Hardness and Isothermal Oxidation Analysis in High-Entropy Alloys of the Fe-Cr-Ni-Co-Si-Al and Fe-Mn-Al-Ni-C Systems with Niobium Addition

• Grant number: 25/12651-3
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: August 01, 2025
• End date: July 31, 2026
• Field of knowledge: Engineering - Materials and Metallurgical Engineering - Physical Metallurgy
• Principal Investigator: Marcelo Falcão de Oliveira
• Grantee: Gabriel Kauan Bianchi de Almeida Leal
• Host Institution: Escola de Engenharia de São Carlos (EESC). Universidade de São Paulo (USP). São Carlos , SP, Brazil

Abstract

High Entropy Alloys (HEAs) have emerged as a promising class of metallic materials capable of combining advanced properties, such as high mechanical strength, good ductility, thermal stability, and excellent performance against corrosion and oxidation. Unlike conventional alloys, which are based on a single principal element with minor additions of other elements, HEAs explore the balanced mixing of multiple elements in similar proportions, leading to stable solid solutions due to their high configurational entropy.Among the most studied families of HEAs are the Fe-Cr-Ni-Co-Si-Al and Fe-Mn-Al-Ni-C systems. The former, known for its stainless character, exhibits good performance in oxidizing and corrosive environments. The latter stands out for its high specific strength (ratio between mechanical strength and density), making it attractive for structural applications where lightweight materials are essential, such as in the automotive and aerospace industries.In this context, the present project aims to investigate the influence of niobium (Nb) addition in alloys based on the aforementioned systems, considering the potential of this element to enhance mechanical properties and oxidation resistance, in addition to its vast abundance in Brazil. Niobium may act as a strengthening agent via solid solution or precipitation and can also contribute to the formation of protective oxides that improve durability under harsh operating conditions.The study will involve the synthesis of model alloys by arc melting, followed by characterization of different compositions containing increasing Nb content. The reference alloys will be (Fe33.5Cr26Ni25Co10Si3Al2.5)100-xNbx and (Fe48Mn26Al16Ni5C5)1-yNby, with x and y ranging from 0 to 9 at.%. The characterization process will include Vickers microhardness testing, density measurements using the Archimedes method, isothermal oxidation studies at 600°C and 900°C for 20 and 100 hours, and complementary microstructural analyses through X-ray diffraction (XRD) and scanning electron microscopy (SEM).In addition to mapping the effects of Nb on the hardness and oxidation behavior of the alloys, this project applies alloy design criteria based on configurational entropy, valence electron concentration (VEC), and elastic strain energy, in order to promote the formation of stable solid solutions with optimized properties. As a result, the project aims to identify more efficient and technologically viable compositions, contributing to the advancement of HEA research and the strategic application of niobium as an alloying element in high-performance engineering materials. (AU)