We have developed computer FEM-models of processes of asymmetrical rolling, asymmetrical cryorolling, asymmetrical accumulating rolling of materials with FCC-, HCP-, and BCC-lattice.
On the basis of computer FEM modeling we have found laws of change of power and force parameters of the asymmetrical rolling process depending of degree of deformation, value of noncoincidence peripheral velocity of rolls, contact friction rate, diameter of working rolls, original thicknesses and widths of sheet raw materials.
It has been shown a feature of power and force parameters of the process of asymmetrical rolling in the severe plastic deformation mode significantly decreases (by a factor of up to 2) of the force of deformation in comparison with standard symmetrical rolling, other conditions being equal. At the same time, rolling momentums increase significantly: by a factor of up to 3 – on a roll rotating with higher velocity and by a factor of up to 2– on a roll rotating with smaller velocity.
We have determined that in case of asymmetrical rolling of heterogeneous layered composites (from the example of FCC aluminum alloys) deformation in the softer of the materials on the interface becomes extremely high (е ≥ 10) while deformation in the harder material remains almost the same (е ≈ 0,8...1,0). Deformation on the interface can provide super-small grains and increased durability of joints of heterogeneous materials metals.
Our researchers have determined laws of formation of heat fields during asymmetrical cryorolling FCC aluminum alloys. We have determined parameters of the technological process that ensure preservation of correct conditions of deformation, technological strategies have been developed for targeted creation of gradient deformation and, accordingly, formation of gradient nanostructures using the asymmetrical thin sheet rolling method with noncoincidence of peripheral velocities working rolls and high contra-directional friction impact in materials with FCC-, HCP- and BCC-lattices.
The Laboratory has developed computer models describing the stress-deformed state of processed materials (Fe, Al, Cu, Ti) during symmetric and asymmetrical rolling or equal channel angular pressing, and torsion under high quasi-hydrostatic pressure. Using FEM modeling we have determined that the scheme of combined simple and pure shear that includes rotational deformation mode and is implemented in asymmetrical rolling is mire efficient in compared to the simple shear scheme implemented in equal channel angular pressing, or the scheme of pure shear implemented in standard (symmetrical) rolling. At optimal parameters of the asymmetrical rolling process true deformation in processed material after one run can reach e ≥ 3…4, which corresponds to 3-4 runs of equal channel angular pressing.
We have developed 2 laboratory methodologies for physical modeling of the asymmetrical rolling process, a method of multi-cycle «compression-shear» deformation of special samples shaped as parallelepipeds with square cross-section and with two parallel cuts on the side surface at an angle of 45 degrees to the vertical axis using the Shimadzu AG-IC 300 kN universal testing machine; a method of physical modeling of the processes of asymmetrical rolling using a specially designed structure of a laboratory device where instead of cylindrical rolls, segments of cylindrical body with individual hydraulic drive and a speed control (frequency converter delta VFD015M21A, 1.5kW 220V).
We obtained testing protocol confirming production of using the method equal channel angular pressing and torsion under high quasi-hydrostatic ultra-fine-grained and nanostructural states in metals with FCC- (aluminum 1050, copper М1), HCP- (titanium ВТ1-0) and BCC- (steel 20) crystalline grid. We have obtained acts of production of samples (aluminum 1050, copper М1, titanium ВТ1-0, steel 20) using the method of equal channel angular pressing, acts of production of samples using the method of torsion under high quasi-hydrostatic (with numbers of full rotations N=1, 2, 4, 8 at room temperature).
Our researchers have shown that torsion under high pressure is more efficient for breakage of structure compared to equal channel angular pressing. Usage of equal channel angular pressing leads to formation of ultra-fine-grained structure with grain size between 100 and 1000 nm while torsion under high quasi-hydrostatic allows to reach grain size between 50 and 200 nm.
It has been demonstrated that evolution of structure of metal in case of standard symmetrical rolling occurs due to band formation which is related to monotonous flow of metal that of characteristic of the scheme with deformation by pure shear.
Using atomistic modeling methods and first-principles computation based on the theory of electron density functional we have found energies of formation and interaction of point defects in the Fe matrix, as well as energy of ordered junctions that are junctions with the four-sublattice model of multi-component solid solution. We have computed possible configurations of point defects and obtained a data array that includes thermodynamic properties (crystalline structure, molar volume, formation enthalpy, and plasticity constants) of the most stable depositing phases induced by deformation in BCC Fe systems under non-equilibrium conditions.
We have conducted first-principle computation of energies of effective cluster interactions in the triple FCC Al-Mg-Mn system. It has been found that the strongest interactions between dissolved elements can be observed when two admixture atoms are close to each other and located in the first and the second coordination spheres. Interactions rapidly decreases with increase of sizes of clusters. Computations of interactions have shown that couples of Mg atoms will be mostly located on the second coordination sphere. This facilitates formation of clusters of Mg atoms in direction <001>.
It has been found that Mn atoms in aluminum matrix are inclined to ordering. Discharges in aluminum systems at early stages form by clusterization of point defects. The discharges remain coherent with the aluminum matrix even being mechanically unstable until they reach threshold critical size.
Our researchers have computed energies of interaction between atoms of Mg and Mn doping elements and vacancies in aluminum matrix. It has been shown that Mg and Mn atoms are bound to vacancies of the first coordination sphere. We demonstrated energy of the bond of the vacancy-Mn complex is significantly higher that in the vacancy-Mg complex. The computer energies of effective cluster interactions allowed to conduct parametrization of free energy of alloys using alloy Hamiltonian and laid the ground to prediction of decay into Al-Mg-Mn. The found energies can be used for conducting atomistic modeling of formation of nanodimensional discharges which allows to understand low of processes of decay at early stages in this system.
We have determined scientifically justified requirements to chemical composition and microstructure of FCC aluminum deformed alloys that ensure possibility of reaching of temporary tensile strength over 500 MPa (at room temperature) and working temperatures of up to 350°С without using the operation of homogenization and quenching. It has been determined that microstructure should meet the following criteria: 1) high volume ratio of reinforcement phases prone to high temperature heating; 2) low diffusional mobility of atoms of doping elements at operational temperatures; 3) high solidus temperature. Objectives of implementation of such structure can are satisfied by the Al-Cu-Mn-Zr(Sс) system. Using the Thermo-Calc program we have determined concentrations of doping components: 1,0-2,5 % Cu, 1,0-2,0 % Mn, 0,2-0,6 % Zr (up to 0,15 % Sc).
Our researchers have shown possibility of full binding of iron and silicon into the Al15(Fe, Mn)3Si2 phase eutectic inclusion of high has favorable morphology. Optimal configurations of these elements have been determined: 0,2-0,5%Fe and 0,2-0,5%Si.
The Laboratory has contributed to development of the «grain boundary engineering» approach to controlling structure of interfaces. During research of structure of samples we have found that with increase of degree of deformation, dislocations localize along boundaries of cells. With increase of deformation mean nonalignment of cells increases forming an ultra-small-grain fragmented structure – harbinger of granular structure. Further deformation leads to activation of rotational deformation modes enduring the settled stage of deformation. Reduction of power of packaging defect leads to changes in deformation organisms when breakage of microstructure is achieved by formation of plus shear. Breakage of structure and grain size distribution is determined by packaging defect energy, in particular, in FCC Al recrystallization begins at relatively low temperatures and therefore in such materials it is hard to obtain an ultra-small-grain structure. Deformational of twinning and dislocation sliding are the two main competing mechanisms of plastic deformation in FCC materials and alloys. Twins are formed either in the process of crystallization or as a result of mechanical or thermal processing. Twins in aluminum aluminum alloys are observed quite rarely due to high energy of packaging defects and thus twins in Al form only only in certain conditions. Molecular dynamic modeling forecasted deformation of twinning and migration of twinning boundaries nanocrystalline Al. Computation of energy of packaging defects is made made within the theory of functional of electron density using the pseudopotential method on the basis of attached waves.
We have shown that temperature correlation of packaging defect energy is significant and it is worth taking into account in modeling plastic deformation. Computation of energy of packaging defects for aluminum alloys was done using the electron density functional theory.
Implemented results of research:
- We have filed 4 patent applications for inventions: «A method of asymmetric cryogenic rolling», «A method of production of thin coils, «A method of production of cold rolled coil», «Motionless deforming element».
- In December 2018 a commercial contract was signed for works in production and delivery of reversing mill DUO for sheet rolling with individual drive for working rolls.
- Our researchers have drafted technical requirement specifications for designing an experimental prototype of an asymmetric rolling mill with individual drives of working rolls that is aimed at implementation of new developed technologies of production of gradient, bimodal, and heterogeneous nanomaterials.
- Our researchers have published 3 scientific articles in journals indexed by the «Web of Science Core Collection» international system and 6 scientific articles in journals indexed by «Scopus».
Education and career development:
- One doctoral dissertations and two candidate dissertations have been defended.
- We have conducted two scientific workshops: one was devoted to the launch of the Laboratory and was held as part of the International Youth Scientific and Practical Conference «Magnitogorsk Rolling Practice 2018»; the other, «Intense plastic deformation of metallic materials» (2018), was held within the Magnitogorsk Week of Materials Science.
Organizational and structural changes:
In 2021, the Laboratory was renamed as the Laboratory for Mechanics of Gradient Nanomaterials named after A. P. Zhilyaev. A unique 400 asymmetric rolling mill that does not have counterparts in Europe and the robotised complex KUKA.
Other results:
We have received grants in the field of scientific research. The grants are supervised by members of the academic staff of the Laboratory.. The topics of the grants are: «Development, theoretical and experimental research of new methods of intense plastic deformation for producing metallic nanostructured sheets of increased durability», «Numerical modeling and development of new hybrid methods of processing of geometrically complex products of super-high durability materials», «Development of the scientific and technological base for producing highly durable ultra-fine-grained aluminum alloys with structures of the composite type».
Collaborations:
- Prof. J/ Szpunar (McGill University, Montreal, Canada), mcgill.ca
- Prof. Amiya Mukherjee (University of California at Davis, CA, USA), ucdavis.edu
- Prof. Maria Dolors Baro (University Autonomy of Barcelona, Bellaterra, Barcelona, Spain), uab.cat
- Prof. Terry McNelley (Naval Postgraduate School, Monterey, CA, USA), nps.edu
- Prof. Oscar Ruano, Dr. Fernando Carreno (Center for Metallurgy (CENIM-CSIC), Madrid, Spain), cenim.csic.es
- Prof. Terence G. Langdon (University of Southampton, Southampton, UK), southampton.ac.uk
- Prof. Jose Maria Cabrera (University Polytechnical of Catalunya, Barcelona, Spain), upc.edu
- Prof. Hailiang Yu (Central South University, Changsha, China), en.csu.edu.cn
- Prof. Puneet Tandon (PDPM Indian Institute of Information Technology, Design and Manufacturing, Jabalpur, India), iiitdmj.ac.in/design.iiitdmj.ac.in
- Prof. Klaus-Dieter Liss (Technion – Israel Institute of Technology), technion.ac.il/en/home-2
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Prof. Megumi Kawasaki (Mechanical, Industrial & Manufacturing Engineering, Oregon State University), oregonstate.edu
