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TRODUCTION

IN recent years, friction stir processing (FSP) has been used as an impressive process in the fabrication of metal matrix composites.[1–3] Since FSP method maintains the material in the solid phase and imposes severe plastic deformation during processing, this helps avoid many of the difficulties related to processing of composites in the liquid phase, such as poor wetting and tendency of particles to form clusters. Initially, FSP was applied to aluminum alloys as a technique for fabrication of aluminum-based composites.[4,5] Subsequently, the very successful implementation of FSP has driven the expansion of this technology to fabricate other composites such as magnesium,[6,7] titanium,[8,9] and steel matrix composites.[10] This practical success necessitates the development of a more fundamental understanding of the FSP process. In addition to this, the final aim is to precise determination of the properties of the fabricated composite. Certainly, having the fundamental knowledge of the structural response to FSP will make it possible to predict the microstructure and, consequently, the properties of the fabricated composite. Limited studies were found in the literature describing the development of crystallographic texture through the AZIZ SHAFIEI-ZARGHANI, Ph.D. Student, and SEYED FARSHID KASHANI-BOZORG, Associate Professor, are with the Center of Excellence for Surface Engineering and Corrosion Protection of Industries, School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, P.O. Box: 11155-4563, Tehran, Iran. Contact email: [email protected] ADRIAN P. GERLICH, Associate Professor, is with the Department of Mechanical and Mechatronics Engineering, University of Waterloo, Waterloo, ON, N2L 3G1 Canada. Manuscript submitted April 8, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A

application of friction stir welding (FSW) or processing on different types of titanium alloys.[11–16] An earlier report provided an assessment of the crystallographic texture in friction stir weld of a b titanium alloy, which retains the metastable b phase after cooling.[11] The results showed that the developed texture was in an excellent agreement with the shear textures reported by Rollett and Wright[17] for bcc of tantalum. Mironov et al.[12] studied the development of grain structure in b phase field during FSW of Ti-6Al-4V alloy. They analyzed the texture of the retained b phase in the deposited weld using electron back-scattered diffraction detector (EBSD). The flow patterns within the stir zone (SZ) were used to approximate the shape of the effective shear plane created by the processing tool. They used this approach in order to rotate the pole figure obtained from the transverse cross section of SZ into an approximate shear frame of reference, with the shear direction (SD) and the shear plane normal (SPN). They concluded that the resultant   texture could be roughly described as the bcc Jð110Þ 112 ideal simple shear texture. In another research, Mironov et al.[14] used similar approac