A. A. Bataev

Nucleation and growth of titanium aluminide in an explosion-welded laminate composite

Processes of nucleation and growth of titanium aluminide in a 23-layer aluminum-titanium composite produced by explosion welding have been studied. In the vortex zones of seven upper welds, microvolumes of melted metal whose microhardness is ∼5500 MPa have been revealed, which corresponds to the microhardness of the intermetallic compound Al3Ti. No formation of titanium aluminide in welded junctions that were not subjected to additional heat treatment has been revealed by X-ray diffraction. The holding of the composites at 630°C is accompanied by the formation of interlayers of intermetallic compounds of the Al3Ti type. Intermetallic compounds of two morphological types are formed in the welds. In the regions of vortex zones, compact precipitates of Al3Ti are formed; in the other regions of the welds, intermetallic compounds in the form of a film are precipitated. The intermetallic compounds of the first type grow more rapidly and in final account absorb the precipitates of the film type. The activation of diffusion in the upper junctions that occurs upon heating of the welded composites is favored by the nonequilibrium state of the material caused by the strain hardening of the initial samples. In the welds located deeper than the 13th layer, no signs of the formation of compact intermetallic compounds have been revealed upon the annealing for 5 h and less.

Peculiarities of Weld Seams and Adjacent Zones Structures Formed in Process of Explosive Welding of Sheet Steel Plates

The structure and mechanical properties of the laminates produced by explosive welding of low carbon steel were investigated. The maximum number of layers in the composites was 21. It was shown that the structure of the composite is not uniform across the thickness of the layers and along the boundaries in the shape of the wave. Transmission electron microscopy revealed that the sizes of the grain-subgrain clusters forming in the weld adjacent zones are about 100…400 nm. The maximum temperature was reached in the areas of the vortices. High-strength martensite was formed in these zones in the process of cooling. The strength properties and toughness of the com-posite is almost 2 times higher compared with the properties of the original plates. It was shown that the boundaries of welds are the barriers inhibiting the development of fatigue cracks.

Metallic glass formation at the interface of explosively welded Nb and stainless steel

The interface between explosively welded niobium and stainless steel SUS 304 was studied using scanning electron microscopy, transmission electron microscopy and energy dispersive X-Ray spectroscopy. The wavy interface along which vortex zones were located was observed. The vortex zones formed due to the mixing of materials typically had amorphous structure. Inoue’s criteria of glass formation were used to explain this result. The effect of the composition, cooling rate and pressure on the glass formation are discussed. The conditions of deformation, heating, and cooling as well as shockwaves propagation were numerically simulated. We show that the conditions of vortex zone formation resemble the conditions of rapid solidification processes. In contrast to the “classical” methods of rapid solidification of melt, the conditions of metastable phase formation during explosive welding are significantly complicated by the fluctuations of composition and pressure. Possible metastable structures formation at the interface of some common explosively joined materials is predicted.

Structural Changes of Surface Layers of Steel Plates in the Process of Explosive Welding

Structural changes developing in surface layers of plates from steel 20 in the process of explosive welding are studied with the help of light metallography and scanning and transmission electron microscopy. Mathematical simulation is used to compute the depth of the action of severe plastic deformation due to explosive welding of steel plates on the structure of their surface layers.

Influence of the explosively welded composites structure on the diffusion processes occurring during annealing

Currently layered composites with intermetallic interlayers are promising materials for many industries. Materials of this type involve composites consisting of titanium and titanium aluminides layers. One of the methods of such composites fabrication is explosive welding and annealing. In this paper the structure and properties of explosively welded multilayered composites is described. Structural studies were carried out by the methods of optical metallography, scanning and transmission electron microscopy. The properties of local zones of material were estimated by the measuring of a microhardness level. The explosive welding process accompanied by the structural changes of material adjacent to “Al-Ti” interfaces. The structural investigation revealed the formation of several areas: vortex zones, which are characterized by aluminum and titanium mixing, and severely deformed areas. These structural features have the strong influence on the diffusion processes occurring during annealing of composites. The most intensive diffusion was observed in the welded joints where the most significant structural changes occurred. It was identified that Al3Ti is only one phase which forms during heat treatment of “Ti-Al” composites. The main conditions of “Ti-Al3Ti” composites fabrication are the correct choice of aluminum and titanium plates thickness and optimal conditions of heat treatment.

Structure and Microhardness of Cu-Ta Joints Produced by Explosive Welding

The structure and microhardness of Cu-Ta joints produced by explosive welding were studied. It was found that, during explosive welding, an intermediate layer 20⋯40 μm thick with a finely dispersed heterophase structure, formed between the welded copper and tantalum plates. The structure of the layer was studied by scanning and transmission electron microscopy. Microvolumes with tantalum particles distributed in a copper matrix and microvolumes of copper particles in a tantalum matrix were detected. The tantalum particles in copper have a size of 5⋯500 nm, with a predominance of 5⋯50 nm particles. A mechanism for the formation of the finely dispersed heterophase structure in explosive welding is proposed. The microhardness of interlayers with the heterophase structure reaches 280 HV, which far exceeds the microhardness of copper (~130 HV) and tantalum (~160 HV). Many twins of deformation origin were found in the structure of the copper plate. The effect of heating temperature in the range from 100 to 900°C on the microhardness of copper, tantalum, and the Cu-Ta welded joint was studied. Upon heating to 900°C, the microhardness of the intermediate layer decreases from 280 to 150 HV. The reduction in the strength properties of the weld material is mainly due to structural transformations in copper.

Mach stem formation in explosion systems, which include high modulus elastic elements

Results of experimental and numerical research of the Mach stem formation in explosion systems, which include high modulus elastic elements, are presented. The experimental data are discussed, and the analysis using ANSYS AUTODYN 11.0 is provided. It is shown that the phenomenon is reproduced for various high explosives. The Mach stem formation is observed in the conditions close to critical conditions of detonation transfer from an active to a passive HE charge. The best conditions for the Mach stem formation have been observed for TG-40/60 (Russian analog of Composition B) with silicon carbide insert heights of 16.5 mm, 18 mm, and 19.5 mm. The physical reason of the phenomenon is the propagation of a convergent detonation wave into highly compressed HE. The phenomenon is reproduced in numerical simulation with ANSYS AUTODYN 11.0. Calculated maximum value of pressure on the symmetry axis of passive HE charge was up to 1.25 Mbar. Results of metallographic analysis of steel identification specimen on the r...

Boride Coatings Structure and Properties, Produced by Atmospheric Electron-Beam Cladding

Structure, microhardness and fracture features of coatings produced by atmospheric electron-beam cladding of amorphous boron were investigated. The coatings were produced by cladding of one, two and three layers of powder. Produced coatings thickness is 550, 750 and 900 μm respectively. The peak level of microhardness is 14000…16000 MPa. By the means of XRD analysis it is stated that the main phases of strengthened layers are FeB and Fe2B borides and eutectic (α-Fe + Fe2B). The coatings after one layer cladding have non-uniform structure with microvolumes having lack of borides. Three-layered coatings are noted for their high brittleness. The best properties are presented by two-layer coatings.

Microstructure and fracture behaviour of flash butt welds between dissimilar steels

Abstract Flash butt welds between high carbon steel and chrome–nickel steel were studied in this article. Light and electron microscopic studies have shown that the welded joints have a complex structure consisting of several phases. In addition to pearlite colonies, austenite microvolumes and regions of high strength martensite, the welds contain brittle inclusions of titanium sulphide and carbide particles. The mechanical behaviour of the welded joints is negatively influenced by the dramatic change in hardness in the weld zone. Fractographic analysis of dynamically fractured welds between carbon steel and stainless steels has shown that the fracture in the weld samples occurs in both steels. This behaviour of the material is caused by the non-uniform distribution of martensitic regions within the weld. The formation of martensitic regions in the structure of the material is a major cause of the reduction in the fatigue crack resistance of the welded joints.

Specific Features of the Nucleation and Growth of Fatigue Cracks in Steel under Cyclic Dynamic Compression

The processes of the fracture of 40Kh and U8 steels under cyclic dynamic compression are studied. It has been found that the main cause for the fracture of the cyclically compressed specimens is the propagation of cracks due to the effect of residual tensile stresses, which arise near the tips of the cracks at the stage of the unloading of the specimens. The growth rate of a crack has the maximum value at the initial stage of its propagation in the vicinity of the stress concentrator. As the crack propagates deep into the specimen, its growth rate decreases and depends only slightly on the real cross section of the specimen. The model of the process of the fatigue fracture of the steels under dynamic loading by a cyclically varied compressive force is proposed. It has been found that the high fatigue endurance is provided by tempering at 200°C for the 40Kh steel and at 300°C for the U8 steel.