Tailoring the thermal shock resistance of titanium carbide by reinforcement with tungsten carbide and carbon nanotubes

Abstract

Titanium carbide (TiC) is reinforced with 3.5wt% of tungsten carbide (WC) and 2wt% of carbon nanotubes (CNTs) in order to improve its thermal shock resistance and mechanical integrity of oxide layer. Three pellets namely, TiC (T-SD), TiC-3.5wt% WC (TW-SD) and TiC-3.5wt% WC-2wt% CNT (TWC-SD) were thermally shocked at 1700°C in an open atmosphere for 10 numbers of thermal cycles. Raman spectra confirmed the retention of CNTs after thermal cycling, which could be attributed to the thermal shielding offered by the molten TiC to CNTs. HR-TEM image infers the collapse of some of the CNTs into carbon structure after the thermal shocks. The mass loss % of T-SD, TW-SD and TWC-SD pellets were found to be 41.5%, 33.3% and 15.13%, respectively after the 10 numbers of thermal cycles. The rate of mass change in T-SD sintered pellet was found to be ~1.4 × 10−3g/min., which got reduced to ~0.4 × 10−3g/min. on addition of 3.5wt% of WC and 2wt% of CNT. Furthermore, reinforcement of 3.5wt% WC and 2wt% CNTs in TiC matrix showed the dramatic increase of 89% in thermal shock resistance parameter (Rst) compared to T-SD pellet. This significant improvement in thermal shock resistance of TWC-SD pellet is mainly attributed to the following three factors viz. (i) higher fracture toughness (ii) higher density and (iii) homogeneous dispersion of CNTs, which hinders the movement of oxygen atoms along the grain boundaries. Hardness of the thermally shocked TWC-SD pellet was found to be 5.1GPa, which was 1.3GPa i.e. ~74% higher compared to thermally shocked T-SD pellet. This increased hardness of thermally shocked TiC matrix has been shown to suppress the crack formation and restrict oxidation.