Multi-channel Spiral Twist Extrusion (MCSTE): A Novel Severe Plastic Deformation Technique for Grain Refinement
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THE grain size of crystalline metals is regarded as a major microstructural aspect affecting both the mechanical and physical properties of a component. Inherently, controlling the grain size produces products with the desired properties. Accordingly, to cope with the never-ending race of tailoring materials with enhanced properties in service conditions, several attempts for the development of feasible grain-refinement techniques have been made and are still in progress.[1] Among these different approaches, the most successful has been the Severe Plastic Deformation (SPD), which has emerged as an effective technique for exposing materials to intensive plastic straining to achieve an ultrafine-grained (UFG) structure.[2,3]
W.H. El-GARAIHY is with the Mechanical Engineering Department, Unayzah College of Engineering, Qassim University, Qassim, 51911, Kingdom of Saudi Arabia and also with the Mechanical Engineering Department, Suez Canal University, Ismailia, 41522, Egypt. D.M. FOUAD and H.G. SALEM are with the Mechanical Engineering Department, The American University in Cairo, Cairo, 11835, Egypt. Contact e-mail: [email protected] Manuscript submitted October 5, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
Currently, researchers are focusing on improving SPD methods tailored for the fabrication of various UFG materials, which exhibit superior properties that are valuable for different industrial applications.[4,5] SPD techniques, unlike conventional methods such as rolling, extrusion, forging, and drawing, refine grain size to the submicron scale and hence strengthen the material and enhance its mechanical properties without the need for introducing modification in the processed billet’s dimensions.[1,2,6–8] The modification in the microstructure when adopting SPD techniques leads to a significant enhancement in functional, physical, chemical, and mechanical properties.[9] Consequently, the interest in SPD stems from the superior properties exhibited by the resultant UFG material.[10] Currently, several alternatives of SPD techniques, which implicitly apply high hydrostatic pressure, are set for fabricating a wide range of materials. Among the most established renowned techniques are Equal Channel Angular Pressing (ECAP)[11–16] and High-Pressure Torsion (HPT),[17–21] which have proven to be very successful early implementations of the principles of SPD dating back to the early 1980s.[2] The ECAP works by pressing a metal rod through an angled channel, typically 90 deg. The process should be repeated several times to achieve optimal results, along with changing the orientation of the billet in each pass.[11] Therefore, the ECAP is considered as a discontinuous process, and for
that reason, the HPT process was introduced. The latter process is conducted via applying severe compressive stresses on a disk to obtain a high frictional force, which results in shearing the disk by torsion all in a single operation.[2] Several researchers have regarded HPT as the most efficient grain-refinement method. However, it is
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