Crystal refinement by cold rolling in NiTi shape memory alloys
|Guru Prasad Dinda , Harald Roesner , Gerhard Wilde|
Forschungszentrum Karlsruhe, Institute of Nanotechnology, P.O.B. 3640, Karlsruhe D-76021, Germany
Repeated cold-rolling with intermediate folding of sheet samples represents a technique to obtain severe plastic deformation that avoids excessive heating at the internal interfaces and that proceeds without the simultaneous action of a high pressure in the range of several GPa. In the present work, bulk nanocrystalline Ni50Ti50 samples with average grain sizes below 10 nm have been synthesized at ambient temperature using two different processing pathways that start from a layered array of individual elemental sheets and alternatively, starting from the prealloyed NiTi intermetallic compound. The development of the microstructure during the different deformation routes was investigated by X-ray diffraction and scanning and transmission electron microscopy as a function of the deformation level. The development of the microstructure during cold-rolling - including the early and the late stages of deformation-induced nanocrystal formation - is analyzed in terms of the major thermodynamic and mechanical properties that govern the intermixing during the deformation treatment. Additionally, the microstructure refinement is discussed with regard to a crystal-to-amorphous transition that can occur during intense mechanical deformation. This work is supported by the DFG under contract no. WI 1899/1-2.
Presentation: oral at E-MRS Fall Meeting 2003, Symposium G, by Guru Prasad Dinda
See On-line Journal of E-MRS Fall Meeting 2003
Submitted: 2003-05-11 18:10 Revised: 2009-06-08 12:55