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.

The present work demonstrates the possibilities of atmospheric air plasma spraying. It presents various approaches to the development and optimization of spraying modes using diagnostic equipment and provides examples of industrial approbation of the technology.

A wide range of properties can be achieved in intermetallic coatings applied by gas detonation spraying (GDS). The properties of Fe-40at%Al GDS layers, however, may change when exposed to temperatures exceeding a threshold level. To characterize such changes, Fe-40at%Al GDS coatings were subjected to systematic dilatometric studies in which temperatures were cycled from room temperature to 1180 °C. The investigation revealed both irreversible and reversible phase transitions as described in the paper. Dilatometry measurements obtained from sintered samples made from the same powder are presented for comparison.

The wear of piston rings in large marine two-stroke diesel engines is a major maintenance cost. Applying coatings with good oxidation, corrosion resistance and high temperature strength, can lower the total maintenance cost. In the past nickel aluminide with chromium carbide have been applied to pistons by thermal spraying. Using laser cladding a suitable microstructure can be formed while at the same time avoiding cracks and bonding issues. In this report powders and coatings were manufactured in order to be able to investigate the dry-sliding wear behavior. Material with three levels of carbides was atomized. Wear test samples were manufactured by laser cladding. The dry sliding wear-mechanism maps are generated by using block on ring test setup where coated blocks slide against cast iron rings. All alloys exhibited regions of plasticity-dominated wear and oxidational wear with a transition region in-between. The carbide-containing alloys showed lower friction and wear in comparison to the carbide free nickel aluminide alloy.

TiAl 3 -Al composite coatings are believed to hold promise for extending the service temperature range of titanium alloys used as structural materials. In this study, 0.6 x 40 mm Ti-6Al-4V specimens are coated with a 30 μm thick layer of TiAl 3 -Al by low-temperature HVOF spraying. Cross-sectional imaging shows that the as-sprayed coatings have a dense laminar microstructure and are well bonded to the substrate. Following the initial examination, the coating samples were placed in a muffle furnace, where they were held at 700 °C for up to 1000 h. Mass gain was detected starting at 200 h and remained nearly constant for the remainder of the test. This is an indication of excellent corrosion resistance, which is verified by SEM cross-sectioning and elemental EDS analysis. A brief explanation of the protective mechanism of the coating is provided.

In the present study, a new multi-chamber detonation sprayer (MCDS) was used to deposit Al 2 O 3 coatings on titanium and carbo steel substrates. SEM, TEM, and XRD analysis of the layer between the coating and substrate revealed the presence of an intermetallic compound that improves coating properties and is conducive to the relaxation of stresses generated during spraying.

A nanostructured WC-CoCr coating was fabricated by HVOF spraying using a new type of WC-CoCr powder in which the CoCr exists in the form of a metallic compound. The CoCr powder constituent was prepared by induction melting and mechanical milling. It was then combined with a WC-Co composite nanopowder and the mixture was agglomerated by spray drying and heat treating. The powders and coatings produced were characterized by means of XRD, EDS, and BSE analysis, nanoindentation testing, and potentiodynamic polarization studies. The results show that the presence of the intermetallic CoCr compound makes nanostructured WC-CoCr coatings harder and much more corrosion resistant than conventional WC-Co-Cr coatings in which Cr exists as an unalloyed metal.

In this study, arrested reactive milling (ARM) is used to prepare Al-Ni composite powder for deposition on copper liners via kinetic spraying. Among the main goals are to obtain a better understanding of how the milling process affects deposition efficiency and the reactivity of the coatings and to find a way to reduce the amount of remaining solid lubricant after milling. Al-Ni powders were produced under a wide range of conditions and heated to various temperatures to eliminate stearic acid. The powders were sprayed using fixed process parameters and deposition efficiencies, reactivities, and heat values were measured and are compared along with coating microstructures. The procedures used are described and the findings of the study are presented and discussed.

Recently a Ti–TiAl 3 metal–intermetallic laminate (MIL) composite attracts growing attention because they have potential application in honeycomb or sandwich components of airplanes and as biomaterial with good bio-compatibility. Of the available processing techniques, diffusion bonding of elemental titanium and aluminum foils is an effective low-temperature method to synthesize the composite, allowing growth of the intermetallic layer. However, application of assembling and multi-pass cold rolling operations leads to fact that this technology is complex and expensive. The use of Cold Spray technology instead of aluminum foils utilization and multi-pass cold rolling to produce the Ti–TiAl 3 MIL composites is believed to be more effective. However, reaction diffusion kinetics of Ti-Al particulate composite differs from that of classical MIL composite and needs to be studied. The task of this paper is to define microstructural changes of Tl-TiAl 3 composite coating during cold spraying and reaction sintering. The optical microscopy, SEM, EDS, X-ray and microhardness examinations are presented and discussed.

A thermal cycling test was carried out in an EB-PVD MCrAlY – superalloy system, the result of which showed that a continuous β-NiAl layer formed in the MCrAlY coating near the coating–superalloy interface. Since β phase can be as a reservoir of Al, the formation of the β layer, in which much Al is reserved, is probably beneficial to the coating’s life. An oxidation-diffusion model was adapted to simulate the development of the microstructures in the coating-superalloy system. The simulation results indicate that the formation of the β layer was strongly related to the high Al activity in the substrate; if the Al activity of the substrate was high enough, a β layer could be built up in the coating near the coating-substrate interface.

In this paper, we reported our investigation on preparing inorganic phosphate ceramic coatings on the surface of γ-TiAl based alloy by air spray. The high temperature performance of the coatings was tested by thermal shock test, cyclic oxidation and isothermal oxidation at 950 °C. The results showed that the coatings exhibited significant improvement on high temperature anti-oxidation performance of the base alloy. No obvious cracks or spalling of the coatings occurred after oxidation experiment under isothermal oxidation condition at 950 °C for 1000 h. The characterization was carried out to analyze the microstructure of the coatings before and after oxidation test.

The main goal of the combined Cold Spray – Sintering technology development is to obtain high density ductile Fe- Al intermetallics based thermal barrier coatings as an alternative to conventional ZrO 2 coatings widely applied in industry. The task of this paper is to examine the structural changes of cold sprayed Al-AISI 316L composite coatings due to synthesis of Fe-Al intermetallics during annealing and find the conditions of high density composite formation. A dense Fe/Al intermetallic-Al composite coating is obtained. Three factors are found to play the main role in the structure formation of dense Fe-Al intermetallic composite coating: i) layered structure, ii) particle size and thickness of Fe and Al layers, iii) annealing temperature.

Protective coatings with high wear, erosion and corrosion resistance are of great importance in many fields of application and in particular, in the electric power generation sector. In this paper, the HP-HVOF (high-pressure high velocity oxy-fuel) technique is used to produce dense rapidly quenched metal-ceramic nanocomposite protective coatings. The powders for the thermal spray process are produced by high energy ball milling using mechanochemical displacement reactions to synthesize ceramic components in-situ at the nanometric scale. Boron nitride solid lubricant is used as a source of nitrogen and boron to precipitate nitride and boride phases in a corrosion resistant iron aluminide metal matrix. The formation of the hard phases during milling and/or thermal treatments is investigated using various analytical methods. The tribological properties of the coatings with and without ceramic additives are reported.

This work shows that with computer-controlled detonation spraying, the phase composition of coatings can be changed relative to that of the feedstock powders. New phases can appear in substantial quantities due to chemical reactions of reduction, oxidation, and nitridation as well as interfacial interactions between phases in composite powders. The key advantage of computer control is that it precisely regulates the quantity and stoichiometry of explosive gas mixtures. It has thereby been found that TiO 2 experiences partial reduction to titanium suboxides and that chemical reactions with nitrogen are also possible. It has also been found that when nitrogen is present, titanium aluminides, Ti 3 Al and TiAl, are likely to form nitrides in the sprayed coatings. Interfacial reactions between the phases of a composite have been studied, and in the case of the Ti 3 SiC 2 -Cu system, it has been found that deintercalation of Si can be prevented by maintaining relatively cold spraying conditions. At higher temperatures, coatings of an unusual phase composition form in which carbon-deficient TiCx inclusions are distributed in the Cu matrix as modified by the dissolution of silicon. The formation of new phases affects coating microstructure development and results in new microstructural features.

This study evaluates the effect of annealing on the microstructure, hardness, and wear resistance of FeAl-WC coatings obtained by cold spraying. As-sprayed deposits exhibited a dense microstructure with uniformly dispersed WC particles in the iron matrix. The Fe(Al) solid solution was transformed to an FeAl intermetallic compound at around 650 °C. Further increases in temperature were found to improve the composite microstructure with a slight decrease in microhardness. Wear resistance peaked at 750 °C, and at 950 °C, a diffusion layer appeared at the bottom of the coating close to the substrate.

In this study, titanium and aluminum powders mixed in different ratios were deposited on stainless steel substrates by warm spraying. Microstructure and composition of as-sprayed and heat-treated samples were characterized and the effect of adding a third element was assessed. It was found that Al content has a major influence on the thickness and porosity of heat-treated Ti-Al coatings and that adding silicon to the powder mixtures reduces the melting point of Al, causing a loss of Al-Si particles during spraying.

This paper presents the results of metallographic investigations of electric arc sprayed composite coatings for the manufacture or refurbishment of bearing components. The materials studied include iron aluminide and aluminum bronze, and their interface microstructure was examined by optical and environmental scanning electron microscopy (ESEM).

Aluminum-titanium powder mixtures were deposited on γ-TiAl alloy substrates by cold spraying then heat treated for 5 h at 600, 650, and 700 °C. SEM and XRD examination showed that the treatment caused Al to diffuse into the substrate where it reacted with Ti, resulting in changes in microstructure. The diffusion of Al left pores in the fringes of the TiAl 3 phase, increasing the porosity of the coatings. A surplus of Al remained in the coatings after heat treatment at 600-650 °C, but at 700 °C, all Al was consumed, contributing to the formation of a continuous TiAl 3 layer.

Four powder blends of Al and Ti were cold sprayed on Ti-Al-Nb substrates at 300°C. Test samples were heat treated in Ar at 500 °C then exposed to 950 °C air for 100-500 h. It was found that oxidation rates were significantly reduced by the coatings, especially those with lower Ti content. However, four-point bending tests revealed that the deposition of the protective layer reduced the flexural strength of the coated substrate. The results indicate that oxidation is not the only factor influencing the mechanical properties of intermetallics at high temperatures.

Thick Fe-Al deposits were produced by low-pressure cold spraying using heated air as the working gas. The coatings were isothermally annealed for two hours in Ar at temperatures from 250 °C to 750 °C. Changes in fracture behavior and microhardness were evaluated along with the microstructure and composition of newly formed phases. The results show that the evolution of intermetallic phases was driven by diffusion at temperatures above 550 °C. The new phases formed a hard skeleton that preserved the general shape of the samples during treatment despite the growth of external dimensions and porosity.