Dynamic strength properties of the surface of an ultra-fine-grained aluminum alloy under conditions of high-speed erosion

The influence of severe plastic deformation on the material surface is investigated under highspeed erosion conditions. The AD1 aluminum alloy was tested with the structure changed by severe plastic torsional deformation.     

Effect of the wetting of grain boundaries on the formation of a solid solution in the Al-Zn system

Phase transitions in the bulk and at grain boundaries in the (Al-20 wt % Zn) alloy have been studied by means of differential scanning calorimetry and transmission electron microscopy. Polycrystals with a high specific area of grain boundaries have been obtained using severe plastic deformation (high-pressure torsion). It has been shown that the Zn-based solid phase completely wets the grain boundaries in aluminum at a temperature of 200°C. The position of the grain boundary solvus line (solubility line), which is above the bulk solvus by 40?C45 K, has been determined.     

Structure,mechanical characteristics,and deformation and fracture features of quenched structural steel under static and cyclic loading after combined strain-heat nanostructuring treatment

In the work, we studied the special features of deformation and fracture of quenched steel 50 (0.51%) under static and cyclic tension after combined strain-heat nanostructuring treatment, which includes fictional treatment with subsequent tempering at 350°C. It is shown that the combined nanostructuring treatment of quenched steel 50 changes the character of plastic flow, making it more uniform, in the loaded material. Under static tension, this shows up as disappearance of the yield plateau early in the process, and under cyclic loading, as suppression of the deformation relief formed by shear and rotational deformation modes. Despite incipient cracks, the hardened surface layer thus escapes complete fracture throughout the fatigue loading and preserves its resistance to mechanical contact action.     

Study of the heat treatment influence on the formation of nanostructured state in bulk titanium nickelide alloys subjected to severe plastic deformation

The influence of annealing on bulk samples of Ti_49.4Ni_50.6 alloy subjected to severe plastic deformation by torsion under high pressure has been studied by transmission electron microscopy and X-ray diffractometry. It is found that a homogeneous nanocrystalline state is formed in the bulk samples after annealing.     

The role of curvature of the crystal structure in the formation of micropores and crack development under fatigue fracture of commercial titanium

The multiscale mechanism of fatigue fracture of titanium with the surface layer hydrogenated under alternating bending at room temperature is studied. It is shown that the generation of the fatigue fracture occurs in the surface layer subjected to plastic deformation in conjunction with an elastically loaded substrate. The latter causes the appearance of a strong curvature of the material and the appearance of micropores in these areas along with any fatigue cracks. The emergence of the local curvature of the crystal structure plays a central role in the origin and the development of the fatigue fracture as the structural phase decomposition of the material under cyclic loading.     

Amorphization of bulk TiNi-based alloys by severe plastic deformation under high pressure torsion

The structure of bulk samples of Ti_49.4Ni_50.6 alloy after severe plastic deformation by torsion (SPDT) under high pressure have been studied by transmission and scanning electron microscopies. It is found that SPDT by five to seven turns led to almost complete alloy amorphization.     

Resistance to dynamic deformation and fracture of tantalum with different grain and defect structures

This paper presents the results of measurements of the strength properties of technically pure tantalum under shock wave loading. It has been found that a decrease in the grain size under severe plastic deformation leads to an increase in the hardness of the material by approximately 25%, but the experimentally measured values of the dynamic yield stress for the fine-grained material prove to be less than those of the initial coarse-grained specimens. This effect has been explained by a higher rate of stress relaxation in the fine-grained material. The hardening of tantalum under shock wave loading at a pressure in the range 40–100 GPa leads to a further increase in the rate of stress relaxation, a decrease in the dynamic yield stress, and the disappearance of the difference between its values for the coarse-grained and fine-grained materials. The spall strength of tantalum increases by approximately 5% with a decrease in the grain size and remains unchanged after the shock wave loading. The maximum fracture stresses are observed in tantalum single crystals.     

High strength and high ductility behavior of 6061-T6 alloy after laser shock processing

The plastic deformation behavior of 6061-T6 alloy which was subjected to severe plastic deformation (SPD) at high strain rates during laser shock processing (LSP) was researched. In LSP-treated materials, the near surface microstructural change was examined by TEM and fracture surfaces after tensile testing were examined by SEM. An increase in strength of metallic materials brings about the decrease in ductility. In this study, the results showed that LSP-treated 6061-T6 alloy exhibited both high strength and high ductility. TEM observation showed that stacking fault (SF) ribbon enlarged, deformation twins formed and twin boundary increased in LSP-treated 6061-T6 alloy. This observation was an indication of stacking fault energy (SFE) decrease. Work hardening capability was recovered after LSP impacts.     

Experimental and numerical analysis of the high-speed deformation and erosion damage of the titanium alloy VT-6

The temporal characteristics of the dynamic fracture of the titanium alloy VT-6 have been investigated under high-speed loading conditions. A relationship has been established between the process of dynamic tension of the specimen according to the Kolsky method and the surface erosion damage. A numerical analysis of the experimental data has been carried out. The method of erosion loading has been further developed as a tool for the dynamic testing of strength properties of materials.     

Crystallization Features of Rapidly Quenched Ti50Ni20Cu30 Amorphous Alloys after High-Pressure Torsion

Physics of the Solid State - The effect of severe plastic deformation under high-pressure torsion (HPT) on the structural properties of rapidly quenched alloys belonging to the quasi-binary...     

Formation of nanostructured states in ternary TiNiFe-based shape memory alloys during megaplastic deformation and subsequent heat treatment

The ternary metastable TiNiFe alloys that exhibit a low-temperature shape memory effect and are subjected to plastic deformation by rolling or high-pressure torsion followed by heat treatment are studied by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and electrical resistivity measurements. It is found that moderate plastic deformation of a Ti₅₀Ni₄₉Fe₁ alloy at room temperature initiates the thermoelastic B2 ? B19’ martensitic transformation and the formation of a developed banded dislocation and twin substructure in the B19’ martensite. This deformation of a Ti₅₀Ni₄₇Fe₃ alloy forms a similar dislocation substructure but in B2 austenite. Megaplastic deformation by high-pressure torsion causes amorphization in the Ti₅₀Ni₄₉Fe₁ alloy and nanofragmentation in the Ti₅₀Ni₄₇Fe₃ alloy. The evolution of the nanostructure and the martensitic transformations in TiNiFe-based ternary alloys is studied during plastic deformation and subsequent annealing at various temperatures.     

Micromechanisms of deformation and fracture in a VT6 titanium laminate under impact load

The paper studies the phase composition, microstructure, and mechanisms of plastic deformation and fracture under impact load in a laminate obtained by pressure welding of VT6 titanium alloy sheets. Under impact loading at 20 and -196°C, the material is delaminated into sheet piles with attendant changes in their fracture rate. At fracture surfaces, the initial crystal structure experiences structural phase decomposition which results in dynamic rotations. In fracture and delamination sublayers, the material is fragmented. The effects are more pronounced at T _def = -196°C.     

Influence of plastic deformation on fracture of an aluminum single crystal under shock-wave loading

The plastic deformation and the onset of fracture of single-crystal metals under shock-wave loading have been studied using aluminum as an example by the molecular dynamics method. The mechanisms of plastic deformation under compression in a shock wave and under tension in rarefaction waves have been investigated. The influence of the defect structure formed in the compression wave on the spall strength and the fracture mechanism has been analyzed. The dependence of the spall strength on the strain rate has been obtained.     

Microstructural evolution of nickel under high-pressure torsion

The evolution peculiarities of grain and defect structures in nickel under high-pressure torsion were studied by transmission electron microscopy and X-ray diffraction analysis. Lattice reorientation mechanisms characteristic of different stages of plastic deformation were disclosed. The conditions and features of cooperative realization of various structure formation mechanisms under severe deformation were discussed.     

Deformation chaos and self-organization at the prefracture stage of 5556 alloy

Based on the analysis of the data of high-speed video recording of the surface of the deformed aluminum-magnesium alloy 5556, it has been found that the unstable plastic deformation associated with the deformation band dynamics tends to deformation chaos with increasing deformation. It has been shown that the ductile fracture of the 5556 alloy with a recrystallized structure should be considered as a global self-organization in a nonlinear nonequilibrium system being in the state of deterministic chaos.     

Interaction of the structural and magnetic subsystems in crystals upon severe plastic deformation by torsion

Interaction between the structural and magnetic subsystems of a crystal has been studied near phase transition lines. The consideration has been performed in terms of the Landau phenomenological theory. It has been shown that severe plastic deformation by torsion leads to a forced formation of a heterogeneous distribution in the magnetic subsystem. A nonsine space modulation of the magnitudes of the magnetic and structural parameters appears near the lines of the magnetic and structural phase transitions. An analysis of the obtained dependences has demonstrated a possibility of designing various distributions of the ferromagnetic vector in crystals under action of severe plastic deformation by torsion.     

Effect of plastic deformation on physical properties and structure of the shape memory alloy Ti<Subscript>49.5</Subscript>Ni<Subscript>50.5</Subscript>

The effect of severe plastic deformation by torsion (SPDT) in Bridgman anvils at a high pressure (6 GPa) on the physical properties and crystal structure of the shape memory alloy Ti_49.5Ni_50.5 has been studied. The behavior of the thermal expansion, electrical resistivity, absolute differential thermopower, Hall coefficient, magnetic properties, and optical characteristics of the amorphous/nanocrystalline and submicrocrystalline alloys obtained by the SPDT with subsequent heat treatment at 800 K has been discussed.     

Self-Sustained Oscillations of the Torque under High-Pressure Torsion in an NdFeB Alloy

JETP Letters - The behavior of an NdFeB-based multicomponent alloy subjected to high-pressure torsion has been studied. The high-pressure torsion results in the partial amorphization of the alloy,...     

Surface nanocrystallization mechanism of a rare earth magnesium alloy induced by HVOF supersonic microparticles bombarding

A nanostructured surface layer with a thickness up to 60 μm was produced on a rare earth Mg-Gd-Y magnesium alloy using a new process named HVOF-SMB (high velocity oxygen-fuel flame supersonic microparticles bombarding). The microstructural features of the treated surface at various depth of the deformed layer were characterized by optical microscopy (OM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) with an aim to reveal the formation mechanism. Results showed that three steps during grain refinement process were found, i.e., twinning dominates the plastic deformation and divides the coarse grains into finer twin platelets at the initial stage, stacking faults are generated and a number of dislocation slip systems are activated leading to the cross slips with increasing strain and strain rate, eventually high-density dislocation networks, dislocation cells and dislocation arrays are formed, which further subdivides the twin platelets and residual microbands into sub-microstructures. As a result, homogeneous nanostructure with a grain size of about 10-20 nm is formed through dynamic recrystallization in the topmost surface layer. Based on the experimental observations, a grain refinement mechanism induced by plastic deformation with higher strain rate during the HVOF-SMB treatment in the rare earth Mg-Gd-Y alloy was proposed.     

High-rate erosion of Ti–6Al–4V ultrafine-grained titanium alloy obtained via intensive plastic torsional deformation

Testing results for Ti–6Al–4V ultrafine-grained titanium alloy obtained via intensive plastic torsional deformation (IPTD) are presented. To estimate the effect of IPTD treatment on the behavior of this material under erosion conditions, special experimental techniques were developed. The ultrafine-grained alloy was tested alongside with the traditional coarse-grained titanium alloy in an erosion wind tunnel in an air flow with corundum particles as an abrasive material. The erosion resistance of the material was estimated from the mass loss of specimens. Despite a considerable increase in the static strength characteristics, the nanostructured material did not demonstrate any increase in its erosion resistance in comparison with the initial alloy.