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 aerothermostructural applications, the understanding of the shockwave interaction using variants of high pressure shock testing facilities together with computational simulation of such interactions are much less explored and reported in published literature. This aspect is even more important for much less explored ceramics, like NbB2-based materials. While addressing this aspect, the present investigation reports the thermo-structural stability of spark plasma sintered NbB2-(0-40) mol.% B4C composites under the hypersonic aerothermodynamic conditions using miniature detonation tube facility. All the ceramic discs underwent mild surface oxidation, as a consequence to impulsive load together with the thermo-mechanical shock. Using the in situ recorded pressure pulse data together with conjugate heat transfer analysis, spatio-temporal evolution of ceramic surface temperature was computationally analyzed for the given test conditions. Importantly, NbB2-(0 and 20) mol.% B4C composite retained structural integrity even after exposure to ten 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 Kingery and Hasselman model. It is observed that NbB2-(0 and 20) mol.% B4C shows higher crack propagation resistance i.e. 20% and 30% respectively, under thermal shock (R^ ) as compared to NbB2-40 mol.% B4C. Interestingly, all the shock exposed NbB2-B4C ceramics show measurable increase in hardness, which is attributed to transient melting and solidification of constituent phases, due to interaction with shock heated gas, for short duration of ~5 ms. Taken together, the present study establishes the potential of NbB2-B4C composites for aerothermostructural applications.