|Number of page(s)||5|
|Section||Applied Research and Applications: Engineering Materials with MT|
|Published online||01 September 2009|
Processing technologies of Ni-Ti based shape memory alloysI. Szurman and M. Kursa
VSB-Technical University of Ostrava, Ostrava, Czech Republic
Published online: 1 September 2009
Transformation characteristics and properties of the Ni-Ti based shape memory alloys are in the first place highly dependent on processing technology. It is known that small deviation from the required composition can cause very important change of transformation temperatures. For this reason it is necessary to pay special attention to the metallurgy of these alloys. The current key technologies for processing are in most cases realised in vacuum, and various methods of melting are used (electron-beam melting, arc melting, induction highfrequency melting). Plasma melting is another possibility. Complications during preparation are caused mainly by carbon, nitrogen and oxygen, which form non-metallic inclusions. Carbon is related to the alloys mainly in the course of their preparation in graphite crucibles. Other problems are connected with observation of appropriate conditions for crystallisation and with related minimisation of possible micro- and macro-segregations. Formation of titanium carbide and titanium oxide in Ni-Ti shifts concentration of individual elements and thus leads also to change of the temperature of martensitic transformation. Creation of a low-melting phase Ti2Ni, which causes a distinct susceptibility to hot formation of cracks, is another issue arising during melting of Ni-Ti alloys. The presented article is focused on comparison of individual methods of preparation of the alloys mentioned above, i.e. induction vacuum melting, plasma and electron-beam melting.
© Owned by the authors, published by EDP Sciences 2009