Effects of adding CNTs on the thermo-mechanical characteristics of hybrid titanium nanocomposites

Feasibility of using carbon nanotubes (CNTs) for improving the thermo-mechanical properties of titanium (Ti) matrix composites (TMCs) is studied by means of a multi-stage micromechanical approach. The hybrid Ti matrix nanocomposite (HTMNC) system consists of Ti-6Al-4 V alloy reinforced by unidirectional SiC fibers and randomly dispersed CNTs. An efficient micromechanics procedure is proposed to investigate the CNT aggregation encountered frequently in real engineering situations. The effects of the SiC fiber volume fraction, off-axis angle, aspect ratio and arrangement type as well as the CNT volume fraction, waviness, aspect ratio and non-uniform dispersion are examined on the HTMNC effective properties. Owing to their high Young's modulus and low coefficient of thermal expansion (CTE), the CNT use into the conventional TMCs is revealed to be effective at improving the resulting HTMNC thermo-mechanical properties. Also, the HTMNC elastic moduli and CTEs tend to further improvement by the use of straight CNTs. However, it is demonstrated that the CNT aggregation has a deterioration effect on the effective properties. Generally, the model predictions agree well with the experimental measurements. The results could be actually useful to guide design of general metal matrix composites containing CNTs with superior thermo-mechanical properties.