Abstract High-resolution electron microscopy and X-ray diffraction are used to study the phase composition and structure morphology of an equiatomic high-entropy AlCuFeCoNiCr alloy prepared by arc melting and the evolution of its structure after thermal (up to 1650°C) and thermobaric action (up to 10 GPa at 1650°C). After arc melting, the alloy structure is microcrystalline dendritic. Copper predominates in dendrites. The interdendritic region has a Widmanstätten structure. B2 (in the matrix) and A1 (in dendrites) structures are formed in the ingot. The microhardness (Hv) of the alloy is ~6500 MPa. A differential thermal analysis curve measured during heating demonstrates three endothermic processes in a sample. In the course of subsequent solidification during cooling at a rate of 1°C/s, the structure characterized by two types of dendrites having a substructure is formed. The dendrites differ in size, shape, and element contents. Like in the case of the arc-melted sample, the interdendritic region exhibits a Widmanstätten structure, but the plates are larger. During crystallization, a separation occurs in the dendrites and interdendritic regions and is accompanied by the precipitation of phases differing in composition and morphology. The hardness of the alloy (Hv) decreases to 5000 MPa. After thermobaric treatment (heating to 1650°C and subsequent cooling at a rate of 1000°C/s under pressures of 3, 5, and 8 GPa), the structure of all samples is uniform and dense. The structure is finer as compared to that observed after heat treatment; there is a correlation, i.e., dendrites of two types are formed, which differ in shape, morphology, and element contents. Dendrites of one type (first type) are enriched in copper, whereas the other dendrites (second type) are enriched in aluminum. Dendrites of both types are bordered with interlayers enriched in copper. The interdendritic region contains a mixture of phases, each of the phases is a solid solution. In accordance with pressure, a structure based on a B2 solid solution or a structure consisting of a mixture of A1, A2, and B2 phases forms in the alloy. The studies showed that, at pressures of 3–4 GPa, Hv is two times lower than that of the initial sample (3300 MPa). As the pressure increases to 5–7 GPa, Hv increases (3500 MPa). At a pressure of 8–10 GPa, the phase composition of the alloy remains similar to that observed at a pressure of 5–7 GPa; almost twofold refinement of the structure takes place, and Hv increases to 4500 MPa.

Influence of Thermal and Thermobaric Actions on the Structure of an AlCuFeCoNiCr HEA Prepared by Arc Melting

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发表日期：

2025年8月1日

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S. G. Men’shikova

摘要

Abstract

High-resolution electron microscopy and X-ray diffraction are used to study the phase composition and structure morphology of an equiatomic high-entropy AlCuFeCoNiCr alloy prepared by arc melting and the evolution of its structure after thermal (up to 1650°C) and thermobaric action (up to 10 GPa at 1650°C). After arc melting, the alloy structure is microcrystalline dendritic. Copper predominates in dendrites. The interdendritic region has a Widmanstätten structure. B2 (in the matrix) and A1 (in dendrites) structures are formed in the ingot. The microhardness (H_v) of the alloy is ~6500 MPa. A differential thermal analysis curve measured during heating demonstrates three endothermic processes in a sample. In the course of subsequent solidification during cooling at a rate of 1°C/s, the structure characterized by two types of dendrites having a substructure is formed. The dendrites differ in size, shape, and element contents. Like in the case of the arc-melted sample, the interdendritic region exhibits a Widmanstätten structure, but the plates are larger. During crystallization, a separation occurs in the dendrites and interdendritic regions and is accompanied by the precipitation of phases differing in composition and morphology. The hardness of the alloy (H_v) decreases to 5000 MPa. After thermobaric treatment (heating to 1650°C and subsequent cooling at a rate of 1000°C/s under pressures of 3, 5, and 8 GPa), the structure of all samples is uniform and dense. The structure is finer as compared to that observed after heat treatment; there is a correlation, i.e., dendrites of two types are formed, which differ in shape, morphology, and element contents. Dendrites of one type (first type) are enriched in copper, whereas the other dendrites (second type) are enriched in aluminum. Dendrites of both types are bordered with interlayers enriched in copper. The interdendritic region contains a mixture of phases, each of the phases is a solid solution. In accordance with pressure, a structure based on a B2 solid solution or a structure consisting of a mixture of A1, A2, and B2 phases forms in the alloy. The studies showed that, at pressures of 3–4 GPa, H_v is two times lower than that of the initial sample (3300 MPa). As the pressure increases to 5–7 GPa, H_v increases (3500 MPa). At a pressure of 8–10 GPa, the phase composition of the alloy remains similar to that observed at a pressure of 5–7 GPa; almost twofold refinement of the structure takes place, and H_v increases to 4500 MPa.