Additive manufacturing and performance tuning of functionally graded Al/AP with continuous change of content

As a typical energetic composite, aluminum (Al)/ammonium perchlorate (AP) has been widely applied in propellants, explosives, and pyrotechnics. To regulate its energy output, a functionally graded Al/AP composite with continuously changing component content was fabricated by 3D printing through a self-designed "partition". The printed functionally graded Al/AP composite was characterized by different techniques. The research showed that the overall structure of functionally graded Al/AP is complete, the internal particles are densely packed and the porosity is small, the phenolic resin binder had good compatibility with powders (Al, AP), and the content of Al and AP in the functional gradient Al/AP strip has achieved continuous gradient change (Al content from 50 wt% to 20 wt%, AP content from 50 wt% to 80 wt%) along a certain direction. Because of the continuous change of the content of different components, functionally graded Al/AP realizes the effective regulation of flame shape, combustion rate, pressure output, and energy release on the macro level. That is, with the increase of Al content, the combustion temperature and heat release gradually increase, and the combustion flame shows the morphological changes of horizontal uniform injection, downward tilt, bright spot injection, and attenuation in turn. With the increase of AP content, the pressure output gradually increases, and the combustion rate first increases and then decreases. These results indicate that functional gradient provides a new strategy for controlling the combustion reaction and energy output of energetic materials. In addition, 3D printing technology provides a feasible method for the preparation of functionally graded materials.