Corrosion Behavior of Selectively Laser Melted CoCrFeMnNi High Entropy Alloy

Jie Ren,Sundeep Mukherjee,Wen Chen,Chaitanya Mahajan,David Follette,Liang Liu

doi:10.3390/met9101029

Jie Ren, Sundeep Mukherjee + Show 4 more

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https://doi.org/10.3390/met9101029

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Abstract

CoCrFeMnNi high entropy alloys (HEAs) were additively manufactured (AM) by laser powder bed fusion and their corrosion resistance in 3.5 wt% NaCl solution was studied by potentiodynamic polarization and electrochemical impedance spectroscopy tests. A systematic study of AM CoCrFeMnNi HEAs’ porosity under a wide range of laser processing parameters was conducted and a processing map was constructed to identify the optimal laser processing window for CoCrFeMnNi HEAs. The near fully dense AM CoCrFeMnNi HEAs exhibit a unique non-equilibrium microstructure consisting of tortuous grain boundaries, sub-grain cellular structures, columnar dendrites, associated with some processing defects such as micro-pores. Compared with conventional as-cast counterpart, the AM CoCrFeMnNi HEAs showed higher pitting resistance (ΔE) and greater polarization resistance (Rp). The superior corrosion resistance of AM CoCrFeMnNi HEAs may be attributed to the homogeneous elemental distribution and lower density of micro-pores. Our study widens the toolbox to manufacture HEAs with exceptional corrosion resistance by additive manufacturing.

Highlights

In recent years, high entropy alloys (HEAs) have received remarkable attention from both academia and industry due to a portfolio of unusual properties including high specific strength [1,2,3,4,5,6], high fracture resistance [7,8], and excellent corrosion and oxidation resistance [9,10]
CoCrFeMnNi HEA was additively manufactured by selective laser meting (SLM) and its corrosion resistance in 3.5 wt% NaCl solution was evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy measurements and compared with the as-cast counterpart
By varying laser power and scan speed, near fully dense CoCrFeMnNi HEA was manufactured by SLM when the volume energy density (VED) was in the range of 62.5–115.6 J/mm3

Summary

Introduction

High entropy alloys (HEAs) have received remarkable attention from both academia and industry due to a portfolio of unusual properties including high specific strength [1,2,3,4,5,6], high fracture resistance [7,8], and excellent corrosion and oxidation resistance [9,10]. Because of the formation of protective passive films on the surface, the corrosion behavior of Cr-, Ni-, and Mo-based HEAs have been widely investigated [12,13,14,15,16]. Most HEAs suffer from inferior flowability or formability in the liquid state to be shaped into useful components by conventional manufacturing routes such as casting [17]. We apply a laser powder bed fusion based AM technique, namely selective laser meting (SLM), to produce CoCrFeMnNi

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