Phase transformations and functional properties of intermetallic Ni-Ti based shape memory alloys after processing and post deformation heat treatment

 

V. S. Kalashnikov¹, V. V. Koledov¹, A. V. Petrov¹, D. V. Gunderov³ , V. A. Andreev², V. G. Shavrov¹, D. V. Kuchin¹, R. M. Gizatullin⁴

¹Kotel’nikov Institute of Radio-engineering and Electronics of RAS

² «Matek-Sma» Ltd.

³Institute of Molecule and Crystal Physics URC RAS

⁴«Nano-dent» Ltd.

 

 The paper is received on December 15, 2015

 

Abstract. An experimental study of the effect of severe plastic deformation (SPD) on the functional properties and phase transformations of the NiTi shape memory alloy (SMA) was carried out. A different technologies of thermochemical processing were applied: equal channel angular pressing (ECAP), warm forging (WF) and the combination of ECAP and WF. Measurements of the strain-stress-temperature  curves of the SMA samples were carried out using original three-point bending setup. It was demonstrated that the samples, processed by combination of ECAP + WF is the most durable, has a yield stress in the range of 1200-1300 MPa and recoverable deformation of 9-10%, significantly exceeding the parameters of other samples: ECAP - yield stress in the range of 900-1000 MPa, revertible deformation 10-11% and WF - yield stress in the range 500-600 MPa at revertible strain 5-6%. It was proposed to characterize the functional properties of SMAs in term of "energy capacity". Investigated in this paper NiTi alloy treated by technology ECAP + TC now shows a record combination of functional parameters and strength.

Key words: shape memory alloys, thermoelastic martensite transformation, nickel titanium, three-point bending technique, functional properties.