Influence of Preparation Conditions On Properties of NiTi Alloy Prepared by TE-SHS Method

Recently, an approximately equiatomic alloy of nickel and titanium has been intensively studied. It is due to its unique properties such as pseudoplasticity, superelasticity and shape memory. Moreover, it possesses sufficient biocompatibility and good corrosion resistance. Therefore it is used for various applications in aerospace, aircraft, military and medical industry. Commonly, this alloy is fabricated by vacuum induction melting (VIM), vacuum arc remelting (VAR), or by their combination (VIM/VAR). Unfortunately, these methods have some disadvantages such as not sufficient purity or inhomogeneity of produced ingots. Therefore new fabrication methods of the NiTi alloy have been explored. A self-propagating high-temperatures synthesis (SHS) seems to be a promising approach of the NiTi alloy fabrication. This method is based on fast heating of green compacts prepared from elemental powders. Diffusion processes and exothermic chemical reactions take place, which leads to the formation of eutectic systems and increasing the temperature of the process. Consequently, the formation of the melt causes to faster diffusion and homogenization of the system. While the plane wave propagation mode (PWP) of SHS has been usually used for preparation of porous NiTi samples, the thermal explosion mode (TE) of SHS has been preferred for production of compact NiTi samples, according to the literature. The microstructure and therefore properties of prepared samples are strongly influenced by many parameters of the SHS process. These parameters include especially heating rate, time of sintering and size of powder particles.

In this work, we focused on the influence of conditions of the TE-SHS method on the microstructure, phase composition, transformational behaviour and mechanical properties of the prepared NiTi samples.