High Entropy Alloys final University of Thessaly（高熵合金最终塞萨利大学）.pdf

University of Thessaly Department of Mechanical Engineering Laboratory of Materials High Entropy Alloys Ioannis S.Aristeidakis Maria-Ioanna T.Tzini Physical Metallurgy M.Sc Supervisor: G. N.Haidemenopoulos January 2016, Volos Abstract The High Entropy Alloys (HEAs) have triggered a new interest in materials design. The main concept of this study is based on the diffusion and the phase transformations, which occur in these alloys. The processing routes for the synthesis of HEAs and the techniques used are classified in four states and each state is described. Thermodynamics parameters and their contribution to the prediction of the HEAs properties have been considered. The kinetics of phase transformation in HEAs are slower than the kinetics of the conventional steels. This behavior is attributed to the sluggish diffusion effect. The diffusion in HEAs is characterized as sluggish due to the complex interactions between the alloying elements and the high activation energy. The competition between configurational entropy and mixing enthalpy is a key factor for the determination of phase transformations. Diffusive transformations, such as the Nucleation and Growth Transformations (NGT) and the Continuous Transformations (CT), have been observed. Nanoprecipitation and eutectic transformations in NGT, as well as order/disorder transformations and spinodal decomposition in CT are the most reported amongst the HEAs references. Simulation models and new thermodynamic parameters have been developed during the past years, in order to predict the microstructure in HEAs. Despite the difficulties regarding computational calculations and experimental procedure, t