Papers by Keyword: Functionally Gradient Coating

Abstract: 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/cm² for 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.

Abstract: Tungsten has been decided as the plasma facing material (PFM) for some high heat flux regions of the divertor in the International Thermo-Nuclear Experimental Reactors (ITER). In this paper, our efforts concentrated on the functionally gradient W/Cu coating fabricated on the oxygen free copper by atmosphere plasma spraying under the inert gases protection. The functionally gradient W/Cu coatings were designed to relieve the thermal stress during the spraying processes. For comparison, the tungsten coatings were also deposited directly onto the copper substrates by the same technology. XRD, SEM and EDS were applied to identify the phases, morphologies and compositions of these coatings. Tensile tests were performed to measure the bonding strength between the coatings and the substrates. Furthermore, water quenching and high heat loading experiments using a pulse laser beam were also carried out to estimate the thermal shock properties of these coatings.

Abstract: For practical applications such as artifical joints and dental implants, there is a strong demand for hydroxyapatite coatings with excellent performances to ensure long-term fixation. In the present study, functionally gradient HA-ZrO2-Bioglass coatings were prepared using net-energy controlled plasma spraying technology. The structural characteristics andmechanical performances of the coatings were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD) and nanoindentation. The results showed that: (1) Pore sizes and compositions of the coatings changed gradually along the vertical substrate, crystal HA with few calcium phosphates was presented in the heat-treated coatings. (2) Surface of the coating was very rough with nano-sized crystalline grains and micropores; (3) Young’s modulus and hardness changed gradually at the range of coating-Ti6Alo4V interface. Compared with HA coatings, the tensile adhesive strength of the functionally graded HA-ZrO2-Bioglass coatings reached 38.6 MPa, much higher than that of single HA coatings.