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Titanium carbide (TiC) is reinforced with 3.5 wt% of tungsten carbide (WC) and 2 wt% 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-3.5 wt% WC (TW-SD) and TiC-3.5 wt% WC-2 wt% 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 −3 g/min., which got reduced to ~0.4 × 10 −3 g/min. on addition of 3.5 wt% of WC and 2 wt% of CNT. Furthermore, reinforcement of 3.5 wt% WC and 2 wt% CNTs in TiC matrix showed the dramatic increase of 89% in thermal shock resistance parameter (R st ) 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 5.1 GPa, which was 1.3 GPa 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. [ABSTRACT FROM AUTHOR]

Al 2 O 3 , Al 2 O 3 -1 wt% Carbon Nanotube (CNT) and Al 2 O 3 -1 wt% CNT-0.5 wt% Graphene Nanoplatelets (GNP) were consolidated by spark plasma sintering at a temperature of 1500 °C. Spray drying technique was used for uniformly distributing the CNTs and GNPs. Fracture toughness of Al 2 O 3 pellet drastically increased to 168% on addition of CNTs, while substantial improvement of 250% was seen on the addition of both CNTs and GNPs. Interfacial shear stress for Al 2 O 3 -CNT-GNP was found to be 350–1100 MPa. Novel toughening mechanisms such as CNT yarning and CNT embedded graphene was found responsible for the drastic improvement in toughness. [ABSTRACT FROM AUTHOR]

TiC, TiC-3.5 wt% WC and TiC-3.5 wt% WC-2 wt% CNT pellets were consolidated using spark plasma sintering technique at 1600 °C and 50 MPa pressure. Spray drying technique was used for the homogeneous dispersion of CNT in TiC matrix. Punch displacement data showed the relatively higher compaction of TiC on addition of 3.5 wt% of WC and 2 wt% of CNT. Raman spectra confirmed the retention of CNTs in spark plasma sintered pellet, While, HR-TEM micrographs infers the defect morphology of CNT after the sintering. Some CNTs were found to be defected with the bamboo like structure, which have ultimately provided the strong interface between TiC and CNT through mechanical interlocking mechanism. Hybrid reinforcement of WC and CNT has played a vital role in increasing the density of TiC pellet from 89% to 99% and in reducing its average grain size by ~ 31%. Further, improvement of 41% in hardness and 42% in elastic modulus were observed in sintered TiC pellet on addition of WC and CNT. Drastic improvement of 141% in fracture toughness value was found which was due to the higher critical energy release rate in TiC-3.5 wt% WC-2 wt% CNT pellet. Interfacial shear stress was evaluated using modified Cox model to investigate the higher critical energy release rate. CNT grain stitching and CNT grain gluing was found to be novel toughening mechanism apart from the conventional mechanism of CNT bridging, crack bifurcation and CNT pull out. [ABSTRACT FROM AUTHOR]

CNTs (2 wt%) reinforced TiC composite with WC (3.5 wt%) as sintering aid was densified using SPS technique at 1600 °C. In-situ formation of wide GNRs (Graphene nanoribbon) was observed due to CNT unzipping in TiC-WC-CNT (TWC) pellet. A phenomenal increase in fracture toughness (∼118%) was observed in TWC pellet compared to TiC. This significant improvement was due to novel toughening mechanisms like GNR grain wrapping, GNR crack bridging and crack bifurcation. Further, TWC pellet showed ∼48% improved thermal shock resistance compared to TiC, which could be due to the suppressed large thermal cracks by CNT and in-situ formed GNR. [ABSTRACT FROM AUTHOR]

This article reports the effect of hybrid reinforcement of carbon nanotubes (CNTs) (1 wt%) and graphene nanoplatelets (GNPs) (0.5 wt%) on electrical conductivity of atmospheric plasma sprayed alumina (Al 2 O 3 ) coating. The uniform dispersion of CNTs and GNPs were observed over Al 2 O 3 matrix. Scratch test revealed the improved inter-splat bonding strength with addition of CNTs and GNPs, which could lead to improved electrical conductivity of Al 2 O 3 coating. The electrical conductivity increased from ~5 × 10 –12 to ~0.7 S/m, by the addition of CNTs (1 wt%) and GNPs (0.5 wt%) in Al 2 O 3 coating. A drastic improvement of ~ 12 orders of magnitude in electrical conductivity was observed in Al 2 O 3 − 1 wt% CNT- 0.5 wt% GNP coatings. This improvement in electrical conductivity was majorly attributed to the lower porosity and strong inter-splat bonding. In addition, availability of more numbers of conductive channels as a result of homogeneous distribution of CNTs/GNPs and clean interface with Al 2 O 3 has played the significant role in enhancement of electrical conductivity. [ABSTRACT FROM AUTHOR]

Hafnium carbide (HfC) along with sintering aids was consolidated at a relatively lower temperature i.e. 1600 °C (i.e. T=~0.41 T m ) under a uniaxial load of 50 MPa by spark plasma sintering. Two different sintering aids such as molybdenum disilicide (MoSi 2 ) and carbon nanotube (CNT) were added to enhance the densification and lower the extent of grain growth in the sintered pellets. Density of the sintered pellet increased from 96.0±0.8% in HfC +5 wt% MoSi 2 (HM) to 99.0±0.5% with the addition of 2 wt% CNT in HfC+5 wt% MoSi 2 (HMC) at sintering temperature of 1600 °C. Further, the extent of grain growth drastically reduced from 204% in HM to 50% in HMC. Analysis of linear shrinkage during densification revealed that CNT addition increased densification rate and decreased the time required to reach the density of 99.0±0.5% at 1600 °C. Increased densification and lower degree of grain growth could be due to the synergistic effect offered by the CNT, which are as follows: (i) Lubrication effect of CNT, (ii) Lower activation energy for grain boundary diffusion (iii) Reduction in liquid phase sintering temperature and (iv) Grain boundary pinning. Fracture toughness of the sintered HM and HMC composite was obtained using indentation technique. By the addition of 2 wt% CNT in HM, drastic increase of 91% in fracture toughness was seen. This significant improvement in fracture toughness was due to the enhanced densification and relatively lower grain size of HMC. Also crack bridging, crack deflection, crack arrest, CNT and graphene sheet pull-out and swording played major role in toughening of HMC pellet. [ABSTRACT FROM AUTHOR]

Carbon nanotube (1 wt. %) and graphene nanoplatelets (0.5 wt. %) reinforced aluminum oxide (Al 2 O 3 ) coating have been deposited on low carbon steel substrate using atmospheric plasma spray technique. Addition of 1 wt. % CNT and 0.5 wt. % GNP has significantly increased the densification from 88% in Al 2 O 3 coating to 97% of the theoretical density in Al 2 O 3 - 1 wt.% CNT- 0.5 wt.% GNP. Relative hardness and elastic modulus has increased by 52% and 48% respectively on synergistic addition of CNT and GNP. Increase in hardness was attributed to improved densification, while increased elastic modulus was due to higher elastic modulus of CNT and GNP and homogeneous distribution of CNT in Al 2 O 3 matrix. An exceptional improvement of 200% in relative fracture toughness was observed in Al 2 O 3 - 1 wt.% CNT- 0.5 wt.% GNP coating. The improvement in fracture toughness is attributed to three major factors viz. (a) increased densification (b) Strong Al 2 O 3 , CNT and GNP interface and (c) various toughening mechanism offered by CNT and GNP such as such as bridging and pull out, crack deflection, GNP Splat gluing, nanomechanical interlock etc. [ABSTRACT FROM AUTHOR]