engleski

Thermodynamic Modelling of Cu-Al-Mn-Ag alloys

Shape memory alloys (SMA) are highly interested functional materials which have the ability to recover their previous form when subjected to thermal or mechanical variations. SMA alloys exhibit unique properties like the shape memory effect, the superelasticity associated with damping capabilities, high corrosion and extraordinary fatigue resistance. Shape memory effect is based on martensitic transformation which represents a diffusionless and reversible solid state phase transformation which occurs between the high-temperature austenite phase and the low temperature martensite phase, and related transformation temperature is crucial for area of SMA alloy application. Cu-Al-Mn alloys under equilibrium conditions, undergoes to decomposition of β-phase to α- and γ2- phase. By fast quenching, decomposition could be suppressed and metastable martensitic phase formed, with 2M or 6M crystal structure, depending of A2 or L21 parent phase. Ternary Cu-Al-Mn alloys and Cu-Al-Mn-Ag were prepared by melting of pure metals in the electric-arc furnace, in argon atmosphere, and casted in the cylindrical mould. Specimens were thermal treated at 900 °C and quenched in water. Calculation of phase diagram was performed by Thermo-Calc program, by minimization of Gibbs free energy of system and CALPHAD method using parameters of pure elements according to SGTE database and optimized thermodynamic parameters for binary and ternary system. Microstructure was determined by Field-emission scanning electron microscope (FE-SEM) and phase elemental analysis was performed by energy dispersive X-ray spectroscopy (EDS). Martensitic and austenitic transformation temperatures were followed by Differential Scanning Calorimetry(DSC). Results showed two-phase morphology in the as-cast state and completely formed martensitic structure, with different types of martensite, in quenched Cu-Al-Mn alloys.

Shape memory alloys, thermodynamic modelling, martensitic transformation

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