More Like this

1. Composition-driven nanotwin engineering in sputtered Ni-Fe and Ni-Cr films: linking fault energetics to twin thickness

   https://doi.org/10.1016/j.actamat.2025.121890  

   Yazdani, Mohammad Hadi; Liang, Aoyan; Maldonado_Otero, Ashley J; Liu, Yi; Farkas, Diana; Hodge, Andrea M; Rupert, Timothy J; Beyerlein, Irene J; Branicio, Paulo S (January 2026, Acta Materialia)

   In this study, molecular dynamics (MD) simulations are combined with magnetron co-sputtering experiments to examine how Ni-Fe and Ni-Cr compositions affect defect energetics and twin microstructure in thin films. These simulations represent the first direct modeling of nanotwin formation during atomistic deposition. Ensemble MD simulations reveal substantial stochastic variability in grain structure and twin development across deposition runs, yet clear compositional trends emerge. Cr-rich Ni-Cr alloys form dense twin networks with narrow spacing, while Fe-rich Ni-Fe alloys exhibit fewer twins with significantly larger spacing. Scanning transmission electron microscopy (STEM) of Ni-Cr films confirms the predicted high twin density and reduced spacing, validating the link between alloy composition and growth twin formation. Notably, both simulations and experiments reveal that the distribution of twin boundary spacings is log-normal, reflecting the stochastic nature of twin nucleation during deposition. Composition-dependent maps from MD simulations further demonstrate that small variations in Ni-Cr and Ni-Fe chemistry can systematically tune twin boundary formation and enable the design of nanoscale twin architectures. This integrated computational-experimental study establishes a clear inverse relationship between stacking fault energy and average twin spacing, offering a pathway for engineering nanostructured coatings with tailored twin networks and enhanced properties. 

   more » « less
2. Elemental partitioning and corrosion resistance of Ni–Cr alloys revealed by accurate ab-initio thermodynamic and electrochemical calculations

   https://doi.org/10.1038/s41529-023-00414-w  

   Huang, Liang-Feng; Xie, Yusi; Sieradzki, Karl; Rondinelli, James M (December 2023, npj Materials Degradation)

   Elemental partitioning during thermal processing can significantly affect the corrosion resistance of bulk alloys operating in aggressive electrochemical environments, for which, despite decades of experimental and theoretical studies, the thermodynamic and electrochemical mechanisms still lack accurate quantitative descriptions. Here, we formulate an ab initio thermodynamic model to obtain the composition- and temperature-dependent free energies of formation (Δ_fG) for Ni–Cr alloys, a prototypical group of corrosion-resistant metals, and discover two equilibrium states that produce the driving forces for the elemental partitioning in Ni–Cr. The results are in quantitative agreement with the experimental studies on the thermodynamic stability of Ni–Cr. We further construct electrochemical (potential–pH) diagrams by obtaining the required Δ_fGvalues of native oxides and (oxy)hydroxides using high-fidelity ab-initio calculations that include exact electronic exchange and phononic contributions. We then analyze the passivation and electrochemical trends of Ni–Cr alloys, which closely explain various oxide-film growth and corrosion behaviors observed on alloy surfaces. We finally determine the optimal Cr content range of 14–34 at%, which provides the Ni–Cr alloys with both the preferred heat-treatment stability and superior corrosion resistance. We conclude by discussing the consequences of these findings on other Ni–Cr alloys with more complex additives, which can guide the further optimization of industrial Ni–Cr-based alloys. 

   more » « less
3. Experimental investigation of the effect of nickel on the electrical resistivity of Fe-Ni and Fe-Ni-S alloys under pressure

   https://doi.org/10.2138/am-2020-7301  

   Pommier, Anne (July 2020, American Mineralogist)

   Abstract Electrical resistivity experiments were conducted on three alloys in the iron-rich side of the Fe-Ni(-S) system (Fe-5 wt% Ni, Fe-10 wt% Ni, Fe-10 wt% Ni-5 wt% S) at 4.5 and 8 GPa and up to 1900 K using the multi-anvil apparatus and the 4-electrode technique. For all samples, increasing temperature increases resistivity. At a specified temperature, Fe-Ni(-S) alloys are more resistive than Fe by a factor of about 3. Fe-Ni alloys containing 5 and 10 wt% Ni present comparable electrical resistivity values. The resistivity of Fe-Ni(-S) alloys is comparable to the one of Fe = 5 wt% S at 4.5 GPa and is about three times higher than the resistivity of Fe = 5 wt% S at 8 GPa, due to a different pressure dependence of electrical resistivity between Fe-Ni and Fe-S alloys. Based on these electrical results and experimentally determined thermal conductivity values from the literature, lower and upper bounds of thermal conductivity were calculated. For all Ni-bearing alloys, thermal conductivity estimates range between ~12 and 20 W/(m⋅K) over the considered pressure and temperature ranges. Adiabatic heat fluxes were computed for both Ganymede's core and the Lunar core, and heat flux values suggest a significant dependence to both core composition and the adiabatic temperature. Comparison with previous thermochemical models of the cores of Ganymede and the Moon suggests that some studies may have overestimated the thermal conductivity and hence, the heat flux along the adiabat in these planetary cores. 

   more » « less
4. Influence of In Situ and Ex Situ Heat Treatments on the Mechanical Behavior of LPBF-Fabricated Fe–Mn–Al–Ni Shape Memory Alloys

   https://doi.org/10.1007/s40830-025-00544-x  

   Algamal, Anwar; Gandhi, Umesh; Qattawi, Ala (June 2025, Shape Memory and Superelasticity)

   Abstract This study investigates the fabrication of Fe–Mn–Al–Ni iron-based shape memory alloys (SMAs) using laser powder bed fusion (LPBF) across a range of laser powers. The influence of energy input on material properties was assessed by evaluating the resulting volumetric energy density. Samples were produced under both as-built conditions and subjected to in situ and ex situ treatments to enhance performance. Mechanical properties were characterized through macro-indentation, Profilometry-based Indentation Plastometry (PIP), and nanoindentation techniques, while room-temperature compression testing was conducted to assess superelastic behavior. Microstructural and phase variations were analyzed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that increasing the fabrication power improved the mechanical properties of the as-built SMAs, with the optimal performance achieved at 175 W. In situ/ex situ treatments led to a significant reduction in strength but enhanced ductility by up to 39%, along with a 52% reduction in microhardness for samples fabricated at 175 W. Overall, the LPBF-produced Fe–Mn–Al–Ni SMAs exhibited good strain recovery and stability, comparable to those produced by conventional methods. This work demonstrates the potential of LPBF in developing Fe–Mn–Al–Ni SMAs with properties matching traditionally manufactured counterparts. Graphical Abstract Mechanical behavior and microstructural features of LPBF-fabricated Fe–Mn–Al–Ni SMA under the effects of in situ and ex situ treatments 

   more » « less
5. Magnetization–structure–composition phase diagram mapping in Co-Fe-Ni alloys using diffusion multiples and scanning Hall probe microscopy

   https://doi.org/10.1038/s41598-022-05121-1  

   Shamsutdinov, Girfan; Zhao, Peng; Bhattiprolu, Sreenivas; Zhao, Ji-Cheng; Nadgorny, Boris (December 2022, Scientific Reports)

   Abstract Transition metal alloys are essential for magnetic recording, memory, and new materials-by-design applications. Saturation magnetization in these alloys have previously been measured by conventional techniques, for a limited number of samples with discrete compositions, a laborious and time-consuming effort. Here, we propose a method to construct complete saturation magnetization diagrams for Co–Fe–Ni alloys using scanning Hall probe microscopy (SHPM). A composition gradient was created by the diffusion multiple technique, generating a full combinatorial materials library with an identical thermal history. The composition and crystallographic phases of the alloys were identified by integrated energy dispersive X-ray spectroscopy and electron backscatter diffraction. “Pixel-by-pixel” perpendicular components of the magnetic field were converted into maps of saturation magnetization using the inversion matrix technique. The saturation magnetization dependence for the binary alloys was consistent with the Slater-Pauling behavior. By using a significantly denser data point distribution than previously available, the maximum of the Slater-Pauling curve for the Co–Fe alloys was identified at ~ 32 at% of Co. By mapping the entire ternary diagram of Co–Fe–Ni alloys recorded in a single experiment, we have demonstrated that SHPM—in concert with the combinatorial approach—is a powerful high-throughput characterization tool, providing an effective metrology platform to advance the search for new magnetic materials. 

   more » « less