Explosive cladding of Cu/Cu systems: An electron microscopy study and a thermomechanical model

Abstract

Transmission electron microscopy investigations were carried out on three explosively cladded Cu/Cu systems: equiaxial small grains, elongated large grains and single crystals. The investigation has shown that the cladding process leads to the formation of a ‘bond zone’ rather than to a ‘planar interface’. The ‘bond zone’ independent of the cladding system could be divided into a few ‘cladding affected regions’ symmetrically extending on both sides of the colliding surfaces. Each of the regions is characterized by a definite structural morphology. Selected area diffraction patterns show that in all three systems, regions characterized by similar structures exhibit the same zone axis, namely 〈111〉 or 〈011〉. The ‘metallurgical bond’ achieved in the cladding process is constituted of small equiaxed recrystallized grains which form the center of the ‘bond zone’. The array of structures in the ‘bond zone’ as well as the dislocation densities result from a combination of three basic processes taking place during explosion cladding: mechanical (deformation), thermal and mass transfer. A theoretical model has been suggested for the treatment of the effects of the thermomechanical process on the annihilation of dislocations and their density distribution after cladding and on the extent of mass transport during transient annealing. The theoretically predicted results were compared with the experimental results obtained by means of transmission electron microscopy. For the Cu/Cu systems the agreement was found to be reasonable. The model presented should enable thermomechanical processes in other similar explosion clad systems to be treated.