Ni/Ti and Ni/Al Laminated Composites Produced by ARB and Annealing: Microstructural Aspects Omid Emadinia 1 , Sónia Simões 1 , Filomena Viana 1 and Manuel F. Vieira 1 1. CEMUC, Department of Materials and Metallurgical Engineering, University of Porto, Portugal Accumulative roll bonding (ARB) is a combination of forming and bonding processes. So, this is a high promising technique to produce bulk solid materials composed of more than one constituent. ARB has been applied to strengthen metals and to produce laminated metal-metal or nonmetal-metal composites, e.g. intermetallic composites, shape memory alloys or reactive foils [1, 2]. Since ARB is performed at room temperature, the formation of new phases can be avoided. This technique is also capable of mass production and it can fabricate thick foils, using simple and cheap equipment. This essay compares two bimodal multilayer foils: Ni/Ti and Ni/Al. Input materials include foils of 99.98 wt% Ni - 125 μm thick, 99.00 wt% Al - 200 μm thick and 99.6 wt% Ti - 200 μm thick. Rolling was done with a strain rate of 20 s -1 at room temperature. Rolled batches after 4 and 10 cycles were characterized by optical and scanning electron microscopies. Energy dispersive spectroscopy (EDS) as chemical analysis technique was used to identify phases evolved in the multilayers during processing. Electron backscattering diffraction (EBSD) technique also assisted phase identification. As it is seen in Fig. 1, Ni has deformed differently in these two bimodal composites: oscillated, continuous lamellas are seen in Ni/Ti foil after 10 ARB cycles while fragmented Ni individuals are observed in Ni/Al foil after 10 cycles. Thickness of Ni layers has reached down to ultrafine and nano scales in vicinity of Ti, Fig. 1(b), and Ni fragments have an average thickness of 21 ±15 μm after 10 cycles of ARB, Fig. 1(d). This is due to the difference of mechanical behavior of the materials, i.e. Ni and Ti have similar tensile strengths and hardening coefficients while Al is a soft material. Production of intermetallic composites through the reaction of the multilayers was also studied, i.e. samples produced after 10 cycles of ARB were annealed at 800 ºC (Fig. 2). The heat treatment was done at vacuum level of 10 -3 Pa, a dwell time of 60 min under a uniaxial pressure of 10 MPa for Ni/Ti, and 240 min under 50 MPa pressure for Ni/Al. The increase of pressure aimed at avoiding void formation and minimizing delamination of layers. These defects are caused by different thermal expansion coefficients of the individual layers and by the volume changes associated with the formation of new phases due to the differences of densities. Annealed Ni/Ti is composed of TiNi matrix with embedded TiNi 3 and Ti 2 Ni particles (white zones and dark regions, respectively) illustrated in Fig. 2(b). No pure Ni was identified in Ti/Ni composite. However, in annealed Ni/Al couple there is a considerable amount of unreacted Ni, Fig. 2(d). Phase identification by EDS for Ni/Al composite was complemented with EBSD analysis. Since, EBSD is a localized characterization technique the presence of AlNi and AlNi 3 as well as residual Ni was proved. Finally, it is concluded that the fabrication of metallic composites through ARB and annealing is very promising if couples have similar mechanical properties. References: [1] Saito, Y et al., Acta Materialia 47 (1999) p. 579 [2] Eizadjou, M. et al., Composites Science and Technology 68 (2008) p. 2003 [3] The authors acknowledge FEDER funds through the program COMPETE–Programa Operacional Factores de Competitividade and also by national funds through Fundação para a Ciência e a Tecnologia under the project PEst-C/EME/UI0285/2013. Microsc. Microanal. 21 (Suppl 5), 2015 © Microscopy Society of America 2015 23 doi:10.1017/S1431927615013926