Structure of a bimetallic strip produced by plasma spraying of a TiAl powder on a niobium sheet

Ti-48 at % Al alloy granules produced by centrifugal spraying are milled into a powder with a particle size of 40–100 μm, and are applied onto a niobium foil using plasma spraying in an argon atmosphere. The fabricated TiAl/Nb bimetallic strip consists of a 100-μm-thick niobium layer and a porous 300-to 400-μm-thick TiAl layer formed by flattened particles. Directly after the preparation of the bimetallic strip, the surface of the TiAl porous layer is rough. Vacuum annealing at 1000, 1100, and 1200°C for 0.5–1.5 h leads to intense pore healing. After deposition and annealing, the interlayer adhesion is strong. The preparation of TiAl granules and spraying of the powder is accompanied by aluminum depletion of the Ti-48 at % Al alloy to 42–45 at % and an increase in the fraction of the α₂-Ti₃Al phase in the deposited layer. The prepared material has a duplex structure. An intermediate diffuse layer characterized by a variable composition and thickness is formed at the interface. This layer consists of two solid solutions; one of them, which is formed at the TiAl layer, is an α₂-Ti₃Al-based solid solution of niobium and the other, which is formed at the niobium foil, is a niobium-based solid solution of titanium and aluminum.