Vacuum arc melted and heat treated AlCoCrFeNiTiX based high-entropy alloys: Thermodynamic and microstructural investigations

• Published in: Journal of alloys and compounds 2022-05, Vol.903, p.163901, Article 163901
• Main Authors: Güler, Saadet, Alkan, Esra Dokumaci, Alkan, Murat
• Format: Article
• Language: English
• Subjects: Alloy systems; Alloying elements; Alloys; Arc heating; CALPHAD; Cooling; Differential thermal analysis; Electric arc melting; Equilibrium; Heat treatment; High entropy alloys; Microstructure; Phase diagrams; Phase transitions; Sigma phase; Software; Thermodynamics; Vacuum arc melting
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2022.163901

•AlCoCrFeNiTix phase diagram was created using Thermo-Calc software.•Both theoretical calculations and experimental investigations were combined.•Equilibrium and non-equilibrium cooling conditions were thermodynamically calculated.•Laves and Sigma phases were also formed according to the increasing titanium content. [Display omitted] The AlCoCrFeNi alloy system is one of the commonly studied high-entropy alloys (HEA). The additional elements like Ti affect the properties of HEAs. In order to predict these effects on the microstructure and the properties of HEAs, a suitable phase diagram is needed. The phase diagrams can be plotted by using thermodynamic software and databases. But experimental studies should be done to control whether this phase diagram is suitable or not. The aim of this study is to propose a phase diagram suitable for the AlCoCrFeNiTiX system by using ThermoCalc software and to compare it with the experimental results. In this work, HEAs were produced by a vacuum arc melting (VAM) method followed by a heat treatment (H-T) process. The stoichiometric amount of Ti was varied-(X = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0). Its effects on the microstructure evaluations and phase transformations in HEAs were investigated. The H-T processes were realized at different temperatures and cooling conditions. The thermodynamic investigations were performed to predict the phases present within as-cast (AC) and heat-treated (HT) HEAs by using Thermo-Calc 2021a Software and its TCHEA4 database. The Calculation of Phase Diagram (CALPHAD) studies were also utilized to plot the phase diagrams for the AlCoCrFeNiTiX system under both equilibrium and non-equilibrium cooling conditions. AC and HT HEAs were characterized by various techniques: scanning electron microscope (SEM) with an energy dispersive spectrometer (EDS), X-ray diffractometer (XRD), differential thermal analysis (DTA), and differential scanning calorimetry (DSC). The phases and the microstructures of AC HEAs were detected as similar to the theoretically obtained alloys under non-equilibrium cooling conditions. While the phases and the microstructures of HT HEAs were detected as similar to the theoretically obtained alloys under equilibrium cooling conditions. As a result, the target alloy composition and production process can be designed depending on the desired properties using the proposed phase diagrams. For example, if the Sigma phase is not desired in the structure, HEAs with Ti1.1 and above co