Stability characterization of diboride composites under high velocity atmospheric flight conditions

Diboride matrix composites have shown very high temperature capability in oxidizing environments that is unrivaled by any other known material. This paper documents recent efforts to develop this class of ceramics as reusable Thermal Protection System (TPS) components for hypersonic vehicles. The ablation response of reinforced diboride composites of zirconium is given from recent tests in the NASA Ames 60 MW Interaction Heating Facility. Material performance was evaluated at surface heat flux conditions ranging from 170 to 800 W/cm2 producing surface temperatures from 1500 to 2800 degrees C. Post-test metallography and chemical analysis was conducted on zirconium diboride (ZrB2) composites which showed the bets performance in these tests. Oxide scales that formed have a structure dependent on reinforcement composition and volume as well as test conditions, and consist of several distinct layers. The surface layer is composed of columnar zirconia embedded in silica rich glass. Beneath this layer a porous zone interfaces with the compact ceramic