Influence of titanium on structure formation, liquation processes and microhardness of structural components of Al – Ni – Ti alloys synthesized from the oxide phases by SHS metallurgy

Abstract

The paper is devoted to revealing the regularities of the influence of titanium (0.91, 2.42, 3.19, 3.39, 4.32 and 8.81 wt.%) on structure formation, nature of element distribution and microhardness of structural components in Al – Ni – Ti alloys by aluminothermy during SHS metallurgy. As the initial composition of the charge were selected the following materials in fractional parts: Al:NiO 2 :CaF 2 :NaNO 3 :TiO 2 = 10:10:12:6: X , where X = 1.5, 4.5, 5.0, 7.0, 10.0. X The structural components in Al – Ni – Ti alloys have been identified by electron microscopy and X -ray spectral analysis XX of elements. In the alloys with 0.91–4.32 wt.% Ti the following phases crystallize: β′ -phase (solid solution of Ni in the nickel aluminide AlNi) Al 3 Ni 2 , Al 3 Ti, Al 3 Ni and α -solid solution of Ni and Ti in aluminum. In an alloy with 8.81 wt.% Ti the β′ -phase turns into a titanium-doped nickel aluminide Al(NiTi) (composition in at.%: 50.53 Al; 1.47 Ti; 48.0 Ni). The increase of titanium content in Al – Ni – Ti alloys increases the solubility of Ni in the β′ -phase and at titanium concentra- tion in the alloy 8.81 wt.% in the aluminide Al(NiTi) up to 48 at.% Ni is dissolved compared to the solubility of nickel (38 at.%) in the alloy with 0.91 wt.% Ti. Increasing the nickel content in the above phases contributes to their microhard- ness from 13 GPa to 14.8 GPa at 8.81 wt.% Ti. Increasing the titanium content in Al – Ni – Ti alloys to 4.32 wt.% increases the solubility of nickel in the nickel aluminide Al 3 Ni, with a higher concentration of titanium (8.81 wt.%) in the nickel aluminide with titanium Al(NiTi) dissolves up to 48.53 at.% Ni, while in the alloy with 0.91 wt.% Ti – only about 1.0 at.% Ni. At the same time, the Al and Ti content in titanium aluminide Al 3 Ti decreases and its microhardness increases. It was not possible to determine the microhardness of Al(NiTi) aluminide because of the formation of a porous structure. In nickel aluminide Al 3 Ni, an increase in titanium content leads to an increase in nickel concentration to 4.32 wt.% Ti followed by a slight increase to 8.81 wt.% Ti. Despite increasing the nickel content and decreasing the aluminum concentration, the microhardness of the nickel aluminide decreases. Apparently, this circumstance is caused by the formation of a porous structure in this phase.