This paper compares two methods for determining the composition of Ti/TiN coatings deposited by reactive plasma spraying. The coatings were obtained by spraying titanium powder in a low-pressure N2/Ar atmosphere. The resulting film has a variable nitrogen content in the form of titanium nitrides, depending on gas partial pressure, total pressure, sample-source distance, and other parameters. The composition of the film was determined using X-ray diffraction and X-ray photoelectron spectroscopy. The two techniques provide similar results and either can be used for the compositional characterization of these coatings.

Plasma-sprayed ceramic coatings are deposited such that flattened splats together with some nonmelted particles are present in the coatings. In this study, the nonmelted particles in plasma-sprayed alumina coatings were examined by scanning electron microscopy, confocal Raman analysis, and X-ray diffraction analysis with the aim of quantitative evaluation of the coating microstructure. Results showed that the nonmelted particles can be clearly identified from the cross-sectional microstructure due to the morphology that results from the high hardness of the nonmelted particles. The obvious gap at the interface between nonmelted particles and the surrounding splats suggests weak interface bonding. Raman analysis revealed that there was little α-Al 2 O 3 phase in the flattened splats region, which confirms that this phase in the coating appears only from nonmelted particles. Attention should be paid to the weak bonding of the nonmelted particles relative to the flattened splats during the preparation of samples for quantitative characterization of coating microstructure.

Two copper powders were deposited with CGT3000 cold gas dynamic spray system on aluminium substrates. The X-ray diffraction patterns allow the characterisation of the microstructure such as grain size, strain in the coating and dislocation densities. Both powders and coatings have been fully characterised. Three methods have been used to interpret the X-ray patterns: the Warren-Averbach method, the Hall Williamson method and the modified Hall-Williamson method. A comparison between the state of the powders before and after deposition will give an insight on the metallurgical processes that take place during the formation of the coating. The influence of the grain size distribution will also be discussed. This article is a follow up of the publication done at ITSC2006: “Comparison Between Coatings from two Different Copper Powders: Mechanical Properties, Hardness and Bond Strength”.

Processing induced residual stresses play an important role in the performance of thermally sprayed coatings. Their precise determination is a key to influence the coating properties by modification of process variables and to understand the processing-property relationship. Among various methods for residual stress measurement, x-ray diffraction holds a specific position by being nondestructive, phase distinctive, localized and applicable for real parts. The sin 2 ψ method is commonly applied for bulk materials as well as coatings. However, the results are often reported without sufficient experimental details and the method is used in its simplified form without justification of certain assumptions. In this investigation, the sin 2 ψ x-ray diffraction method was used to measure residual macrostress in plasma sprayed Ni, NiCrAlY and ZrO 2 +8%Y 2 O 3 coatings. Reproducibility of the method was tested and the assumptions allowing its use are discussed and experimentally verified. For Ni coatings, a comparison with blind hole and neutron diffraction measurements is presented. The results are discussed with respect to processing, structure and properties of the coatings.

A Ni-Al pseudo-alloy powder was studied from the point of view of spheroidization during spraying by a water-stabilized plasma gun. The powder particles of irregular shape were conglomerates of elemental Ni and Al, the average Al content being 9.7 %. To conserve the shape and composition of particles flying in the plasma stream, these were trapped in liquid nitrogen. Scanning electron microscopy and X-ray microanalysis were used to obtain information about particle shape and element distribution. Most plasma sprayed particles trapped in liquid nitrogen were composed of a Ni-Al alloy, where the Al content varied in a wide range. Spherical "caps" composed of Al-oxide covered partially their surfaces. It follows that on the interface between molten Ni and Al, the interaction of both components gave rise to a Ni-Al alloy. On the contrary, if Al was exposed to air, it oxidized rapidly during the flight of the particles. The X-ray diffraction lines of the metallic phase in the particles trapped in liquid nitrogen were shifted from the positions corresponding to pure Ni as observed in the feedstock powder. This, together with the line asymmetry, showed the presence of Ni-Al alloy containing varying amounts of Al. The X-ray diffraction did not find any elemental Al in the liquid nitrogen trapped powder, i.e. neither in the metallic phase nor in the "caps". This means that all Al accessible to the ambient oxygen was converted into oxide. The "caps" contained metastable γ- and δ- Al 2 O 3 . The mechanism of the "cap" formation appears to be based on the fact that after an acceleration and melting period, significant slowing down of a molten particle occurs. Due to the drag forces, the lighter Al 2 O 3 melt concentrates on the rear part of the droplet surface. The main condition, under which this mechanism holds, is the presence of two immiscible melts in the droplets and the significantly differing densities of both melts.

The paper aims at the development of coating having a gradient of crystal grain size. Thick, inner layer was plasma sprayed using coarse TiO 2 powder. This layer has the thickness ranging from 30 to 50 µm. Thin, outer layer of thickness smaller than 10 µm, was plasma sprayed using different aqueous suspensions of fine powders of TiO 2 . The morphology of coarse and fine powders was characterized using scanning electron microscope (SEM) X-ray diffraction (XRD). Electronic emission was tested using home made setup. X-ray diffraction enabled to find out an interesting result which is formation of a mixture of rutile and anatase in suspension sprayed coatings. This was also confirmed by Raman spectroscopy investigations. The technology of suspensions plasma spraying was optimized to obtain homogeneous and dense deposits. The sizes were in the range of tenth to one hundred nanometers in initial powders and get clearly smaller in the coatings sprayed using coarse powder but remained quite similar in suspension sprayed films. X-ray photoelectric spectroscopy (XPS) was used to analyze quantitatively TiO 2 powders and coatings. Electronic emission was correlated with phase composition of the coating and their grain size.

This paper aims to measure the residual stresses of plasma sprayed oxide ceramic deposits using the X-ray diffraction method and measure the Young’s Modulus in specially designed four-point bend test device. Aluminum oxide and chromium oxide coatings are made with a water stabilized plasma spray gun. The paper analyzes the microstructure and the phase composition. The X-ray diffraction method is used to determine residual stresses on the layer surfaces. The same method is used for the local measurement of surface tensions in a four-point bending device built into an X-ray diffractometer. This device also enables the force applied and the specimen deflection to be measured. Effective modules of elasticity are determined from the gradient from load to deflection during bending. The results of the tension measurements and the values calculated from the applied force are compared. Paper includes a German-language abstract.

In the current study, the oxidation of hardmetal coatings (WC-12%Co, WC-17%Co, WC-10%Co4%Cr, WC-20%“CrC”-7%Ni, Cr 3 C 2 -25%NiCr, (Ti,Mo)(C,N)-29%Ni and (Ti,Mo)(C,N)-29%Co) in the temperature range 350- 900°C was studied for test durations ranging from 2 h to 128 h. The formation of oxide scales was investigated by X-ray diffraction, as well as by optical microscopy and SEM (including EDX) of coating cross sections. For coatings obtained by spraying with DJH 2700 and TopGun HVOF systems, the phase composition had only a moderate influence on high-temperature oxidation behavior in atmospheric conditions. The first oxides detectable by X-ray diffraction appeared on the coating surfaces after oxidation at 350°C for 128 h for all coatings. Pronounced oxidation (formation of oxide scales with thicknesses of greater than 10 µm) started at 600°C. Oxide scale growth differed significantly above this temperature among the hardmetal compositions studied here. WC-20%"CrC"-7%Ni and Cr 3 C 2 -NiCr had the highest oxidation resistance, with the oxide scale thicknesses lying below 10 ìm after oxidation at 800°C and 900°C for the two materials, respectively.

The aim of this preliminary investigation was to ascertain the synergetic potential of two process technologies of thermally spraying and HIPing (Hot Isostatic Pressing) for tribological applications and address the key design factors, which need to be considered for successful applications of HIPed thermal spray WC-NiCrBSi coatings. The relative performance of the as-sprayed and hot isostatically pressed WC-NiCrBSi functionally graded coatings was investigated in sliding wear conditions. Results indicate that HIPing post-treatment can improve the sliding wear resistance of WC-NiCrBSi coatings. These coatings were deposited by a High Velocity Oxy-Fuel - JP5000 system and HIPing process was carried out at two different temperatures of 850°C and 1200°C. This study shows that un-capsulated HIPing can be successfully applied to functionally graded WC-NiCrBSi coatings, which has economical as well as technical incentives for industrial applications. Sliding wear tests were carried out using a high frequency reciprocating ball on plate rig using steel and ceramic balls. Results are discussed in terms of powder manufacture method, microstructural investigations, phase transformation, mechanical properties and residual stress investigations. Phase analysis by X-ray diffraction revealed transformations, which altered the phase composition such as the elimination of secondary phase W2C and metallic W and the formation of new phases containing Ni, Si and B after the post-treatment. The measurements of hardness, Young’s modulus and residual stress indicate that substantial improvements can be achieved due to simultaneous application of temperature and pressure during the HIPing post-treatment. Hardness and Young’s modulus measured by indentation method, increased after the HIPing process due to the transformations in the morphology and phase composition of the coatings. The residual stress evaluations by sin2Ψ technique using synchrotron x-ray diffraction showed a relaxation of residual stress fields in the coating with increasing temperature of the HIPing process.

Influence of induction plasma gas composition on Ti coatings microstructure and composition has been studied. Plasma sprayed Ti powder and coatings were prepared by using induction plasma system. Spheroidization of irregular shaped particles was observed in the powder collected after spraying with Ar-air plasma. Microstructures of the coatings were analyzed by a high-resolution scanning electron microscope. Image analysis of the backscattered images of the cross-sectional view of the coatings was used to calculate coating porosities. X-ray diffraction analysis was also performed to identify secondary phases, which have been formed in the coatings during plasma spraying. Partially induced nanostructures were observed in fractured areas in the coatings. The nanostructures were preferentially formed on the surface of splats. X-ray diffraction pattern reveals that a secondary phase has been formed in the coatings during spraying with air vol. at 16 % and 20 % in plasma gas. Changes of the coating density and thermal diffusivity were studied with respect to the formation of secondary phases and induced nanostructures.

Due to good performance in abrasive and sliding wear and enhanced oxidation behavior, coatings based on Co-Cr-W alloys are widely used in industrial applications, where the material is exposed to high temperature. Within the scope of this study, a Co-based alloy similar to commercial Stellite 6, which additionally contains 20.6 wt.% of vanadium, was deposited by Twin Wire Arc Spraying (TWAS). Multi-criteria optimization using statistical design of experiments (DoE) have been carried out in order to produce adequate coatings. The produced coatings have been analyzed with respect to their tribological behavior at elevated temperatures. Dry sliding experiments were performed in the temperature range between 25°C and 750°C. Oxide phases were identified in the investigated temperature range by X-ray diffraction (XRD) using synchrotron radiation. The V-doped Stellite-based coating possesses a reduced coefficient of friction (COF) of about 0.37 at elevated temperatures (above 650°C), which was significant lower when compared to conventional Stellite 6 coating that serves as reference. In contrast, both produced coatings feature a similar COF under room temperature. X-ray diffraction reveals the formation of cobalt vanadate and vanadium oxides above 650°C. The formation of vanadium oxides exhibits the ability of self-lubricating behavior, thus leading to enhanced tribological properties.

Ni-Al intermetallic alloys are known for exhibiting superior high temperature properties. Processes such as thermal spray, combustion synthesis, physical vapor deposition and laser have been used to produce these coatings. However, the deposition of these alloys by means of plasma transferred arc (PTA) has not been widely studied. This study evaluated Ni-Al coatings processed in-situ by PTA. Coatings were processed with Ni and Al elemental powders (65%atNi-35%atAl) onto an AISI 1020 steel substrate. Different current intensities were used (70 to 120 A) to produce different dilution levels and thus different Fe contents in the coatings. The stand torch off was 10.0 mm. The plasma gas, shield gas and powder carrier gas flows were 2.0, 15.0 and 1.0 l.min-1, respectively. The powder feed rate was 5.8 g.min-1 and a travel speed of 100 mm. min-1 was used. The coatings were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, optical microscopy and instrument indentation tests. The development of Ni aluminides was confirmed by X-ray diffraction for all current intensities. It was verified that the microstructure, hardness and the elastic modulus were influenced by current intensity and by the Fe content in the coatings.

Flame-sprayed coatings of alumina were produced by an oxyacetylene flame spray system in order to study the phase transformations that occurs on alumina during the spraying. The X-ray diffraction pattern of the alumina powder to be sprayed, showed the main presence of the stable phase alpha alumina and an impurity probably resulting from the process of purification of alumina. For as-sprayed coatings, phase changes occur. The X-ray diffraction pattern shows the presence of the stable form alpha alumina, but also the metastable form gamma alumina and amorphous alumina. True density measurements were done using a helium pycnometer, as an aid to observe the phase transformations. The density of the powder to be sprayed was 3.98 g/cm 3 and the density of the as-sprayed coatings was 3.62 g/cm 3 . This change of density is linked to the phase transformation during spraying. Scanning electron microscopy (SEM) of the incident particles was made after 1 second of deposition onto glass substrates in order to observe the degree of melting of the incident particles, by analyzing their profiles (degree of flattening).

As part of a characterization and mechanical research about hydroxyapatite (HA) plasma deposits for hip prosthesis, we addressed the problem of determining their crystallinity. A traditional normalization method employed by several laboratories is based on X-ray diffraction by a powder mixture of the investigated HA sample with a standard of crystalline powder, namely Al 2 O 3 . This method is quite unsatisfactory, as very often delivers unreasonable results. In order to overcome these difficulties we investigated some new methods for determining the crystallinity of HA sample, which are based on X-ray diffraction. All these methods provide reasonable results.

Thermally sprayed coatings have residual stresses due to the processing techniques where the particles go through thermal softening / melting, high velocity impact and rapid solidification. The nature and magnitude of residual stresses in these coatings determine the bond strength and failure mechanisms. This investigation thus involves a non-destructive neutron diffraction residual stress evaluation of suspension high-velocity oxy-fuel (S-HVOF) thermal sprayed alumina and YSZ coatings onto 304 stainless steel substrates. SHVOF spray is a high deposition efficiency process to deposit coatings from sub-micron or nanometric feedstock particles. Neutron diffraction measurements were performed at the UK ISIS facility, using ENGIN-X pulsed neutron diffractometer to obtain through thickness residual stress profiles. The Z-scanning method was used to avoid pseudo-strains in the neutron diffraction measurements near the coating surface whereby the incident neutron beam/gauge volume was partially submerged and traversed vertically out of the horizontal coating surface. The residual stress in the alumina coating was compressive across the whole thickness while the stress changed from tensile to compressive in the YSZ coatings. The residual stress measurements were complemented by lab based X-ray diffraction residual stress measurement techniques. Depth sensing indention of the coatings were also performed to gain a comprehensive understanding of the stresses in SHVOF sprayed ceramic coatings.

Thermal spray coatings of new MoB/CoCr cermets were developed. The mechanical behavior of HVOF-sprayed MoB/CoCr novel composite coatings was evaluated via Vickers microhardness. Microstructure of the coatings on 316L stainless steel substrates, as well as powders, were studied with optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD). X-ray microanalysis of the coatings was carried out using energy dispersive X-ray spectrometer (EDS) attached to the SEM. The distributions of microhardness values of the coatings were analyzed via Weibull statistic. Weibull analysis revealed a bimodal distribution of Vickers microhardness values. Such distribution was attributed to the presence of melted and unmelted phases in the resultant coating produced from the microstructured powder feedstock. The excellent mechanical properties of the coating are due to the MoB/CoCr powder, which results in the formation of complex ternary transition metal boride hard particles that exhibit exceptional mechanical properties.

Molybdenum disilicide (MoSi 2 ) is a suitable material for high temperature applications especially because of its excellent high temperature oxidation resistance. For several high temperature applications MoSi 2 shows high potential to be used as a protective coating. The oxidation behaviour of HVOF sprayed MoSi 2 coatings is studied at 1500 °C. The oxidation tests are carried out in a simultaneous thermogravimetric device and the mass change is measured in dependence on the oxidation time. The microstructure of the coatings before and after oxidation is examined by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDXS). The mass of the coating increases according to a parabolic function. During the oxidation test the microstructure changes significantly from a typical thermal spray coating microstructure with lamellae, pores and a phase mixture of MoSi 2 and Mo 5 Si 3 to a two phase system with sharply separated grain boundaries. On the surface of the coating a silicon dioxide layer with a thickness of less than 10 µm is formed.

Calcium phosphate (Ca-P) coatings have been used as surface coatings on porous metallic implants in dentistry and orthopaedics for the last twenty years. These Ca-P coatings, nominally hydroxyapatite (HA), have been shown to promote bone fixation and osteconductivity on Ti and Ti alloy substrates used for those purposes. Such coatings can be formed by different methods including plasma spray. In addition to the well known advantages of the plasma spray technique to deposit coatings, a new version of this technique, i.e. solution precursor plasma spray (SPPS), has been reported to produce submicron/nanocrystalline structured coatings. Nanocrystalline HA coatings may improve the resorption of the coating in the body, avoiding the irritant effect of large particles which may be seen in current thermal sprayed HA coatings. The main purpose of this work was to study the suitability of a sol-gel Ca-P solution precursor (calcium nitrate tetrahydrate and ammonium dihydrogen phosphate) as feedstock for the air plasma spray (APS) coating technique. We report on the formation and the characteristics of the coatings so formed on Ti6Al4V substrates. The presence of different Ca-P crystalline and amorphous phases was assessed by X-ray diffraction analysis. The X-ray photoelectron spectroscopy technique was used to characterize the surface chemical composition of the Ca-P coatings. The microstructural features of the coatings were characterized by scanning/transmission electron microscopy combined with image analysis in order to evidence the presence of submicron/nanocrystalline Ca-P features. Final results are discussed in terms of the spraying parameters. Abstract only; no full-text paper available.

Plasma sprayed ceramic coatings have much lower stiffness in comparison to sintered ceramics. The reason for that is their characteristic microstructure with porosity and microcracks. Microcracks decrease the interlamellar cohesion in vertical direction, but also affect the individual splat properties in the horizontal direction. For that reason sealing treatments are often applied with plasma sprayed ceramic coatings in order to improve their corrosion resistance and mechanical properties. In this paper the effect of aluminum phosphate sealing treatment on the elastic properties of plasma sprayed Al 2 O 3 and Cr 2 O 3 coatings were studied. Residual stresses in the plane of coating surfaces were compared using the X-ray diffraction analysis (XRD). A special four point bending device, designed for the X-ray diffractometer, was used in determining the effect of additional load on coating elastic behavior. In as-sprayed alumina coatings tensile stresses of about 400 MPa were detected while only about 40 MPa of compressive stresses were measured in the as-sprayed chromia coatings. Microstructural characterization revealed that sealing treatment had apparently affected the coating microstructure and filled some microcracks and interlamellar spacings. As a result, in both sealed coatings, compressive stresses of about 100 up to 150 MPa were observed. Also a better stiffness of both materials was detected during the bending of specimens. In addition, the sealing treatment increased nearly ten times the Young’s modulus, determined by XRD analysis under various tensile loads.

Plasma sprayed oxide coatings are widely used in applications where the surface properties of the coatings dictate the performance of the coating. The knowledge of chemical surface properties of plasma sprayed oxide coatings is very limited and to our knowledge surface chemical studies of these coatings have not been published. Surface properties of common plasma sprayed oxide coatings exposed to water based electrolytes were evaluated using several surface sensitive techniques such as X-ray photoelectron spectroscopy (XPS) and electrophoretic mobility studies. The dissolution behaviour of the coating materials were studied using inductively coupled plasma-mass spectroscopy (ICP-MS). Other characterization techniques included X-ray diffraction (XRD) and scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (EDS). The correlation between chemical stability, bulk and surface properties of the coatings were evaluated. Obtained results are compared with published values of traditionally manufactured oxide counterparts.