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Modifying the surface properties of energetic materials with coating has theoretical and practical significance in the field of their application. Wax, in its role as a functional lubrication layer, has found extensive utility in mitigating the sensitivity of explosives to external stimuli. This study aims to investigate the friction behavior and temperature rise of β-HMX (cyclotetramethylenetetranitramine) crystals with and without the wax coating, and friction coefficient, frictional temperature rise, and the frictional work-heat conversion rate were systematically analyzed. The experimental results show that regardless of single and reciprocating scratch conditions, the wax coating significantly reduced the coefficient of friction of the β-HMX surface by up to 63% and effectively suppressed the temperature rise during friction by up to 83%. Further analyses reveal that upon single scratch conditions, the frictional work-heat conversion rate of the pristine β-HMX surface was about 42%, while that of wax-coated surface increases to about 30% with the frictional power density which involves the contact pressure, sliding speed, and the friction coefficient. In contrast, upon reciprocating scratch conditions, the frictional work-heat conversion rate of the uncoated β-HMX surface decreases with increasing sliding cycles, which was related to the increase in surface temperature and potential surface damage. The frictional work-heat conversion rate of wax-coated surfaces increases with increasing sliding cycles until the contact pressure was high enough that the lubricating effect of the wax layer diminished and the conversion rate began to decrease. The obtained results not only pave the way for understanding the friction energy regulation and desensitization mechanism of wax on the surface of energetic crystals at the micro and quantitative levels, but also provide necessary basis for establishing friction hotspot models under dry friction and wax lubrication conditions from the aspects of friction characteristic parameters, frictional temperature rise, and work-heat conversion rate.
© The Author(s) 2025.
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