Neutron diffraction analysis uncovers abnormal intergranular strain release and water-assisted phase transitions in HMX explosives, suggesting a mechanistic basis for microcrack formation.
Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) is one of the most widely used explosives. Problems about phase state and unrecoverable damage are significant in the application of HMX and HMX-based polymer-bonded explosive (PBX). Recently, the acceleration of δ- to β-HMX retransformation in humid atmosphere was reported. However, the function of water was not well understood. In this paper, we studied the mixed phase during δ- to β-HMX-d8 retransformation with neutron diffraction. Evidence of γ-HMX-d8 is specially focused to estimate whether the hydrated phase is part of the δ- to β- phase retransformation. Besides, in situ high-pressure neutron diffraction of HMX-based PBX was performed to study the evolution of intergranular strains in special structures such as twin plane, cleavage planes, and slip systems. We observed an abnormal release of strain on certain planes under applied pressure which had not been reported. This abnormal phenomenon was considered to explain the formation of microcracks in HMX.
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