Hypersonic Plasma Particle Deposition of Nanostructured Coatings and Micropatterns

Nanostructured materials are attractive candidates for advanced friction and wear-resistant coatings due to their potentially enhanced mechanical properties. We have developed a one-step method called hypersonic plasma particle deposition [1] to produce and deposit nanoparticles using a thermal plasma reactor. Particle synthesis is achieved by dissociating vapor phase reactants in the plasma, and quenching the hot gas in a supersonic nozzle expansion. Particles are deposited on a substrate by hypersonic impaction to form a film, or are deposited as micropatterns using a process called focused particle beam deposition [2]. In-situ particle size distribution measurements are performed using a sampling probe interfaced to an extraction/dilution system for measurement by a scanning electrical mobility spectrometer.

Characterization of Nanoparticle Films and Structures Produced by Hypersonic Plasma Particle Deposition

ABSTRACTThere is great potential for the use of nanostructures in numerous applications. Investigation of nanoparticle films and structures is an important area of research for the production of nanoengineered devices. However, for these devices to become a reality, a production method that can yield high-rate synthesis of nanostructured powders is necessary. The hypersonic plasma particle deposition (HPPD) process has been shown to be capable of such high-rate production of nanoparticle films and structures. Versatile in its ability to manufacture nanoparticles of different chemistries HPPD also has the capability of in situ particle consolidation and assembly. In this study, chemically diverse films and structures have been produced by HPPD on a variety of substrates. Using novel specimen preparation techniques, these nanoparticles have been characterized by TEM. Fundamental issues of importance have been investigated for both the nanoparticle structure and the constituent nanoparticles. These issues include nanoparticle crystallinity and defect structure. The chemical homogeneity and structural characteristics of the deposition are also investigated. This application of microscopy to aid process development has resulted in insights into the nanoparticle formation process and the dynamics of the HPPD process.

Thermal Spraying of Nanostructured Coatings by Hypersonic Plasma Particle Deposition

A novel plasma spray process for producing nanostructured coatings, hypersonic plasma particle deposition (HPPD), has been experimentally investigated. In HPPD, vapor phase precursors are injected into a plasma stream generated by a DC arc. The plasma is quenched by supersonic expansion through a nozzle into a vacuum (~ 2 torr) deposition chamber. Ultrafine particles nucleated in the nozzle are accelerated in the hypersonic free jet downstream of the nozzle and inertially deposited onto a substrate. The short transit times between the nozzle and the substrate (< 50 μs) prevent inflight agglomeration, while the high particle deposition velocities result in the formation of a consolidated coating. We have investigated the production of silicon and silicon carbide coatings using SiCl4 and CH4 precursors. Silicon deposits analyzed by transmission electron microscopy were found to have nanostructured regions with grain sizes varying from 5-20 nm. Corresponding particle size distributions measured before deposition using an extractive aerosol probe peaked around 15 nm, suggesting negligible grain growth occurred in the samples studied. Silicon carbide particle size distributions measured at various deposition chamber pressures verify that the low residence time characteristic of the HPPD process minimizes in-flight agglomeration.