A. M. Patselov

Formation of vortices during explosion welding (titanium-orthorhombic titanium aluminide)

The possibility of cladding commercially pure titanium by a plate of orthorhombic titanium aluminide has been investigated. The bimetallic joints of orthorhombic titanium aluminide (Ti-30Al-16Nb-1Zr-1Mo) with commercially pure titanium have been obtained by explosion welding. It has been found that the weld joint investigated had a multilayer structure consisting of a zone of continuous deformation observed in both materials, a zone of titanium recrystallization, and a transition zone near the interface. Wave formation and formation of isolated vortex zones have been observed. It has been found that upon explosion welding the bonding of the surfaces is effected via melting and subsequent mixing (in the zone of vortices) and the transfer of particles of one metal into another with the formation of particle tracks (outside the zone of vortices). A possible scenario of the formation of the vortex zone in the melt with a subsequent eutectic decomposition is proposed. The structure of the vortex zones was found to consist of an ultrafine mixture of α and β grains (both phases are disordered) with the grain size changing in the limits of 50–300 nm. The regions of transition from the vortex zone to the region of continuous deformation of the aluminide and to the recrystallized zone of titanium have been investigated.

Microheterogeneous Structure of Local Melted Zones in the Process of Explosive Welding

The dispersed structures formed in the process of explosive welding and solidification after melting were investigated in areas near the interface. It was shown that melting can be initiated by particles flying away as a result of granulating fragmentation. This is the fastest process during explosive welding, which is similar to fragmentation in conventional explosions with the formation of fragments but occurring in the presence of a barrier. The reaction between the particles and their environment may lead to local heating sufficient for melting. This is confirmed by the observation of numerous particles of the refractory phase within the local melted zones. In the absence of mutual solubility of the initial phases, the solidified local melted zones are to a certain extent analogous to colloidal solutions of immiscible liquids. Correlations between the typical temperatures were obtained that determine the conditions for the formation of various types of colloidal solutions.

Deformation Behavior of Intermetallics: Models and Experiments

A sufficiently general thermally activated mechanism for extension of dislocations in some preferential direction was proposed. This mechanism comprises a necessary step of dislocation transformations that lead to blocking. The reasons for blocking of different types of dislocations in different materials are diverse. A new concept was developed concerning the possibility of thermally activated blocking of superdislocations in the absence of external stresses. Some experiments with single crystals of Ni3(Al, Nb) were performed. They included no-load heating after preliminary low- or high-temperature deformation. It was found that the initial dislocation structure, which included curvilinear dislocations, transformed to a set of long rectilinear blocked superdislocations after no-load heating. The experimental results confirmed theoretical assumptions on the possibility of thermally activated transformations of superdislocations to indestructible barriers in the absence of external stresses.

Some features of the formation and destruction of dislocation barriers in intermetallic compounds: II. Observation of blocked superidislocations upon heating without stress

Experiments have been performed which reveal that heating in the absence of an external stress after a preliminary both low-temperature and high-temperature deformation of intermetallic compounds leads to a fundamental change in their dislocation structure. For the investigation, [251] single crystals of Ni3(Al, Nb) have been used. The low-temperature deformation was performed at −196°C; the high-temperature deformation, at 800°C. It has been found that the initial dislocation structure consisting of curvilinear dislocations was changed upon heating without a load by a set of rectilinear blocked dislocations. It has been shown that upon heating after a preliminary low-temperature deformation the barriers present in the structure belong to the cubic cross-slip plane, whereas upon heating after high-temperature deformation, to primary cubic slip planes. It has been found that the decisive effect on the blocking of superdislocations upon heating without stress comes from one of the dislocations that compose the superdislocation, namely, either a superpartial dislocation in the case of low-temperature deformation or a simple partial dislocation in the case of high-temperature deformation. The concept of the possibility of thermoactivated blocking of superdislocations in the absence of external stresses suggested in part I of this work [Phys. Met. Metallogr. 102, 61–68 (2006)] has been confirmed experimentally.

Fragmentation processes during explosion welding (review)

The fragmentation during explosion welding is briefly reviewed. Fragmentation of partitioning type (FPT), which consists in partitioning into particles that either fly away or join each other, is detected. FPT is an analog of the fragmentation during an explosion that was studied by Mott. In both cases, the flight of particles (fragments) takes place, and the integrity of the material is retained in FPT. FPT is a powerful channel for the dissipation of supplied energy, since the surface of flying particles has a large total area.

Synthesis and properties of Ti-Al laminated composites with an intermetallic layer

Metal-intermetallic laminated composites are fabricated upon reaction sintering of titanium and aluminum foils of various thicknesses. The mechanical properties of the composites with various metallic and intermetallic component contents are estimated using static and dynamic tests. The mechanical properties of the laminated composites are found to be anisotropic during static and dynamic loading.

Effect of plastic deformation on disordering and ordering processes in the intermetallic compound Ti3Al

Samples of a Ti3Al intermetallic compound have been subjected to cold plastic deformation with different logarithmic (true) strains e up to 10.3 using high-pressure torsion (HPT) under a pressure of 9 GPa. Formation of the disordered phase depending on the strain has been studied by X-ray diffraction and electron microscopy. At the degrees of deformation e = 8.7–10.3, a nanostructured disordered phase with a crystal size of mainly 5–15 nm is formed. Recovery of the ordered structure occurs in a temperature range of 400–600°C and is accompanied by the recrystallization of the deformed structure. In recrystallized grains of the ordered phase, antiphase domains appear in the form of oriented plates.

Structural and phase transformations in ferromanganese alloys during deformation under pressure

Using optical metallographic, TEM, Mössbauer spectroscopy, and X-ray analysis the structural and phase transformations in Fe-(3–55) wt % Mn alloys during shear deformation under pressure were investigated. It is established that a large deformation under high pressure causes the formation of a nanocrystalline structure with grain sizes of 40–60 nm. Nanostructure increases the hysteresis of inverse (hcp-fcc) transformation and stabilizes the (hcp) ɛ phase in alloys containing more than 40 wt % Mn, up to normal conditions. The Fe-3 wt % Mn alloy after shear under pressure treatment became nanostructured, retaining the original bcc phase state.

Formation of Intermetallic Compounds During Explosive Welding

Transition states between traditional, i.e., plain and wavy, shapes of the interface during explosive welding were studied. A sequence of the transition states was found for the studied copper-titanium and copper-tantalum joints. Some transition states are common for the joints under study, while others are only typical of the copper-titanium joints, due to sufficiently high solubility of original elements. A transition state has been found, during which cusps, even though they are solid phase, look like splashes on the water. The key role of these splashes is that they evidence the lower boundary of the ‘weldability window.’ The study found certain self-organization processes of the cusps that cause them to turn into a quasi-wavy shape of the interface, and then, as the welding mode is intensified, into a wavy shape. The role of intermetallic compounds was analyzed, due to which a wave only consists of cusps in case mutual solubility of original metals is sufficiently high.

Structure of the transition zone and its influence on the strength of copper-tantalum joint (Explosion welding)

The joint of copper and tantalum, metals without mutual solubility, formed by explosion welding is studied. The mechanism of the influence of mutual solubility on the structure of the transition zone is established. It is demonstrated that the interface contains heterogeneities, and their role in the strength of the materials joint is revealed. A microheterogeneous structure of the joint zones is detected.