| Abstract: |
Recent advances have made possible to obtain Ultra High Molecular Weight Polyethylene (UHMWPE) coatings by cold spray method which was previously impossible when nano-ceramic particles were used as an additive to UHMWPE feedstock. But, the exact role of nano particles is largely not understood. In this research work, UHMWPE particles, with 0%, 2%, 4%, 10% of fumed nano alumina (FNA, 13nm primary particle), are impacted/deposited on to a target Al surface in an isolated manner, by reducing the particle flux, at different particle velocities and particle temperatures. The experiments were performed using a downstream injection low pressure cold spray machine. Particle velocities and particle temperatures were controlled by varying the carrier gas pressure and temperature. The impact behavior of UHMWPE was analyzed using SEM, FIB and high-speed camera. Effect of increase in gas temperature showed a significant variation in the deposition. It was seen that without the nano particles, the evolution of deposited particles/mm2 was almost linear. But, with the addition of FNA, the number of deposited particles/mm2 increased significantly and also showed a peak in the number deposited at 4%. The deposited particles were further analyzed using FIB where particle was cut along the cross section to observe the polymer/metal interface and the aspect ratio (spherical particle will have an aspect ratio close to 1 and deformed particle will be less than 1) of the particle under impact. It was seen that nano particles induced plastic deformation during impact. Finally, High speed camera showed that particles are moving at an incidence velocity of 180-200m/s and rebound velocity of 40-50m/s. This suggests that particles lose a significant amount of their kinetic energy during the impact.
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