V. N. Serebryany

Influence of alloying with hafnium on the microstructure, texture, and properties of Cu–Cr alloy after equal channel angular pressing

AbstractEqual channel angular pressing (ECAP) results in grain refinement of the Cu–0.7xa0% Cr alloy with an average grain size of 320xa0±xa073xa0nm. Addition of hafnium leads to a further decrease of average grain size down to 225xa0±xa082xa0nm and to an increase of the fraction of high angle boundaries from 40 to 53xa0%. The microhardness of the Cu–0.7xa0% Cr–0.9xa0% Hf alloy is higher than that of the Cu–0.7xa0% Cr alloy in the quenched state, after ECAP followed by annealing in the temperature interval of 400–550xa0°C during which aging occurs. Compared with the quenched state, ECAP increases the tensile strength of the Cu–0.7xa0% Cr and Cu–0.7xa0% Cr–0.9xa0% Hf alloy by a factor of 2.3 and 2.2, respectively. Aging leads to additional strengthening. Compared with the Cu–0.7xa0% Cr alloy, the strength of the Cu–0.7xa0% Cr–0.9xa0% Hf alloy after ECAP and after subsequent aging is 1.3 and 1.5 times higher, respectively.n

Texture and structure contribution to low-temperature plasticity enhancement of Mg-Al-Zn-Mn Alloy MA2-1hp after ECAP and annealing

Equal channel angular pressing (ECAP) in magnesium alloys due to severe plastic shear deformations provides both grain refinement and the slope of the initial basal texture at 40°–50° to the pressing direction. These changes in microstructure and texture contribute to the improvement of low-temperature plasticity of the alloys. Quantitative texture X-ray diffraction analysis and diffraction of backscattered electrons are used to study the main textural and structural factors responsible for enhanced low-temperature plasticity based on the example of magnesium alloy MA2-1hp of the Mg-Al-Zn-Mn system. The possible mechanisms of deformation that lead to this positive effect are discussed.

The Role of Structure and Texture Factors in the Ductility and Deformability Improving of Magnesium Alloys Subjected to ECAP

Equal channel angular pressing (ECAP) in magnesium alloys due to the severe plastic shear deformations provides both grain refinement and the slope of the initial basal texture at 40-50 ° to the pressing direction. Such changes in microstructure and texture contribute to the improvement of low-temperature ductility and deformability of the alloys. On the basis of analysis of data from various researchers, the main structure and texture factors affecting on the ductility increase of the Mg-Al-Zn-Mn alloys were defined.

Effect of equal-channel angular pressing and annealing conditions on the texture, microstructure, and deformability of an MA2-1 alloy

Equal-channel angular pressing (ECAP) of am MA2-1 alloy according to routes A and Bc is used to study the possibility of increasing the low-temperature deformability of the alloy due to grain refinement and a change in its texture. To separate the grain refinement effect from the effect of texture on the deformability of the alloy, samples after ECAP are subjected to recrystallization annealing that provides grain growth to the grain size characteristic of the initial state (IS) of the alloy. Upon ECAP, the average grain size is found to decrease to 2–2.4 μm and the initial sharp axial texture changes substantially (it decomposes into several scattered orientations). The type of orientations and the degree of their scattering depend on the type of ECAP routes. The detected change in the texture is accompanied by an increase in the deformability parameters (normal plastic anisotropy coefficient R, strain-hardening exponent n, relative uniform elongation δu) determined upon tensile tests at 20°C for the states of the alloy formed in the IS-4A-4Bc and IS-4Ao-4BcO sequences. The experimental values of R agree with the values calculated in terms of the Taylor model of plastic deformation in the Bishop-Hill approximation using quantitative texture data in the form of orientation distribution function coefficients with allowance for the activation of prismatic slip, especially for ECAP routes 4Bc and 4BcO. When the simulation results, the Hall-Petch relation, and the generalized Schmid factors are taken into account, a correlation is detected between the deformability parameter, the Hall-Petch coefficient, and the ratio of the critical shear stresses on prismatic and basal planes.

Structure and Properties of Cu Alloys Alloying with Cr and Hf after Equal Channel Angular Pressing

Equal channel angular pressing (ECAP) results in grain-subgrain structure formation in Cu0.75 %Cr alloy with the average size of structure elements of 320 ± 73 nm Addition of hafnium into the Cu-Cr alloy leads to decrease of average size down to 225±82 nm and to increase of the high angle boundaries fraction from 40% to 53%. Microhardness of the Cu-0.7 %Cr-0.9 %Hf alloy is higher, than of the Cu-0.75 %Cr alloy, as after ECAP, so after heating when the aging processes occur in the temperature interval 400–550 °С. The strength in the tension tests of the Cu-0.7 %Cr-0.9 %Hf alloy after ECAP rises in 2.2 times compared with the quenched state. The aging leads to additional strength growth by 19%.

Fatigue strength of a magnesium MA2-1 alloy after equal-channel angular pressing

The fatigue strength of a magnesium MA2-1 alloy is studied after annealing and equal-channel angular pressing (ECAP). The ultrafine-grained structure formed upon ECAP is shown to increase the plasticity of the material during static tension, to decrease the cyclic life to failure, and not to decrease the fatigue limit. The mechanisms of crack nucleation and growth during cyclic deformation are investigated.

Structure, texture, and mechanical properties of an MA2-1hp magnesium alloy after two-stage equal-channel angular pressing and intermediate annealing

The effect of two-stage equal-channel angular pressing (ECAP) on the microstructure, the texture, and the mechanical properties of an MA2-1hp magnesium alloy is analyzed. ECAP leads to the formation of a submicrocrystalline structure with an average grain size of 640 nm, which includes Mg17Al12 phase particles with an average grain size of 240 nm and a volume fracture of 5.5%. A scattered tilted basal texture forms after ECAP, and its experimental pole figures are used for calculating orientation distribution functions and determining the volume fractions of the main orientations and the Schmid factors for different deformation systems. An increased activation of basal slip is found after both the first and the second stages of ECAP. As a result of two-stage ECAP, the strength properties of the alloy that correspond to the minimum acceptable values achieved by direct compression are obtained. Ductility is 44 and 18% after the first stage of ECAP plus subsequent annealing and after the second stage, respectively, which is almost four and two times higher than the initial value. The resulting strength mechanical properties of the alloy after the first and the second ECAP stages are analyzed using the Hall-Petch relation.

Evaluation of the normal anisotropy coefficient in AZ31 alloy sheets

The Taylor-Bishop-Hill model of plastic deformation is used to determine the dependence of normal anisotropy coefficient R on angle α in the sheet plane (α = 0 in the rolling direction) from texture in the form of the coefficients of expansion of an orientation distribution function into a series in generalized spherical functions for AZ31 magnesium alloy sheets. The calculated values of R(α) are compared to the experimental values obtained during tensile tests under normal conditions (20°C) and at 180°C.

Pole Figure Measurement Plan Influence on Accuracy ODF Coefficients Determined by Modified Harmonic Method

Influences of an X-ray experimental texture plan and of pole figure primary errors on the accuracy of the ODF coefficients are discussed. A modified harmonic method, which is a statistical method of ridge estimates, has been used for ODF restitution from pole figures. The plan of measurement of the pole figures was analysed on the basis of minimization of the primary experimental errors and the errors of the ODF restitution method. Principles of the optimum texture plan construction for hexagonal metals (magnesium example) and for the URD-6 texture diffractometer are considered.

Investigation of Texture Structure and Mechanical Properties Evolution during Hot Deformation of 1565 Aluminum Alloy

The article is devoted to study of mechanical properties and texture evolution during thermal mechanical treatment of new aluminum 5XXX series alloy (1565 ch in Russian naming system). For the investigation of deformation behavior of 1565ch alloy a Gleeble axial compression mode is used. The expression for steady flow stress as the functions of temperature of deformation and strain rate is obtained. For texture evolution investigation industrial mills is used. Texture evaluation is performed using the orientation distribution function (ODF) calculated from the X-ray direct pole figures