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1. Rough diamond anvils: Steady microstructure, yield surface, and transformation kinetics in Zr

   Lin, Feng ; Levitas, Valery I. ; Pandey, K. K. ; Yesudhas, Sorb ; Park, Changyong. ( August 2022 , ArXivorg)

   Study of the plastic flow and strain-induced phase transformations (PTs) under high pressure with diamond anvils is important for material and geophysics. We introduce rough diamond anvils and apply them to Zr, which drastically change the plastic flow, microstructure, and PTs. Multiple steady microstructures independent of pressure, plastic strain, and strain path are reached. Maximum friction equal to the yield strength in shear is achieved. This allows determination of the pressure-dependence of the yield strength and proves that ω-Zr behaves like perfectly plastic, isotropic, and strain path-independent immediately after PT. Record minimum pressure for α-ω PT was identified. Kinetics of strain-induced PT depends on plastic strain and time. Crystallite size and dislocation density in ω-Zr during PT depend solely on the volume fraction of ω-Zr. 

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2. Rough diamond anvils: Steady microstructure, yield surface, and transformation kinetics in Zr

   Lin, Feng ; Levitas, Valery ; Pandey, Krishan ; Yesudhas, Sorb ; Park, Changyong ( August 2022 , arXivorg)

   Study of the plastic flow and strain-induced phase transformations (PTs) under high pressure with diamond anvils is important for material and geophysics. We introduce rough diamond anvils and apply them to Zr, which drastically change the plastic flow, microstructure, and PTs. Multiple steady microstructures independent of pressure, plastic strain, and strain path are reached. Maximum friction equal to the yield strength in shear is achieved. This allows determination of the pressure-dependence of the yield strength and proves that omega-Zr behaves like perfectly plastic, isotropic, and strain path-independent immediately after PT. Record minimum pressure for alpha-omega PT was identified. Kinetics of strain-induced PT depends on plastic strain and time. Crystallite size and dislocation density in omega-Zr during PT depend solely on the volume fraction of omega-Zr. 

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3. Rules of plastic strain-induced phase transformations and nanostructure evolution under high-pressure and severe plastic flow.

   Lin, Feng ; Levitas, Valery I. ; Pandey, K.K. ; Yesudhas, Sorb ; Park, C ( May 2023 , arXivorg)

   Severe plastic deformations under high pressure are used to produce nanostructured materials but were studied ex-situ. We introduce rough diamond anvils to reach maximum friction equal to yield strength in shear and perform the first in-situ study of the evolution of the pressure-dependent yield strength and nanostructural parameters for severely pre-deformed Zr. ω-Zr behaves like perfectly plastic, isotropic, and strain-path-independent. This is related to reaching steady values of the crystallite size and dislocation density, which are pressure-, strain- and strain-path-independent. However, steady states for α-Zr obtained with smooth and rough anvils are different, which causes major challenge in plasticity theory. 

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4. In-situ study of rules of nanostructure evolution, severe plastic deformations, and friction under high pressure

   https://doi.org/10.1080/21663831.2023.2231983  

   Lin, Feng ; Levitas, Valery I. ; Pandey, Krishan K. ; Yesudhas, Sorb ; Park, Changyong ( September 2023 , Materials Research Letters)

   Severe plastic deformations under high pressure are used to produce nanostructured materials but were studied ex-situ. Rough diamond anvils are introduced to reach maximum friction equal to yield strength in shear and the first in-situ study of the evolution of the pressure-dependent yield strength and radial distribution of nano structural parameters are performed for severely pre-deformed Zr.ω-Zr behaves like perfectly plastic, isotropic, and strain-path-independent and reaches steady values of the crystallite size and dislocation density, which are pressure-, strain- and strain-path-independent. However, steady states forα-Zr obtained with smooth and rough anvils are different, causing major challenge in plasticity theory. 

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5. Tensorial stress-plastic strain fields in α - ω Zr mixture, transformation kinetics, and friction in diamond-anvil cell

   https://doi.org/10.1038/s41467-023-41680-1  

   Levitas, Valery I. ; Dhar, Achyut ; Pandey, K. K. ( September 2023 , Nature Communications)

   Various phenomena (phase transformations (PTs), chemical reactions, microstructure evolution, strength, and friction) under high pressures in diamond-anvil cell are strongly affected by fields of stress and plastic strain tensors. However, they could not be measured. Here, we suggest coupled experimental-analytical-computational approaches utilizing synchrotron X-ray diffraction, to solve an inverse problem and find fields of all components of stress and plastic strain tensors and friction rules before, during, and after α-ω PT in strongly plastically predeformed Zr. Results are in good correspondence with each other and experiments. Due to advanced characterization, the minimum pressure for the strain-induced α-ω PT is changed from 1.36 to 2.7 GPa. It is independent of the plastic strain before PT and compression-shear path. The theoretically predicted plastic strain-controlled kinetic equation is verified and quantified. Obtained results open opportunities for developing quantitative high-pressure/stress science, including mechanochemistry, synthesis of new nanostructured materials, geophysics, astrogeology, and tribology.

    

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