fe–Hf, Cu–Ni–Ti, Cu–Ni–Hf, Cu–Ti–Zr, Cu–Ti–Hf, Ni–Ti–Zr і Ni–Ti–Hf systems were determined by high temperature calorimetry. The isotherms of integral enthalpy of mixing in the investigated systems were described using Redlich–Kister–Muggianu equation. It is shown that there is an intense chemical interaction between the components of the melts, which is expressed in the mostly negative values of the mixing enthalpies. Analysis of the topology of isotherms of
the integral enthalpy of mixing of three-component melts at 1873 K indicates that pair interactions play a significant role in the considered systems. The role of electron acceptor in the interaction belongs to the Fe, Co, Ni, Cu, and the role of electron donor belongs to the Ti, Zr, Hf.
Within the framework of the associated solution model (ASM), the thermodynamic mixing functions of melts of the investigated systems were described over the entire composition range and in a wide temperature range, and it was shown that the inherent for them mostly negative deviations from ideality
increase with decreasing temperature. A thermodynamic database that describes the functions of glass-forming melts of the Co–Cu–Fe–Ni–Ti–Zr–Hf system is created. This database is based on self-consistent parameters ASM and mathematical models for melts of 21 binary and 16 ternary systems. The obtained
database has been used for modeling of the temperature and concentration dependences of the thermodynamic mixing functions of liquid alloys of the
quaternary Cu–Ni–Ti–Zr, Cu–Ni–Ti–Hf, Cu–Ni–Zr–Hf, Cu–Ti–Zr–Hf, Ni–Ti–Zr–Hf and the quinary Cu–Ni–Ti–Zr–Hf systems and for calculation of thermodynamic functions of mixing of 21 equiatomic quinary liquid alloys of the Co–Cu–Fe–Ni–Ti–Zr–Hf system.
The composition of the associated solution was calculated within the framework of ASM and the degree of short-range chemical order was estimated as
the total molar fraction of Σxаssoc associates in the melts of two-, three-, four- and five-component systems. It was shown that the degree of the short-range chemical order in the melts of glass-forming systems is significant and increases with decreasing of temperature. Using the empirical rule, the concentration regions of amorphization for Cu–Ti–Zr, Cu–Ni–Ti, Cu–Ni–Zr Cu–Ni–Hf and Ni–Ti–Zr melts were interpreted, and the concentration regions of amorphization were predicted for Co–Cu–Ti, Co–Cu–Zr, Co–Cu–Hf, Cu–Fe–Ti, Cu–Fe–Zr, Cu–Fe–Hf, Cu–Ti–Hf, Cu–Zr–Hf, Ni–Ti–Hf, Ni–Zr–Hf, Cu–Ni–Ti–Hf, Cu–Ni–Ti–Zr, Cu–Ni–Zr–Hf, Cu–Ti–Zr–Hf, Ni–Ti–Zr–Hf and Cu–Ni–Ti–Zr–Hf melts.
Within the framework of the CALPHAD method, a thermodynamic description of the Cu–Ti–Hf system has been performed for the first time, and new
thermodynamic descriptions of the Ti–Zr and Cu–Ti–Zr systems have been developed.
Within the framework of the CALPHAD method, a database of parameters of models of thermodynamic properties of melts and boundary solid solutions
based on pure components for the multicomponent Co–Cu–Fe–Ni–Ti–Zr–Hf system was developed. The database contains information on the parameters of models of thermodynamic properties of liquid alloys and solid solutions of twenty-one binary systems and sixteen ternary systems. The parameters of the models of excess Gibbs energy presented in the database were used for the calculation of metastable phase transformations with the participation of supercooled liquid alloys and boundary solid solutions of the binary Fe–(Ti, Zr,Hf) systems and of the ternary Co–Cu–(Ti, Zr, Hf), Cu–Fe–(Ti, Zr, Hf), Cu–Ni–(Ti, Zr, Hf), Cu–Ti–(Zr, Hf), Cu–Zr–Hf, Ni–Ti–(Zr, Hf), Ni–Zr–Hf systems.
Keywords: high-temperature calorimetry, enthalpies of mixing, alloys based on iron, cobalt, nickel, copper, titanium, zirconium and hafnium, thermodynamic
properties of liquid alloys, associated solution model, CALPHAD method, stable and metastable diagrams, concentration regions of amorphization of melts
