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

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.