Explosion bonding

The quality of bonding is related direcdy to the size and distribution of solidified melt pockets along the interface, especially for dissimilar metal systems that form intermetaUic compounds. The pockets of solidified melt are brittle and contain localized defects which do not affect the composite properties. Explosion-bonding parameters for dissimilar metal systems normally are chosen to minimize the pockets of melt associated with the interface. 

When the explosion-bonding process distorts the composite so that its flatness does not meet standard flatness specifications, it is reflattened on a press or roUer leveler (ASME SA20). However, press-flattened plates sometimes contain localized irregularities which do not exceed the specified limits but which, generally, do not occur in roU-flattened products. 

Ra.m Tensile. A ram tensile test has been developed to evaluate the bond-2one tensile strength of explosion-bonded composites. The specimen is designed to subject the bonded interface to a pure tensile load. The cross-section area of the specimen is the area of the aimulus between the outer and inner diameters of the specimen. The specimen typically has a very short tensile gauge length and is constmcted so as to cause failure at the bonded interface. The ultimate tensile strength and relative ductihty of the explosion-bonded interface can be obtained by this technique. 

Hardness, Impact Strength. Microhardness profiles on sections from explosion-bonded materials show the effect of strain hardening on the metals in the composite (see Hardness). Figure 8 Ulustrates the effect of cladding a strain-hardening austenitic stainless steel to a carbon steel. The austenitic stainless steel is hardened adjacent to the weld interface by explosion welding, whereas the carbon steel is not hardened to a great extent. 

Vessel heads can be made from explosion-bonded clads, either by conventional cold- or by hot-forming techniques. The latter involves thermal exposure and is equivalent in effect to a heat treatment. The backing metal properties, bond continuity, and bond strength are guaranteed to the same specifications as the composite from which the head is formed. AppHcations such as chemical-process vessels and transition joints represent approximately 90% of the industrial use of explosion cladding. 

Chemical-Process Vessels. Explosion-bonded products are used in the manufacture of process equipment for the chemical, petrochemical, and petroleum industries where the corrosion resistance of an expensive metal is combined with the strength and economy of another metal. AppHcations include explosion cladding of titanium tubesheet to Monel, hot fabrication of an explosion clad to form an elbow for pipes in nuclear power plants, and explosion cladding titanium and steel for use in a vessel intended for terephthaHc acid manufacture. 

Perhaps the most extensive appHcation for conversion-rolled, explosion-bonded clads was for U.S. coinage in the 1960s (34) when over 15,900 metric tons of explosion-clad strip that was suppHed to the U.S. Mint helped alleviate the national silver coin shortage. The triclad composites consist of 70—30 cupronickel/Cu/70—30 cupronickel. 

Explosion-bonded metals are produced by several manufacturers in the United States, Europe, and Japan. The chemical industry is the principal consumer of explosion-bonded metals which are used in the constmction of clad reaction vessels and heat-exchanger tube sheets for corrosion-resistant service. The primary market segments for explosion-bonded metals are for corrosion-resistant pressure vessels, tube sheets for heat exchangers, electrical transition joints, and stmctural transition joints. Total world markets for explosion-clad metals are estimated to fluctuate between 30 x 10 to 60 x 10 annually. 

The electrolytic cells shown ia Figures 2—7 represent both monopolar and bipolar types. The Chemetics chlorate cell (Fig. 2) contains bipolar anode/cathode assembhes. The cathodes are Stahrmet, a registered trademark of Chemetics International Co., and the anodes are titanium [7440-32-6] Ti, coated either with mthenium dioxide [12036-10-17, RUO2, or platinum [7440-06-4] Pt—indium [7439-88-5] Ir (see Metal anodes). Anodes and cathodes are joined to carrier plates of explosion-bonded titanium and Stahrmet, respectively. Several individual cells electrically connected in series are associated with one reaction vessel. 

Another process involves explosive bonding. The corrosion-resistant metal is bonded to a steel backing metal by the force generated by properly positioned explosive charges. Relatively thick sections of metal can be bonded by this technique into plates. 

Some of the restrictions on the use of aluminum are caused by manufacturing and fabrication problems and by its low mechanical strength. However, aluminum is widely used and is competitive with Type 316 stainless steel in many instances. The explosion-bonding process has made the aluminum cladding of steel practical, and... 

Hill, B. and Trueb, L. F., Resistance of Explosion-bonded Stainless Steel Clads to Intergranular Corrosion and Stress Corrosion Cracking , Corrosion, 25, 23 (1969)... 

There is an increasing interest in explosive bonding as a means of bonding aluminium-steel and other composite cladding systems. 

Transition joints are used to join dissimilar metals where flanged, screwed, or threaded connections are not practical. They are used when fusion welding of two dissimilar metals forms interfaces that are deficient in mechanical strength and the ability to keep the system leak-tight. Transition joints consist of a bimetallic composite, a stainless steel, and a particular kind of aluminum bonded together by some proprietary process. Some of the types in use throughout the cryogenic industry are friction- or inertia-welded bond, roll-bonded joint, explosion-bonded joint, and braze-bonded joint. 

Ref Dr H. Freiwald of Saint Louis Laboratory, Germany private communication, 12 Sept 1962 Note See also in Vol 3 of Encycl, pp C396-L ff 1960. Detaclad Process or Explosive Cladding, also called Explosive Bonding was developed by the duPont Co (See Vol 3 of Encycl, pp D96 D97)... 

Explosive Bonding, also called Explosive Cladding. See Detaclad Process in Vo 1 3, pp D96"L to D97... 

Explosive Bonding Analog is described by J.E. Kowalick D-R. Hay in Frankford Arsenal, Report A7l—7, Aug 1971, entitled "A Flow Analog for Explosive Bonding . Order as AD 730299 from NTIS, US Dept of Commerce, PO Box 1553, Ravensworth, Va 22151. Abstracted in Expls Pyrots 5(3)... 

Explosive Bonding, Mechanism of. An aero-hydrodynamic analogy is used to construct a description of the formation of wavy interfaces during expl bonding, which is described by J.T. Kowalick D.R. Hay in Metallurgical Transactions, Vol 2, July 1971, pp 1953-58... 

DuPont s Delay Electric Caps, such as Acudet Mark V and MS (Millisecond) Delay (Ref 6, pp9l DuPont s Detaclad (Explosion-Bonded Clad Metal), Ref 6, op 14-15. See also Vol 3 of Encycl, p D96-L... 

Common materials as austenites, titanium, Hastelloys, tantalum, nickel, and silver are used to avoid corrosion attack. These materials are used as lining materials in vessels or as explosion-bonded steel sheets. The sheets are formed to parts of an internal liner of a vessel, and these parts are welded, using special welding procedures, to a complete liner. 

---