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

Using the laser-induced projectile impact testing (LIPIT), the extreme plastic and adhesive responses of polystyrene-polydimethylsiloxane block copolymer (BCP) microparticles are investigated to provide the ultra-high-strain-rate behavior of individual BCP feedstock powders during their collisions with a stationary substrate in the cold spray additive manufacturing process. The onset of BCP microparticle adhesion to the substrate is precisely predicted by the maximum coefficient of dynamic friction, quantified from the angled collisions, and by the spectra of the coefficients of restitution. This finding confirms the direct correlation between friction and adhesion mechanisms in the ultra-high-strain rate regime and its significance in the consolidation process of BCP feedstock powders. Furthermore, the impact-induced adiabatic shear flows create structural ordering of initially disordered nanostructures of the block copolymers consisting of glassy and rubbery domains while generating a temperature rise beyond their glass transition temperatures. In addition to the conventional strain-hardening effect in homopolymers, nanoscale morphological ordering can provide another strain-hardening mechanism of BCP feedstock microparticles in the cold spray of additive manufacturing.