Metallic implants for orthopedic or dental use are often coated with a plasma-sprayed hydroxyapatite (HA) layer. In this study, HA coatings are applied to titanium substrates of varying thickness and laser shock adhesion tests are performed using different laser spot diameters. The objective is to investigate the effect of different shockwave regimes on interfacial debonding and the potential consequences of laser shock adhesion testing. HA coatings exhibiting different levels of adhesion were subjected to laser shock experiments and subsequently examined using nondestructive inspection techniques. The results are presented along with suggestions for developing a robust laser shock adhesion test.

When testing the thermal cycling resistance of thermal barrier coatings, the surface temperature of the materials must be controlled so that test results can be used for coating life prediction. In this study, the temperature at the surface of plasma-sprayed TBCs was controlled during thermal shock testing using feedback from a double-color IR thermometer and high-rate cooling. The results are presented and discussed, highlighting the capability of the recently designed thermal shock test.

Despite the wide application of powder metallurgy in the field of additive manufacturing, a general understanding of the spreadability of powder particles in electron beam powder bed fusion (EB-PBF) is lacking. This paper presents the results of a literature review on particle flowability and spreading in additive processes. Different flowability tests are described and spreading mechanisms for different powder-bed processes are reviewed. A technique is proposed to study spreadability in which a single layer of powder is ‘frozen’ in the as-spread condition by contact sintering and then characterized using white-light interferometry. A standard method to calculate powder-bed density is defined based on this approach, and correlations between density, packing factor, and flowability are established.

In this work, the effects of plasma spray process variables are systemized in various process schemes. On this basis, different approaches to improving process reliability are described and assessed paying particular attention to in-flight particle diagnostics. A new test applying spray bead analysis is introduced and the first results are presented.

The residual stresses present in coatings and layer composites are influenced not only by the thermal and mechanical loads generated during manufacturing, but also by the mechanical and thermophysical properties of the coating and substrate materials. In-process measurement of transient, process-induced stresses may thus enable the manufacturing of coated parts with a residual stress state that lies within a predefined application-oriented stress regime. This paper presents a quasi-nondestructive method by which such measurements may be obtained. A small amount of material is removed from the surface of a part by laser ablation, while optical interference sensors monitor surface deformation caused by stress relaxation and heating due to absorbed laser energy. The new method is evaluated by four-point bend testing using Al5754 plates coated with Al/TiO 2 by atmospheric plasma spraying.

This paper presents a thickness measurement method that can be used during thermal spraying. The new method is based on photogrammetry and image reconstruction and is able to measure complex 3D shapes with continuous contours. Initial results demonstrate the nondestructive nature of the method as well as its accuracy, versatility, and speed.

The aim of this study is to clarify the factors that control the macroscale strength of cold spray coatings by evaluating local strength at the microscale. Using pure copper powder and high-pressure cold spray equipment, thick (15 mm) copper layers were deposited on aluminum substrates. The coatings were evaluated by SEM and EBSD analysis, then freestanding Cu specimens were fabricated in a FIB system, where in-situ micro tensile tests were carried out. The results are presented and discussed along with the role of microvoids.

A series of abradability tests were conducted on AlSi-hBN coatings, which are commonly used in the compressor section of aeroengines for clearance control. The coatings were sprayed on test plates to a thickness of 1.9-2.0 mm and ground to a finish of 10 μm with 400 grit paper. The tests were carried out in an automated test rig with adjustable temperature, blade tip velocity, and incursion rate. The rig is configured such that the coatings are exposed to rotating blades, making contact with the tips as they pass. In this study, investigators monitored the number of contacts, removing and examining abraded coating samples at a given count total ranging from 200 to 4000. It was found that wear characteristics change with each contact between the coating and blade tip, indicating that pass number is a factor that must be considered when testing abradable coatings.

This study investigates a new evaluation method that has the potential to differentiate between particle interfaces and grain boundaries in cold spray coatings. The method uses confidence index (CI) and image quality (IQ) values obtained from EBSD analysis to determine the location of grain boundaries as well as grain orientation and crystallinity of the deposit. In the case of a cold-sprayed copper deposit, the new method helps to explain the observed characteristics of the coating.

Adhesion strength of thermally sprayed coatings is usually measured in accordance with the tensile method specified by ISO 14916. A major limitation of the method, however, is that it cannot measure adhesion strengths greater than that of the glue used to prepare the test specimen. Indentation testing, by virtue of its simplicity and practicality, is a promising alternative in such cases. Collaborative work has been conducted by members of the Japan Thermal Spray Society (JTSS) to establish a standard method for measuring coating adhesion using a conventional Vickers indenter. This paper provides an overview of the experimental and theoretical work that was done and describes the criteria proposed to quantify adhesion strength based on standardized test procedures.

Gate valves used in oil and gas production undergo stringent qualification before going into service. During qualification there is no external lubrication, leaving contact surfaces susceptible to friction evolution and wear. The work presented in this paper was carried out to better understand the changes that can occur during qualification and where and when the limit for mild wear and stable friction is reached. Ni-Cr alloy gate valve components were coated with WC-CoCr by HVOF spraying and dry sliding wear tests were conducted in nitrogen and in air. The coatings were then evaluated by means of SEM, EDX, and XRD analysis, nanoindentation and surface roughness measurements, and compression tests on micropillars milled out by FIB. Similar tests and analyses were performed on gate valves returned from the field. Examination of the valves that had been in service revealed the presence of oxygen rich layers on polished surfaces due to opening and closing of the gate. Such layers were also observed in coating samples following tribological testing. Initial surface roughness was found to play a role in the development of the oxygen rich layers as well as friction evolution.

This work investigates the reliability and reproducibility of scratch testing for YSZ and TiO 2 coatings deposited on NiCr bondcoats by plasma spraying. Scratch tests were conducted on cross-sections of the spray coatings. An image of the scratched area was taken after testing using an optical microscope in order to determine failure mode. With a statistical evaluation, the adhesion and cohesion strength were determined. The results show that cross-sectional scratch testing is effective for estimating the adhesion and cohesion strength of plasma spray coatings.

The aim of this study is to determine what types of spray coated metals are desirable for inhibiting iron dissolution in marine environments as a countermeasure against biofilm formation. Experiments were conducted in a closed-loop system in which water continually circulates from a basal water tank through a transparent column where test specimens are immersed. The water flows through an open-air channel on its return to the tank where it is exposed to ambient bacteria. Steel and stainless steel substrates were prepared by plasma and HVOF spraying and, in some cases, a silicon-based sealant was applied. Test specimens were placed in the biofilm reactor and taken out and examined after 5 to 10 days. Substrate surfaces and corrosion products were analyzed by optical microscopy, x-ray diffraction, 3D surface profiling, and low-pressure SEM. Detailed results are presented and discussed in the paper.

In this investigation, particle image velocimetry (PIV) diagnostics were employed to analyze the spray produced by a two-fluid atomizer as used in suspension plasma spraying (SPS). This led to a change in the design of the atomizing nozzle in order to achieve a high-speed spray with narrow distributions in droplet size. The resultant spray was characterized and the diagnostic was adapted accordingly. Various suspensions of YSZ powders were then injected into the plasma under different conditions and particle velocities were determined and correlated with the coating morphologies obtained.

This work assesses the potential of using an ultrasonic probe attached to the back of the substrate to monitor the cold spraying process. While this is only a preliminary study, focusing more on presenting the results than analyzing them, a few conclusions may be drawn. With acoustic sensing, not only can the final value of thickness be estimated, it is also possible to see the dynamics of how the buildup takes place in real time. As shown in the data plots, the buildup process for aluminum-alumina composites is fairly universal across the spray with slower buildup at the outer edges of the coating. More importantly, it is shown that nozzle speed, spray diameter, and thickness estimates fit well with measured values.

“Testing Method for Thermal Cycle and Thermal Shock Resistance of Thermal Barrier Coating (TBC)” is a Japanese Industrial Standard (JIS) newly established by the Minister of Economy, Trade, and Industry in 2008, after deliberations by Japanese Industrial Standards Committee, in accordance with the Industrial Standardization Law. The standard specifies a testing method that evaluates the spalling resistance of TBCs based on operating conditions in gas turbines. This paper provides an overview of the standard along with examples of its use.

In the present work, pure Al and Al-Al 2 O 3 composite coatings are deposited by cold spraying while measuring in-flight particle velocities. Residual stresses, evaluated using the Almen curvature method, X-day diffraction, and modified layer removal, are correlated with particle velocity, coating thickness, and alumina content. Peening stresses due to plastic deformation were estimated to be less than 100 MPa and are shown to be nearly constant through the thickness of the coatings.

This paper evaluates an electrochemical mapping method for determining the corrosion resistance and structural integrity of thermally sprayed coatings. In the test setup, a potentiostat is suspended over the test sample, forming an electrochemical cell. The circuit is completed through an electrolyte-containing porous tip. Capillary forces keep the electrolyte on the surface of the tip, preventing transfer to the substrate surface. In the investigation, electrochemical, spatially resolved measurements are carried out on flame and vacuum plasma sprayed nickel-base coatings and compared with the results of salt spray testing. It is observed that the new method offers many advantages being faster, nondestructive, and quantitative in nature. Paper includes a German-language abstract.

Arc spraying is an economical method for applying metallic layers due to its high spray rates and uniform melting of spray particles. The main disadvantage is the difficulty in achieving sufficient particle velocity to ensure good layer adhesion. This study investigates the influence of nozzle geometry, arc power, and gas pressure on the size and velocity of particles in an arc spray jet. The experiments were conducted using particle image velocimetry (PIV) to measure the spatial and velocity distribution of particles in flight. For X45Cr13 steel, particle velocities were found to be between 85 and 95 m/s at a gas volume flow of around 1 m 3 /min. Velocities of up to 150 m/s were ultimately achieved, but at the expense of higher atomizer gas consumption. Paper text in German.

A simple test procedure, based on steady state flow through a membrane, has been developed for measurement of the gas permeability of specimens over a range of temperature. The reliability of this equipment has been verified by testing solid disks containing single perforations and comparing the measured flow rates with those expected on the basis of laminar flow. Coatings of yttria-stabilised zirconia have been produced by plasma spraying in vacuum and in air. The specific permeability of these coatings has been measured at temperatures ranging up to 600°C, using hydrogen gas. It has been found that permeability is increased for coatings produced with longer stand-off distances and at higher pressures. Porosity levels have been measured using densitometry and microstructural features have been examined using SEM. A model has been developed for prediction of the permeability from such microstructural features, based on percolation theory. Agreement between predicted and measured permeabilities is good, although it is clear that more comprehensive data are needed in order to validate the model systematically.