Amorphization of Titanium Nickelide by means of Shear under Pressure and Crystallization at the Subsequent Heating

Abstract:

Transmission electron microscopy and X-ray diffraction were used to study structural changes in the Ti-50.5 at. % Ni alloy upon severe plastic deformation by shear under pressure and subsequent heating. An increase in the degree of deformation leads sequentially to a martensite transformation, twinning of martensite crystals, formation of reorientation bands, development of rotational modes of deformation, formation of a nanocrystalline structure, and finally amorphization. A scheme of the formation of amorphous structure of the alloy during deformation is suggested based on the observed structural changes. It has been found that a reverse martensitic transformation might be one of mechanisms of plastic deformation of the alloy. Therefore, as the degree of deformation increases, first forward and subsequently reverse martensitic transformations can occur. The formation of an amorphous structure starts as the degree of deformation reaches 4.2 (one revolution of Bridgman anvils); at a degree of deformation of 6.8 (5 revolutions of the anvils), the process is virtually completed. The crystallization of the amorphous alloy upon heating starts even at 200°C. However, upon heating up to 300°C (for 0.5-h holdings), the kinetics of crystallization is slow. After annealing at 350°C, the complete crystallization with the formation of a nanocrystalline structure with a grain size of 20-70 nm takes place

• Periodical: Materials Science Forum (Volumes 738-739)
• Pages: 525-529
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.738-739.525
• Online since: January 2013
• Authors: Natalya Frolova, Vitaly Zel'dovich, V.P. Pilyugin, Vyacheslav Gundyrev, Alexander Patselov
• Keywords: Twinning, Amorphous Structure, High Pressure Torsion, Martensite Transformation, Nanocrystalline Structure

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DOI: 10.4028/www.scientific.net/msf.738-739.525

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