Experimental Investigations And Thermodynamic Modeling Of The Al-Cu-Mn, Al-Cu-Si, Al-Mg-Ni And Ni-Ti-Si Systems

The CALPHAD(CALculation of PHAse Diagram)technique is a powerful method in many applications where modeled Gibbs energies and derivatives thereof are used to calculate properties and simulate phase transformations of multicomponent materials.Chemical potentials and the thermodynamic factor calculated with CALPHAD can be used in diffusion simulations.The driving force results from CALPHAD combine with Landau theory are used to simulate the microstructure evolution.The successful use of CALPHAD in these application relies on the development of high quality multicomponent databases.The construction of these databases is a very demanding task in material science.Al-based alloys are widely used in transportation,architectural ornament,wrapping,spaceflight and other industry field due to their exellent mechanical and physical properties.Cu,Fe,Mg,Mn,Ni,Si,Ti and Zn are the important alloying elements in the Al-based alloys.To develope properties with superior Al-base alloys and to design alloys processes effectivity,the accurate phase diagram and thermodynamical description of the multi-component Al-based system are needed.As a part of the project "Experimental investigation,thermodynamic modeling and simulation of microstructure evolution of multi-component Al-based alloy system",the present work is aimed at the investigation the phase relationship and thermodynamic property of the Al-Cu-Mn,Al-Cu-Si, Al-Mg-Ni and Ni-Ti-Si temary systems via key experiment and CALPHAD technique.(1)The Cu-Mn binary system was reinvestigated experimentally. The transition temperature of the invariant reaction:(βMn)+γ→(αMn) was accurately determined,and the liquidus in the composition range of 26～93 at.%Mn were measured.Thermodynamic optimization for the Cu-Mn system was performed with the present experimental data and data from the literature.Based on the description of Cu-Mn system and the thermodynamic parameters of the Al-Mn and Al-Cu systems available form literature,the Al-Cu-Mn system were assessed using the CALPHAD method.A set of self-consistent thermodynamic paramenters of the Al-Cu-Mn system were obtained.Comparisons between the calculation and experiment show good agreement.The liquidus projection and reaction scheme for the entire Al-Cu-Mn system are presented for the first time.(2)The isothermal sections at 500 and 600℃for the Al-Cu-Si system were investigated via experiment.Based on the present experimental data and literature data,the thermodynamic modeling of the individual phases in the Al-Cu-Si system were performed.A set of self-consistent thermodynamic paramenters were obtained for the Al-Cu-Si system with reproducing all the accepted experimental data. The invariant equilibria,liquidus projection and reaction scheme for the entire Al-Cu-Si system are also presented.(3)After abundant experiment,we finally obtained a novel method to prepare Mg base sample viz.powder moulding and sintering.Based on this method we determined the isothermal sections at 700 and 427℃for the Al-Mg-Ni ternary system for the first time.These experimental data will be used in the thermodynamic modeling of the Al-Mg-Ni system.(4)A thermodynamic modeling for the complex Ni-Ti-Si system was conducted based on the CALPHAD tecnique.The order/disorder transitions between disordered Bcc_A2 and ordered Bcc_B2 phases as well as between disordered Fcc_A1 and ordered L1₂ phases were successfully described with a two-sublattice model,respectively.A novel method to modeling a complex ternary system with multi-compound was obtained.Comprehensive comparisons between the calculation and measured phase diagrams showed good agreement,and the invariant reaction temperatures are satisfactorily accounted for by the thermodynamic description.The liquidus projection and reaction scheme for the entire system were also presented.