Production and Characterization of Cr44Co35Ni16Al5 Duplex Multi-Principal Element Alloy by Directional Solidification

Abstract

Multi-principal element alloys (MPEAs) and high-entropy alloys (HEAs) represent a new class of materials, which do not have a major alloying element, being composed primarily of concentrated solid solutions of several different alloying elements. Several alloys of different compositions of this class have already been studied, and the literature gives a special focus to multicomponent alloys that involve mixtures of transition metals belonging to the 3-d family of the periodic table, that is, metals between Ti and Cu. Among these alloys, numerous compositions of the CrCoNiAl system stand out for having excellent properties, such as strength, ductility and corrosion resistance. The development of these alloys has given focus to the search of compositions that form face-centered cubic (FCC) structures. However, there are studies that indicate that duplex alloys, which present microstructures composed of both body-centered cubic (BCC) and face-centered cubic (FCC) phases, are capable of presenting excellent mechanical properties.In this project, an ingot of the Cr44Co35Ni16Al5 alloy will be manufactured, which was chosen based on thermodynamic analyzes and calculations carried out with the Thermo-Calc® software. This alloy belonging to the CrCoNiAl system presents a promising composition for the formation of a duplex structure. The ingot of this alloy will be manufactured through directional solidification experiments in a transient heat extraction regime.The objectives of this work are: i) the development of the directional solidification process in transient heat extraction regime using MPEA Cr44Co35Ni16Al5; ii) Microstructural analysis with effective correlation with cooling rate, whose variation will be determined experimentally through the use of thermocouples; and iii) Evaluation of mechanical and corrosion properties resulting from samples solidified under different conditions of cooling rates.Thermodynamic calculations were performed that point to some promising compositions of the CrCoNiAl system for the formation of a duplex structure. The selected alloy will then be manufactured by these thermodynamic methods through directional solidification experiments in a transient heat extraction regime, in order to analyze and correlate the microstructural parameters and thermal solidification parameters for the duplex FCC + BCC alloys in the CrCoNiAl system. They will be studied in the as-cast state of fusion by optical microscopy, scanning electron microscopy (SEM) and transmission microscopy (TEM). Vickeres microhardness and traction mechanical tests will also be carried out, as well as corrosion tests.