Tensile behaviour of laminated titanium-intermetallic composite synthesised using titanium and copper foils
Marek Konieczny
Quarterly No. 2, 2009 pages 117-121
DOI:
keywords: laminated composite, intermetallics, mechanical properties, deformation
abstract Ti-intermetallic laminated composites have been fabricated via reaction synthesis in vacuum using 0.15, 0.20 and 0.25 mm thick foils of titanium and 0.05 mm thick foil of copper with controlled temperature and pressure. Effects of treating time at 900°C were studied by interrupting the reaction progressing after 0.5 and 5 hours. 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 were formed. The intermetallics layer consisted of thin layers of Ti2Cu, thick layers of TiCu and the reaction zone consisting of TiCu4 particles in Ti3Cu4+Ti2Cu3 matrix. 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 other phases. As a result, after 5 hours of treating the intermetallic layer was transformed almost wholly into TiCu, but with a thick Ti2Cu interphase layer. The mechanical properties and fracture behaviour of the fabricated composites were examined through tensile test. The results showed that treating time at 900°C was a main factor determining properties because it led to an increase in volume fraction of the intermetallics. Unfortunately, long heat treatment caused a degradation of the intermetallic layers by oxidation because implemented vacuum was not high enough. After 0.5 hour of treating at 900°C the oxides on interlayer had no significant influence on the strength of the layers. EDX results showed that after long heat treatment the oxides were captured in the growing intermetallic layers to form inclusions or voids. This resulted in the formation of weak points in the intermetallic layers, from which cracks would have initiated easily, leading to premature failure of the layers during loading. Investigations indicated that the yield strength of all fabricated composites increased with increasing of the treating time. On the other hand, after 0.5 hours of treating the composites had higher ultimate tensile strength and higher strain at fracture. The results also showed that the composites exhibit a good cohesion between titanium layers and layers of intermetallic phases during tensile test.