2017 Fiscal Year Annual Research Report
Development of polymer coatings by cold-spray
| Project/Area Number |
17J02142
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| Research Institution | Tohoku University |
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Principal Investigator |
RAVI KESAVAN 東北大学, 工学研究科, 特別研究員(DC2)
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| Project Period (FY) |
2017-04-26 – 2019-03-31
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| Keywords | cold spray / high strain rate / UHMWPE / compression sintering / Mechanical testing / X Ray Tomography |
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| Outline of Annual Research Achievements |
The research work was based on understanding of cold-spray coating mechanism of Ultra-High Molecular Weight Polyethylene (UHMWPE). The work identified the fundamental parameters responsible for the deposition and coating buildup of UHMWPE and UHMWPE-Fumed Nano Alumina (FNA) composite particles in terms of understanding the interaction of UHMWPE with Al substrate (impacting particle-substrate interaction) during a high-speed impact and UHMWPE with already deposited UHMWPE particles (impacting particle-deposited particles) leading to a buildup in the coating.
The Deposition efficiency was seen to increase when gas temperature and FNA content in the feedstock was increased. Rebound or deposition of UHMWPE particles on Al surface depended upon whether UHMWPE particles after impact furnished a contact area with an interfacial bond stronger than elastic strain energy of the particle. FNA provided OH bonds at the contact surface to increase the window of deposition.
The morphological (via SEM and X-Ray Tomography) and mechanical characterization showed that when UHMWPE was processed under high loading conditions (using compression sintering technique), FNA particles reinforced the UHMWPE interface. Most likely phenomena for reinforcement is believed to be a percolating interfacial zone comprising of a co-continuous network of polymer chains and FNA particles wetted by polymer chains. On the contrary, when UHMWPE was processed under low loading conditions, FNA particles weakened the interface by acting as defect disallowing the inter-grain chain diffusion during sintering.
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| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
In this research, the plan for the year first half of the fellowship period was to elucidate the coating formation mechanism of polymers during cold-spraying which was successfully understood in the research work performed. In addition to the plan proposed, new insights on the polymer chemistry at high heating rates, polymer deformation mechanism at high strain rates, interface sintering and interactions between polymer and nanoceramic particles were understood from the research work.
The cohesive strength of the polymer and polymer-nanoceramic interfaces were successfully measured. Other functional properties like cavitation erosion resistance are yet to be measured due to lack of availability of the facility at Grenoble University, France.
Based on the research plan proposed, it was also possible to attend two conferences at ITSC 2017 and ICFD 2017 and publish a peer-reviewed article in Additive Manufacturing.
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| Strategy for Future Research Activity |
As a future work, I would like to optimize the cold-spray additive manufacturing technique for polymers from the knowledge gained from elucidating the mechanism of coating formation. Based on the first half of the study, the polymer deposition and buildup was largely affected by particle temperature, velocity, and surface activity of nanoceramic additives. Firstly, new nozzle designs will be employed to achieve better particle heating and acceleration. Secondly, in-situ modification of feeding polymer particles will be performed. Focus will be to increase its activity by employing laser-assisted heating of particles and substrate. Also planned is the utilization of other nanoparticles to provide stronger bridge bonds between particle-substrate and particle-particle.
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