Insights into the microstructure of K-state inhomogeneous solid solutions

YM Li and LW Qin and DC Mao and WT Liu and HJ Liu and Z Tian and ZD Li and WK Le, JOURNAL OF ALLOYS AND COMPOUNDS, 1043, 183890 (2025).

DOI: 10.1016/j.jallcom.2025.183890

The K-state, commonly present in multi-transition-metal alloys, significantly influences their physical and mechanical properties due to its complex microstructure. Although generally regarded as an inhomogeneous solid solution, its precise structural characterization remains challenging. In this study, molecular dynamics (MD) simulations were employed to investigate microstructural evolution during the preparation of NiCrAlFe precision resistance alloy. The microstructure of the K-state was further analyzed using Largest Standard Cluster Analysis (LaSCA) and transmission electron microscopy (TEM). The results demonstrate that during tempering, the fraction of face-centered cubic (FCC) atoms increases with temperature, while the number of hexagonal closepacked (HCP) atoms (mainly composed of twinning structures) decreases due to their transformation into FCC. This HCP-to-FCC transition leads to the formation of energetically stable double hexagonal close-packed (DHCP) structures, which consist of L12 short- range ordering (L12-SRO) and associated stacking faults. Notably, a strong correlation was observed between the temperature-dependent evolution of DHCP structure and the variation in the electrical resistivity of the alloy. Additionally, the population of topologically close-packed (TCP) atoms decreases during tempering, forming a continuous three-dimensional skeleton that characterizes the K-state. It is revealed that the microstructure of the K-state comprises nanoscale L12-SRO and DHCP precipitates dispersed within the FCC matrix, accompanied by the TCP-based skeleton. Both types of precipitates maintain semi-coherent interfaces with the matrix and are surrounded by dense edge dislocation networks, which are identified as key factors governing the properties of K-state alloys. This study provides a theoretical foundation for the design and performance enhancement of K-state alloys.

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