A new family of spherical powders produced by the spray drying route has been developed. This paper describes as an example the manufacturing method of an Y2O3-coated aluminum powder. Atmospheric Plasma Spraying (APS) was used to test the corresponding coatings. Morphology and phases of powders and coatings were investigated by optical and scanning electron microscopy while the level of porosity was evaluated using image analysis. Results show that homogenous composite coatings can be obtained from cladded spray dried powders.

Deposition of amorphous aluminium powder using cold spray technology as a corrosion prevention measure was studied. Amorphous aluminium (Al-Ni-Ce) powder was successfully deposited on 7000-series aluminium substrates using cold spray parameters of 1.7 MPa under compressed air and temperature of 450°C. The coatings were subjected to tensile bond strength measurement and comparative studies with cold sprayed pure Al6061 coatings were conducted. The results obtained showed that the amorphous aluminium coatings exhibited better adhesive strength. In addition, salt-water immersion test was conducted. The Al-Ni-Ce coating not only demonstrated better corrosion resistance but also exhibited evidence of passivation of surface imperfections such as scratches in the coatings.

This study assesses the influence of powder morphology on the microstructure and bond strength of cold-sprayed aluminum. Aluminum powders with spherical and irregular particle shapes were deposited on shot-peened steel. The feedstocks were mixed with alumina powders, either spherical or angular in shape, to improve coating properties. Coating samples and powder mixtures were examined by means of SEM and XRD analysis and pull-off tests were conducted to evaluate coating adhesion. It was found that alumina addition reduces porosity and increases hardness and that aluminum-alumina mixtures with the same particle shape are more suitable for producing dense coatings with high bond strength.

The low-pressure cold spray (LPCS) technique could be an attractive method for copper metallization of ceramic substrates to power module applications due to its one-step quick and low-temperature process. However, manufacturing pure copper coating on a ceramic substrate by LPCS is still challenging due to its low deposition efficiency and poor adhesion strength. Our previous study successfully demonstrated the possibility of obtaining a zirconia substrate's metallization by using a feedstock powder mixture of copper and aluminum. However, the copper content in the coating was not high enough for power module applications. Therefore, in this study, we aim to improve the copper content in the coating layer composed of the composite powder deposited by LPCS on alumina and zirconia substrates. The influence of the gas pressure and standoff distance on the copper content and coating thickness are evaluated. The coating build-up with a high copper content and thickness is highly dependent on the kinetic energy of particles, enhanced by high gas pressure and short stand-off distance.

It was possible to fabricate cubic-AlN (c-AlN) based coating through the reaction between Al powder and the N 2 /H 2 plasma in APS system. The fabricated coating was about 100 μm with hardness about 540 Hv, which is much higher than the hardness of Al. The formation of the cubic phase in APS is directly related to the rapid solidification phenomena of plasma spraying process. The sprayed powder particles show rapid cooling rates upon impact with the substrate, which prevent its complete crystal growth. The nitride content increased with the spray distance due to increase the flight time of Al particles in the N 2 plasma. Using smaller particle size improved the nitriding reaction at short spray distance due to increasing the particle temperature. However increasing the particle temperature leads to excessive vaporization of Al particles and completing nitriding reaction during flight, therefore suppressing the coatings thickness. The nitriding reaction of the larger particle size Al powders can be enhanced through NH4Cl powders addition. That NH4Cl addition changed the reaction pass way from liquid-gas to vapor-phase intermediate mechanism.

Aluminum nitride (AlN) is one of the attractive ceramics with respect to its excellent mechanical and electrical properties. In this study, AlN coatings were fabricated and the influence of feedstock powders was investigated by reactive RF (Radio Frequency) plasma spraying. Two different particle sizes of commercial aluminum (Al) powders and Al/AlN mixed powders were used as the feedstock powder. The feedstock powder was injected into a RF plasma, and sprayed particles were deposited onto carbon steel or quartz substrates. As a result, it was possible to fabricate thick and dense AlN coating using smaller particle size of Al powders and quartz substrate. However, many agglomerates were formed in the coatings. On the other hand, 50 wt% or above of AlN addition in the feedstock powders was effective to prevent the formation of the agglomerates. Therefore, Al/AlN mixed powder with smaller particle size was useful for fabrication of AlN coatings by reactive RF plasma spraying.

Abradable coatings are used in gas-turbine engines to optimize compressor performance by maintaining tight blade tip clearances. The most common such coatings are thermally sprayed Al-Si/polyester, Al-Si/graphite, and Ni/graphite. Al-Si/graphite coatings have performed well in terms of wear but are prone to corrosion, which can lead to spalling and a reduction in engine efficiency. In this paper, we chart the development of a powder-based Al-Si/BN abradable material designed to overcome in-service corrosion and analyze laboratory and engine testing results.

In an emerging thermal spray process a coating is formed by exposing a metallic or dielectric substrate to a high-velocity jet of solid-phase particles, which have been accelerated by a supersonic gas jet at a temperature much lower than the melting or softening temperature of the particle material. This is known as "Cold Gas-Dynamic Spray" (CGDS) method. Using this method, 2618 Al substrates were coated with nickel-aluminum bronze powders (~100 and ~400 mesh) in an effort to obtain improved wear resistance. The coatings have been examined for their microstructure, hardness, and bond strength. Triple lug shear tests performed on coated panels provided quantitative measurement of the coating/substrate interfacial shear strength. The steady state wear rates were determined using the pin-on-rotating ring test at a pressure of 690 kPa and a sliding velocity of 9 m/s. The wear resistance of the nickel-aluminum bronze coatings is discussed in conjunction with scanning electron microscopy (SEM) examination of the wear tracks and metallography of the polished transverse cross-sections. Though the coatings are not completely free from porosity, they exhibit high interfacial shear strength and wear resistance due to the low-temperature, ballistic impingement of the powders in the cold gas-dynamic spray method. The ~400 mesh powder coating shows higher interfacial shear strength and wear resistance in comparison with the ~100 mesh powder coating.

NiAl coating can be used as bond coats for thermal barrier coatings (TBCs) with good ductility and excellent resistance against high temperature oxidation. In this study, nickel-coated aluminum composite powders were used to prepare NiAl intermetallic compound coatings on nickel-based superalloys using an air plasma spray (APS), high-velocity oxygen-fuel (HVOF) and cold spray (CS) processes. Different spraying parameters in the HVOF and CS processes were used to make different coating microstructures, and the coating prepared by the APS technique served as a control for the HVOF and CS processes. The microstructure and phase constitution of the coatings were studied using XRD, SEM and EDS. The results indicate that the deformation behavior of the NiAl powder was different under the different spraying parameters. Less defects of oxides and inclusions were observed in the CS coatings compared with the HVOF coatings.

Plasma spraying of aluminum oxide is attracting great interest as a method for depositing economical coatings for use in the semiconductor equipment industry. The microstructure and mechanical properties of the sprayed aluminum oxide coatings are critical to the coating usage in the semiconductor equipment application. The influence of powder size on the coating microstructure and mechanical properties for coatings used in this industry is investigated.

In this study, the dust explosion properties of aluminum, titanium, zinc, and iron based alloy powders were evaluated by JIS Z 8818: “Test method for minimum explosible concentration of combustible dusts,” IEC 61241-2-3 (1994-09) Section 3: “Method for determining minimum ignition energy in dust-air mixtures,” and JIS Z 8817: “Test method for explosion pressure and rate of pressure rise of combustible dusts.” The test are described and the results are presented and discussed.

Cold gas dynamic spray has significant potential for load-bearing repairs of high-value metallic components, as it is capable of producing pore and oxide-free deposits of significant thickness and with good levels of adhesion and mechanical strength. However, recently published research has shown that the rapid solidification experienced by gas atomised powders during manufacture can lead to a non-equilibrium powder microstructure, including clusters of dislocations as well as significant localised segregation of alloying elements within each particle. This paper reports on an investigation into the solution heat treatment of a precipitation hardenable aluminium alloy powder. The objective was to create a consistent and homogeneous powder phase composition and microstructure before cold spraying, with the expectation that this would also result in a more favorable heat treatment response of the cold spray deposits. Aluminium alloy 7075 gas atomized powders were solution heat treated at 450 °C for 5 hours in a sealed glass vial under vacuum and quenched in water. The powder particle microstructures were investigated using scanning electron microscopy with electron back scatter diffraction (SEM/BSE) and optical microscopy. The dendritic microstructure and solute segregation in the gas atomized powders was altered, with the heat-treated powder particles exhibiting a homogeneous distribution of solute atoms. The influence on the mechanical properties of the powder particles was studied using micro-indentation. The heat-treated powders exhibited a hardness decrease of nearly 25% compared to the as-received powders. This paper relates the behavior and the deformation of both as-received and heat-treated powders during spraying (single particle impacts), comparing the measured hardness with the deformation effect and the material jetting occurring upon impact.

Aluminium alloys are extensively used materials which can be found in all kinds of industrial applications. They have distinctive advantages such as a high strength/weight ratio, an excellent workability and a good corrosion behaviour. However, aluminium alloys have wear resistance properties which limitate further use of these alloys. Plasma transferred arc surfacing (PTA) using the DCCP-technology (Direct Current Combined Polarity) was used for enhancing wear properties of different aluminium alloys (AlMgSi0.5, AlSi12) by the formation of an alloyed layer with added ceramics. Hardness of the base material could be increased by more than two times while the wear resistance of the modified aluminium alloy was about ten times higher compared to the base material. Paper text in German.

Pure metal coatings have successfully been cold sprayed on to carbon fiber reinforced polymers (CFRPs) in previous studies at McGill University. As a means to improve coating conductivity for lightning-strike protection (LSP) purposes, coatings with mixed metal powders were sprayed. There is also the possibility of improving the deposition efficiency (DE) since single component tin coatings previously had a maximum DE of only 20%. The studied coatings were based on a mix of tin and aluminum powders, the latter being a metal commonly used in the aerospace industry for its lightweight properties. The different coatings were characterized and compared to results on pure tin coatings and on mixed Sn-Cu and Sn-Zn coatings. The DE was measured for different conditions and compared to those of previous studies. Mixing tin and aluminum powders is discussed and various mechanisms related to cold spraying mixed powders on CFRPs are explored.

Nanostructured materials are of widespread interest because of the unique properties they offer. We have demonstrated that nanocrystalline 6061 and 5083 aluminum powders, prepared using liquid nitrogen (LN2) ball milling, can be consolidated using the cold spray process. TEM analysis of the cold spray coatings reveals that the cold spray process caused significant grain refinement. Gas atomized 6061 and 5083 aluminum powders were ball milled in liquid nitrogen resulting in a powder microstructure containing 250-400 nm grains. Cold spray coatings prepared using these feed stock materials exhibited homogenous microstructures with grain sizes of 30-50 nm. TEM analysis of the as-received powders, ball milled powders, and coatings are shown. Mechanical property measurements made using nano-indentation techniques show that the hardness of the coatings prepared using the LN2 ball milled 6061 is approximately double the hardness of the coatings prepared using the same powder in its as-received condition.

FeAl Intermetallic compounds have excellent wear resistance and high temperature oxidation resistances. The low temperature brittleness makes intermetallic compound materials more suitable to be applied in the form of coating to protect materials from high temperature oxidation and wear. In the present study, a iron/aluminum composite coating was produced by cold spraying of iron and aluminum powder mixtures and then was annealed at different temperatures to aim at forming an iron aluminide intermetallic based coating. The deposition behavior of iron and aluminum powder mixtures and microstructural characteristics of the as-sprayed deposit were examined by scanning electron microscopy (SEM). The kinetics of the phase transformation of the as-sprayed iron/aluminum composite deposit to iron aluminide was characterized by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The results showed that after heat treatment at a temperature of 600°C, intermediate phase Al 5 Fe 2 coexisted in the deposit with remaining Fe and Al. With increasing heat treatment temperature to 900°C, the deposits consisted of mainly FeAl phase and a trace of remaining Fe phase.

Porous copper coatings, which act as wicks for liquid transport, were fabricated using a flame spraying process. Copper and aluminum powders were fed independently into the spray torch and deposited on copper substrates to form a composite coating. The aluminum was subsequently removed using chemical leaching leaving a porous copper coating behind. Varying the feed rate of aluminum powder allowed the coating porosity to be controlled. Channels to enhance liquid flow were made in some of the porous copper coatings by placing pieces of aluminum wire mesh on the copper substrate before spraying. During spraying the sprayed powders passed through the mesh opening and created pyramid shaped arrays on the substrates. The groove width was controlled by using different wire mesh sizes. Coatings were made with porosity varying from 2 to 44 %, and groove width ranging from 0.16 to 0.53 mm. The capillary performance of the coatings was evaluated experimentally by measuring the rate of rise of ethanol in the coatings. The rate of rise increased with coating porosity, and decreased with groove width.

Presently, the self-propagating high-temperature synthesis (SHS) has found wide use in the production of compacts and powder materials, and also in the fabrication of end products. Yet, a disadvantageous feature of the standard SHS process, which can be overcome in part by running the synthesis reaction under pressure, is that it fails to provide the possibility of obtaining high-density materials and products. It is therefore of interest to develop a combined process which would allow one to apply a two-component Ni-Al coating with prescribed stoichiometric composition by cold spraying of a nickel-aluminum powder mixture followed by self-propagating high-temperature synthesis of a target intermetallide (Ni3Al or NiAl) by treating the surface layer of the cold sprayed coating with a highly-concentrated energy flux (argon plasma jet). Preparation methods for nickel-aluminum powder mixtures (in particular, mechanochemical activation) intended for cold spraying process are discussed. Computational experiments were performed to substantiate the choice of stationary, traveling and pulsed energy sources for subsequent initiation of SHS in the heterogeneous layer deposited onto a steel substrate. A model was developed to predict the local phase state of the material synthesized in the coating; this model involves the state diagram of the Ni-Al system. The characteristics of sprayed coatings were examined. The developed approach is shown to offer much potential in practical applications.

The excellent wear-resistant performance of cast iron coatings considerably depends on the formation of graphite structure with an inherent self-lubricating property. In the present study, two types of cast iron powders produced by gas- (GA) and water-atomization (WA) were deposited on an aluminium alloy substrate by atmospheric DC plasma spraying. WA powders are generally characterized by high oxygen content, irregular appearance and inexpensiveness compared with those of GA powders. Although alloying elements of silicon and aluminium work as a strong graphitizer and anti-oxidizer, graphite structures are not recognized in coatings sprayed with as-atomized high silicon and aluminium powders. Therefore, either pre-annealing of powders or post-annealing of coatings is required to achieve cast iron coatings containing graphite structure. A marked decrease in graphite occurs to the coatings with pre-annealed GA powder, since there exists precipitated graphite mainly on a GA powder surface. A short period of post-annealing is also valuable for graphitization. The weak oxide layers are observed in coating cross-sections with GA and WA powder, however, their oxidized levels are much lower than those with bearing steel powder containing low silicon and aluminium. Hence, graphitized cast iron coatings sprayed with inexpensive WA powder exhibit a splendid anti-wear performance.

Coating build-up mechanisms and properties of cold sprayed aluminum-alumina cermets were investigated. Two spherical aluminum powders having average diameters of 36 and 81 microns were compared. Those powders were blended with alumina at several concentrations. Coatings were produced using a commercial low pressure cold spray system. Powders and coatings were characterized by electronic microscopy and microhardness measurements. In-flight particle velocities were monitored for all powders. The deposition efficiency was measured for all experimental conditions. Coating performance and properties were investigated by performing bond strength test, abrasion test and corrosion tests, namely, salt spray and alternated immersion in salt water tests. These coating properties were correlated to the alumina fraction either in the starting powder or in the coating.