A methodology development for nanostructured composite particle synthesis for Cold Spray Additive Manufacturing
University of New Brunswick
Cold Spray Additive Manufacturing (CSAM) is being used to overcome the disadvantages of conventional manufacturing by introducing layer-by-layer build-up and avoiding thermally induced processing challenges through kinetic energy deposition. The present study focuses on multi-material CSAM deposits, specifically metal matrix composites (MMC) and ceramic-metallic (cermet) composites. The synthesis of MMC feedstock was carried out using high-energy mechanical alloying (HE-MA) and two material systems were designed based on deposit strength and lightweight criteria: Al6061-graphene nanoplatelets (GNP) and Al6061-nanodiamond (ND). The research question governing the two systems was uniquely formulated to address the influence of MMC composition, particle size, and shape on the cold spray (CS) deposit microstructure and bonding characteristics at the particle-particle and particlesubstrate interface. The particles and deposits were characterized utilizing experimental and analytical techniques which provided insights into particle size distribution (PSD), morphology and microstructural evolution, elemental composition, crystallite size reduction, microstrain formation, and embedment of GNP and ND over the milling duration. The results indicated that it was feasible to obtain the desired PSD for the CS deposition with >80% (by volume) particles lying in the 5-104 μm range using 5-mm-diameter balls, 10:1 ball-to-powder ratio (BPR), and 4 hours of milling. The second class of multi-material CS deposit explored was ceramic-dominant cermet. This work provided experimental findings from spraying an 85wt.%Al2O3-15wt.%Al6061(T6) cermet composite at two gas stagnation pressures of 1.7MPa and 2.4MPa onto two substrates: AISI 1018 and 17-4PH steels. Higher gas stagnation pressure was responsible for greater alumina retention in deposits without any discernible change in deposit interface hardness. Vickers indentation fracture test (VIFT) and residual stress measurements were employed to evaluate the interface bonding and deposit characteristics. Interface toughness increased by 8% when sprayed at a lower stagnation pressure of 1.7 MPa on AISI 1018 in comparison to 17-4PH (4.63 MPa-m1/2 vs. 3.69 MPa-m1/2). The laser shock peening (LSP) technique showed a change in stress profiles from tensile to compressive (with the greatest value decreasing from +197 MPa to -274 MPa). Overall, the presented work provided new and promising results concerning CS composite particle deposition. The insight gained requires further research incorporating other Cermet compositions.