Preceramic Route Research Articles

High temperature tribological behavior of polymer-derived Ta4HfC5 nanoceramics

The wear-resistant Ta4HfC5 nanoceramics were prepared via polymer preceramic routes. Tribological behavior of the generated nanoceramics from room temperature to elevated temperatures was investigated. The results shows that the coefficient of friction (COF) of the Ta4HfC5 sliding against Si3N4 first increases and then decreases with the rise of temperature, reaching as low as about 0.20 at 800 °C. The low COF at 800 °C is dominantly ascribed to the formation of oxide tribo-film on the worn surface. The fine microstructure benefiting from the polymer precursor synthesis imposes positive effect to the reduction of friction coefficient at the high temperature.

Synthesis of Zirconium diboride based ultra high temperature ceramics via preceramic route

The present work focuses on the synthesis of ZrB2 based ceramics via a preceramic route, which involves the preparation of ceramic slurry with Zirconium silicate or zircon (ZrSiO4), boron carbide (B4C), phenolic resin and ethanol as the raw materials in stoichiometric amounts. The slurry is cured and then pyrolysed at 1500 °C and 1650 °C in argon atmosphere under a well-defined heating schedule. The heat treated samples were analysed by XRD (X-Ray Diffraction), Fourier Transform Infrared (FT-IR) spectroscopy, particle shape and size analyzer and Scanning Electron Microscopy (SEM). Complete conversion of the reactants to ZrB2–SiC occurred at 1650 °C, while the XRD and IR spectra of sample pyrolysed at 1500 °C indicated the presence of zircon along with silica. SEM images of ZrB2–SiC powder showed coral like microstructure with an average particle size of 6.6 μm.

Thermal Barrier Coating on Metallic Substrates by Preceramic Route

A low cost, easily processable, multi layered functionally graded ceramic coating of thickness ~1000 µm was developed to protect metallic substrates from the risk of thermal oxidation. It consists of a four layered functionally graded coating consisting of aluminide layer followed by an intermediate zirconia as thermal insulative layer, an alumina layer serving as buffer layer with the outer most high emissivity layer to provide the required emissivity. All the layers were brush coated and the specimens were cured at 150°C. The solar absorptivity and emissivity of the coating was found to be 0.82 and 0.88 respectively. 15CDV6 plate of 150 x 150 x 5 mm was coated with multilayer thermal barrier coating of thickness ~ 1 mm. The coated sample was subjected to a heat flux of 8.5 W/cm2for 1035 secs to evaluate the thermo-responsive behaviour of the coating. Maximum back wall temperature measured was 299°C. The coating methodology is simple compared to complicated plasma techniques which can be applied on complex shaped substrates and all operations are carried out at low temperatures, below 150°C ensuring no deterioration of structural properties of the substrate.