High Speed HPT Technology for Obtaining Fe-Mn-Si-Cr Active Elements

This paper is concerned with introducing an adapted high pressure torsion (HPT) method for severe plastic deformation (SPD) of hard-to-deform shape memory alloys (SMAs) or for obtainment of SMA active elements with complicated form. HPT technology is one of the most widely used method for severe plastic deformation enabling to obtain ultrafine structures after a couple of turns at high pressure (GPa). The results of this method are limited, in case of hard-to-deform SMAs, as well as in the case of complicated shapes of severely deformed active elements. The method introduced in this paper enables to obtain active elements with conical shape, starting from ring-shaped Fe-Mn-Si-Cr SMAs, and to apply high rotation speed (x10²s^-1) on the active surfaces of sintered-carbide anvils. During time intervals of seconds the entire sample volume is heated and simultaneously deformed to final shape. Although hot severe plastic deformation occurs, it starts at minimum possible temperatures for the specific alloy, because of the high pressure applied by means of the inferior punch. By reason of heat transfer, from sample to HPT tools, the fine structure achieved in SPD process is preserved. The hardness and microstructure variations caused by HPT were examined and discussed.

 Keywords: Severe plastic deformation, high pressure torsion, Fe-Mn-Si-Cr shape memory alloy, grain size, structure