Executive Summary : | In liquid propellant rocket engines, thin nozzle liners which are used for regenerative cooling experience very high heat flux and steep thermal gradient across the thin walls. Due to this steep thermal gradient across the thin liners, the cooling channel slot fails or warps (dog house effect). This deteriorates the efficiency and reusability of the rocket nozzle component. This study proposes depositing thin thermal barrier coating (YsZ) over nozzle liners (CuCrZr), by which the thermal gradient across the CuCrZr nozzle liner decreases. Thus, it could possibly increase the life and efficiency of the nozzle liner. The work focuses on cladding YsZ based thermal coating on the CuCrZr (substrate or nozzle liner) with NiCrAlY as bond coat using Laser Directed Energy Deposition (LDED) process. As, LDED process offers capability in controlling the chemical composition across the entire build, it was selected as a tool for TBC deposition. The failure of TBC clad over CuCrZr substrate was reported in literature. To overcome this the proposed work focusses on functionally grading the clad between CuCrZr and NiCrAlY. The grading is planned across CuCrZr or NiCrAlY interface as it is the point of failure as reported in published literature. Process parameters and gradient condition will be optimized using the observations from single track and multilayer clad studies. Direct and graded clads will be analyzed for dilution and bond strength between clad or substrate. In addition, thermal cycling experiments will be conducted for both direct and graded clads. Optimum grading condition will be selected by evaluating the life of the clad after thermal cycling. Microstructural characterization, residual stress measurement and thermal diffusivity measurement of all clads will be carried out. |