چكيده به لاتين
Throughout few recent decades, using metal tubes have increased because of their exellent mechanical and physical properties. Therfore, producing nano-structural materials have been investigated by lots of reaserchers. Initially, severe plastic deformation methods were limited on special shapes. Over time, producing common specimens like tubes were considered. One of the severe plastic deformation methods for tubular products was friction assited tube straining method which was presented recently. With regard to this method for producing high strength tubes, there are some limitations that can be refered to executing this process in two steps. Therefore, modified friction assisted tube straining method was presented in this study in order to processing the process in a single step. For this purpose, initially a die was designed for continuous process and many experimental tests for finding appropriate parameters like feed rate and rotational speed were done. Feasibility of the process was indicated at feed rate 0.08 rev/min and rotational speed 710 rev/min. Mechanical poperties and microstructure of specimens were examined by longitudinal and peripheral tensile tests, micro-hardness and optical microscopy. Results showed that tensile strength and hardness were increased considerably in longitudinal and peripheral directions. Also, microstructure was refined significantly. Approximately, elongation of processed specimen was constant which showed higher performance of this process rather than other SPD methods. The best strength of processed specimens is 325 MPa ( in peripheral direction) which is increased 85.7 percent. Elongation to fracture ratio for processed specimen in longitudinal direction was decreased to %16. Grain size of annealed specimen was 76 that is reduced to 7 and 9 in peripheral and longitudinal directions, respectively. Hardness of specimen was increased by 50.8 percent to the maximum value 72.4 Hv.
