ICMCTF2016 Session TS2-1: Thermal Spray Technologies and Coatings

Aerosol deposition (AD), or vacuum kinetic spray (VKS), refers to a process for the fabrication of ceramic films based on the high velocity impact of fine particles upon a substrate. The process offers exciting possibilities for both rapid prototyping and large scale manufacturing of thick film functional ceramics because of several attributes: a wide range of film thickness (1 to >100 mm), high deposition rates and low process temperature. Moreover, AD results in unique microstructures with beneficial characteristics including nano-crystallinity and near theoretical density. Process modifications and post-deposition heat treatment steps can also yield films with controlled porosity and/or grain size.

The “normal” AD process typically gives films with a distinctive surface of cratering and relatively high roughness. Factors which influence the extent of cratering will be discussed. The use of powder mixtures can be used to build porosity into the film. This can be in the form of a fugitive phase or a solid state reaction between two ceramic components which leaves behind porosity. This presentation will reveal the unique microstructures and textures of AD films using several metrology tools including SEM, AFM and scanning white light profilometry. Implications and exploitations of these microstructures will be discussed.

Aerosol deposition is a room-temperature thick-film deposition technique that produces dense polycrystalline films tens to hundreds of microns thick and at a very high deposition rate. Two distinct features of aerosol deposition are the ability to produce films with the same stoichiometry as the dry powdered precursor material and the ability to perform the deposition with all constituents at room temperature. Ferromagnetic materials, such as yttrium iron garnet and barium ferrite, are important for device components operating at microwave frequencies. In this talk, we present structural and morphological results on these materials deposited by aerosol deposition. We also demonstrate preliminary results on applications of these films for selected microwave components.

Dense nano-structured ceramic films were deposited at room temperature by spraying ceramic granules in a vacuum. Granules were flowable soft agglomerates of primary particles and their average size was several tens of micrometers. The process is named as granule spray in vacuum (GSV). GSV shares many things with Aerosol deposition (AD). However, the biggest difference between GSV and AD is what pass the nozzle; granules for GSV vs. individual primary particles for AD. Since well flowing granules were used, a long term stability of feeding and a large scale feeding were accomplished. It allowed a large area deposition of ceramic films in a short time. Also, feeding rate of granules was controlled independently of the carrier gas flow. Therefore, effect of the material feeding rate and that of the carrier gas flow rate on the film deposition were separately investigated.

Ceramics often exhibit very little plastic deformation before brittle fracture, limiting materials integration and applications. A process to fabricate ceramic films at nominal room temperature (RT) in solid-state, Aerosol Deposition (AD), has been demonstrated in literature since the early 2000's. High velocity ceramic particles impact on substrates, deform, and form films under vacuum. AD eliminates high processing temperatures, enables materials integration, where ceramics are deposited on metals, plastics, and glass at RT. The fundamental mechanisms for ceramic particle deformation/bonding in AD are not well understood. We utilized atomistic simulations and transmission electron microscopy (TEM) to study deformation behavior and consolidation of alumina particles in AD films. In our previous work, atomistic simulations of compressed 10 nm alumina particles and in situ micro-compression in the TEM of 300 nm alumina particles showed that dislocation plasticity preceded fracture. Moreover, direct observation of dislocation nucleation and movement within the particles was recorded. In this work, we investigate alumina particle consolidation in AD films by performing atomistic simulations of alumina particle impacting on alumina and thorough characterization of AD alumina films.

B.L. Boyce, K. Hattar, and D.C. Bufford were supported by the Department of Energy (DOE) office of Basic Energy Sciences, Materials Science and Engineering. This work was performed, in part, at the Center for Integrated Nanotechnologies (CINT), and Office of Science User Facility operated for the U.S. DOE Office of Science. This work is supported by the Laboratory Directed Research and Development program at Sandia National Laboratories, a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. DOE's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Furthermore, when nickel powders are also injected together with Si, Si-Ni nanocomposite particles, in which Ni containing particles are directly attached onto the Si nanoparticles, are produced at the same production rate with the case of Si only. Furthermore, detailed analysis of electron microscopy have revealed that the attached Ni particle has an epitaxial interface with Si via the formation of NiSi2 phase. As a result, as one expects additional functionalities, such as mechanical reinforcement and electric conduction paths, the batteries using these Si-Ni nanocomposite particles have shown a significant increase in the cycle capacity compared to the case with Si only. The formation of such composite particles can be reasonably explained by the co-condensation of high temperature Si and Ni vapor mixture during PS-PVD. Together with the detailed formation paths of the nanocomposite particles in other Si-M systems, feasibility of PS-PVD for the anode material production will be discussed in the presentation. This work was partly supported by NEXT Program (GR020) and Grant-in-Aid for Scientific Research (B) 15H04152 of Japan.

WC based composites are highly wear resistant materials that are conventionally fabricated as coatings by thermal spray processes. However, the high temperature of thermal spray often results in decarburization and a deterioration of the wear resistance. An alternative is to use cold spray to deposit WC based composite coatings. The lower temperature allows one to retain the composition of initial WC feedstock but the cold spray process is only recently being researched for development of composite coatings. In this study, feasibility of cold spraying WC-Ni coatings was explored. The WC and Ni powders were fed to a de Laval nozzle from separate hoppers with independent feed rates. By adjusting feedrates, a blend of Ni-50vol.% WC was sprayed, which resulted in a composite coating of Ni-10.5vol.% WC. Microstructural characterization including morphology of Ni splats and retention, distribution, and fragmentation of WC was performed by SEM. Mechanical properties of coatings were investigated by nano- and micro-indentation. The wear behavior of coatings was studied with sliding wear tests using a 6.35 mm diameter WC ball. All tests were conducted in dry air with a sliding speed of 3 mm/sec, a track length of 10 mm, and normal load of 5 N. WC-Ni coatings were more wear resistant than cold-sprayed Ni coatings. Microstructural analysis was conducted to study the mechanism accounted for enhancement in wear resistance of cold sprayed WC-Ni coating. The worn surface and subsurface was observed by means of SEM assisted with focus ion beam (FIB) cutting and electron channeling contrast imaging (ECCI). The formation of 'islands' of compacted oxides near WC particles was observed as a possible mechanism for improved sliding wear performance of WC-Ni coating. The correlations between the subsurface microstructure induced by wear, their mechanical properties measured by nano-indentation and the wear behavior of the coatings will be discussed.