Structure and Microhardness of Cu‐Ta Joints Produced by Explosive Welding

Abstract

The structure and microhardness of Cu-Ta joints produced by explosive welding were studied. It was found that, during explosive welding, an intermediate layer 20⋯40 μm thick with a finely dispersed heterophase structure, formed between the welded copper and tantalum plates. The structure of the layer was studied by scanning and transmission electron microscopy. Microvolumes with tantalum particles distributed in a copper matrix and microvolumes of copper particles in a tantalum matrix were detected. The tantalum particles in copper have a size of 5⋯500 nm, with a predominance of 5⋯50 nm particles. A mechanism for the formation of the finely dispersed heterophase structure in explosive welding is proposed. The microhardness of interlayers with the heterophase structure reaches 280 HV, which far exceeds the microhardness of copper (~130 HV) and tantalum (~160 HV). Many twins of deformation origin were found in the structure of the copper plate. The effect of heating temperature in the range from 100 to 900°C on the microhardness of copper, tantalum, and the Cu-Ta welded joint was studied. Upon heating to 900°C, the microhardness of the intermediate layer decreases from 280 to 150 HV. The reduction in the strength properties of the weld material is mainly due to structural transformations in copper.

Structural Properties of Interfacial Layers in Tantalum to Stainless Steel Clad with Copper Interlayer Produced by Explosive Welding

“…In the present work the most regions inside the solidified melt zones near the Ta/Cu interface, were indexed as 'pure' Ta or Cu, with some quantity of not or mis-indexed pixels [11,30,31]. Figure 5a shows an SEM/EBSD image with a vortex region along the SS/Cu interface.…”

“…The Cu-Ta system is characterized by nearly zero mutual solubility of the components in the solid-state [28,29] and high structural and mechanical stability at elevated temperatures. Greenberg et al [30], Maliutina et al [31] as well as Bataev et al [11] have shown that explosively welded Ta and Cu sheets exhibit a heterophase mixture in the reaction region with the size of the dispersed Ta and Cu particles similar to those of colloids. As also documented by Bataev et al [11] and Parchuri et al [32], the Ta x Cu 1-x based intermetallics or decagonal quasicrystals were found to coexist along with pure Ta and Cu particles in the solidified melt zones at the Ta/Cu interface.…”

“…For the particular case of Ta/Cu metal composition, a possible mechanism of intermediate heterophase region formation was proposed by Maliutina et al [31]. In this mechanism there is not necessary to exceed the melting point of Ta since the globular particles of Ta are plunged into solidified Cu.…”

“…However, it is very difficult to state without any doubt, whether this mechanism is the only one or just dominant. The weak point of the mechanism proposed in [31] is that the matrix is not pure copper but is mostly a solid solution of Ta in the Cu (see Figure 8). However, aside from the limited information on the phase constitution in the Cu-Ta immiscible systems, the formation of metastable phases can be expected due to rapid cooling during solidification of melted volumes, as described for other processes in [33][34][35][36][37]41,42].…”

Formation of a Transition Zone Structure in Welded Joints between Dissimilar Steels

“…However, the width of these layers is considerably smaller than after TIG welding [5,6]. The probability of unfavorable structure formation is reduced by the use of the explosion welding technique due to a high speed of the process, but, at the same time, the appearance of mixed zones of welded materials is not excluded [10][11][12][13][14]. Contact welding defects are an intensive mechanical mixing of materials due to the applied load, and diffusion processes [8,[15][16][17].…”