Study On The Defect Evolution Of β→δ Retransformation In HMX Under Thermal Stimulation

With the rapid development of modern military technology,weapons systems have higher requirements for survivability and effectiveness in complex environments,and the quality requirements of explosives that play a key role in weapon damage capabilities are also increasing.However,the deficiencies of explosive crystals are unavoidable.Whether in the process of crystal growth or in the further preparation,storage,transportation,and use of explosives,under the influence of external environment such as temperature,pressure,and humidity,explosive crystals will generate some new defects on the basis of the original defects.Among them,the phase transition process under the thermal stimulation will also bring defects to the explosive crystals,such as the HMX,which occurs β→δ phase transition in the range of 165 and 210 °C,forming a stress concentration within the HMX,resulting in a lot of cracks,holes,and even broken.The defects generated during these phase transitions will form “hot spots” in the process of detonation,affecting the stability and work ability of the explosives,which is not conducive to the effective performance of weapons systems.In order to suppress the adverse effects of defects caused by phase transformation on the macroscopic properties of explosives,in order to be able to effectively control the formation and propagation of defects during phase transformation,we studied the defect evolution of the single crystals and single wafers under thermal stimulation by the optical microscopy-hot stage combination technology and in-situ X-ray small angle scattering technology(SAXS).The main work of the thesis is as follows:(1)The β-HMX micron single crystals in the size range of 100 μm ? 800 μm were prepared by using acetone solvent evaporation method under low vacuum.At the same time,high-quality first class seed crystals were prepared using the acetone evaporation method under low vacuum and the acetone solvent slow volatilization method under normal pressure.Then,the first class seed crystals were grown into a single crystal of β-HMX with a size in the range of 5 mm ? 10 mm using a suspension method,which provided sufficient samples for microscopic real-time observation and SAXS experiments.(2)The defect evolution of β-HMX micron-sized single crystals in the range of 100 μm ? 800 μm under thermal stimulation was observed in real time using optical microscopy-hot stage technology.The results show that the number of defects and the size of the crystal have an important influence on the evolution of defects in a single independent single crystal.In the evolution of defects in attached crystals,the attachment of two crystals affects the evolution of defects.In the defect evolution of twins,the position of the twin plane is closely related to its defect evolution.(3)According to the β-HMX single crystals in the size range of 5 mm ? 10 mm,using powder GeO2 as internal standard material,the diffraction signal of all exposed crystal surface was obtained by powder X ray diffraction internal standard method.Through powder diffraction precision,zero point offset correction and crystal plane angle calculation,the crystal surface of β-HMX were indexed as(1 0 0),(0 1 1),(-1 1 1)and(0 2 0).(4)The β-HMX single crystals in the size range of 5 mm ? 10 mm were cut using a diamond wire cutter to obtain single wafers of various crystal planes.Then the in-situ SAXS was used to characterize the defect evolution of single wafer under thermal stimulation.The data all show that the defect evolution of β-HMX single wafer under thermal stimulation evolves in the original defect direction and has certain directionality.