Comparisons of the microstructures and micro-mechanical properties of copper/steel explosive-bonded wave interfaces

Abstract

This paper presents a systematic study of the differences in the microstructures and micro-mechanical properties of various Cu/Fe wave interfaces prepared by explosive welding. These wave interfaces, fabricated by different parameters, have been divided into four categories according to variations in their microstructures and the element distribution: vortex region, transition layer, interface without metal bonding, and interface with defects. In the wave interfaces, nanocrystalline areas filled with nano-copper and nano-iron grains (50 nm), medium-sized grains (300 nm), coarse grains (1 μm) and finer nanocrystals (5 nm) or amorphous phases in wave interfaces. The variations in the grain size contribute to the inhomogeneity of hardness distribution in the first kind of interface, the vortex region. In the second kind of interface, the transition layer, both EDS and TEM measurements reveal a gradient in the element contents due to atomic diffusion. This transition layer possesses rather higher and more uniformly distributed nano-hardness (up to 15.75 GPa) because of the combined effects of fine grain strengthening and work hardening. The third kind of interface with an abrupt change in element distribution does not form metal bonds at the boundaries. Additionally, a comprehensive analysis on these four kinds of interfaces suggests that the second type of interface (transition layer) is the ideal one.