Assessment of plasma sprayed carbon nanotube reinforced Al2O3-based nanocomposite with micro-scratching

An efficient Al2O3-based nanocomposite coating was developed to fabricate the top thermally insulative layer of the thermal barrier coatings (TBCs). Here, Al2O3-based coatings were prepared by atmospheric plasma spraying and the scratch properties were investigated using progressive-load scratching. Scratch mechanism and the role of carbon nanotube (CNT), 3 and 8 mol% Y2O3 stabilized ZrO2 (3YSZ and 8YSZ, respectively) during progressive load scratching were analysed. The investigations revealed that the Al2O3-based nanocomposite coatings were showed a high scratch coefficient (0.165-0.219) compared to that of monolithic Al2O3 (0.128). Also, the monolithic Al2O3 coating showed a decent scratch resistance (0.35 mm(3)N(-1) m(-1)) compared to 3YSZ/8YSZ and CNT reinforced nanocomposite (0.49-69 mm(3)N(-1) m(-1)). It was attributed to the synergistic effect of hardness, fracture toughness and the bonding of the reinforcement with the matrix Al2O3. The work of adhesion of lamella in the YSZ and CNT reinforced nanocomposite was measured as 1.16-2.75 x 10(3) J, which is lower (up to 2.5 times) than the monolithic Al2O3 (2.91 x 10(3) J). It is attributed to the poor bonding of CNTs with the lamella contains Al2O3 and YSZ. Further, the failure of the nanocomposite coatings, such as flaking and chipping were resisted by CNT. Nevertheless, CNT addition declines the scratch toughness of the nanocomposite coatings (1.05-2.04 MPa.m(0.5)). It endorses no effective contribution of CNT in the scratch toughness of the coatings. Meanwhile, the mere addition of 8YSZ and 3YSZ in the Al2O3 matrix showed an increment (10.5% and 67.5%, respectively) in the scratch toughness compared to that of monolithic Al2O3 (2.37 MPa.m(0.5)) coating.

Automated summary

An efficient Al2O3-based nanocomposite coating was developed for the top thermally insulative layer of thermal barrier coatings (TBCs), showing higher scratch coefficient and decent scratch resistance compared to monolithic Al2O3. However, the addition of carbon nanotubes (CNT) in the nanocomposite coatings did not significantly improve the scratch toughness. On the other hand, the mere addition of 8YSZ and 3YSZ in the Al2O3 matrix showed an increment in scratch toughness compared to that of monolithic Al2O3 coating.