Dynamic Channel Angular Pressing Research Articles

Evolution of the structure upon heating of submicrocrystalline and nanocrystalline copper produced by high-rate deformation

Methods of electron microscopy, dilatometry, and microhardness and resistivity measurements have been used to study the effect of annealing on the process of recrystallization of a mixed submicrocrys-talline+nanocrystalline (SMC+NC) structure of 99.8% copper produced by high-rate (∼105 s−1) deformation using dynamic channel angular pressing (DCAP). It has been shown that the SMC+NC structure of copper is thermally stable upon heating to a temperature of 150°C. It has been found that the ρ/ρ0 ratio of copper with an SMC+NC structure at a temperature of 4.2 K is considerably (by 5 times) higher than ρ/ρ0 of copper in the annealed coarse-grained state. This effect is due to a high concentration of defects and a high degree of dispersity of the copper structure after DCAP. Changes in the microhardness and in the resistivity (at a temperature of 4.2 K) of the SMC+NC copper after annealing characterize the level of relaxation processes.

Structure of titanium subjected to dynamic channel-angular pressing in copper shells

It has been established using metallography and electron microscopy that the dynamic channel-angular pressing of titanium in cylindrical copper shells of a sufficient thickness removes the effects of localized deformation in the form of cracks and adiabatic shear bands, which were observed upon deformation without shells. This mode of deformation is effected via the formation of numerous twins; as a result, the initial grains become divided into small regions. Together with twins of ordinary morphology in the form of plates, there are observed wavy bent “noncrystallographic” twins, whose appearance is caused by the rotational deformation modes. Twins in the form of rods have been revealed, which sometimes are grouped into lamellar packets arranged perpendicularly to the longitudinal axis of the sample. The formation of numerous twins in titanium during dynamic channel-angular pressing leads to an increase in the microhardness by 15–35%. Twinning can be used to increase the strength characteristics of titanium, additionally to the creation of nanocrystalline and submicrocrystalline structures.

Dispersion of the Structure in Al-Based Alloys by Different Methods of Severe Plastic Deformation

Structural and phase transformations in V95 (type of A7075) alloy upon high pressure torsion (HPT) up to high strain and upon dynamic channel angular pressing (DCAP) were studied using electron microscopy (TEM, SEM) and x-rays diffraction. It was established that the nanostructure with average grain size of 80-55 nm and hardness value of 2.5 GPa is formed by HPT at strain of e=5.5-6.4. It was shown the hardening metastable phase MgZn2 precipitates from supersaturated α-solid solution during dynamic deformation aging; its quantity grows with increasing of strain. Ultra fine grained structure with high- angle boundaries is formed in V95 alloy after already 2 cycles of DCAP. The average grain size is 200 nm in DCAP samples.

High-speed deformation of metallic materials using channel angular pressing for producing an ultrafine-grained structure

The possibility of producing an ultrafine-grained structure of metals and alloys by dynamic channel angular pressing is discussed using titanium, copper, and aluminum-based alloys as an example. It is established that even one-pass deformation allows one to produce a submicrocrystalline structure with a grain size of 30–350 nm and to enhance the strength properties at a high retained plasticity.

Structure of titanium after dynamic channel angular pressing at elevated temperatures

Dynamic channel-angular pressing of titanium at a temperature of 500°C has been performed. An increase in the temperature prevented the formation of cracks and adiabatic-shear bands that usually occur upon pressing at room temperature. As a result of dynamic pressing of titanium at 500°C, there is obtained a structure which represents a dispersed mixture of fine recrystallized grains and unrecrystallized regions (duplex structure). The formation of recrystallized grains is caused by a local increase in the temperature in the sites of deformation localization and is a mechanism of relaxation of accumulated stresses. The recrystallized grains are grouped into inclined extended shear bands (large-scale relaxation) and into short bent chain of clusters, which are located between inclined bands (small-scale stress relaxation). The unrecrystallized regions consist predominantly of elongated subgrains formed as a result of deformation and dynamic polygonization. The microhardness of titanium in the recrystallized regions is equal to 1980 MPa, that in unrecrystallized regions, to 2150 MPa.

Formation of a submicrocrystalline structure upon dynamic deformation of aluminum alloys

Light and electron microscopy and X-ray diffraction were used to study the microstructure and phase composition of the bulk samples of the multicomponent Al-based alloys (Al-3003 and Al-5556) produced by the method of dynamic channel angular pressing (DCAP). The relation between the geometry of channels, pressure in the sample, high rate mode of loading, and specific features of the microstructure arising in metal under investigation are stated. It was established that even after one DCAP pass, material hardening occurred and the grain size radically decreased to less than 0.5 μm. The microhardness increased from the initial value by a factor of 1.5–2. It was discovered that the structure becomes fragmented and consists of grains with a developed substructure and displays a high density of dislocations after one pass. With increasing number of passes, the fraction of the grains separated by high-angle grain boundaries increases and the density of dislocations decreases.