bluuebunny/crossref_metadata_2025 huggingface dataset:
Improvements in HVOF Sprayed Cermet Coatings Produced from SHS Powders
Authors: Blatchford M.T. , Jones M. , Horlock A.J. , McCartney D.G. , Shipway P.H. , Wood J.V.
Published: June 2022

It has been shown that high velocity oxy-fuel (HVOF) thermal spray coatings with good wear resistance can be produced from Ni(Cr)-TiC powders manufactured by self-propagating high temperature synthesis (SHS) reactions. In the present work the process was expanded to include additions of Mo and W with the objective of modifying the carbide phase in an attempt to increase the wear resistance further. The effect of changing the matrix, i.e. substituting Fe for Ni, and changing the ceramic phase from TiC to TiB2 was also examined. The feedstock powder and resultant coatings are characterised in terms of x-ray diffraction analysis and scanning electron microscopy while the coating properties are measured by microhardness and dry sand rubber wheel (DSRW) abrasive wear testing. The results show that Fe(Cr)-TiB2 and Ni(Cr)-(W, Ti)C coatings have wear rates comparable to that of conventional Cr3C2-NiCr coatings produced from sintered and crushed powder, but further improvements are needed to achieve the wear resistance of WC-Co coatings.
Composites Made of Metal Foams with Thermally Sprayed Coatings
Authors: Maurer M. , Lugscheider E.
Published: June 2022

Scientist and engineers show an increasing interest in metal foams. Recent activities are not only limited to the different techniques which already exist to produce and characterise metal foams, but also focus on further steps that these fairly new materials have to pass before entering mass production. Metal foams do not possess a high strength; to increase their mechanical properties and to improve the surface finish, thermally sprayed coatings can be applied. A metal foam is mainly characterised by its alloy composition, its density and the size and shape of the cells and pores. The quality of the coating depends on the coating material, the chosen process, the preparation of the surface, spraying parameters and the adhesion of the coating. The main focus of this paper is to reveal the necessary requirements to realise a sound composite made of a thermally sprayed coating onto metal foam. Basic investigations are carried out and during a later stage of the project parameters are to be identified which allow to describe the properties of the new composite material. The priority within this project will be on aluminium foams.
Properties of Al2O3 Coatings Sprayed by HFPD
Authors: Fagoaga I. , Barykin G. , de Juan J. , Soroa T. , Vaquero C.
Published: June 2022

Ceramic oxides can be deposited by the High Frequency Pulse Detonation process leading to coatings with unique properties as result of simultaneous melting and high velocities of the sprayed particles. In this paper, several Al2O3 based powders have been HFPD sprayed and the resulting coatings characterized. For this purpose, microstructural evaluation, XRD phase analysis and functional behavior (dielectric strength and wear resistance) have been tested.
Structure & Properties of HVOF Sprayed NiCrBSi Coatings
Authors: Calla E. , Modi S.C.
Published: June 2022

NiCrBSi spray and fuse types of coatings are routinely applied on various jobs where metallurgical bond of the coating to the substrate is desired. These coatings require a subsequent fusing operation at temperature of about 1050°C. In the present study NiCrBSi coatings were formed by the HVOF process and by the conventional spray and fuse route. The coatings were characterized for their microstructure, hardness and porosity. The aim of this study was to see whether HVOF spraying NiCrBSi spray and fuse powder could cause instant fusing of the coating without the need for additional fusing operation. XRD study of the coatings was also carried out to find out the difference between the spray and fused NiCrBSi coatings and the HVOF sprayed coatings. The HVOF spraying of NiCrBSi was carried under different set of parameters to determine the effect of spraying parameters on the properties of coating.
Spray Powders and Coatings on the Basis of Titanium Suboxides
Authors: Berger L.-M. , Thiele S. , Nebelung M. , Storz O. , Gasthuber H.
Published: June 2022

Titanium suboxides form a class of ceramic materials possessing such technically interesting properties as electrical conductivity and solid lubrication. Consequently, these materials have a high potential for application as thermally sprayed coatings. In this paper the preparation and characterisation of two spray powders of different composition by agglomeration and sintering with a narrow range of the value n in TinO2n-1 is described. Powders were characterised by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), thermogravimetric measurements (TG), helium pycnometry, nitrogen adsorption and mercury intrusion techniques. The sprayability was tested by plasma spraying. The coating structures were studied by optical microscopy, XRD, TG and TEM. Although the powders were only partially oxidized as a result of the spray process, the crystallographic structure was changed significantly, according to XRD and TEM investigations. As an alternative method of preparation of titanium suboxide spray powders, the reduction of a fused and crushed spray powder with hydrogen is described. Powder particle shape and size distribution are not changed in this process.
Characterization and Mechanical Properties of Flame Sprayed Hydroxyapatite/Polymer Composite Coatings
Authors: Sun L. , Berndt C.C. , Gross K.A.
Published: June 2022

Hydroxyapatite/polymer composite coatings of different volume ratios were produced using a Plastic Flame Spray (PFS) system. The intent of this processing is to obtain a coating with an optimal combination of biological and mechanical properties of these two materials for skeletal implants. The composite coatings were produced with a mechanical blend of EMMA and hydroxyapatite powder from a fluidized bed powder feeder. Characterization was conducted by scanning electron microscopy on the surface morphology, polished cross-sections and fracture surface morphology of the coatings. The bioactivity of the coatings was evaluated with a calcium ion meter, and the stress-strain behavior was investigated by tensile testing. The biological and mechanical properties were found to be related to the volume and the distribution of the hydroxyapatite in the polymer matrix.
Surface Modification of Recycled PET Plate by Particle Implantation and Deposition with Plasma Spraying
Authors: Kanazawa T. , Ohmori A. , Matsusaka S.
Published: June 2022

The polyethylene terephtalate (PET) is widely utilized for high performance as a food and beverage container due to its excellent mechanical and chemical properties. The consumption of PET material is expected to increase more rapidly. Consequently, the recycling of waste PET is urgently needed to reduce environmental problems and economic costs. The purpose of this research is to endow waste PET materials with a new function by spraying of metal and ceramics such as Cu and TiO2. The recycled PET plate substrate for plasma spraying was prepared from waste PET bottles. It is found that Cu and TiO2 powder could be sprayed on the surface of the recycled PET plate without heat damage and transformation of the substrate. In specific spray conditions, the implantation of melted Cu and TiO2 particles, which retained their original shape, into the PET substrate was also observed and this is an unusual phenomenon in plasma spraying. In this research, the possibility of production of functional PET plates with electric conductivity and wear resistance was found by controlling the plasma spray conditions.
Structure and Properties of HVOF Sprayed Amorphous Polymer Matrix Nanocomposite Coatings
Authors: Knight R. , Fang X. , Twardowski T.E.
Published: June 2022

The high velocity oxy-fuel [HVOF] combustion spray technique has previously been shown 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. Use of an amorphous matrix material, polycarbonate, will enable the role of matrix crystallinity on the structure and properties of thermally sprayed polymer matrix nanocomposite coatings to be separated from effects resulting from the reinforcing phase. An amorphous, commercial polycarbonate powder with a broad particle size distribution and irregular particle morphology has been successfully deposited by HVOF spraying using hydrogen as fuel gas. Polycarbonate matrix coatings up to 18 mils thick with zero to 10 vol. % loadings of nano-sized hydrophobic and hydrophilic silica, and carbon-black have been sprayed onto Al substrates. Results from optical microscopy. X-ray diffraction, scratch, density, microhardness and dilute-solution viscometry measurements will be presented. These indicate that incorporation of the nanosized filers improved the scratch resistance and microhardness of the coatings by 50 % and 23 %, respectively, relative to sprayed pure polymer. Some degradation of the polymer matrix was also detected, with molecular weight being reduced from 17,000 in the feedstock to ~5,000 in the sprayed deposits. The influence of variations in process parameters such as fuel:oxygen ratio, total gas flow, spray distance, nozzle length, total travel distance, and spray distance/nozzle length ratio on coating structure will also be addressed. The threshold loading of silica in the polycarbonate matrix for which dense coatings can be obtained has also been determined.
Cold Sprayed Nanostructured WC-Co
Authors: Karthikeyan J. , Kay C.M. , Lindemann J. , Lima R.S. , Berndt C.C.
Published: June 2022

The cold spray process was used to prepare nanostructured WC-Co coatings. The coating microstructural characteristics and phase composition were analyzed via optical microscopy, SEM and XRD. The morphology and microstructure of the nanostructured WC-Co powder were also analyzed by SEM and XRD. A 10µm thick coating was achieved. The results show that there is no degradation of the WC-Co powder during the cold spray process and well-bonded and phase-pure WC coating can be produced by the cold spray process.
Low Pressure Plasma Spraying of Sol-Gel Al2O3/SiC Nanocomposite Coatings
Authors: Jiansirisomboon S. , Roberts S.G. , Grant P.S.
Published: June 2022

This paper describes the manufacture of a new ceramic coating system based on Al2O3/SiC nanocomposite powder prepared by sol-gel processing followed by low pressure plasma spraying (LPPS) onto stainless steel substrates. In order to produce nanocomposite coatings of good adhesion and low porosity, the substrates were water-cooled to minimise thermal stresses associated with coefficient of thermal expansion mismatch and a CoNiCrAlY bond coat was used. The sol-gel powder feedstock and the as-sprayed coatings have been characterised by a combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray diffraction (XRD), and Nuclear Magnetic Resonance (NMR). The coating characteristics were compared with a reference Al2O3 coating prepared from commercial feedstock powder. The thermal exposure of the sol-gel powder during spraying caused phase-changes and phase-decomposition. Examination of the sprayed coatings showed that it was possible to maintain the 20-200 nm SiC particles in the final Al2O3/SiC nanocomposite coating. The coatings also contained both stable α-Al2O3 and metastable γ-Al2O3. Some minority phases such as silica and aluminosilicate formed in the sol-gel feedstock powder were fully decomposed during LPPS. This preliminary study indicates that sol-gel and LPPS processing is a potential route for the manufacture of nanocomposite coatings, which may offer significant improvements in some aspects of coating properties.
Effects of Operating Parameters on High Definition Single Wire Arc Spraying
Authors: Carlson R. , Heberlein J.
Published: June 2022

Operating parameters which affect the droplet generation characteristics for a single wire arc spray, SWAS, torch have been studied. The droplet size distribution, velocity, axial divergence, and deposition efficiency can be controlled by the selection of wire size, wire feed rate, arc voltage, and gas jet back pressure. Coatings have been formed under a variety of operating conditions with structures from 3 mm to 4.5 mm in width. The average deposition efficiency is greater than 80 % and the average axial divergence angle is 2.4°. The SWAS torch has been shown to operate for extended periods of time with minimal erosion of non-consumable electrode.
Influence of Anode Nozzle and External Torch Contour on the Quality of the Atmospheric DC Plasma Spray Process
Authors: Henne R.H. , Bouyer E. , Borck V. , Schiller G.
Published: June 2022

By means of Schlieren photography, enthalpy probe, mass spectrometry and the particle measuring system DPV 2000 the influence of the internal and external anode nozzle and torch geometry, on plasma jet quality for atmospheric plasma spraying was investigated. It turned out that there is a strong geometrical effect of the inner contour and that with a proper expansion of the hot core of the plasma jet a considerable improvement of the melting and deposition quality can be obtained. Also the outer torch contour is of influence on the spray process because it controls the formation and the intensity of turbulence and the interaction of the plasma jet with its surrounding and hence the cold gas entrainment.
A New Powder Feeder for the Transport of Ultrafine Powders
Authors: Dvorak M.D. , Dietrich F.
Published: June 2022

Advanced spraying technologies as High Pressure-HVOF Spraying or Cold Gas Spraying as well as new concepts for the next generation of plasma sprayed TBC's demanding spray powders with strongly decreased powder grain sizes (< 15µm or even less). Although, with decreasing powder grain size the flowability of the powder is also decreased, causing finally problems in the transport of powder. Within this paper a new powder feeder design will be presented, that makes the precise feeding of ultrafine powders possible, even through feeding lines several meters in length. All known powder feeders for thermal spraying use the pneumatic convey for powder transport through the feeding line. In opposite, the new developed powder feeder is using the dense phase convey of powders. The powder transport can be compared with the transport of a liquid in an hydraulic system. The new powder feeder shows no restrictions in the flowability of a powder. The feeding of normal spray powders (carbides, oxides, metals) as well as submicron powders were successfully tested. Feeding rates from several grams per hour to hundred kilogram and more per hour can be realised, depending on the design of the system. The transport through feeding lines longer than 10 meters also causes no difficulties. The system is self-cleaning and there are no mechanical parts in contact with the powder.
Coatings and Applications Produced by Purecoat, an Improved Shrouding Technique
Authors: Lester T.
Published: June 2022

Arc spraying has always been the most cost-effective way of thermal spraying metal alloys but oxide content and degradation of the alloy by loss of particular alloying elements have limited quality of the coatings. In this paper a process is described which greatly reduces degradation and improves coating density and oxide content. Corrosion behaviour both in aqueous and high temperature environments is markedly improved. For aqueous applications coatings of Inconel 625 were tested in a potentio-dynamic cell and by salt spray testing to evaluate both the inherent properties and the permeability of the coating and significantly improved behaviour was found in both cases. For high temperature corrosion, samples of FeCrAl were tested in air and in a sulphidising environment with and without thermal cycling. Coatings of NiCrAl and NiCrTi were also examined. The coating types and test regimes were aimed at specific practical applications such as fireside corrosion in boilers and waste incinerators, hot oxidation of flare stack burners etc. In the aqueous situation valves and process vessels are being examined as candidate applications for Inconel 625 coatings.
A Comparative Study on HVOF, Vacuum Plasma Spray and Axial Plasma Spray for CoNiCrAlY Alloy Deposition
Authors: Scrivani A. , Groppetti R. , Bardi U. , Lavacchi A. , Rizzi G.
Published: June 2022

In the aerospace field as well as in the stationary gas turbine field, thermal sprayed coatings are used to improve the surface properties of Nickel-super-alloys materials. Coatings are commonly used as bond coat and antioxidation materials (mainly MCrAlY alloys) and as thermal barrier coatings (mainly Yttria partially stabilized Zirconia) In the present study, our purpose was to assess the properties of thermally sprayed bond coat CoNiCrAlY comparing the performance of three different techniques: Vacuum Plasma Spray (VPS), High Velocity Oxygen Flame (HVOF) and Axial Plasma Spray (AxPS). The quality of the deposited films has been assessed and compared from the point of view of structural (porosity, oxide concentration, unmelted particles presence) and mechanical characteristics (hardness, adhesion). Furthermore, a study of the surface composition and morphology has been carried out. Specific efficiency trial has been carried out to compare the efficiency of the three examined technologies. We observed that the highest quality films are obtained by VPS, but that also HVOF and AxPS sprayed films have interesting properties which can make their use interesting for some applications in view of the lower cost of HVOF and AxPS.
Analysis of Porosity and Cracks in Cross Sections of Plasma Sprayed Oxide Coatings
Authors: Koschlig T. , Lallement R.
Published: June 2022

Microstructure of plasma-sprayed thermal barrier coating has an influence on the lifetime under service conditions in aero engine. This paper focuses on problems of preparing and comparing ceramic samples and characterising microstructure features such as porosity and cracks within coating cross sections by image analysis. The results can be used for developing standards and best practices for characterization plasma-sprayed coatings. The methodology was evolved to relate coating microstructure to spraying parameters and properties of coating. It would help to develop new ceramics coatings or optimise them.
Microstructural Studies of Thermally Sprayed Deposits by Neutron Scattering
Authors: Keller T. , Wagner W. , Ilavsky J. , Margandant N. , Siegmann S. , Pisacka J. , Matejicek J. , Barbezat G. , Fiala P. , Pirling T.
Published: June 2022

Technological properties of thermally sprayed deposits are to a great extent related to the underlying microstructure. The present project aims to relate macroscopic properties of metallic coatings to their microstructure. For this purpose, thermally sprayed deposits of nickel based alloys (NiCr, NiCrAlY) were manufactured by various spraying techniques - atmospheric and vacuum plasma spraying, flame spraying, high velocity oxygen fuel and water-stabilized plasma spraying. One of the key microstructural features is the void system. This system is usually characterized by the total volume of voids, the so called porosity. An additional characteristic parameter of the void system is the specific surface area. The method of anisotropic Small Angle Neutron Scattering (SANS) in the "Porod Regime" allows the determination of the anisotropic specific surface area of the complex void system that consists of intralamellar cracks and interlamellar pores. In contrast to optical microscopy, the SANS technique is capable of resolving the pore structure down to the nanometer scale, and the measured specific surface area represents a statistically relevant average value for the whole illuminated sample volume which is usually a few mm3. Besides the presence of voids and cracks the performance of thermally sprayed coatings is also significantly influenced by residual stresses. In the present work residual strains were determined by the technique of neutron diffraction as well as by bending tests, i.e. laser profilometry of the substrate before and after the spraying process. The specific surface area and the residual stresses are discussed with respect to total porosity, the presence of secondary phases like oxides and wear behavior. Special attention is drawn to the anisotropy of the apparent surface area, which is discussed with respect to the anisotropy of macroscopic properties like electrical resistance.
Mechanisms of High Hardness in Cr3C2-NiCr Cermet Coatings Formed by Vacuum Plasma Spraying
Authors: Tomita T. , Takatani Y. , Tani K. , Harada Y.
Published: June 2022

Hardness and microstructure of Cr3C2-NiCr coating formed by vacuum plasma spraying process (VPS coating) were investigated in compare with that formed by High Velocity Oxygen Fuel Spraying process (HVOF coating). The results are as follows. (1) The hardness of VPS coatings in as sprayed condition was HV1243 ± 80, which was much higher than that of HVOF coatings, HV958±44, and never went down under HV1100 even after heat treatment at 1273K for 3.6ks. (2) VPS coating presents dense lameller structures composed of Cr2C3, Cr7C3 and γ-NiCr phase, while HVOF coating presents lameller structures with many fine gaps, composed of Cr2C3, Cr7C3, γ-NiCr phase and relatively large amounts of Cr2O3. (3) The reason why such high hardness was obtained in VPS coating, has been considered due to their dense lamella structures.
Effect of Plasma Fluctuations on In-Flight Particle Parameters
Authors: Bisson J.F. , Gauthier B. , Moreau C.
Published: June 2022

The influence of arc root fluctuations in DC plasma spraying on the physical state of the particle jet is investigated by correlating individual in-flight particle temperature and velocity measurements with the instantaneous voltage difference between the electrodes. In-flight diagnostics with the DPV-2000 sensing device involves two-color pyrometry and time-of-flight technique for the determination of temperature and velocity. Synchronization of particle diagnostics with the torch voltage fluctuations is performed using an electronic circuit that generates a pulse when the voltage reaches some specific level; this pulse, that can be shifted by an arbitrary period of time, is used to trigger the acquisition of the pyrometric signals. Unlike what has been predicted by numerical modeling, time-dependent particle temperature and velocity due to power fluctuations induced by the arc movement can be very important. Periodic variations of the mean particle temperature and velocity, reaching ΔT= 600°C and Δv = 200m/s, are recorded during a voltage cycle. Moreover, very few particles are detected during some part of the cycle. The existence of quiet periods suggests that particles that are injected at some specific moments in the plasma are neither heated nor accelerated efficiently. To our knowledge, this is the first time large time-dependent effects of the arc root fluctuations on the particle state (temperature and velocity) are experimentally demonstrated with quantitative measurements.
On-Line Monitoring (SDC) Through Coating Surface Temperature of Residual Stresses in APS WC-Co17wt% Coatings on Hastelloy X
Authors: Renault T. , Vardelle M. , Fauchais P. , Hoffmann H. , Braillard F.
Published: June 2022

During last 10 years, it has been pointed out that the reproducibility and reliability of air plasma sprayed (APS) coatings depend, among other parameters, on the particle velocity and temperature distributions prior to their impacts to the target surface. On-line control systems have been designed to follow these parameters in the harsh environment of booths. However, in spite of significant strides, works have yet to be carried out to establish relationships between deposit properties and in-flight particle parameters and/or surface target temperature, roughness and oxidation stage. The SPCTS laboratory at the University of Limoges has developed the SDC (Spray and Deposit Control) system in collaboration with SNECMA Services. It controls the stability of the spray jet and the mean particle trajectory together with the target surface temperature. It has been used with a device allowing to measure the deflection of a rectangular beam during APS of WC-Co17wt% or ZrO2+8wt%Y2O3 powder on Hastelloy X (Ni base alloy) substrate. The aim of this study was to determine which spray parameters influence the residual stresses, in order to achieve a mean compressive residual stress in the WC-Co17wt% coating on Hastelloy X and to control it with the deposit temperature.
Diagnostic of In-Flight Particle Properties and Resulting Coating Qualities on Atmospheric Plasma Spray Process
Authors: Lugscheider E. , Fischer A. , Koch D. , Papenfuß N.
Published: June 2022

Thermal spray technology became established in various parts of industry (e.g. aircraft industry, medical industry etc.). Some of the applications are highly sensitive, therefore the coating quality plays an important role. Most of the common quality control methods are based on destructive testing methods which are undesirable for economical reasons. In recent years the interest in non-destructive online measurement methods increased and still is growing. More detailed knowledge of the relationship between process parameters can help to improve the coating quality standards and to understand different phenomena in thermal spraying. This will make online process control possible and improves the acceptance of thermal spray technology. In this paper results of fundamental studies on the atmospheric plasma spraying process (APS) are presented. Al2O3 and NiCr powder were sprayed as model materials. In the experiments modem on-line monitoring systems were used to investigate the entire process from gun parameters to the coating quality. The faces in this paper are set on investigations of the in-flight properties of spray particles with the particle sensor DPV 2000 and their relationship with resulting coating properties. A method will be presented to extract characteristic values (velocity and temperature) out of the spray process with DPV 2000. With this method the APS-process was monitored and process parameters were correlated with main coating properties.
Plasma Jet Properties in a New Spraying Process at Low Pressure for Large Area Thin Film Deposition
Authors: Dorier J.L. , Gindrat M. , Hollenstein C. , Loch M. , Refke A. , Salito A. , Barbezat G.
Published: June 2022

This paper describes an experimental investigation of plasma jet properties of a DC torch operated at low pressure (below 10 mbar). A modified enthalpy probe system is described, which allows gas sampling from the plasma jet at pressures down to the mbar range. Measurements of the specific enthalpy, temperature and velocity throughout the jet for different pressures are presented and discussed. In the pressure range investigated, the jet flow is supersonic and compressible theory is used to infer the velocity from the dynamic pressure measured at the probe tip. In addition, optical emission spectroscopy of the plasma jet is used to evidence the differences of these low-pressure plasmas with respect to common, atmospheric pressure thermal jets. These preliminary measurements are the starting points towards a better understanding of plasma jets at low operating pressures in view of new process development and optimisation.
The Relationships Between In-Flight Particles Characteristics and Coating Properties Under Plasma Spraying Conditions
Authors: Planche M.P. , Normand B. , Suzon E. , Coddet C.
Published: June 2022

The effects of the plasma spray process parameters on the microstructure and properties of coatings have been recognized for a long time. It is now clearly proved that the quality and the properties of the deposits are strongly dependent on the in-flight particle characteristics as well as on the splat morphology. The aim of this study was to examine in detail: firstly the interaction between an Al2O3/13%TiO2 powder and the spraying process, secondly the splat formation in order to understand the morphology of the deposits. A good way to reach a better understanding of the particle/ plasma interaction is to determine the particle parameters at impact. The particles parameters: velocity, temperature and diameter, prior to their impact on the substrate were measured by the DPV-2000 diagnostic system. The effect of particle velocity, temperature and size on the splat morphology and deposits properties for different plasma conditions were examined. The splat morphology was characterized using the Sommerfeld dimensionless number, K; the value of which is directly related to the impact mode. These analyses were correlated to microhardness, roughness and to the tribological properties of the coatings.
Visualization of the Impact of Drops on a Substrate in Plasma Spraying: Deposition and Splashing Modes
Authors: Escure C. , Vardelle M. , Vardelle A.M. , Fauchais P.
Published: June 2022

In plasma spraying, the dynamics of droplet deformation and cooling on the substrate determines the geometry of the resulting splat, the porosity formation and the quality of contact between the splat and the underlying layer, thereby controlling the properties of coatings. The process of splat formation depends on the droplet velocity, size, molten state, chemistry and angle of impact, and on the substrate material, roughness, temperature and surface chemistry. This paper concentrates on investigating the way the droplets impact onto the substrate. A fast-imaging camera is used to observe the impact of plasma-sprayed alumina droplets on cold and hot substrates. Three modes of impact are observed: splashing, deposition or rebounding. A droplet is said to splash when it disintegrates totally or partially into secondary droplets after impacting onto the surface while it is said to deposit if the liquid material spreads and solidifies on the surface with a minimum splashing. The results are expressed in dimensionless form as a correlation between the impact mode and the Sommerfeld parameter K. The latter quantifies the importance of the particle parameters at impact (temperature, velocity and size) and viscous and surface tension forces. It is found that, when K is higher than 57.7, the splashing mode prevails as already found in a variety of different fields for droplets impacting on surfaces.
The Interrelationship Between Particle Velocity and Temperature, Splat Formation and Deposition Efficiency in Detonation Sprayed Alumina Coatings
Authors: Sundararajan G. , Sivakumar G. , Srinivasa Rao D.
Published: June 2022

It is well accepted that the morphology and microstructure of the splats have a strong influence on the characteristics and properties of thermally sprayed coatings. McPherson has made pioneering and outstanding contributions in the above area, especially for plasma sprayed coatings. Recently, splat morphology - microstructure - properties correlation has also been attempted in the case of HVOF thermal spray coatings. However, only limited data is available in the case of detonation sprayed coatings inspite of the fact that DS coatings have been available commercially for a long time. In the present work, the influence of particle velocity and temperature on the splat morphology and also area coverage of the splat has been studied for detonation sprayed Al2O3 particles on a mild steel substrate. Further, the effect of two detonation spray process variables namely, oxy fuel ratio and shot frequency on splat morphology and splat area coverage has been evaluated. The above correlation has then been utilized to understand the variation of deposition efficiency of detonation sprayed Al2O3 coatings on mild steel as a function of spray process parameters.
Development of a Coupled Model to Predict Droplet Deformation and Solidification During Splatting
Authors: Hale D.L. , Berry R.A.
Published: June 2022

Thermal spray is a melt-spray process in which material is melted and accelerated to high velocities, impinges upon a substrate, and rapidly solidifies to form a coating. Modeling the deposition dynamics of droplets is a key step towards understanding the evolution of a coating microstructure, since a coating is built up from the successive accumulation of many deformed, solidified droplets. This paper discusses some special effects testing of a particle model being developed by the authors to simulate the mechanics and thermodynamics associated with the simultaneous flattening and solidification of a fully liquid or partially solidified droplet. Rigorous validation of the numerical algorithm must necessarily be performed via this separate effects testing.
Mechanical Properties of Thermal Spray Coatings
Authors: Varis T. , Rajamäki E. , Korpiola K.
Published: June 2022

Under load and stress thermal spray coatings have unique behaviour as compared to the bulk materials. The aim of this study was to define the mechanical properties of thermal spray coatings and consider the effect of external stress on coatings under test conditions. Five HVOF or Plasma spray coatings: NiCr, WC-CoCr, Al2O3-TiO2, Al2O3, and Cr2O3 were studied. Mechanical properties, such as elastic modulus (E), and tensile strength (a) were measured. Behaviour of some coatings in different loading conditions (tension and compressive) was studied.
Bonding Strength Test and Biological Evaluation of Plasma Sprayed HA-Based Composite Coatings
Authors: Zheng X.B. , Ding C.X.
Published: June 2022

To improve the bonding strength of HA coating, several HA-based composite coatings (HA/Ti, HA/ZrO2 HA/ZrO2SiO2 and HA/NiCr composite coatings) have been fabricated via atmospheric plasma spraying. The bonding strengths of fabricated specimens were tested by ASTM C-633 method. The bioactivity of composite coatings was evaluated by examining carbonate-containing apatite formation on their surfaces in simulated body fluid (SBF). In vitro cell cultures were carried out to examine the biocompatibihty of composite coatings. The results obtained revealed that the addition of metal or ceramics in HA improved the bonding strength of coating significantly except HA/ZrO2-SiO2 composite coating. In SBF test, all of these four coatings were covered by carbonate-containing apatite after immersed in SBF, indicating good bioactivity for composite coatings. The results of cell cultures produced the testimony of excellent biocompatibihty for the coatings except that HA/NiCr composite coating possessed cytotoxicity. By comprehensive survey of bonding strength, bioactivity and biocompatibihty, HA/Ti and HA/ZrO2 composite coatings were candidates of prospective biocoatings.
Characterization and Tribological Properties of Electroless Plated Ni-Co on Plasma-Sprayed Cr3C2-NiCr Coating
Authors: Li J. , Ding C.
Published: June 2022

Microstructure of electroless plated Ni-Co coating on plasma-sprayed Cr3C2-NiCr coating which was previously applied onto lCrl8Ni9Ti stainless steel was characterized, and its tribological properties during sliding against different materials were evaluated. It was found that the electroless plated Ni-Co coating on the Cr3C2-NiCr coating had lower cobalt content and a finer structure than that deposited directly on lCrl8Ni9Ti stainless steel. All the self-mated as-sprayed Cr3C2-NiCr coating, the self-mated electroless plated Ni-Co coating on the Cr3C2-NiCr coating, the self-mated electroless plated Ni-Co coating on lCrl8Ni9Ti stainless steel and the frictional pair of the electroless plated Ni-Co coating on lCrl8Ni9Ti stainless steel against the Cr3C2-NiCr coating exhibited higher friction and wear coefficients during sliding. The frictional pair of the electroless plated Ni-Co coating on the Cr3C2-NiCr coating against the Cr3C2-NiCr coating displayed excellent tribological properties with a friction coefficient of 0.10 and a wear coefficient less than 10-6 mm3 Nm-1 during dry sliding in air. The electroless plated Ni-Co coating on the Cr3C2-NiCr coating somewhat reduced friction and wear coefficients during sliding against plasma sprayed TiO2 coating. The above results could be attributed to that the electroless plated Ni-Co coating on the Cr3C2-NiCr coating could weaken the adhesive intensity between the suitable counterpart materials during sliding.
Importance of the Adhesion of HVOF Sprayed Coatings for Aqueous Corrosion Resistance
Authors: Kuroda S. , Kawakita J. , Fukushima T. , Tobe S.
Published: June 2022

Importance of coating adhesion in a corrosive environment was studied experimentally. Tensile adhesion strength of HVOF sprayed 316L stainless steel and Hastelloy C coatings were tested in as-sprayed condition as well as after immersion in seawater. It was found that the adhesion strength of the stainless steel coatings degraded rapidly whereas that of the Hastelloy coatings remained almost intact. Specimens with an artificial defect were also immersed in seawater. The cross sectional observation after the test revealed that the corrosion at the coating-substrate interface proceeded much faster with the stainless steel coating as compared to the Ni-base alloy coating. A model experiment to simulate the galvanic corrosion of a coating-substrate couple was carried out and no significant difference in the galvanic current density was found between the two coatings when coupled with the steel substrate. The tightness of the coating-substrate interface was then tested with a fluorescent dye penetration test. The dye could penetrate the boundary between the stainless steel coating and the substrate whereas the boundary between the Ni-base alloy coating and the substrate was so tight that no penetration occurred. The size of the micro-gaps at the coating-substrate boundary was discussed from the viewpoint of classical Washburn-Ridiel theory. It was concluded that such micro-gaps between the coating and substrate must be eliminated for these barrier-type coatings to be used in corrosive environments. Heat treatment was highly effective for suppressing the preferential corrosion at the coating-substrate boundary.
Relationship of Corrosion Resistance–Coating Structure of HP/HVOF Carbide and Metallic Coatings
Authors: Shmyreva T. , Wang D. , Thorpe R.
Published: June 2022

A study was carried out on the corrosion resistance of the JP- 5000 coatings of Superalloy 625, WC-12%Co, WC-17%Co, WC-10%Co-4%Cr and Cr3C2-25NiCr materials and comparisons made with chrome plating. The coating corrosion resistance was evaluated using the standard salt fog test (ASTM B117) and also by submersion tests in 10% FeCl3 solution (ASTM G48), in 10% HNO3 and in 0.1M H2SO4 + 0.2M HCl solutions. The coating corrosion mechanisms in relationship with the coating microstructure and phase constitutions are discussed. The test results show that the HP/HVOF coating corrosion resistance can be significantly improved through spray parameters and coating structure optimization. All coatings tested herein having optimum microstructure and phase constitutions have shown improved corrosion resistances in comparison with chrome plating.
Influence of Thermal Treatments in the Corrosion Behaviour of HVOF Cr3C2-NiCr Coatings
Authors: Guilemany J.M. , Fernández J. , Delgado J. , Benedetti A.V.
Published: June 2022

Thermal spray coatings as Cr3C2-NiCr obtained by high velocity oxy-fuel spraying (HVOF) are mainly applied due to their behaviour against aggressive erosive-abrasive and corrosive atmospheres and their thermal stability at high temperatures. In order to increase the corrosion protection that it offers to the substrate trying to close the interconnected pores, it is possible to apply a thermal treatment with the gun during the spraying of the coating. This treatment could be applied in different ways. One of these ways consists of spraying only a few layers of coating followed by thermal treatment and finally the spray of the rest of layers. This thermal treatment on spraying is studied related to the corrosion properties of the system. The study comprises the electrochemical characterisation of the system by open circuit potential (OC), polarisation resistance (Rp), cyclic voltammetry (CV) and impedance spectroscopy measurements (EIS). Optical and scanning electron microscopy characterisation (OM and SEM) of the top and cross-section of the system has been used in order to justify the electrochemical results.
Modification of Ceramic Thermal Spray Deposit Microstructure Implementing Laser Treatment
Authors: Montavon G. , Coddet C.
Published: June 2022

Microstructural features such as cracks, pores and delaminations are known to significantly affect the properties of thermal spray ceramic coatings. As an example, tensile properties depend mostly on the size, the shape and on the degree of clustering of pores since highly clustered porosity generates regions of poor mechanical properties from where cracks easily propagate through the entire volume. Another example concerns the corrosion resistance of coated components which is significantly degraded when pores are connected. To circumvent such disadvantages, several post-treatments may be implemented. The most commonly used is sealing of pores by impregnation using either low melting temperature metallic alloys or organic materials. In addition to be a costly additional step to the deposit manufacturing process, the coating working temperature limit is significantly reduced. Therefore, numerous works along the twenty past years have been devoted to find ways to densify ceramic coatings. Among these treatments, the use of high energy laser beams was very often considered. This paper aims to bring a contribution to those efforts by presenting results concerning the laser treatment of zirconia thermal spray coatings.
Acoustic Emission Techniques for Life Prediction of TBCs Under Thermal Cycling Conditions
Authors: Robin P. , Gitzhofer F. , Boulos M.I.
Published: June 2022

A thermal cycling test rig and procedure was designed in order to predict the life expectancy of Thermal Barrier Coatings (TBC) under thermal cycling conditions similar to those meet in combustion chambers. Two 2kW-halogen lamps highly focused on the TBC were used to expose the surface of the coating to an intense heat flux. A 25x100 mm TBC is Air Plasma Sprayed (APS) centered onto a substrate 25x370 mm. The thermal cycling can be done either under inert or oxidizing atmosphere in order to separate oxidation-induced acoustic emissions from that resulting from the mismatch of the Coefficient of Thermal Expansion (CTE) of the coating compared to that of the substrate. Two transducers located at each end of the substrate monitor the Acoustic Emission (AE) signals emitted by crack initiation and/or propagation, were recorded and analyzed in order to deduce available information about TBC behavior under thermal load. The use of two transducers with a time of flight approach provides a valuable means of identifying both the crack formation and its location. This thermal cycling test is adequate for the study of various samples, like welded substrates coated with TBC or TBC coated around holes. The presence of cracks is observed using metallography preparation and microscopic observation.
The Evolution of the Plasma Spraying Technology During the Last Ten Years
Authors: Barbezat G.
Published: June 2022

The plasma spray technology has shown a considerably evolution during the last 10 years. Modeling and diagnostic methods also have shown a strong development and offer tools for a better characterization and simulation of the plasma spray processes. In the same time some new types of plasma torches were developed. The motivation for the development primarily was the productivity measured in spray rate and deposition efficiency. However the necessary level of energy used for the melting and the accelerating of the powder was not always considered as important factor. In the future this factor certainly will take more importance. The reliability of the process becomes to be considered as a major aspect. During the last decade two directions of development were taken. One direction is the axial injection of the powder in the plasma jet. This process allows an excellent control of particles trajectories and looks as attractive process, however the stability of the arc root is not really realized through the axial injection. The stability of plasma spray process can be increased using the principle of cascaded anode to fix the arc root and provide quasi constant condition for the melting and accelerating of the injected powder. The current density of the cathode plays an important roll regarding the time life and also the stability of the process. It was realized an improvement of a factor 5 to 10 of time life of cathode by the using a multi cathode plasma torch with low current density. This technology shows a significantly improvement by the deposition of metallic alloys and ceramic regarding the productivity and the constant quality level of the coating.
Blast Erosion Properties of Erosion-Resistant Thermally Sprayed Coatings
Authors: Sonoya K.
Published: June 2022

The present investigation compares blast erosion characteristics of coatings that are prepared with abrasion resistant surface treatment materials and various consolidation processes. Furthermore, it elucidates operating mechanisms in blast erosion of various sprayed coatings. The investigation presents the blast erosion test conditions and assessment of test results and discusses the effects of coating materials on abrasion loss and impingement angle on abrasion loss. It includes illustrations on SEM observation and cross-sectional observation of damaged areas. In addition, information on blast erosion resistant characteristics of materials tested and wear mechanism in blast erosion is also provided.
Corrosion and Wear Properties of Different Weld Overlays
Authors: Rogne T. , Berget J. , Fostervoll H. , Nilsen N.I.
Published: June 2022

Different weld overlays were welded by using different weld processes. Both Ni based alloys and Co based alloys were welded on either a c-steel (Weldox 700) or a stainless steel similar to superduplex (UNS 32760). The weld overlays were investigated and compared with respect to effect of the number of layers, chemical compositions of the surface, critical crevice corrosion temperature, microstructure, hardness, friction coefficient, adhesive and abrasive wear resistance. Wear testing was performed on the Co based alloys only. Some electrolytically deposited Ni-coatings were also investigated with respect to crevice corrosion. Both an austenitic and a superduplex stainless steel were tested as reference materials.
Influence of Process Variables on the Plasma Sprayed Coatings: An Integrated Study
Authors: Vaidya A. , Bancke G. , Sampath S. , Herman H.
Published: June 2022

The current study was undertaken as part of an ongoing effort at CTSR towards development of 'Process Maps' for thermal spray coatings of molybdenum. Extensive study of the spray stream of molybdenum powders in a plasma jet was carried out. The study was undertaken for three distinct nozzle (anode) geometries and different spray conditions for each nozzle. The results demonstrate that the particle velocities and temperatures vary in an interdependent manner over a narrow range for any single nozzle. When nozzles with different geometeries are used the velocity and temperature range can be extended considerably. By estimating the residence time of particles in the plasma jet and defining a 'melting index' for the particles, a cross comparison of nozzles provides insight into the particle state achieved in each case.
Roadmaps: Use of ATE Drives Changes in FA: A Commentary
Authors: Wagner Larry , Nguyen Peter
Published: June 2022

Many standard physical failure site isolation techniques require an electrical stimulus to drive test devices into a failing condition. This function has been provided by bench test electronics for some time, but increasing device complexity is causing a migration to more sophisticated equipment such as pattern generators and logic analyzers. In anticipation of further increases in pin count and density, a new class of small footprint testers is emerging. These portable systems, called ASIC verification testers, facilitate the transfer of ATE test programs to failure analysis laboratories at relatively low cost.