Impact of Sintering Temperature of the Mechanical Properties of a Fe20Cr20Mn20Ni20Ti10Co5V5 Medium Entropy Alloy

Abstract

Medium entropy alloys (MEAs) are new emerging engineering alloys comprising four principal elements characterised by a low enthalpy of mixing and entropies of formation between 1 and 1.5 molar gas constant. They have high strength, wear, and thermal properties. MEAs have generated interest as an alternative material in the last two decades in nuclear, aerospace, and high strength engineering applications. In this research a medium entropy alloy Fe₂₀Cr₂₀Mn₂₀Ni₂₀Ti₁₀Co₅V₅ with principal elements Fe, Cr, Mn, and Ni was fabricated using spark plasma sintering. Elemental powder mixture was sintered at temperatures of 870^oC, 900^oC and 950^oC under 35 bar pressure under an inert argon atmosphere for 45 minutes using an FCT Systeme GmbH spark plasma sintering machine. After sand blasting the densities of the samples were measured before grinding, polishing, and etching for characterisation. Microstructure analysis was carried using scanning electron and optical microscopy. Microhardness was measured using Falcon 507 hardness tester, modulus using by Anton-Paar Nanoindenter and wear using Anton-Paar TRB3 Tribometer. The elements form a solid solution with presence of a hard μ phase and soft γ-phase were observed. The hardness of the alloys sintered at 870^oC and 900^oC were 397 and 424 Vickers respectively. The alloy sintered at 950^oC showed a hardness of 674 Vickers. After annealing the hardness increased to 736 Vickers. The modulus of elasticity and creep resistance increased after heat treatment at 700^oC.The other alloys showed a decrease in hardness and other properties after annealing. Unlike in steels, where annealing reduces, in this alloy annealing increased hardness at an appropriate temperature. Fe₂₀Cr₂₀Mn₂₀Ni₂₀Ti₁₀Co₅V₅ MEA exhibited good thermal stability. Further work on the alloy will involve its crystallography, and feasibility for use elevated temperature energy applications such as fuel cells, turbines and wear resistant machine components.