Исследованы многослойные композиты, изготовленные cваркой взрывом и состоящие из чередующихся пластин ниобия и алюминия. Проведена термическая обработка полученных образцов — отжиг при 700, 800, 900 °C под нагрузкой и без нее. Определены структура, предел прочности при растяжении, ударная вязкость и микротвердость композитов по Виккерсу. Показано, что вблизи границ раздела, где происходило локальное расплавление и быстрое затвердевание, образовались зоны перемешивания, состоящие из неравновесных фаз, интерметаллидных частиц NbAl3 и Nb2Al, а также нерастворившихся объемов ниобия. Повышение температуры отжига от 700 до 900 °C вызвало рост интерметаллидных включений, что привело к появлению трещин в реакционном слое и значительному ухудшению механических свойств. Наибольшие значения предела прочности (700 МПа) и ударной вязкости (86 Дж/см2 ) образцов получены после отжига под давлением при 900 и 800 °C соответственно. Оптимальным режимом, благоприятно влияющим на прочностные характеристики и способствующим сохранению бездефектной структуры, является отжиг при 700 °C под давлением 30 МПа.

Al3Ti-based alloys attract exceptional attention due to their high specific mechanical properties. However, their application is still insufficient due to their low ductility and fracture toughness. Several approaches were previously proposed to address these problems. The first one is stabilization of the cubic modification of titanium trialuminide by alloying. Another approach consists in fabricating metal-intermetallic laminated composites (MIL). In this study, we combined both methods to synthesize the first MIL composite with cubic Al3Ti inter-layers. Copper additions were used to stabilize the cubic modification of Al3Ti and produce a novel Ti-Al5CuTi2 MIL composite. First mechanical characterization by indentation tests showed that the binary Al3Ti intermetallic tended to crack at a load of 0.2 kg while the fracture was not observed in the Al5CuTi2 layers at least at a load of 1 kg. These results are an indirect evidence of a higher ductility and fracture toughness of the composite with cubic Al3Ti compared to tetragonal one. The sequence of the phase transformations in the Al-Ti-Cu system was studied using in situ synchrotron X-ray radiation diffraction. The formation of Al5CuTi2 occurred via several intermediate stages including eutectic melting of Al and Cu and the formation of binary AlCu and Al3Ti compounds. (C) 2018 Elsevier Ltd. All rights reserved.

In this study, a laser cladding technique was used to produce a protective TiAl-based coating on TA6Zr4DE near-alpha titanium alloy. Ti48Al2Cr2Nb powder was used as a cladding material. The microstructure of samples was characterized using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Fully lamellar microstructure consisting of γ-TiAl (fcc) and α2-Ti3Al (hcp) phases was observed in the coating. Oxidation resistance of substrate and coating was evaluated by heating the samples in an air atmosphere at 700, 800 and 900 °С during 100 h. The oxidation process of TA6Zr4DE alloy surface led to a formation of multilayered oxide films as result of repeated growth and peeling. The coated samples showed better oxidation resistance in whole temperature range compared to that of the substrate. This behavior was explained by the composition of the cladded layer. Niobium and chromium contained in the cladded powder inhibited the intensive growth of TiO2 (rutile) and contributed to the formation of a protective layer composed mainly of alumina.

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 paper, weld joints between VT1-0 titanium and AISI 321 austenitic stainless steel using laser welding were obtained. To improve the quality and strength properties of joints, two types (SS–Cu–Nb/Ta–Ti) of explosively welded four-layered composite inserts were used. Barrier layers were different from each other by refractory metal. The effect of intermediate material inserts, in particular tantalum and niobium, on microstructure, chemical composition, strength properties, and fracture behaviour of weld joints was studied. Microstructural studies have revealed two bonding types as results of welding method combination. At copper–stainless steel interface, severely deformed zone characterized by low etch ability was observed. Technological parameter’s optimization provided high joint quality and absence of defects in the weld joints. According to results of strength tests, it was found that the composite insert material affects the strength of the joints. The highest ultimate tensile strength and yield strength were detected for joints containing niobium foil.

Intermetallic clads were obtained on the basis of the titanium workpieces. The cladding was carried out using a non-vacuum electron beam treatment technique. A powder mixture which contained 16.97 Al - 28.27 Ti - 41.07 CaF2 - 13.69 LiF (wt. %) was used for cladding. Two regimes with the beam current of 16 mA and 18 mA were used. The beam current influenced significantly the structure and phase composition of clads. In case of the electron beam treatment with a beam current of 16 mA a lamellar structure consisted of a mixture of AlTi3 and AlTi was fabricated. An increase of the beam current to 18 mA led to the formation of an AlTi3 acicular structure. Microhardness and wear resistance of the intermetallic coating was significantly higher in comparison with cp-Ti. The maximum microhardness of clads was 480 HV. A wear rate of clads was 10 times lower than that of cp-Ti.

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.

Investigations of welded joints as well as strength properties of composites formed by explosive welding of plates from titanium alloy VT20 and stainless steel 09Cr18Ni10Ti with interlayer's employment are conducted. The duty of interlayers are performed by the plates of tantalum or "brass - tantalum". It results in the suppression of brittle intermetallic phase's formation in the joining zone and obtaining the welds characterized by lack of defects that reduce fracture strength of materials. By the means of a microstructural analysis it is found that in the bonding zone the copp er and iron as well as titanium and tantalum based solid solutions are formed. By the means of a transmission electron microscopy the deformation twins are detected in some grains of melted zone between copper alloy and stainless steel. There is evidence that twinning is the predominant deformation mechanism of explosive welding process. At the welding interface of brass and tantalum plates the structure represents a mechanical mixture of copper and nano dispersive inclusions of beta - tantalum. The level of layers joining strength is used as a criterion of mechanical properties of composite materials. The maximum ultimate strength 420 MPa is characteristic of composite materials with interlayers from brass and tantalum. The strength of composite materials with tantalum plate as interlayer is 22 % less than the composite with "brass - tantalum" interlayers. This reduction is probably due to the molten zones formation in the thin surfaces layers of plates between stainless steel and tantalum. During crystallization of these zones the low plastic tantalum and iron based chemical compounds were formed. Insertion of two layered "brass - tantalum" interlayer between stainless steel and titanium alloy is reasonable to increase the strength properties of composites.

В работе сваркой взрывом было сформировано бездефектное соединение между пластинами титана и никелевого сплава с использованием промежуточных слоев, состоящих из тонколистовых пластин чистых материалов (меди и тантала). Характер взаимодействия свариваемых материалов способствует тому, что в процессе сварки не образуются нежелательные химические соединения, приводящие к падению механических свойств.

Explosive welding was used to form reliable joining between commercially pure titanium and stainless steel. To prevent cracking at the interface induced by brittle intermetallic bronze - tantalum interlayer was used. Microstructural characterization of produced composite was analyzed using optical and scanning electron microscopy as well as energy dispersive analysis. Determination of structure has revealed no micro defects such as cracks in the composite. Intermediate layer of 5 μm thick at the bronze - tantalum interface was formed. Structure of intermediate layer corresponds to highly dispersed mixture of tantalum and copper alloy particles. Ultimate strength of 4 layered composite is 1000 MPa that exceeds of ultimate strength of composite produced without interlayer. Analysis of fractograph indicates a high adhesion level between interactive materials.

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 mu m 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 ... 50nm 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 280HV, which far exceeds the microhardness of copper (similar to 130HV) and tantalum (similar to 160HV). 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 degrees C on the microhardness of copper, tantalum, and the Cu-Ta welded joint was studied. Upon heating to 900 degrees C, the microhardness of the intermediate layer decreases from 280 to 150HV. Thereduction in the strength properties of the weldmaterial is mainly due to structural transformations in copper.