Properties, Production and Applications of NiTi Shape Memory Alloy

The Ni-Ti alloys with approximately equiatomic chemical composition are one of the most important materials from the shape memory alloys. Excellent properties such as shape memory effect and superelasticity are based on the phase transformation between austenite and martensite structure of the NiTi phase. In the past the investigation of the preparation methods was focused on melting metallurgyvacuum induction melting and arc re-melting and powder metallurgy routes like self-propagating high-temperature synthesis, hot isostatic pressing and spark plasma sintering. In the last several years importance of the additive manufacturing has increased significantly. This paper deals with formation of the Ni-Ti intermetallic phases between the nickel and titanium layers deposited on each other by direct energy deposition energy method. The varied mixture of the Ti2Ni, NiTi and Ni3Ti phases was formed in agreement with the binary Ni-Ti phase diagram. Some problems like cracking and nickel loss have to be solved by preheating of platform or adjustment of laser parameters.

Formation of Intermetallics Layers in Ni-Ti System Prepared by Direct Energy Deposition

Salvetr¹,

Vavřík²,

Školáková³

et al. 2019

Effect of Nickel Particle Size on Eactive Sintering Production of Niti Shape Memory Alloy

Novák¹,

Marek²,

Dvořák³

et al. 2016

This work is focused on the description of the influence of the particle size of nickel on the synthesis of NiTi shape memory alloy by reactive sintering with high heating rate (300 °C.min-1). It was found that coarse nickel powders undergo only a limited thermally-activated reaction. On the other hand, too fine powders support the low-temperature (500-800 °C) diffusional formation of Ni-Ti intermetallics which could then suppress the rapid thermallyactivated reaction. The optimum powder fraction of nickel to obtain the material with the lowest porosity and fraction of undesirable Ti2Ni phase is 25-45 µm.

Contribution of Microscopy to Clarify the Mechanism of Ni-Ti Phases Formation During Reactive Sintering

Novák¹,

Salvetr²,

Nová³

et al. 2016

NiTi alloy exhibits the shape memory effect, which implies the application in medicine and also many industrial branches. This paper is devoted to the manufacture of these alloys by the use of powder metallurgy using reactive sintering. This method could enable easier production of this alloy and achievent of higher purity. However, for the optimization of this technology, the deeper knowledge of the mechanism of the process is needed. This work uses microscopy on real powder mixtures subjected to reactive sintering, as well as on model samples processed under various conditions.