Computational and Microstructural Stability Analysis of Shock Wave Interaction with NbB2-B4C-Based Nanostructured Ceramics.

Abstract

Despite extensive research on developing different transition metal boride composites for aero-thermostructural applications, the understanding of the shockwave interaction using high pressure shock testing facilities and computational simulation of such interactions are much less explored. This aspect is even more important for much less explored ceramics, like NbB2-based materials. While addressing this aspect, the present investigation reports the thermostructural stability of spark plasma sintered NbB2-(0-40) mol % B4C composites under the hypersonic aero-thermodynamic conditions using a miniature detonation-driven shock tube facility. All the ceramic discs underwent mild surface oxidation, as a consequence to impulsive load together with the thermomechanical shock. Using the in situ recorded pressure pulse data together with conjugate heat transfer analysis, spatiotemporal evolution of ceramic surface temperature was computationally analyzed for the given test conditions. Importantly, the NbB2-(0 and 20) mol % B4C composite retained structural integrity even after exposure to 10 shock pulses with maximum reflected shock temperature and pressure of 5000 K and 37.5 MPa, respectively. In contrast, NbB2-40 mol % B4C underwent structural failure by shattering to pieces. An attempt has been made to rationalize such results on the basis of thermal shock resistance parameters, estimated using the Kingery and Hasselman model. It is observed that NbB2-(0 and 20) mol % B4C shows higher crack propagation resistance, that is, 20 and 30%, respectively, under thermal shock (R″) than NbB2-40 mol % B4C. Interestingly, all the shock exposed NbB2-B4C ceramics show a measurable increase in hardness, which is attributed to transient melting and solidification of constituent phases due to interaction with shock heated gas, for a short duration of ∼5 ms. Taken together, the present study establishes the potential of NbB2-B4C composites for aero-thermostructural applications.