Description
The interest in NiTi as a shape memory and super-elastic material has been significant over the past few decades. Combustion synthesis has the advantage of being a process of low-thermal budget due to its use of the exothermic heat of reaction between elemental powders to spontaneously generate the intended product. However, to date the combustion synthesis of NiTi has been plagued by the almost unavoidable formation parasitic phases within the product microstructure such as Ti2Ni and Ni4Ti3 which have been shown to alter the overall composition of the intended NiTi phase, and are detrimental to the mechanical properties. The present paper describes a novel process that can produce Ti2Ni and Ni4Ti3-free NiTi microstructures. Current activated reactive spin casting (CARSC) was used for the first time to produce NiTi from elemental powders of Ni and Ti producing flat interfaces. A novel devise (Reactive Spin Caster) and high vacuum system was designed and fabricated to accomplish this. The effects of disc temperature and speed on the developed macro- and microstructures are discussed. An increase in disc temperature was found to have a beneficial effect on the spreading of the electrically-reactively melted NiTi. The disc speed was found to affect both the macro and microstructure of the Ni-Ti product. The highest disc speed produced the thinnest NiTi interface (~400 microns) with a microstructure that contained austenitic NiTi as the major phase with martensitic NiTi as a minor one, with no parasitic phases.
