Structural changes during formation of laminated titanium-intermetallic composite

Marek Konieczny Politechnika Świętokrzyska, Katedra Metaloznawstwa i Technologii Materiałowych, al. 1000-lecia PP. 7, 25-314 Kielce, Poland

Quarterly No. 2, 2008 pages 168-171

DOI:

keywords: laminated composite, titanium, copper, intermetallic compounds

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abstract Well-bonded and almost fully dense laminated composites have been fabricated successfully by reactive sintering in vacuum using Ti and Cu foils. Since the copper layers were completely consumed by forming phases, the final microstructure consisted of alternating layers of intermetallic phases and unreacted titanium. Effects of treating time at 900C and the microstructural changes were studied by interrupting in steps the reaction progressing after 0.5, 1, 2, 3, 4 and 5 hours. With the liquid phase appearance a fast growing of the layers containing intermetallic phases was observed. Because the structure resulting from solidification of locally melted reaction zone contained phases rich in copper (especially TiCu4), melting consumed more copper than titanium. For this reason, the boundary between the intermetallic layers and copper migrated toward the copper side. Microstructural investigations by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDX) showed that after 0.5 hour of heat treatment at 900C intermetallic compounds: Ti2Cu, TiCu, Ti3Cu4, Ti2Cu3, TiCu4 and solid solution Ti were formed. After the completely consumption of Cu, the intermetallics layer consisted of thin layers of Ti2Cu (adjacent to eutectioid layer and titanium), thick layers of TiCu and the reaction zone consisting of TiCu4 particles in Ti3Cu4+Ti2Cu3 matrix. The particles were probably produced by stresses resulting from the growth of the intermetallic layer. Since titanium could diffuse through the Ti2Cu and TiCu layers to the reaction zone, it leaded to the growth of TiCu at the expense of TiCu4, Ti3Cu4 and Ti2Cu3. As a result, the TiCu compound became dominant phase if the treating time was longer than 1 hour. After 5 hours of treating the intermetallic layer was transformed almost wholly into TiCu, but with a thick Ti2Cu interphase layer. The formation of the TiCu phase is thermodynamically favoured over the formation of the other phases and can be understood from the steps occurred through a series of solid-liquid and solid state reactions involving TiCu4 as one of the starting phases.