Investigation of Heat Transfer to HfB2-SiC-Based Ceramics in Underexpanded Dissociated-Nitrogen Flows and Analysis of the Surface

Experiments on heat transfer to HfB2-SiC-based ceramics specimens in underexpanded supersonic flows of high-enthalpy nitrogen are performed on the VGU-4 induction high-frequency (HF) plasmatron of the Institute for Problems in Mechanics of the Russian Academy of Sciences. The nitrogen plasma flows in the discharge channel of the plasmatron and the underexpanded dissociated-nitrogen flow past a cylindrical model with the ceramics specimen was simulated numerically within the framework of the Navier–Stokes and simplified Maxwell equations. Basing on the comparison of the experimental and calculated data the possible range of the effective coefficient of the heterogeneous nitrogen atom recombination on the ceramics surface is determined as a function of its total emissivity at a temperature of 2000°C. The microstructure and the element and phase compositions of the surfaces of the HfB2-SiC-based ceramics specimens and the HfB2-SiC-G-based ceramics specimen modified by two volume percents of graphene are studied after they have been subjected to the action of supersonic flow of partially dissociated nitrogen.