Elsevier

Materials Characterization

Volume 75, January 2013, Pages 51-62
Materials Characterization

The problem of intermixing of metals possessing no mutual solubility upon explosion welding (Cu–Ta, Fe–Ag, Al–Ta)

https://doi.org/10.1016/j.matchar.2012.10.011Get rights and content

Abstract

On the basis of the results obtained for joints of dissimilar metals such as copper–tantalum and iron–silver, the reason of immiscible suspensions mixing upon explosion welding has been cleared out. It has been found that the interface (plain or wavy) is not smooth and contains inhomogeneities, namely, cusps and local melting zones. The role of granulating fragmentation providing partitioning of initial materials as a main channel of input energy dissipation has been revealed. It has been shown that in joints of metals possessing normal solubility the local melting zones are true solutions, but if metals possess no mutual solubility the local melting zones are colloidal solutions. Realization of either emulsion or suspension variant takes place. The results can be used in the development of new joints of metals possessing no mutual solubility.

Highlights

► Immiscible pairs Ta/Cu and Fe/Ag are welded successfully by explosive welding. ► Fragmentation provides for partitioning as the main energy dissipation channel. ► Immiscible metals form colloidal solid solutions during solidification. ► Melting and boiling temperatures ratio determines the colloidal solution type. ► Local melting zones being in suspension form enhance welds hardening.

Introduction

Explosion welding process is very high-velocity and a little similar to other ways of materials junction, but some of joints could not be obtained in other manner. The characteristic times are duration of the welding approximately 10 6 s, rate of deformation 104–107 s 1, cooling rate 105 K/s. This process, being outwardly simple one, has a very complex physical nature, and thus requires not only a detailed structural analysis, but also a new approach. With all the variety of materials and welding regimes the key issue is a problem of intermixing in the transition zone near the interface [1], [2], [3]. Intermixing takes place as a result of a strong external action, which involves large plastic deformation (including pressure, shear components, rotatory moments of the stress, strain inhomogeneity, etc.), friction of surfaces, the effect of cumulative jet and some other factors. But so far it remains unclear how even at such a strong external action intermixing occurs in so short time while welding. More urgently the question rises when we are talking about materials that possess no mutual solubility, even in the liquid state.

Welded joints of metal-intermetallic possessing a normal mutual solubility in both liquid and solid states had been investigated previously [4], [5], [6], [7]. Commercially pure titanium was chosen as a metal, and orthorhombic titanium aluminide based alloys (“aluminide” for short) were selected as an intermetallic compound. Depending on welding conditions, different joints have been obtained and for convenience are entitled as follows: (Aw), (Ap), (Bw), (Bp), where the subscript indicates the interface shape (plain or wavy). Orthorhombic alloys containing 16 at. % Nb and 23 at. % Nb were used in joints of A type and B type, correspondingly. In some joints a melting along entire interface was observed, while the local melting zones with vortex structure take place for others. In any case, the melts are true solutions.

To find out how important is the presence of mutual solubility of the starting materials for explosion welding, metals (copper–tantalum, iron–silver), forming immiscible suspension in liquid state, were selected. “Why the intermixing of immiscible suspensions occurs?” is the question which we try to answer in this paper.

Section snippets

Experimental

The welding both of investigated joints and titanium–aluminide ones has been carried out by Central Research Institute of Structural Materials “Prometey,” St. Petersburg, Volgograd State Technical University, OJSC Ural Plant of Chemical Engineering, Ekaterinburg. The welding was carried out using different schemes and parameters, and on the basis of the results obtained, joints to be studied had been selected. We restrict our considerations by giving only the basic welding parameters in Table 1.

Results

The results of studies into two phenomena, fragmentation and formation of colloidal solutions, will be presented below. The term “fragmentation” is generally used for formation of disoriented microvolumes inside a substance. Usually fragmentation (dislocation cells, tangled configurations, bands, recrystallized grains) is observed after severe plastic deformation. Such kind of fragmentation hereinafter referred to as “traditional” is observed also after explosive welding. However there is no

Discussion

The source of energy is well known to be the explosives providing high-intensity shock wave excitation and high speed of solids. Major part of chemical energy of explosives is converted into the kinetic energy of flyer plate. The strong weld joint formation is possible if kinetic energy excess was removed from near-weld seam area by any means. In this case, dissipative structures can be formed, mainly, these, from all possible ways of the process development, choose the one possessing the

Copper–tantalum Joint for Chemical Reactor

The chemical reactor vessel scheme is shown in Fig. 15 [14]. It is made of carbon steel–copper–tantalum composite material by means of explosion welding. The inner shell consists of tantalum, corrosion resistance of which is the key moment of the reactor design. The outer shell consists of carbon steel, but copper is used as the interlayer.

As shown in Ref. [14], both of the interfaces have wavy shape, the wavelength and amplitude of Cu–Ta interface change along entire interface, and their

Conclusions

  • 1.

    The structure of welded joint of metals possessing no mutual solubility (copper–tantalum, iron–silver) has been studied. Upon explosion welding the interpenetration of metals has been found to occur by means of cusps formation, ejection of one metal into another, and local melting zone appearance.

  • 2.

    The role of granulating fragmentation (GF) providing partitioning as a main channel of input energy dissipation has been revealed. GF is a result of microfracture accompanied by agglomeration of

Acknowledgments

Electron microscopic studies were performed at the Electron Microscopy Center of Collaborative Access, Ural Branch, Russian Academy of Sciences.

This work was financially supported by the Russian Foundation for Basic Research, project no. 10-02-00354, projects 12-2-006-UT, 12-U-2-1011, 12-2-2-007 of the Ural Division of the Russian Academy of Sciences, and by the National Target Program of Ukraine “Nanotechnologies and Nanomaterials,” no. 1.1.1.3_4/10_D.

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