Fluoropolymer and other polymer materials are extremely difficult to coat using solid-state deposition techniques such as cold spraying. In this study, fluoroethylene propylene (FEP) is cold sprayed onto a metallic substrate in order to investigate the effect of powder size, gas temperature and pressure, and substrate surface treatments. A powder modification technique that uses fumed nanoceramic particles as an additive to the feedstock is evaluated as well. The results show that the deposition efficiency of FEP is affected by particle size, gas temperature, and traverse speed as well as the added nanoceramic which, in this case, is either silica or alumina. It is also shown that the hydrophobic properties of the fluoropolymer are retained in the coatings and that adhesion between the coating and substrate plays a critical role.

Lowering the impurity content in the thermal barrier coating has the effect of improving the high temperature stability and service life. SiO 2 , Al 2 O 3 , TiO 2 and Fe 2 O 3 are several common low melting point oxide impurities in the YSZ (Yttria- Stabilized Zirconia) top coatings, and they all have some influence on the performance of the coatings. But there is no quantitative research on the relationship between impurity content and the properties of the coatings. In this paper, YSZ spraying materials with SiO 2 , Al 2 O 3 and Fe 2 O 3 with the content changing from less than 0.01wt% to 1wt% were designed. The bond coatings were all NiCoCrAlY and were prepared by HVOF (High-Velocity Oxygen-Fuel). The top coatings were prepared by APS (Atmospheric Plasma Spraying). The microstructure, phase structure and thermal shock resistance of the above coatings were investigated. The results showed that the increase of oxide impurity content was more prone to thermal shock failure. It shows that the oxide impurity has a significant influence on the properties of YSZ coating.

A new method to fabricate micro-nano scaled surface with super-hydrophobicity is introduced in the present paper. Micro-nano hierarchical structure coatings based on silica (SiO 2 ) micron particles were successfully deposited on the stainless steel substrates by high-velocity oxygen fuel (HVOF) spraying which were modified by 1,1,2,2- Tetrahydroperfluorodecyltrimethoxysilane (FAS) to reduce surface energy. The influences of the HVOF process parameters on the wettability of the coatings were investigated. The coatings were characterized by scanning electron microscopy (SEM), 3D laser microscopy (LSM), and Fourier transform infrared spectrometer (FTIR). The results show that the as-sprayed surfaces exhibit micro-nano hierarchical structure. The water droplets are strongly adhesive to the as-sprayed surface, while by FAS absorbing treatment, the surfaces exhibit super-hydrophobicity, whose contact angle with water droplets are as high as 150°, and the water droplets tend to roll on the surface with extremely low adhesion with a sliding angle of 3°

This paper discusses results of research concerning the microstructure and scuffing resistance of HVOF sprayed WC- 12Co nanostructured and conventional coatings under dry friction conditions. The observations were carried out by means of a Falex type tester. It was found that HVOF sprayed nanostructured WC-12Co coatings showed the most homogeneous structure, the greatest scuffing resistance and the highest hardness.

In the current investigation plasma spray technique was used for depositing hydroxyapatite (HA) and hydroxyapatite – silicon oxide (SiO 2 ) coatings on 316L SS substrate. In HA-SiO 2 coating, 20 wt% SiO 2 was mixed with HA. The feedstock and coatings were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) / energy-dispersive X-ray spectroscopy (EDX) analyses. The corrosion resistance of the uncoated, HA coated and HA + 20 wt% SiO 2 coated 316L SS was investigated by electrochemical corrosion testing in simulated human body fluid (Ringer’s solution). After the corrosion testing, the samples were analyzed by XRD and SEM / EDX analyses. The addition of SiO 2 reduces the crystallinity of the coating. The corrosion resistance of the 316L SS was found to increase after the deposition of the HA + 20 wt% SiO 2 and HA coatings.

Plasma sprayed ceramic coatings are widely used for thermal barrier coating applications. Commercially available mullite powder particles and a mixture of mechanically alloyed alumina and silica powder particles were used to deposit mullite ceramic coatings by plasma spraying. Microstructure and morphology of both powder particles as well as coatings were investigated by using scanning electron microscopy (SEM). Phase formation and degree of crystallization of coatings were analyzed and estimated by using X-ray diffraction technique. Differential thermal analysis (DTA) method was used to study the phase transformation of coatings. Results indicated that the porosity level in the coating deposited using mullite as initial powder particles was lower than that deposited using the mixed powder particles. The crystallization degree of the coating deposited using the mixed powder particles are higher than that deposited using mullite powder particles. DTA curves of coatings deposited using the mixed powders have showed some phase transformation due to the crystallization of the retained amorphous phases such as mullite and alumina in the coatings. The degree of crystallization of both as sprayed coatings was significantly increased after post deposition heat treatments.

The protection of metallic components against severe operating conditions has motivated the development of coatings for a wide range of applications. In particular, ceramic coatings can be used to protect components that operate under high temperatures and corrosive environments aiming to extend their service life. Several Thermal Spray processes can be used to process ceramic coatings on the metals, taking advantage of the mechanical bond typical of these processes. The exception is the Plasma Transferred Arc (PTA) process which results in a metallurgical bond between the coating and the substrate metal. This study analyzed the potential of PTA to process ceramic coatings on a steel substrate. Powder mixtures of aluminum (Al) and silicon oxide (SiO 2 ) were deposited using three deposition currents aiming to synthetize alumina coatings “in situ” as the reaction between Silicon Oxide and Aluminum powders occurred. X-Ray diffraction, Scanning electron microscopy, Semi-quantitative chemical analysis by EDS and microhardness were used to analyze the processed surfaces. Coatings characterization confirmed that the synthesis of alumina occurred but it was not completed and a two layer coating was formed. A layer near the fusion line composed of Fe-Al matrix with Fe 3 Al precipitates and an external layer of Al, Si, and Al 2 O 3 . An increased in the iron content in the coating due to the higher interaction of the plasma arc with the substrate reduced the amount of Alumina formed.

Hydroxyapatite (HA) is preferred for its ability to interact with living bone, resulting in improvements of implant fixation and faster bone healing. In this study, a small amount of silicon dioxide (~ 2wt%) was introduced into HA slurry which was subsequently spray-dried into powder. A silicon modified HA coating was then deposited onto Ti-6Al-4V alloy substrates by atmospheric plasma spraying technology. Scanning electron microscopy (SEM), X-ray diffraction and X-ray photoelectron spectrometry, and Raman spectrometry were employed to investigate the surface chemistry that would directly influence bone forming cell proliferation. Additionally, the adhesive bonding strength of the as-sprayed coatings were specified measured using a universal testing system. The fracture surfaces after tensile test were also investigated by SEM.

An alternative method to produce bulk nanocrystalline materials and avoid the powder compaction step is to produce amorphous material by rapid solidification followed by controlled heat treatment to introduce nanocrystalline structure. The extremely high cooling rates in plasma sprayed particles give rise to formation of nonequilibrium phases, which may become amorphous for certain materials. Five different materials studied in this work are based on near-eutectic mixtures of alumina, zirconia and silica. The powder feedstock materials have been plasma sprayed using water stabilized plasma torch (WSP) and subsequently heat-treated to prepare nanocomposite materials with varying nanocrystallite size. The as-sprayed materials have very low open porosity and are mostly amorphous. The as-sprayed amorphous materials crystallize at temperatures around 950°C with an associated volume shrinkage of 1-2%. The resulting structure is best described as nanocomposite with very small crystallites (12 nm on average) embedded in inter-crystallite network. Role of the silica compound on phase composition, microstructure, and mechanical properties of the as-sprayed and annealed materials is discussed. Elastic properties were measured for the nanocrystalline materials. The as-sprayed amorphous materials exhibit high hardness and high abrasion resistance. Both properties are significantly improved in the heat treated nanocrystalline samples.

Mathematical models for simulation of motion and heating of fine ceramic particles in plasma and laser spraying, as well as under conditions of a new technological process, i.e. hybrid laser-plasma spraying, are proposed. Trajectories, velocities and temperature fields of fine SiO 2 particles being sprayed using the argon plasma jet, CO 2 -laser beam and their combination have been calculated. It is shown that the space-time distribution of temperature in spray particles greatly depends upon the spraying method.

Reactively thermal sprayed coatings based on in-process reactions during flight and after impingement offer superior properties compared with conventional coatings because it has in-situ formed fine and uniformly dispersed stable hard phases. In the present work, composite powder composed of plated nickel, fine SiO 2 particulates and Al-Si-Mg core particles with water glass binder (SiO 2 /Ni/Al-Si-Mg) was deposited onto an aluminum substrate to fabricate composite coatings by using HVOF (high velocity oxyfuel), RF (radio frequency) and DC (direct current) plasma spraying methods. The amount and constituents of phases formed during reactive thermal spraying were found to be different depending upon the methods used where in-process reactions differently proceed. Consequently, reactively sprayed composite coatings mainly consist of Mg 2 Si, MgAl 2 O 4 , NiAl 3 and Al-Si matrix through the exothermic reaction of SiO 2 and nickel with molten Al-Si-Mg alloy. The depletion of magnesium in the composite powder is responsible for the obtained lower hardness of composite coatings sprayed by RF plasma spraying which offers the highest molten droplet temperature.

The high velocity oxy-fuel (HVOF) combustion spray technique has been shown previously to be an excellent solution for depositing crystalline matrix nano-reinforced polymer coatings. Dense polymer coatings can be produced by controlling both the particle dwell time in the HVOF jet and through substrate thermal management. In composite materials, it is often desirable to incorporate the maximum amount of reinforcing material into the polymer matrix to achieve optimum mechanical properties. The experiments described here were performed to determine the maximum amount of different scales of silica particles that could be incorporated into a nylon 11 matrix and the time required to do so. Ashing results indicated a maximum amount of silica that can be incorporated. Also, the maximum level of silica incorporation occurs in a shorter time than previously believed. Microscopy, however, indicated that other physical changes continued to occur within the powders when ball milling was allowed to continue beyond this time.

Nanopowders of amorphous SiO 2 , with typical particle sizes of 30-80 nm, were treated under non-equilibrium plasma conditions created by a capacitively coupled (CC) RF discharge in pure methane or ethane. The gas flow rate was varied between 0.02-0.06 slpm, with reactor pressures maintained between 1000 and 5000 Pa, and applied RF power inputs between 700 and 1500 W. The plasma properties were monitored through measurements of the C 2 rotational and the atomic hydrogen excitation temperatures. The compositions of the gases that passed through the plasma were analyzed by mass-spectrometry. In spite of the evidence indicating the presence of C n H 2n+2 and C n H 2n (n=1-3) species, as well as acetylene, in the discharge, the homogeneous formation of soot was not observed. At the same time, introduced nanoparticles acted as centers for the inception and growth of C:H thin coatings in the form of polymer-like hydrocarbon layers, whose thickness lay between < 5 - 30 nm. The results of TEM, IR spectroscopy, thermo-gravimetric and precision calorimetric analyses performed on the plasma treated powders provided evidence for the formation of an amorphous, high density C:H matrix on particles' surfaces.