Thermodynamic Assessments Of The Precious Metal Binary Systems Between PM(Ag,Au,Pt,Pd) And TM(Fe,Co,Ni,Cu)

Precious metals,called new modern metals,play an irreplaceable role in the fields of national defence,modern industry and biomedicine because of their excellent physical and chemical properties.When alloying with transition metals(Fe,Co,Ni,Cu),it can not only reduce the consumption of precious metals,but also endow noble metals with new diversified performances.However,due to the high price and limited reserves of noble metals,it is an urgent issue to guide the alloy design of precious metals materials through phase diagram and thermodynamic theory.In this work,to do spade work for establishing multi-element thermodynamic database for precious metals,thermodynamic assessments for precious metals base alloys using CALPHAD technique have been performed.The main research results obtained in this work are as follows:(1)Pt-Fe binary system is an important binary system in precious metal alloys,however,the available thermodynamic assessment of Pt-Fe is inconsistent with the phase equilibria and thermodynamic data,so Pt-Fe system was re-evaluated and optimized in our work.The liquid,BCC and FCC disordered phase were modeled as sub-regular solution model,the L12 type of Fe3Pt,FePt3 and the L10 type of FePt ordered phases were modeled with four-sublattice model and modify compound energy formalism.Finally,the calculated Pt-Fe phase diagram agrees well with phase equilibrium data,and the calculated thermodynamic properties are consistent with thermodynamic data such as the enthalpy of mixing and component activities of the disordered FCC phase,the component activities of liquid phase at different temperatures and the enthalpies of formation of the ordered FCC phases.A set of self-consistent thermodynamic parameters of the Pt-Fe binary system was obtained.(2)Au-Cu binary system is one of the most common used binary systems in precious metal alloys,however,the thermodynamic model of the ordered phase in the current thermodynamic evaluation work is not reasonable,and can't be compatible with other precious metal systems.The Au-Cu binary system was re-assessed in this work,and the initial values of the ordered phase parameters in the four-sublattice model and modify compound energy formalism(MCEF)were deduced theoretically in this work,the parameters of the ordered phases can be determined more simply and effectively.Finally,the calculated phase diagram of Au-Cu binary system agrees well with the phase equilibrium data,and in addition,the calculated enthalpy of mixing of liquid phase and the enthalpies of formation of all ordered phases are consistent with the experimentally determined thermodynamic data.(3)The precious metals(Ag,Au,Pt,Pd)and the transition metals(Fe,Co,Ni,Cu)can constitute 22 noble metal binary systems in total.Except the Pt-Fe and Au-Cu systems which were thermodynamically re-assessed in our work,there are 17 precious metal binary systems with the published thermodynamic studies.The left 3 noble metal binary systems.which are Ag-Pt,Au-Pd and Pt-Pd,can't be thermodynamically evaluated now because of the limited experimental information.The 19 precious metal binary systems have been thermodynamically analyzed and calculated in this work.As a result,a thermodynamic database of precious metals has been established,which contains 8 components,including Ag,Au,Pt,Pd,Fe,Co,Ni and Cu.It has laid the foundation for further research work on the thermodynamic database of precious metal multicomponent alloys.