Theory And Experimental Research Of Phase Diagram Topology Relationship In Multicomponent Al-based Alloys

Development of calculated science promotes design of materials. As one of embranchment in calculated material thermodynamic, CALPHAD can calculate complex multicomponent phase diagram, phase transition temperature and each phase content vs.temperature,etc, which provides important information for describing evolvement of microstructure.Combining thermodynamic simulation and modern experimental technology,phase diagram calculation links composition, structure and preparation process,so as to forecast and design material from micromechanism to macroscopical capability.Usually,phase diagram reach limited in simplex temperature section or restricted component range.It's not enough faraway.Al-based alloys have been used in spaceflight and other industry field due to their excellent integrative performance.Be,Cu,Fe,Mg, Mn,Si,Ni and Ti are all important alloying elements which can improve the qualities of the Al-based alloys.To better Al-based alloys' comprehensive qualities,some models in phase equilibrium calculation were introduced in this thesis necessary and then phase topology of several important ternary systems were investigated via experiment and optimization:(1)The Al-Be,Be-Si binary phase diagram were determined experimentally.Thermodynamic optimization for the Al-Be and Be-Si system were performed using the CALPHAD technique applied to newly measured phase diagram data and the data from literature.These descriptions for these two binary systems were then combined with the thermodynamic parameters in the Al-Si systems to synthesize a thermodynamic description for the Al-Be-Si ternary system.The comparisons show good agreement between calculation and experiment. It is the most integrated experiment research and the most exact description for this ternary system since 1906.(2)Phase relationship in the whole composition range of Fe-Mn-Si ternary system was investigated via experiment.A set of thermodynamic parameters were obtained by applying the CALPHAD technique.These parameters can not only describe stable phase diagram in Fe-Mn-Si system,but also can simulate martensitic transition of metastable hcp phase.It has notable significance for material design and development.(3)Via different experiment technique,eliminated divadcation in Al-Ni-Ti ternary system.1000℃isothermal section was determined for the first time.A new ternary phaseÏ„5 occurs as an equilibrium phase in the Al-rich corner.The composition of this phase is Al₆₅Ni₂₀Ti₁₅. Experimental data for temperatures above 900℃up to melting was supplied.The liquidus projection and reaction scheme are also presented.(4)Because of the absence of experimental data in the Mg-included system,there have no report on calculated phase diagram.Selected five ternary systems(Mg-Mn-Si,Mg-Mn-Ni,Mg-Ni-Zn,Mg-Si-Zn,Mg-Ni-Si) trial calculation were performed by CALPHAD.The effect is satisfactory and the result can be used to guide farther experiment.All of phase diagram and thermodynamic experimental data for each system were critical evaluated.Base on universal Gibbs energy database unified boundary binary model,all of binary and ternary systems can be unionized in a database.This technique,which combines key experiment(XRD,DTA,SEM/EDX,etc.)and phase diagram calculation to construct phase topology relationships in whole component and temperature range,not only can used in Al-based alloys system,such as this work,but also can generalize to other important industry system.