Response of Silicon Nitride Ceramics under High-enthalpy Plasma Flows

Silicon nitride ceramics were prepared by means of a hot-press sintering method. The ablation behavior was studied by plasma wind tunnel tests. The data suggested that, under low heat flux and stagnation pressure conditions, the ablation process was controlled by the atomic oxidation of Si₃N₄, leading to the elimination of Si₃N₄. By contrast, the erosion was mainly produced by the decomposition of Si₃N₄ under high heat flux and stagnation pressure conditions. Under these conditions, a fraction of Si phase, formed upon decomposition of Si₃N₄, was volatilized. The remained Si had melted due to high temperatures and scoured away from stagnation point area, generating mushroom-shaped samples.