Innovative micro-synthesis of high entropy alloys based on CoCrFeNi

In a research article recently published in the Journal of Materials Science and Technology, scientists have developed a high throughput microsynthesis method based on hot isostatic pressing to simultaneously synthesize and characterize a large number of high entropy alloys from a phased array system.

To study: High throughput synthesis allowed exploration of high entropy alloys based on CoCrFeNi. Image Credit: Javier Ruiz / Shutterstock.com

The researchers used CoCrFeNi as the base alloy and added 9 other transition metals in different proportions to make 85 alloys. This process is both cost effective and rapid in the analysis of a large number of combinatorial alloy systems.

Why are high throughput synthesis methods essential for high entropy alloys?

High entropy alloys (HEA) contain five or more primary elements in equal, nearly equal, or relatively high proportions. They provide a wide field for experiments with different alloy compositions. Adding each different element further expands the composition pool exponentially. One-to-one synthesis and characterization of all of these compositions is inefficient. Thus, there is a need to develop efficient high throughput genome sequencing methods and materials for HEA.

Currently, laser additive manufacturing (LAM), combinatorial thin film synthesis, and rapid prototyping processes are used for the synthesis of large HEA compositions. Likewise, several calculation methods, such as phase diagram calculations (CALPHAD), first-principle calculations, parametric criteria and machine learning are used for large-scale analysis of HEA compositions.

Cantor alloy (CoCrFeNiMn) is one of the most studied HEA compositions. It has a five-element equiatomic composition with a single FCC phase. However, many elements can still be added to the cantor alloy and the resulting composition-treatment-structure-property relationships can be investigated.

About the study

In this study, the manganese (Mn) in the cantor alloy was replaced by 8 other main elements based on transition metals to form 85 alloy compositions. These additive metals are copper (Cu), titanium (Ti), niobium (Nb), tantalum (Ta), molybdenum (Mo), tungsten (W), aluminum (Al) and silicon Si ). In addition, the synthesized alloy compositions include 1 quaternary, 9 quinary and 36 senary alloy systems.

A high throughput hot isostatic pressing (HT-HIP-MSA) microsynthesis approach was used for the synthesis of the alloy system. First, the researchers made 85 cells bearing matrices with a honeycomb structure using LAM. Then, mechanically crushed powders of the 13 main elements were loaded into each cell with varying compositions, then placed in a carbon steel container. The container was subjected to a HIP treatment, in which it was heated at 1000 and 150 MPa pressure for 4 hours under an argon atmosphere followed by slow cooling at a rate of 10 / min to obtain 85 samples with distinct compositions.

Observations

From the X-ray fluorescence data (µ -XRF), it was evident that CoCrFeNi-MnX kept a single FCC phase with an addition of Mn ranging from 0.5 to 3 atomic ratio. In addition, as the Mn content increases, the corresponding major peak shifts to the left, confirming the increase in lattice parameters due to the large radius of Mn. The result of X-ray diffraction (XRD) indicated that no intermetallic compound was formed by the addition of Cu, but it tends to form two phases of solid solution of FCC due to the large positive enthalpy. of Cu with other components.

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In addition, Al has been shown to destabilize the FCC structure of HEA. As the amount of Al increased from 0.5 to 3 atomic ratio, the primary phases of CoCrFeNi-AlX the alloys went from the single FCC phase to the FCC + BCC phase to the BCC phase. This result was also the same for Nb, Mo, Ta and W. In addition, an excess of alloy additions of Nb or Ta encouraged the formation of lava phases in CoCrFeNi-NbX and yourX HEA. In addition, an excess of Nb or Ta alloy additions encouraged the formation of lava phases in CoCrFeNi-NbX and yourX HEA. CoCrFeNi-MoX and WX the alloys showed a solid solution phase BCC and µ phases of tetragonal closed compaction.

In addition, an increase in Ti and Si led to the formation of FCC to FCC + intermetallic complex (IM) to IM phases. In HEAs containing Ti, the negative enthalpy of Ti with Fe, Ni and Cr promotes the formation of intermetallic B2 compounds and phase washed with BCC solid solution phase. In addition, most of the quinary and senar alloys have shown destabilizing behavior.

Conclusion

In this study, researchers developed a honeycomb-shaped container to efficiently synthesize 85 combinatorial alloy compositions from 13 main elements using the HT-HIP-MSA process. Co, Cr, Fe and Ni were the basic elements common to all the compositions.

The idea of ​​these four basic main elements was adopted from the proven studies of the cantor alloy. The different measurements indicated the extended solubility of Mn in the single phase FCC CoCrFeNi-MnX alloys, the destabilizing behavior for most quinary and senary alloys, and the discrete reinforcing behavior in solid solution of the additive elements. It has also demonstrated a very efficient and cost effective synthesis method for the analysis of other HEA systems in the future.

Reference

Zhao, L., Jiang, L., Yang, L., Wang, H., Zhang, W., Ji, G., Zhou, X., Curtin, W., Chen, X., Liaw, P., Chen, S., Wang, H., High throughput synthesis has allowed exploration of high entropy alloys based on CoCrFeNi, Journal of Materials Science and Technology, 2021, ISSN 1005-0302

https://www.sciencedirect.com/science/article/pii/S1005030221009877

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