Mechanism of FCC structure formation in NiCoFeCuMn equiatomic high-entropy alloys

Four high-entropy alloys are prepared by an arc furnace under argon atmosphere. The microstructure and the properties of the alloys are investigated. The results show that NiCrCuCoFe alloy consists of a single FCC solid solution. When Al presents in the alloys, the microstructures of the alloys change to a BCC+ FCC solid solution. It is indicated that Al element promotes the formation of BCC solid solution, and Si and Mn promote the formation of complicated compounds. The hardness of alloys with BCC structure is higher than that of the alloys with FCC structure. The complicated compounds are formed, the hardness increases further. The highest hardness of the alloys reaches 882 HV due to the strengthening of the second phase precipitation.

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Microstructural Stability of the CoCrFe2Ni2 High Entropy Alloys with Additions of Cu and Mo

Metals ◽

10.3390/met11121994 ◽

2021 ◽

Vol 11 (12) ◽

pp. 1994

Author(s):

Isaac Toda-Caraballo ◽

Jose Antonio Jiménez ◽

Srdjan Milenkovic ◽

Jorge Jimenez-Aguirre ◽

David San-Martín

Keyword(s):

Enthalpy Of Mixing ◽

High Entropy Alloys ◽

Surprising Result ◽

Microstructural Stability ◽

Rich Phase ◽

High Entropy ◽

Single Face ◽

Precipitation Phenomena ◽

The Stability ◽

Fcc Structure

New High Entropy Alloys based on the CoCrFe2Ni2 system have been developed by adding up to 10 at. % of Cu, Mo, and Cu + Mo in different amounts. These alloys showed a single face-centred cubic (FCC) structure after homogenization at 1200 °C. In order to evaluate their thermal stability, aging heat treatments at 500, 700, and 900 °C for 8 h were applied to study the possible precipitation phenomena. In the alloys where only Cu or Mo was added, we found the precipitation of an FCC Cu-rich phase or the µ phase rich in Mo, respectively, in agreement with some of the results previously shown in the literature. Nevertheless, we have observed that when both elements are present, Cu precipitation does not occur, and the formation of the Mo-rich phase is inhibited (or delayed). This is a surprising result as Cu and Mo have a positive enthalpy of mixing, being immiscible in a binary system, while added together they improve the stability of this system and maintain a single FCC crystal structure from medium to high temperatures

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Intermetallic Phases in High-Entropy Alloys: Statistical Analysis of their Prevalence and Structural Inheritance

Metals ◽

10.3390/met9020247 ◽

2019 ◽

Vol 9 (2) ◽

pp. 247 ◽

Cited By ~ 13

Author(s):

Ming-Hung Tsai ◽

Ruei-Chi Tsai ◽

Ting Chang ◽

Wen-Fei Huang

Keyword(s):

Statistical Analysis ◽

Structure Formation ◽

Statistical Approach ◽

Intermetallic Phases ◽

High Entropy Alloys ◽

High Entropy ◽

Future Design ◽

Existing Structures ◽

Structural Inheritance ◽

Second Phases

Strengthening high entropy alloys (HEAs) via second phases is a very effective approach. However, the design of intermetallic (IM) phases in HEAs is challenging, mainly because our understanding of IM phases in HEAs is still very limited. Here, a statistical approach is used to enhance our understanding towards IM phases in HEAs. A database consisting of 142 IM-containing HEAs was constructed. Our aim is twofold. The first is to reveal the most common IM phase types in published HEAs. The second is to understand whether HEAs inherit their IM structures from their binary/ternary subsystems, or whether they tend to form new structures irrelevant to their subsystems. The results show that the five most prevalent IM structures in the HEAs surveyed here are Laves, σ, B2, L12, and L21. This trend is evidently different from the overall trend among known binary/ternary IMs. As for structural inheritance, all the IM phases contained in the alloys are existing structures in the binary/ternary subsystems of the respective alloys. This suggests that the compositional complexity in HEAs does trigger additional complexity in IM structure formation. These findings have important implications in the future design and development of HEAs.

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