Cold-Sprayed Boron-Nitride-Nanotube-Reinforced Aluminum Matrix Composites with Improved Wear Resistance and Radiation Shielding

In this study, the influence of cold-spray processing on the integration of 1D boron nitride nanotubes (BNNTs) into aluminum (Al) matrix composite deposits is delved into. Successful deposition of Al-BNNT composite is achieved by pre-spray dispersion of BNNTs in Al powder via wet mixing aided by ultrasonication. Pure Al powder deposition at 380 degrees C is limited by nozzle clogging, restricting the deposit thickness to 0.2 mm, while the presence of BNNTs enables longer spraying due to nozzle cleaning and damping by hard BNNTs, allowing thicker Al-BNNT deposits of about 2 mm. Microstructural analysis reveals severely deformed Al splats decorated with a uniformly distributed network of BNNTs at the intersplat boundaries, reducing the porosity from 8% to 4% and increasing the splat flattening by 40%. Tribological testing demonstrates resistance of BNNTs to normal force, resulting in a 21% improvement in coefficient of friction and a 65% reduction in wear volume in the Al-BNNT composite. Additionally, incorporating 3 vol.% BNNTs enhances the neutron radiation shielding by 35%. These improvements in the composites are attributed to reduced porosity and the inherent properties of BNNTs, such as high strength, the ability to produce tribofilm lubrication during dry sliding wear, and their high neutron absorption cross-sectional area.