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In this work, the formation of intermetallics in Ni–Ti system by reactive sintering at 500 and 650 °C was studied. Mechanism and kinetics of the reactions leading to Ni–Ti phases were determined by DTA and the application of an experimental model consisted of nickel-plated titanium. It was found that Ti 2 Ni phase forms already at 500 °C. At 650 °C this phase undergoes a reaction with nickel to NiTi and Ni 3 Ti. The reactions were determined to be diffusion-controlled. The formation of Ni 3 Ti contributes to the porosity evolution during reactive sintering production of NiTi alloy. [ABSTRACT FROM AUTHOR]

Reactive sintering is currently considered as a promising production route for titanium aluminides in many research works. However, the published descriptions of the reaction mechanism are contradictory or lacking, especially at the temperatures below the melting point of aluminium. This work aims to fill this gap, providing the description of the reactive sintering process at the temperatures between 400 and 900 °C. The phases' formation sequence and reaction kinetics were studied and explained using experimental model (Ti/Al diffusion couple) and real reactively sintered samples of equiatomic Ti-Al compressed powder blend. Moreover, phase formation was thermodynamically assessed. It was revealed that Ti 2 Al 5 phase formed preferentially. This phase has not been reported previously as a starting phase in reactive sintering. According to results obtained by experimental model, its formation is controlled by diffusion at 700 °C. This phase reacted with aluminium forming pure TiAl 3 phase or with titanium, resulting in TiAl phase. Subsequently, TiAl phase reacted with titanium, leading to the Ti 3 Al phase, or with already present Ti 2 Al 5 phase yielding TiAl 2 intermetallic compound. Titanium-rich Ti 3 Al phase could form only at the temperature of 600 °C or above. Image 10885 • Phase formation is controlled by diffusion. • Ti 2 Al 5 phase forms preferentially. • Ti reacts above 600 °C, Al starts to react under its melting point. [ABSTRACT FROM AUTHOR]