This paper provides an overview of chemical vapor deposition (CVD) and atomic layer deposition (ALD) processes and the advantages they offer physical vapor deposition for the application of friction and wear coatings for micromechanical assemblies and components. It explains how hard and solid lubricant phases can be applied by these non-line-of-sight deposition methods, achieving nanoscale conformality and coating uniformity on buried surfaces and interfaces. It also discusses inherent disadvantages and explains how plasma excitation can be incorporated in either process to overcome material limitations.

A new coating process called polymer thermal spraying (PTS) was recently developed to accommodate the deposition of heat sensitive polymeric materials over a broad range of substrates. The novel process uses an electro-resistive element to heat the main process gas, which could be air, any pure gas, or gas mixture. This paper describes the process and presents three case studies in which it is used to produce blast mitigation coatings for civil structures, super-hydrophobic coatings for corrosion protection, and flame resistant polyimide syntactic foams for thermal insulation.

The aim of this study is to propose coatings that could potentially replace hard chromium as a means of corrosion and wear protection. Two NiCrBSi coatings are evaluated, one produced by laser cladding, the other by atmospheric plasma spraying with a post-laser treatment. Although laser-clad NiCrBSi exhibits the best technical properties, the APS coatings were found to be more environmentally justifiable based on the use of life cycle assessment (LCA) software.

Nanocomposite epoxies are novel sealants developed especially for sealing metalized coatings. In order to test the corrosion protection performance of arc-sprayed aluminum coatings plus this sealer, steel panels were coated and placed in a corrosion test site on the East China Sea. Test panels were mounted in a marine atmosphere zone, seawater splash zone, tidal zone, and full-immersion zone. Several tests were conducted including corrosion and coating adhesion tests. This paper presents the results obtained from composite-coated steel panels after three years of seawater exposure.

The aim of this work is to assess the ability of pulsed gas dynamic spraying to deposit coatings on the inside surface of cylindrical workpieces. Thick dense copper coatings are produced on flat surfaces and on the inner surface of cylindrical workpieces using a specially designed gun extension. The coatings are evaluated based on microstructure and microhardness in order to determine if the copper has the same characteristics on all surfaces. A comparison between pulsed gas and cold gas dynamic sprayed copper coatings is also presented.

This study compares the tribological performance of HVOF and HVSFS coatings applied to gray cast iron and aluminum cylinder liners. Five different materials, including Fe alloy, FeCrMo, CrC-NiCr, NiCrBSi, and WC-Co, were sprayed using a conventional HVOF torch operated by a six-axis robot while the liners were manipulated by means of a rotary table. A similar setup was used to spray TiO 2 -TiC coatings, but the gun was modified for nano-sized particles in a suspension fed axially into the combustion chamber. Coating microstructures were examined using optical and SEM imaging and friction and wear properties were determined through oscillating friction wear tests. The results obtained are compared to state-of-the-art cylinder liners.

This paper presents recent developments in thermal spray coating technology for thermal power plants. As for thermal barrier coatings for gas turbines, to accommodate the high gas temperatures required to improve thermal efficiency, a new ceramic topcoat material with low conductivity was developed. As for wear-resistant coatings for boiler parts, a C-Cr-Fe alloy coating was developed that is lower in cost than conventional chromium carbide cermet. Field tests of boiler parts show that the erosion wear rates of these coatings are as good or better than that of conventional cermet.

This work investigates some of the unique properties that can be achieved by combining materials with positive and negative thermal expansion coefficients. In the experiments, different mixtures of MCrAlY, WO 3 , and Y 2 O 3 powders are deposited on stainless steel substrates by laser cladding and HVOF spraying. To facilitate the formation of negative expansion coefficient particles in a positive expansion coefficient matrix, nucleation centers are created by ion implantation followed by heat treating. SEM examination and XRD analysis of the coatings obtained confirm the viability of the processing approach.

This study investigates the influence of spraying distance and substrate orientation on the formation of metallic coatings by detonation spraying. Deposition efficiency was determined for aluminum, copper, titanium, and steel powders sprayed at different distances on substrates oriented at different angles. The results show that detonation products maintain their influence on sprayed particles even outside the barrel despite the pulsed nature of the detonation spraying process. Numerical calculations of particle acceleration and heating inside the barrel are performed for several materials and a theory of the processes outside the barrel is proposed. Optimal spraying parameters allowing 60-80% deposition efficiency are defined and experimentally validated for the materials studied.

This paper discusses the double-arc phenomenon that occurs in plasma arc spraying and its prevention through the use of a bi-anode torch. It also presents the results of a study that compares voltage-current characteristics of the arc for different plasma gases and arc root attachment points. It is shown that the arc has different electrical characteristics when changing from the first to the second anode, which is explained using a simplified arc model.

Aluminum-based composite coatings reinforced with different volume fractions of SiC particles were deposited on aluminum substrates by means of pulsed gas dynamic spraying using a mechanically mixed composite feedstock powder. Microstructural features of the coatings are examined and their hardness is reported. The results show that the high fraction of SiC particles in the feedstock powder are retained in the coatings and that increasing SiC content in the aluminum matrix significantly improves coating hardness. The highest hardness value was obtained for a coating with 28 vol% SiC. Beyond that, coating hardness decreased, which is attributed to increasing porosity and decreasing cohesion between deposited aluminum-based particles.

This study analyzes the effects of laser remelting on the morphological structure and adherence of flame-sprayed PEEK coatings on stainless steel. Different types of lasers were used with wavelengths of 1.064 mm (Nd:YAG), 10.6 mm (CO 2 ), and 0.88 mm (diode). It was found that the longer the wavelength, the more compact the coating, but the less well-adhered. By making adjustments to compensate for the wavelength-dependent absorption coefficient of PEEK, both coating properties were improved.

In this study, a variety of yttria-stabilized zirconia (YSZ) coatings have been obtained by plasma spray physical vapor deposition with fine powders at high power. The coating structures were found to change significantly with powder feed rate, but less with substrate temperature and rotation speed. Porous YSZ coatings with a feather-like structure and low thermal conductivity were deposited at rates as high as 220 μm/min. These results demonstrate the potential of plasma spray physical vapor deposition for producing thermal barrier coatings.

A low-temperature, atmospheric-pressure spraying process was recently developed that facilitates the formation of highly functional films on any type of substrate using metal or nonmetal powders. This paper describes the new process and explains how different parameters, such as spraying distance, exit gas velocity, nozzle diameter, and particle size, affect the thickness, area, and composition of copper and barium titanate films on alumina, copper clad, and wafer substrates.

In this study, fine aluminum powder was cold sprayed onto aluminum substrates, some of which were polished, some grit blasted, and some pretreated using a nano-pulsed Nd:YAG laser. In the latter case, the laser is coupled with the cold spray gun and the irradiation treatment occurs just prior to deposition. To better understand the interaction mechanisms involved with laser pretreating, coating-substrate interfaces were examined on thin-foil specimens and adhesion strength was determined by laser shock testing. The results show that substrate pretreatment with a nano-pulsed laser significantly improves the coating-substrate interface as well as coating adhesion.

WC-based cermet coatings were deposited by HVOF spraying in order to study the effects of laser remelting on coating microstructure, hardness, and dry sliding wear behavior. It was found that the laser treatment eliminates porosity and contributes to increased hardness and enforced metallurgical fusion between the coating and substrate, effectively improving adhesion and wear resistance.

Since many years, aluminum alloys are established as lightweight construction materials. To reach a partial wear protection for aluminum components in conjunction with seal faces, inlays, made of wear resistant materials, are commonly used. Problems concerning this approach are the necessary space and the endurance strength of the inlay - part joint. In the following paper an alternative for the replacement of the inlays by cladding with an innovative and easy to handle short arc technology will be discussed. This technology offers the potential to control the energy input into the substrate and so the formation of brittle intermetallic phases in the aluminum-steel interface as well as the thermal stresses. The usage of new nano crystalline solidifying wear resistant iron-based feedstock materials with advantageous physical and mechanical properties enables further applications beside the wear protection of surfaces, for example as metallic heat insulation layer with a low heat conductivity, close to the values of ceramics.

In order to address deficiencies in thermal spray coatings applied using air plasma spraying (APS) and high velocity oxygen fuel (HVOF), namely, adhesion, cohesion, porosity and line of sight limitations, novel hybrid coatings using post - thermal spray chemical vapor deposition via the pack cementation process were developed. Coatings based on tungsten carbide-cobalt chrome and chrome carbide-nickel chrome followed by boron or chrome diffusion were applied to multistage and single stage pump components for severe service applications in sand and alumina catalyst. Field testing established the effectiveness of using the dual coating approach.

The objective of the present work is to produce Mg-PSZ (magnesia partially stabilized zirconia) powders that were used to coat oxygen sensor tubes by plasma spraying. It is well known fact that zirconia based oxide thin films are the most widely used material as ionic conductors of oxygen. In this study, MgO stabilized ZrO 2 powders were produced by the sintering and crushing method. Starting powders were a high grade ZrO 2 , and a natural hydromagnesite (Mg-HC) as MgO source. ZrO 2 , and MgO were mixed in the compositions of ZrO 2 - 9mol % MgO. The mixtures were ball milled by using ZrO 2 balls. The fine powders were stabilized via thermal treatment in air at 1540°C for 24 hours. The powders were calibrated to the correct particle size distribution for plasma spraying. All powder samples were characterised by a well-defined techniques with an exhibited an average particle size of 10 µm. The powders consisted of monoclinic, tetragonal and cubic phases. They were sprayed by plasma spray to produce high temperature Mg-PSZ coatings on oxygen sensor tubes. It is worthwhile to point out that high temperatures were generated in the plasma spray jet, and the rapid quenching of the molten Mg-PSZ droplets deposited on the cold substrate subsequently occurred. After this process, thermal treatments were carried out to improve the film density and microstructural stability.

Al-Cu-Cr quasicrystalline (QC) coatings were deposited onto mild steel Q235A substrate by low power plasma spraying. The plasma torch was designed such that the powders can be injected axially (parallel to the axis of the plasma arc) into the region between the anode and cathode, and the carrier gases were transferred to the plasma flame, so the heating efficiency of the powders is greatly increased and the velocity of particles is much higher than an externally-fed powder system. The Al-Cu-Cr QC coatings were sprayed via this new technique at different plasma power (3~7kW) by controlling the secondary plasma gases (H 2 and N 2 ) flow or changing the arc current. The results show that, the original powder was mainly composed of a dominant icosahedral quasicrystalline phase I-Al 65 Cu 24 Cr 11 and a minor monoclinic θ-Al 13 Cr 2 . However, besides these two phases, body-centered cubic α- Al 69 Cu 18 Cr 13 , the approximant to quasicrystal I-Al 65 Cu 24 Cr 11 , has been detected in as-sprayed coatings. On the other hand, peak intensity of QC phase I-Al 65 Cu 24 Cr 11 decreased and that of crystalline phases (θ-Al 13 Cr 2 or α-Al 69 Cu 18 Cr 13 ) increased as the plasma power was increased.