Search

The paper is devoted to the study of the structure and properties of the Ni3Al intermetallic obtained by spark plasma sintering and modified with 0.2 wt.% of boron. It is shown that, in the structure of the material, in addition to the Ni3Al intermetallic, there are regions represented by a mechanical mixture. The mechanical mixture is characterized by cube-shaped nickel aluminide particles surrounded by a matrix of solid aluminum solution in nickel. These regions have a coarser morphology and are better manifested on intermetallic samples modified with boron than in similar samples without additional alloying elements. It is shown that the boron microaddition positively affects the strength and toughness of the synthesized materials. The ultimate strength increases from 400 to 720 MPa; impact strength increases from 5.3 to 14.2 J/cm2.

Ti/Ni alloy-based laminate composite materials were produced by explosive welding with two thin intermediate layers of tantalum and copper placed between Ti and Ni alloy layers. The influence of the thickness of the Cu interlayer (0.1–0.7 mm) on the structure and mechanical properties of the explosively welded composites was examined. Investigations carried out by optical and scanning electron microscopy showed the formation of an inhomogeneous structure in the vicinity of the interfaces with zones of local melting and cavities within these zones. The wavelength and the amplitude at the interface between the copper and tantalum interlayers changed with the thickness of the copper layer. In order to evaluate the mechanical properties of the composites containing copper interlayers of different thicknesses, microhardness, tensile, and bending tests were performed. As the thickness of the copper layer was decreased to 0.3 mm, the tensile and bending strengths of the laminate composites increased.

In this study, forty-layered Ti-Al composites were fabricated in a single-shot explosive welding process. The structure of the composites was thoroughly investigated using scanning and transmission electron microscopy. Particular attention was paid to the structure of the mixing zones (vortexes) arising at the interfaces during explosive welding. The complicated process of mixing and rapid solidification of these zones led to formation of different stable and metastable structures. The vitrification of vortexes, formation of “disordered” Ti3Al and ordered solid solution of Al in hexagonal-Ti and Ti in FCC-Al were observed and discussed with respect to the conditions of solidification. Subsequent heat treatment was carried out at 640 °C under atmospheric and at 3 MPa pressure. For comparison, there were produced reference samples by reaction sintering at the same conditions as for the heat treatment. The heat treatment and reaction sintering promoted the formation of stable Al3Ti phase between Ti and Al. It was found that preliminary explosive welding accelerated the formation of Al3Ti layer and made heat treatment duration four times shorter. The application of pressure was found to play an important role at the final stage of heat treatment after explosion welding to avoid formation of defects between the plates. Keywords: Explosive welding, Multilayer, Titanium, Aluminum, Intermetallic, Composite

In this study Ti-Ta-Zr coatings fabricated on VT1-0 titanium substrates by non-vacuum electron beam cladding in one, two and three passes were investigated. Coatings were characterized by a high quality; such defects as cracks and voids were not observed. The structure of coating was commonly dendritic. The acicular structure in the one-layered coating and in the first layer of multilayered coatings was revealed by using scanning electron microscopy (SEM). The results of the energy dispersive X-ray (EDX) analysis indicated the presence of tantalum and zirconium segregations in dendrite arms and in the space between them. It was found that dendritic branches contained the maximum of tantalum while an increased amount of zirconium was concentrated in the interdendritic space. The maximum concentration of alloying elements (56.87 wt. % Ta and 22.22 wt. % Zr) was obtained in the layer cladded in the third pass of an electron beam. The microhardness of Ti-Ta-Zr layers rose from 4.5 GPa to 6 GPa with an increase in .the percentage of alloying elements

The structure of composites formed by explosive welding of thin sheets of tool and austenitic steels was studied by structural analysis methods. It is shown that the quenching and tempering of composites leads to the formation of complicated structure containing, along with layers of dissimilar steels, layers with new chemical compositions. Due to the structural changes there is an 2-fold increasing of impact toughness.

The analysis of fine structural changes occurring in the surface layers of dynamically interacting pieces of carbon steels of different chemical composition is conducted. Transformations occurring in ferrite and pearlite are investigated using transmission electron analysis. Based on the results of mathematical modeling, the distribution of temperature fields in dynamically interacting steel billets is established. It is found that the results of numerical modeling correlate with the experimental data. To determine the degree of hardening of the material of the welded plates hardness measurement was conducted using a Vickers microhardness tester.

Metal-intermetallic lamellar (MIL) composites with different intermetallic phase volume fraction (from 47 to 78 %) obtained by reactive spark plasma sintering (SPS) of Ti and Al foils enclosed in Ti shells were investigated. It was shown that increase of titanium aluminide volume fraction in the composites had no influence on their compressive strength at the loading along the layers. Compressive strength at the aforementioned loading conditions was 775 – 790 MPa. However, at the loading of materials in the direction perpendicular to layers the compressive strength value raised from 655 to 760 MPa with increase of titanium volume fraction in the material.

Microstructure and mechanical properties of copper and tantalum joints produced by explosive welding technology were characterized. It was established by structural analysis technique that mixing of copper and tantalum at the interface occurs due to a nonequilibrium process. The mixing zone consists of tantalum globular particles which sizes vary from 8 to 40 nm. In the close vicinity to the interface copper grains contains a lot of microtwins bundles. Their formation plays a crucial role both in the microstructure evolution and fragmentation process of copper grains. Microhardness of copper-tantalum mixing zone is 2800 MPa which is 2 times higher than that of initial materials. The tensile test has shown the significant growth of composite yield strength in comparison with that of initial materials.

In this study the structure and properties of surface-alloyed cp-titanium layers obtained by non-vacuum electron beam cladding of niobium carbide powders were analyzed. A thickness of coatings fabricated by single-layer cladding was 1.3 mm. Cladding of the second layer led to an increase in the thickness by 0.8 mm. It was found that titanium carbide particles of different morphology acted as strengthening structural elements. The X-ray diffraction (XRD) analysis revealed the presence of α-Ti (α'-Ti), β-Ti, and TiC in the cladded layer. The results of the energy dispersive X-ray (EDX) analysis indicated the presence of Nb in the titanium matrix as well as in the carbide phase. However, such phases as NbC and (Nb, Ti)C were not identified by the XRD analysis. Transmission electron microscopy (TEM) revealed zones containing an increased amount of Nb. The structure of these zones was represented by the β-Ti and ω-Ti precipitation. An average microhardness value of cladded layers was approximately 330 HV.