Experimental Investigation And Thermodynamic Modeling Of The Sc-Ni,Al-Li-Zr And Al-Sc-Zr Systems In Al Alloys

Al-based alloys have found wide application in the aerospace and automotive industry due to their excellent comprehensive perfomance. Sc, Ni, Li and Zr are important alloying elements or additive in the multiple commercial aluminum alloys. CALPHAD technique which is based on thermodynamic model is an effective and widely utilized method for assessment and calculation of phase diagrams. In the present work, the Sc-Ni, Al-Li-Zr and Al-Sc-Zr systems are assessed via the CALPHAD method coupled with key experiments or first-principles calculations for the formation enthalpy of compounds. The main research results obtained are shown as follows:(1) Based on critical assessment of the literatures data, the phase relationship of the Sc-Ni system on the whole composition range and parts of invariant reaction temperatures were investigated by means of XRD, SEM/EDX, EPMA, DTA and DSC. Five compounds (ScNi5, Sc2Ni7, ScNi2, ScNi and Sc2Ni) were observed in the present experiment. Their enthalpies of formation at 0 K were computed via first-principles calculations to supply referabel thermodynamic data for the modeling. One single function was used to describe the Gibbs energies of both the ordered Bcc_B2 (ScNi) and disordered Bcc_A2 phase. The presently obtained thermodynamic paremeters for the Sc-Ni system can reproduce the experimental data reasonably.(2) Based on critical assessment of the literatures data, the modeling of compound ?2 was determined. The enthalpies of formation of compounds ?1 and ?2 were computed via first-principles calculations to supply referable thermodynamic data for the modeling. Based on the literatures data, a thermodynamic description of the Al-Li-Zr system has been carried out, and a set of thermodynamic parameters has been obtained. The agreement between calculation and experimental is resonable.(3) The preliminary thermodynamic description for Al-Sc-Zr system was conducted after assessing the literatures data. The three-phase region, AlZr3+Hcp_A3+?, was determined by means of XRD?SEM and EPMA. A further thermodynamic optimizing for the Al-Sc-Zr system was then conducted by considering the reliable experimental data from the literature and the present work. A set of self-consistant thermodynamic parameters was obtained for the Al-Sc-Zr system which can well describe the experimental data reasonably. The liquidus projection was also proposed based on the present work.