Nanostructure and properties of the large size Ti49,4Ni50,6 alloy samples, subjected to High Pressure Torsion Deformation with subsequent annealings

Aleksander V. Lukyanov 1Dmitry V. Gunderov 1Egor A. Prokofiev 1V. G. Pushin 2

1. Institute of Physics of Advaced Materials, Ufa State Aviation Technical University (IPAM USATU), 12 K. Marx st., Ufa 450000, Russian Federation
2. Russian Academy of Sciences, Ural Division, Institute of Metal Physics, 18 S.Kovalevskaya str., GSP-170, Ekaterinburg 620219, Russian Federation

Abstract

TiNi-based alloys are the functional materials with shape memory effect (SME). It was demonstrated that perspective way of improving properties of metals and alloys is formation of NC structure using methods of the severe plastic deformation (SPD). In earlier works amorphous and nanocrystalline (NC) structures in TiNi have been processed by high pressure torsion (HPT). Subsequent annealings lead to the formation of nanostructured state. However, these works considered only small HPT-processed samples 5-10 mm in diameter and approximately 0.1-0.15 mm in thickness, which hampered the investigation of mechanical properties and shape-memory effects and did not allow to use high-strength NC TiNi for practical application. A new HPT equipment was used in this work for the first time. It allows to produce large size HPT samples of Ti49,4Ni50,6 alloy with the diameter of 20 mm and thickness of 1 mm. TEM studies of microstructure showed that the samples processed by HPT had amorphous-nanocrystalline state with the size of nanocrystals less than 20 nm. Fabrication of NC structure by subsequent annealings of such HPT samples is first investigated as well. After annealing at 400ºС (1 hour) samples underwent a complete nanocrystallization and an average grain size constituted 30 nm. The subsequent annealing at 500ºС leads to grain growth up to 50 nm. Microhardness measurements showed values increasing from initial 1800 MPa to 5600 MPa after HPT processing. Nanocrystalline state results in the record value of strength for this material - 2600 MPa. Thus, HPT combined with subsequent annealings at varying temperatures allowed to obtain integral nanostructured Ti49.4Ni50.6 specimens with various grain sizes. Now, it is possible to carry out complex investigations of NC structure effect on mechanical and functional properties of TiNi alloys. Besides, it became possible to use such samples as a semi-product for various practice application.

 

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Presentation: Poster at E-MRS Fall Meeting 2007, Symposium E, by Aleksander V. Lukyanov
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-14 13:01
Revised:   2009-06-07 00:44