Microstructure and Properties of Multilayer Niobium-Aluminum Composites Fabricated by Explosive Welding

In this study, a layered composite material consisting of alternating aluminum and niobium layers and cladded on both sides with titanium plates was obtained by explosive welding. Microstructure of the composite was thoroughly studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), as well as by energy dispersive X-ray spectroscopy (EDX) and electron backscattered diffraction (EBSD). Microhardness measurements, tensile test, and impact strength test were carried out to evaluate the mechanical properties of the composite. Formation of mixing zones observed near all interfaces was explained by local melting and subsequent rapid solidification. Mixing zones at Nb/Al interfaces consisted of metastable amorphous and ultrafine crystalline phases, as well as NbAl3 and Nb2Al equilibrium phases. Niobium grains near the interface were significantly elongated, while aluminum grains were almost equiaxed. Crystalline grains inside the mixing zones did not have a distinct crystallographic texture. Microhardness of Al/Nb mixing zones was in the range 546–668 HV, which significantly exceeds the microhardness of initial materials. Tensile strength and impact strength of the composite were 535 MPa and 82 J/cm2, respectively. These results confirm the high bonding strength between the layers

On the texture and superstructure formation in Ti–TiAl3_3–Al MIL composites

In recent decades, metal-intermetallic laminated (MIL) composites are of great interest to the scientific community. The intermetallic layers in such composites possess a strong crystallographic texture and can form various superstructures. However, these effects are rarely discussed in the literature. By application of synchrotron X-ray diffraction (SXRD) we show, that an intermetallic layer in explosively welded and annealed Ti-Al-based MIL composite consists of two modifications of titanium trialuminide: TiAl$_3$ with a D0$_{22}$ structure and its superstructure Ti$_8$Al$_{24}$. According to SXRD analysis, the volume fraction of the Ti$_8$Al$_{24}$ modification increases from Al/intermetallic interface towards Ti/intermetallic interface. This may be caused by the lack of Al for the formation of stoichiometric titanium trialuminide near the interface with Ti, which leads to the formation of a long-period structures having Ti$_{1+x}$Al$_{3-x}$ stoichiometry. Two types of fiber texture were formed in the titanium trialuminide layer: [001] near the Ti/intermetallic interface and near the Al/intermetallic interface, which is caused by peculiarities of Ti and Al atoms migration. To explain the features of the forming texture, hypothetical mechanisms of Al and Ti diffusion in the intermetallic layer are discussed in this study: a vacancy diffusion, an interstitial diffusion, and a six jump vacancy cycle (6JVC)

In situ synchrotron X-ray diffraction study of reaction routes in Ti-Al3Ti-based composites: The effect of transition metals on L12 structure stabilization

In the last few decades, Ti-Al$_3$Ti composites have attracted great attention due to their outstanding mechanical characteristics, such as low density, high specific strength and stiffness, and ballistic properties. However, their application is still limited due to the low ductility and fracture toughness of the Al$_3$Ti phase. A promising way to improve the composite’s properties is to transform the Al$_3$Ti crystal structure from the tetragonal D0$_{22}$ type to the cubic L1$_2$ type. In this study, the stabilization of the L1$_2$ structure of titanium trialuminide during the fabrication of the Ti-Al3Ti composite is discussed. For this reason, the method of in situ synchrotron X-ray diffraction analysis was used to observe the reactions in the ternary Ti-Al-M systems (where M is Zn, Au, Ag, Ni, Pd, Pt, Mn, Fe, Co or Cr) during heating from room temperature to 830 °С. Zn and Ag were found to be the most efficient stabilizers of the L1$_2$ structure. In composites alloyed with Fe, Co, and Cr, the L1$_2$ structure of Al$_3$Ti was not stabilized. Formation of L1$_2$-structured titanium trialuminide in the remaining systems was accompanied by the formation of a large number of co-products. To select the elements stabilizing L1$_2$ structure in the composite with an excess amount of Ti, the following principle was formulated: the preferable stabilizers are the elements with FCC and HCP structures and a melting temperature below 1100 °С, and which do not form refractory Al-rich binary compounds with a melting point above 1000 °С