Extreme Plasticity, Adhesion, and Nanostructural Changes of Diblock Copolymer Microparticles in Cold Spray Additive Manufacturing

Using the laser-induced projectile impact testing (LIPIT),theextreme plastic and adhesive responses of polystyrene-polydimethylsiloxaneblock copolymer (BCP) microparticles are investigated to provide theultra-high-strain-rate behavior of individual BCP feedstock powdersduring their collisions with a stationary substrate in the cold sprayadditive manufacturing process. The onset of BCP microparticle adhesionto the substrate is precisely predicted by the maximum coefficientof dynamic friction, quantified from the angled collisions, and bythe spectra of the coefficients of restitution. This finding confirmsthe direct correlation between friction and adhesion mechanisms inthe ultra-high-strain rate regime and its significance in the consolidationprocess of BCP feedstock powders. Furthermore, the impact-inducedadiabatic shear flows create structural ordering of initially disorderednanostructures of the block copolymers consisting of glassy and rubberydomains while generating a temperature rise beyond their glass transitiontemperatures. In addition to the conventional strain-hardening effectin homopolymers, nanoscale morphological ordering can provide anotherstrain-hardening mechanism of BCP feedstock microparticles in thecold spray of additive manufacturing.