Phase, Composition and Structure Changes of CoCrNi-Based Concentrated Alloys Resulting from High Temperature Oxidation.

Monika Vilémová,Zdeněk Weiss,Jiří Matějíček,Zdeněk Chlup,Štefan Csáki,Hynek Hadraba,Tomáš Chráska,František Lukáč

doi:10.3390/ma13102276

Abstract

In this work, CoCrNi, FeCoCrNi and CoCrFeMnNi concentrated alloys with a Y-Ti oxide particle dispersion were prepared by mechanical alloying and Spark Plasma Sintering. The alloy consists of an FCC Ni-based matrix with a Y-Ti oxide dispersion and additional phases of Cr23C6 and Cr2O3. The effect of Fe, Mn, and Y-Ti oxide particles on the formation of oxide scales and the composition of the adjacent CoCrNi and FeCoCrNi alloys was studied. It was found that alloys without Mn in their composition form a protective Cr2O3 scale. The Cr23C6 particles provide an alternative mechanism for balancing the chromium loss during the oxidation. Y and Ti from the oxide particles participate in the formation of the protective oxide scales. Fe promotes Y and especially Ti diffusion through the Cr2O3 scale, resulting in the formation of Ti-depleted regions in the alloy. The findings will serve for the further development of these new materials.

Highlights

Conventional materials fail to satisfy requirements in a number of advanced applications
The development of so-called high-entropy alloys (HEAs) was driven by interest in exploring the central regions of multicomponent phase diagrams and resulted in the finding that such a concentrated material composition might lead to single-phase solid solution instead of the expected number of intermetallic phases [1]
Recent studies prove that exceptional mechanical properties can be achieved even for medium-entropy alloys such as CoCrNi and FeCoCrNi, especially when coupled with particle dispersion [5,15,16]

Summary

Introduction

Conventional materials fail to satisfy requirements in a number of advanced applications. The oxidation behavior of nickel-, iron-, and cobalt- containing alloys was extensively studied in systems with two major elements. Recent studies prove that exceptional mechanical properties can be achieved even for medium-entropy alloys such as CoCrNi and FeCoCrNi, especially when coupled with particle dispersion [5,15,16]. Y2 O3 may be enriched by Ti; this has been shown to further increase the high temperature resistance and radiation damage resistance [17] Another proven effect of yttrium addition is the enhancement of oxidation resistance [18]. With the need to find suitable materials for advanced applications, it is necessary to study and understand the overall high-temperature behavior of new multi-component materials with concentrated compositions. The results were compared with the results of CoCrFeMnNi high-entropy alloy, which served as a reference

Materials and Methods

Results and Discussion

Oxidation

SEM the scales oxide coupled scales coupled plots ofdistribution elemental

23 C6 and Cr dispersion andCradditional