TECHNICAL ARTICLE Characterization of Explosion-Bonded Ti-Alloy/Steel Plate with Ni Interlayer I. Rosenthal • A. Miriyev • E. Tuval • A. Stern • N. Frage Received: 27 November 2013 / Revised: 16 January 2014 / Accepted: 28 January 2014 Ó Springer Science+Business Media New York and ASM International 2014 Abstract A three-layered explosion-welded (EXW) plate consisting of Ti-alloy/Ni/steel was investigated. Both the Ti/Ni and Ni/steel interfaces displayed a wavy shape typ- ical of the EXW process, which reflects the occurrence of massive mass transfer during bonding. New phase forma- tion was not observed at the Ni/steel interface, while, according to the SEM, XRD, and nanoindentation testing, the formation of brittle intermetallic phases took place at the Ti-alloy/Ni interface. These intermetallics serve as the weakest part of the joint and determine a brittle mode of fracture under tensile stress. The tensile strength of the joint is about 300 MPa, which is determined by interme- tallic phases formed at the Ti/Ni interface. Keywords EXW  Solid state welding  Ti  Steel Introduction The explosion bonding process (explosion-welded, EXW) for both similar and dissimilar metals was developed in the USA, in the late 1950s, as a solid state welding technique. During recent decades, the influence of various practical conditions on explosion welding has been extensively explored. Different metal combinations, geometrical arrangements, detonation parameters, etc. have been stud- ied in order to find practical criteria of weldability and of high interfacial bond strength [1–13]. It was established [10–16] that the explosion-bonded structural transition joint (STJ) provides a fast and efficient medium to attach two different metals, steel and Ti-alloys for instance, with satisfactory properties. Commercial explosion bonding procedure allows direct joining of titanium alloys to steels with hardness values up to 450 HV and yield strength values up to 750 MPa; however, when steel displays ele- vated hardness and yield strength values it is necessary to use a low yield strength thin interlayer, such as Ni, Cu, etc. In this study, Ti-alloy/steel explosion-bonded plate with a Ni interlayer (Fig. 1), supplied by ATI-Allegheny Tech- nologies Inc, was investigated. Characterization Procedure Materials The as-received EXW plate (160 9 75 9 20 mm) consists of three layers: Ti-alloy, steel, and a nickel interlayer (Fig. 1). The composition of each layer according to energy dispersive x-ray spectroscopy (EDS) analysis is presented in Table 1. Ultrasonic Testing (UT) and Scanning Acoustic Microscope (SAM) The UT measurements were performed using a 6 MHz (Ba6-5) probe. Each sub-specimen was divided into 40 points and then scanned with the probe. SAM can detect sub-micron air gaps, as thin as 0.1 lm, inclusions, micro cracks, and adhesion defect with resolu- tion of 5 lm. The image of a bond is recorded in reflection mode; i.e., the same lens was used in both transmitting and receiving the acoustic signal. The measurements were performed on an internally built SAM apparatus using a I. Rosenthal (&)  A. Miriyev  E. Tuval  A. Stern  N. Frage Department of Materials Engineering, Ben-Gurion University of the Negev, Beersheba, Israel e-mail: idanros@bgu.ac.il 123 Metallogr. Microstruct. Anal. DOI 10.1007/s13632-014-0120-1