The cold gas dynamic spray process, or cold spraying (CS), represents a radical departure from conventional thermal spray (TS) methods in that the deposition process relies purely on kinetic energy rather than on a combination of thermal and kinetic components. A potential advantage of this process over TS is the ability to generate dense coatings retaining initial material chemistry and phase composition with a very little oxidation. Also, low temperature process (no bulk particle melting) eliminates solidification stresses and enables thicker coatings. However, hard brittle materials like ceramics can not be sprayed without using ductile binders. In this study, magnetic alloys such as FeSiBNbCu also called Finemet and FeSiBNbCu-Al with various percentages of Aluminum coatings were synthesized using cold spray technique in order to produce ferromagnetic materials. Ultra-fine grain coatings were obtained using FINEMET nanostructured powders mixed with Aluminum as ductile binder in order to improve adherence. Magnetic measurements revealed a soft magnetic character for all the powders and the coatings. 25% of Al was considered as ideal to produce a homogenous coating with suitable magnetic properties.

In recent years, nano alumina/titania ceramic composite coatings have been investigated and exhibited very attractive properties in several mechanical applications such as wear resistance. One of the reasons for significant improvement of those coatings properties is considered to be “nanostructure” preserved in the coating during depositions. Thus, it is of interest to introduce nanostructure with high aspect ratio into coatings and to investigate the effects on the coating properties, especially fracture properties. In this study, alumina/titania composite powders were fabricated by spray dry procedure, which consist of the alumina nano particle (~50nm) and the titania nano fibers (diameter 100~200nm, length 2~3µm). The developed powders were sprayed by APS process. The deposited coatings contain fibrous titania structures which were not melted during deposition. Fracture resistance was evaluated as a function of a crack length by Double Cantilever Beam (DCB) Test for the coatings fabricated under various spray conditions and corresponded to the microstructure.

Plasma sprayed yttria-stabilized zirconia coatings were deposited using nanostructured and conventional powders with optimized process parameters. The sliding wear of both coatings against stainless steel were examined with a block-on-ring test under dry friction condition. It was found that the friction coefficients and wear rates of coatings deposited using the nanostructured powder were lower than that of coatings deposited using the conventional powder. The high wear resistance of the plasma sprayed ZrO 2 coating using the nanostructured powder is attributed to its enhanced cohesion, improved microhardness and homogeneous microstructure.

Nanostructured coatings of Al 2 O 3 and ZrO 2 (1.5% Y 2 O 5 ) are produced by suspension plasma spraying, introducing the liquid feedstock internally into the central part of three converging plasma jets of a Mettech Axial III torch (Northwest Mettech Corp.). Spraying nanosized ceramic powders in a liquid carrier can yield thinner coatings with more refined microstructures than conventional plasma spraying. In-flight particle states are measured for a number of plasma conditions of varying torch current, gas flow rates and compositions (Ar, H 2 , N 2 ), and related to the resulting microstructure and phase composition in the coatings, as determined by EDS, SEM and XRD. Results show that particle velocities up to 600 m/sec can be reached, yielding high impact velocities and cooling rates. Some comparison is made to previous work performed using external injection of a suspension droplet stream into a conventional dc plasma flame. At optimized conditions, dense γ-Al 2 O 3 deposits with an average crystallite size below 30 nm are obtained at deposition efficiency above 80%, which was not previously attainable. Eutectic alumina-zirconia composite coatings with a finely layered lamellar structure are also realized. The laminates have potential advantages as thermal barrier coatings with beneficial properties arising from nano-composite components.

This work describes the synthesis and characterization of nanostructured coatings produced by low pressure plasma spraying (LPPS) of cryomilled NiTi powder. Ni and Ti powders (60 and 40 wt %, respectively) were cryomilled together and LPPS sprayed onto stainless steel substrates. The elemental powders reacted and alloyed during cryomilling forming a nanocrystalline grain structure with nanodispersed oxide and nitride phases. These nanodispersoids are formed due to contamination by the milling media (liquid nitrogen). After spray deposition, the coatings presented a nanostructured microstructure with enhanced mechanical properties when compared with conventional NiTi coatings sprayed under the same conditions. High hardness and toughness values together with intrinsic corrosion resistance of the NiTi alloy lead to the formation of an attractive coating material for applications where corrosion and wear resistance are required. The ability to synthesize the NiTi from elemental Ni and Ti powders and the refinement of the microstructure achieved during milling makes the cryomilling process together with thermal spray of the nanostructured NiTi coatings a unique process and coating to be used in engineering applications. Abstract only; no full-text paper available.

Based on the previous studies of nanostructured WC based coatings, various improvement methods of the coatings were attempted. On of the method was to improve the feedstock materials via a partial flocculation method. This method uses a special technology to form spherical spray dried powders using nanostructured starting materials. According to this method, morphology and porosity level of the feedstock material was controlled. In addition, the basic principle of this method will be introduced. A few other methods are tried to improve the feedstock materials including carbon addition and a Co coating method. The coating morphology and characteristics are analyzed and wear performance is compared. The carbon contents, porosity, phases, and wear loss by a sand abrasion test will be presented in details. Abstract only; no full-text paper available.

The wear characteristics of plasma spray coated layer of Alumina-Titaina composite powder have been investigated, in this study, focusing on the effect of particle size of Alumina powder and parameters of plasma spray coating process. Alumina-Titania composite powders were artificially agglomerated into the size suitable for plasma spray coating process. The process condition for plasma spray coating has been optimized through a statistical data treatment method i.e. response surface analysis. Mechanical properties of coated layer have been measured as a function of the initial Alumina particle size. The structure of Alumina nano-powders in the coated layer was found to be affected by flow rates of Ar and H 2 gases, and the power of plasma in a combinational way. The relationship between the wear characteristics of coated layer and process parameters and microstructure of the coated layer was elucidated, by measuring the size distribution, temperature, and velocity of traveling Alumina-Titania composite powder agglomerates. Abstract only; no full-text paper available.

A particle-sampling probe has been designed and constructed for the continuous collection of nano-powders produced by the plasma spray synthesis (PSS) process. The probe comprises a powder sampling line (inner tube), a quench gas line (outer tube) and a water-cooling jacket surrounding the outer tube. A sample holder is disposed at the exit of the inner tube to hold a standard 3.08 mm diameter TEM copper grid which is used to collect the powders by means of the pumping pressure differential. Quenching gas is introduced to the probe, via the outer tube to quench and entrain the as-synthesized clusters. After each sample collection event, the inner tube can be cleaned in-situ by means of a water injection, and then dried using a compressed gas flow. The results obtained to date indicate that the sampling probe location in the plasma reactor and the quenching gas flow rate employed are the most important parameters involved in the satisfactory operation of the sampling probe.

The synthesis of nanoscale particles has received considerable attention because of the potential for new materials and unique properties. The novel properties and the numerous applications of nanophase materials, especially ceramic nanopowders, have attracted many scientists and engineers to invent and explore the preparation methods of ceramic nanoparticles. Induction plasma is used to synthesize cathode materials for fuel cells. Solid oxide fuel cells (SOFCs) are very promising energy conversion systems. SOFCs are based on an oxide-ion conducting electrolyte and they offer a clean, low-pollution technology to electrochemically generate electricity at high efficiencies. These fuel cells provide many advantages over traditional energy conversion systems including high efficiency, reliability, modularity, fuel adaptability, and very low levels of SOx and NOx emissions. It has been found that La1-xSrxMO3-d, (M= Fe, Co etc) are perovskite materials widely considered as the Intermediate Temperature SOFC cathode materials of choice. In particular, La0.6Sr0.4Co0.2Fe0.8O3-δ is extensively used for IT-SOFCs because its thermal expansion coefficient is relatively close to that of the common electrolytes. In this paper, the nanopowders of SOFC cathode materials were synthesized by thermal plasma spray technique. The results of their structure, morphology and particle size distributions will be presented. Abstract only; no full-text paper available.

Thermal spray coatings were deposited by the HVOF technique using two grades of WC-VC-Co powders (WC- 10VC-12Co and WC-10VC-17Co), produced by agglomeration and sintering, from WC, VC and Co starting powders. The coatings were sprayed by a commercial enterprise producing WC-Co thermal spray coatings, using the same spray parameters as for WC-Co coatings. This paper presents results from the characterization of the powders as well as the results of abrasion and erosion tests performed under identical conditions on the new WCVC- Co coatings and on standard WC-Co coatings of equal cobalt content. Under many conditions, the WC-VC-Co coatings performed better than the standard coatings, despite their deposition conditions not having been optimized.