Study On The Phase Diagram And Thermodynamics Of The Ti-RE(RE=Ce,Er,Tm,Y) And Ti-V-M(M=Nb,Si,Ta) Systems

Titanium and titanium alloys have comprehensive properties,such as good corrosion resistance,high heat resistance and high specific strength.As an important structural materials,they are widely used in aerospace,petrochemical,biomedical and other fields.Ce,Er,Tm,Y,V,Nb,Si and Ta are the common alloying elements or additive elements in the Ti-based alloys.In order to develop properties with superior Ti-based alloys and to improve their preparation processes,it is necessary to obtain the accurate phase diagram and thermodynamic description of the multi-component Ti-based system.For the time being,there are no reports on the thermodynamics of phase diagram for Ti-RE(RE=Ce,Er,Tm,Y)and Ti-V-M(M=Nb,Si,Ta)systems.In response to this phenomenon,the phase diagram thermodyanmic of the Ti-RE(RE=Ce,Er,Tm,Y)four binary systems and Ti-V-M(M=Nb,Si,Ta)three ternary systems have been systematically investigated by means of CALPHAD(CALculation of PHAse Diagram)method and used the Thermo-Calc software.The main results are as following:(1)Based on the available experimental phase equilibria data in the literature,thermodynamic assessment of the Ti-RE(RE=Ce,Er,Tm,Y)binary systems were carried out by means of the CALPHAD method.The solution phases,i.e.,liquid,bcc(?Ti,?Ce,?Y),hep(aTi,Er,Tm,?Y)and fcc(?Ce,?Y),are described by the substitutional solution model.A set of self-consistent thermodynamic parameters were firstly obtained for each of these binary systems.By comparing with the experimental data,the thermodynamic parameters was obtained in the present work can accurately describe the experimental phase equilibrium data.(2)Based on the thermodynamic descriptions of the constitutive binary systems(Ti-V,Ti-Nb5 Ti-Ta,V-Nb and V-Ta)as well as the experimental phase equalibria data of the ternary systems available in the literature,the Ti-V-Nb and Ti-V-Ta ternary systems have been evaluated using the CALPHAD approach.There are no ternary compounds in these ternary systems.The solution phase,i.e.bcc(?Ti,V,Nb,Ta)and hep(aTi)were described by the substitutional solution model.An optimal set of thermodynamic parameters for the Ti-V-Nb and Ti-V-Ta ternary systems were obtained.Liquidus and solidus surface projection and some representative isothermal sections and vertical sections were calculated.By comparing with the experimental data,the calculated phase diagram has agree well with the literature experimental data by the present modeling.(3)Based on the phase equilibrium data reported in the literature,the phase diagram thermodynamic of the Ti-V-Si system has been systematically investigated by means of key alloy and CALPHAD method coupled with First-Principles calculation.By preparing key alloys,the 800? isothermal section of the Ti-V-Si system was determined by means of XRD and SEM/EDX techniques.The formation enthalpies of the inter-terminal compounds at OK were calculated via the First-Principles and regard as the initial value of the optimization calculation.Thermodynamic description of binary compounds with solubility was performed using the sublattice model.Based on the crystal structure and solubility of the ternary compound ?-(TixV1-x)Si,it is thermodynamically modeled using a sublattice model(Ti%,V)1(Ti,V%)1Si2,which is described as a linear compound.The thermodynamic optimization of the Ti-V-Si system was carried out by means of CALPHAD method,and a set of thermodynamic parameters describing this system was obtained.In the present work,the calculated isothermal sections has an agreement with the experimental data.In addition,the liquid surface projection and scheil reaction scheme for the entire system were also plotted.Figure[22]table[10]reference[143].