Microstructures of Al7.5Cr22.5Fe35Mn20Ni15 High-Entropy Alloy and Its Polarization Behaviors in Sulfuric Acid, Nitric Acid and Hydrochloric Acid Solutions

Chun-Huei Tsau,Po-Yen Lee

doi:10.3390/e18080288

Abstract

This paper investigates the microstructures and the polarization behaviors of Al7.5Cr22.5Fe35Mn20Ni15 high-entropy alloy in 1M (1 mol/L) deaerated sulfuric acid (H2SO4), nitric acid (HNO3), and hydrochloric acid (HCl) solutions at temperatures of 30–60 °C. The three phases of the Al7.5Cr22.5Fe35Mn20Ni15 high-entropy alloy are body-centered cubic (BCC) dendrites, face-centered cubic (FCC) interdendrites, and ordered BCC precipitates uniformly dispersed in the BCC dendrites. The different phases were corroded in different acidic solutions. The passivation regions of the Al7.5Cr22.5Fe35Mn20Ni15 alloy are divided into three and two sub-regions in the solutions of H2SO4 and HNO3 at 30–60 °C, respectively. The passivation region of the Al7.5Cr22.5Fe35Mn20Ni15 alloy is also divided into two sub-domains in 1M deaerated HCl solution at 30 °C. The Al7.5Cr22.5Fe35Mn20Ni15 alloy has almost equal corrosion resistance in comparison with 304 stainless steel (304SS) in both the 1M H2SO4 and 1M HCl solutions. The polarization behaviors indicated that the Al7.5Cr22.5Fe35Mn20Ni15 alloy possessed much better corrosion resistance than 304SS in 1M HNO3 solution. However, in 1M NaCl solution, the corrosion resistance of the Al7.5Cr22.5Fe35Mn20Ni15 alloy was less than 304SS.

Highlights

High-entropy alloys are alloys that have more than four elements, and the content of each element is in the range of 5–35 atomic percent
A portion of the interdendrite fragments still arranges in lines, and a portion of the interdendrite fragments randomly distributes within the dendrite
The body-centered cubic (BCC) phase is the dendrite matrix and the face-centered cubic (FCC) phase is the interdendrite by comparing the intensities of the X-ray diffraction (XRD) peaks and the scanning electron microscope (SEM) micrograph

Summary

Introduction

High-entropy alloys are alloys that have more than four elements, and the content of each element is in the range of 5–35 atomic percent. Because high-entropy alloys contain many major elements, their properties are not dominated by any one element Aside from the mechanical properties of high-entropy alloys that are investigated, their corrosion behaviors are studied [10,11,12]. Alx CrFe1.5 MnNi0.5 alloys [13] possess good workability, precipitation hardening, and high-temperature oxidation resistance. The hardness of both Al0.3 CrFe1.5 MnNi0.5 and Al0.5 CrFe1.5 MnNi0.5 alloys is higher than HV950 after aging treatment. The enhanced pitting corrosion resistance of anodic treated Alx CrFe1.5 MnNi0.5 (x = 0, 0.3, 0.5) alloys in.

Experimental

Results and Discussion

SO4 and 1M

Conclusions