HENRYK PAUL, LIDIA LITYŃ SKA-DOBRZYŃ SKA, and MARIUSZ PRA _ ZMOWSKIThe microstructure changes and the phase constitution within the layers close to the bonding interface strongly influence the properties of bimetallic strips. In this work, the layers near the interface of explosively welded aluminum and copper plates were investigated by means of microscopic observations, mostly with the use of transmission electron microscopy (TEM) equipped with energy dispersive spectrometry (EDX). The study was focused on the identification of the intermetallic phases, the possible interdiffusion between the copper and the aluminum, and the changes in the dislocation structure of the parent plates. In macro-/mesoscale, the interfaces were outlined by a characteristic sharp transition indicating that there was no mechanical mixing between the welded metals in the solid state. In micro-/nanoscale, the layers adhering to the interface show typical deformed microstructure features, i.e., structure refinement, elongated dislocation cells, slip bands, and microtwins (in copper plate). The internal microstructure of the intermetallic inclusion is composed mostly of dendrites. The electron diffractions and TEM/EDX chemical composition measurements revealed three crystalline equilibrium phases of the c-Al 4 Cu 9 , g-AlCu, and H-Al 2 Cu type (the last one was dominant). However, most of the observed phases of the general Cu m Al n type (also crystalline) do not appear in the equilibrium Al-Cu phase diagram. Inside the intermetallic inclusions, no significant regularity in the phase distribution with respect to the parent sheets was observed. Therefore, it was concluded that the processes occurring in the melt determined their local chemical composition.

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The microstructure of an explosive cladding joint formed between parallel Zr700 alloy and carbon steel plates was examined with the use of scanning and transmission electron microscopes equipped with energy dispersive spectrometry. The study focused on near-the-interface microstructural changes and possible interdiffusion between the plates. At the macro-scale, the interfaces were outlined by a characteristic sharp transition, indicating that there was no mechanical mixing between the welded metals in the solid state. At the micro-scale, the melted zones often showed non-uniform swirl-like areas of a similar contrast. The nano-scale analysis revealed that the melted areas were composed of mixed amorphous and nano-crystalline phases. The bonding was always achieved by way of surface melting of the joined materials, which might be invisible for observation methods other than transmission electron microscopy.

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he effect of interfacial microstructure on the electro-mechanical properties of explosively welded titanium and copper plates is discussed. Mechanical testing proved that using detonation velocities ranging from 2000 to 3000 m s À1 and stand-off distances from 1.5 to 9.0 mm, joints that satisfy the strength criteria for a good quality clad were produced. Scanning electron microscopy images show that all interfaces exhibit a wave character. It was noticed that as the stand-off distances and detonation velocities increase, the amplitude and period of the waves, as well as the quantity of the melt zones, increase as well. Also, as the interface waviness and volume fraction of the melt zones increase, the resistivity increases substantially. The experimental data demonstrate that the bonding between both metals is always achieved by surface melting of several tenths of a nanometer, which can be detected only by transmission electron microscopy. Most of the phases that form within the melt zones do not appear in the equilibrium phase diagram and show an amorphous/nano-grained structure. Only a very small amount of equilibrium phases such as CuTi 3 , Cu 3 Ti, Cu 4 Ti 3 was revealed employing synchrotron X-ray diffraction.