GR12 Composite Plate With Explosive Welding

Metallographic observation Figure 1 shows the microstructure photo of the bonding interface of the explosive composite plate. Generally, the interfaces of composite plates after explosive welding include straight, wavy interfaces and melting layers. It is generally believed that composite plates with wavy bonding interfaces have better performance. In the process of explosive welding, the metal in the bonding zone will deform to different degrees under the action of high pressure and instantaneous impact load. It can be seen from Figure 1 (a) that the interface of the composite plate shows obvious wavy combination and repeats periodically along the explosion direction.

Figure 1 (b) shows the microstructure of the steel side of the composite plate. It can be seen that the tensile and fibrous plastic deformation occurs in the microstructure grain of the side, and is strongest near the interface. The microstructure from the interface bonding zone to the matrix can be subdivided into fine grained zone, fibrous zone and original microstructure zone, and the width of the fine grained zone is relatively narrow.

On the titanium side near the interface, no plastic deformation characteristics similar to that of the steel side are found, but there are inclined lines with an approximate 45 ° angle to the bonding interface and extending to the titanium side, and there are many inclined lines at the wave crest, which are called adiabatic shear lines, as shown in Figure 1 (c). Due to the high pressure instantaneity of the explosive welding process, titanium with low toughness has no time to carry out plastic deformation in the way of sliding and twinning, but can only be deformed in the way of shearing. The continuous track of its shearing point forms an adiabatic shear line. It is generally believed that the generation of adiabatic shear lines is related to the impact toughness and explosive load of materials.

In the process of explosive welding, the metal jet fluctuates due to the pressure fluctuation, causing the jet to be periodically captured by the base clad plate, thus forming a unique vortex structure, as shown in Figure 1 (d). There may be pores, cracks and impurities in the vortex. This is because in the process of explosive welding, on the one hand, the welding time is short, the cooling is very fast, and the involved gas may not be discharged in time; On the other hand, these gases are closed in the vortex under the action of strong turbulence, which makes it difficult to discharge, thus forming pores. The formation of cracks is mainly due to the internal stress caused by too fast cooling rate. Impurities are mainly formed when the jet washes the surface. Because these defects only exist in the melting block, they will not have a great adverse effect on the interface bonding. It is also because of the existence of the vortex, which increases the bonding area between the base plates and is conducive to improving their bonding strength.

In the process of explosive welding of dissimilar metals, the metal at the interface may produce local melting and form brittle phase at the interface under the action of complex thermal cycle, which may reduce the bonding strength and even cause cracking. Therefore, it is necessary to analyze the phase structure composition at the interface. Figure 2 shows the measured XRD analysis curve of the bonding interface area of the titanium-steel explosive composite plate. It can be seen that the interface bonding area is mainly composed of α- Ti, B-Ti and a-Fe basic phase composition; At the same time, a small amount of FeTi and Fe2Ti intermetallic compounds were also formed. The reason may be that the local melting area of the interface precipitates during the cooling process of explosive welding due to the limitation of solubility, or that T and Fe react with each other at the interface. In general, due to the small number of brittle phases formed in the bonding interface of the composite plate, the subsequent test and analysis results in this paper do not have a significant adverse impact on the mechanical properties of the composite plate.