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1. Short-range ordering mechanics in FCC materials

   https://doi.org/10.1016/j.ijplas.2024.103919  

   You, Daegun; Celebi, Orcun Koray; Gengor, Gorkem; Mohammed, Ahmed_Sameer Khan; Abuzaid, Wael; Sehitoglu, Huseyin (March 2024, International Journal of Plasticity)

   NA (Ed.)

   Short-range order (SRO) has a crucial impact on the mechanical strength of metallic alloys. Recent atomistic investigations defined an average SRO and attempted to correlate it with the yield strength. We propose that the local change in SRO upon slip advance must dictate the strengthening, and we elaborate the methodology to establish the “SRO change” on a slip plane considering the Wigner-Seitz cell. The model captures the variation of lattice resistance (Critical Resolved Shear Stress; CRSS) in the crystal as the SRO changes depending on the probability of neighboring atoms. The methodology was applied to Ni-V binary alloys for a wide range of compositions and stacking fault widths. The complex variation of CRSS with compositional variations shows good agreement with limited experimental results. 

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2. Short-range-order degree dominated physical and mechanical properties of refractory multi-principal element alloys: a first-principles study

   https://doi.org/10.1088/1402-4896/ad3a49  

   Yu, Libo; Li, Jia; Liaw, Peter K; Fang, Qihong (May 2024, Physica Scripta)

   Abstract The degree of short-range order (SRO) can influence the physical and mechanical properties of refractory multi-principal element alloys (RMPEAs). Here, the effect of SRO degree on the atomic configuration and properties of the equiatomic TiTaZr RMPEA is investigated using the first-principles calculations. Their key roles on the lattice parameters, binding energy, elastic properties, electronic structure, and stacking fault energy (SFE) are analyzed. The results show the degree of SRO has a significant effect on the physical and mechanical properties of TiTaZr. During the SRO degree increasing in TiTaZr lattice, the low SRO degree exacerbates the lattice distortion and the high SRO degree reduces the lattice distortion. The high degree of SRO improves the binding energy and elastic stiffness of the TiTaZr. By analyzing the change in charge density, this change is caused by the atomic bias generated during the formation of the SRO, which leading to a change in charge-density thereby affecting the metal bond polarity and inter-atomic forces. The high SRO degree also reduces SFE, which means the capability of plastic deformation of the TiTaZr is enhanced. 

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3. Ubiquitous short-range order in multi-principal element alloys

   https://doi.org/10.1038/s41467-024-49606-1  

   Han, Ying; Chen, Hangman; Sun, Yongwen; Liu, Jian; Wei, Shaolou; Xie, Bijun; Zhang, Zhiyu; Zhu, Yingxin; Li, Meng; Yang, Judith; et al (August 2024, Nature Communications)

   Abstract Recent research in multi-principal element alloys (MPEAs) has increasingly focused on the role of short-range order (SRO) on material performance. However, the mechanisms of SRO formation and its precise control remain elusive, limiting the progress of SRO engineering. Here, leveraging advanced additive manufacturing techniques that produce samples with a wide range of cooling rates (up to 10⁷K s⁻¹) and an enhanced semi-quantitative electron microscopy method, we characterize SRO in three CoCrNi-based face-centered-cubic (FCC) MPEAs. Surprisingly, irrespective of the processing and thermal treatment history, all samples exhibit similar levels of SRO. Atomistic simulations reveal that during solidification, prevalent local chemical order arises in the liquid-solid interface (solidification front) even under the extreme cooling rate of 10¹¹K s⁻¹. This phenomenon stems from the swift atomic diffusion in the supercooled liquid, which matches or even surpasses the rate of solidification. Therefore, SRO is an inherent characteristic of most FCC MPEAs, insensitive to variations in cooling rates and even annealing treatments typically available in experiments. 

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4. Multi-scale investigation of short-range order and dislocation glide in MoNbTi and TaNbTi multi-principal element alloys

   https://doi.org/10.1038/s41524-023-01046-z  

   Zheng, Hui; Fey, Lauren T.; Li, Xiang-Guo; Hu, Yong-Jie; Qi, Liang; Chen, Chi; Xu, Shuozhi; Beyerlein, Irene J.; Ong, Shyue Ping (December 2023, npj Computational Materials)

   Abstract Refractory multi-principal element alloys (RMPEAs) are promising materials for high-temperature structural applications. Here, we investigate the role of short-range ordering (SRO) on dislocation glide in the MoNbTi and TaNbTi RMPEAs using a multi-scale modeling approach. Monte carlo/molecular dynamics simulations with a moment tensor potential show that MoNbTi exhibits a much greater degree of SRO than TaNbTi and the local composition has a direct effect on the unstable stacking fault energies (USFEs). From mesoscale phase-field dislocation dynamics simulations, we find that increasing SRO leads to higher mean USFEs and stress required for dislocation glide. The gliding dislocations experience significant hardening due to pinning and depinning caused by random compositional fluctuations, with higher SRO decreasing the degree of USFE dispersion and hence, amount of hardening. Finally, we show how the morphology of an expanding dislocation loop is affected by the applied stress. 

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5. Simultaneously enhancing the ultimate strength and ductility of high-entropy alloys via short-range ordering

   https://doi.org/10.1038/s41467-021-25264-5  

   Chen, Shuai; Aitken, Zachary H.; Pattamatta, Subrahmanyam; Wu, Zhaoxuan; Yu, Zhi Gen; Srolovitz, David J.; Liaw, Peter K.; Zhang, Yong-Wei (December 2021, Nature Communications)

   Abstract Simultaneously enhancing strength and ductility of metals and alloys has been a tremendous challenge. Here, we investigate a CoCuFeNiPd high-entropy alloy (HEA), using a combination of Monte Carlo method, molecular dynamic simulation, and density-functional theory calculation. Our results show that this HEA is energetically favorable to undergo short-range ordering (SRO), and the SRO leads to a pseudo-composite microstructure, which surprisingly enhances both the ultimate strength and ductility. The SRO-induced composite microstructure consists of three categories of clusters: face-center-cubic-preferred (FCCP) clusters, indifferent clusters, and body-center-cubic-preferred (BCCP) clusters, with the indifferent clusters playing the role of the matrix, the FCCP clusters serving as hard fillers to enhance the strength, while the BCCP clusters acting as soft fillers to increase the ductility. Our work highlights the importance of SRO in influencing the mechanical properties of HEAs and presents a fascinating route for designing HEAs to achieve superior mechanical properties. 

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