This study assesses the influence of powder morphology on the microstructure and bond strength of cold-sprayed aluminum. Aluminum powders with spherical and irregular particle shapes were deposited on shot-peened steel. The feedstocks were mixed with alumina powders, either spherical or angular in shape, to improve coating properties. Coating samples and powder mixtures were examined by means of SEM and XRD analysis and pull-off tests were conducted to evaluate coating adhesion. It was found that alumina addition reduces porosity and increases hardness and that aluminum-alumina mixtures with the same particle shape are more suitable for producing dense coatings with high bond strength.

Zn coatings have been applied on steel substrates used by Renault for the manufacturing of car bodies. We had the task to make these on-line thin coatings on smooth and non de-oiled surfaces with a translation speed of 1 m/s. Furthermore, in certain cases, these coatings were situated on a visible surface of the car body and on a precise position. The coating process must be adapted to the clean conditions of the current automotive industry. The development of this application has been focused mainly on the study of a new zinc powder grade as well as on the projection procedure which had to adapt to the constraints and to the productivity of an automotive manufacturing line. Cold Spray addresses all these requirements. Positive results obtained on the mechanical examinations, the accelerated corrosion tests and chippings tests demonstrate that such new coatings meet the specifications of the customer for this kind of processes.

The studying of splats in thermal spray is prominent to improve coating properties due to better understanding of coating build-up mechanisms. Most of studies, however, devoted to splats rest on physical aspects of the build-up, which feature the behaviour of a single particle impinging on a substrate. These studies involve the nature, velocity and intrinsic characteristics of the particle. The present work deals with the study of the splat-substrate interface using an ultra-sonic (U.S.) technique. This technique is based on the determining of splat-substrate adhesion (for an elementary splat or a group of splats) to help in the optimising of spraying conditions. APS copper splats were studied for Al-based substrates. This U.S. technique was already tested successfully for adhesion control of thermally-sprayed coatings in Basel, Switzerland. Further development then related to the specific experimental set-up for splat analysis using several transducers. This involved the use of various frequencies, various sizes for the focal spot and various scan velocities. In this study, results from this U.S. technique were discussed in the light of the observation of cross-sections of U.S.- controlled splats. U.S. C-Scan images were shown to fit well with cross-sectional images. In a general conclusion, the work showed the feasibility and efficiency of advanced U.S. control of splats to promote thermally-sprayed coatings whatever the process, i.e. plasma spray, flame spray, HVOF or cold spray.

The present work deals with the application to actual in industrial conditions of the promising results of the study on adhesion, as presented at the previous edition of ITSC’2004 in Osaka, Japan. These industrial parts were typical of those produced in workshops for aircraft-aerospace, petro-chemical, printing works industries etc…. Thermal spray processing of industrial parts tested in this study are numerous, primarily air plasma spraying (APS), HVOF and conventional flame spray with or without remelting. Ultrasonic NDT facilities are now installed in an actual industrial workshop and show the reliability of the testing method and related results. For every tested part, digital ultrasonic testing was carried out to be compared to results from conventional adhesion tests according to EN 582 standard. U.T. results were quite in keeping with those from EN 582 testing. However, in addition, ultrasonic testing exhibited the any heterogeneity when existing, (local weak zones) at the coating-substrate interface. This resulted in easy discriminating of adhesive areas from cohesive areas. Results of this work obtained in a real workshop environment leaves promising expectations for ultrasonic testing to meet results from conventional EN 582 adhesion testing when applied to industrially-produced parts. Ultrasonic testing results in a low-cost NDT method which should compete with current high-cost control. Moreover, ultrasonic NDT looks more reliable in so far as the whole part can be controlled due to scanning of the whole surface.

Coating-substrate adhesion in cold spray is a paramount property, the mechanisms of which are not yet well elucidated. These mechanisms are governed by metallurgical and morphological phenomena occuring when cold-sprayed particles impinge on the substrate. To go into these mechanisms, due to the intrinsic characteristics of the cold spray process, i.e. the low-temperature and high velocity of the particles, direct observation and control of inflight particles and related phenomena (especially when impinging) cannot be done easily. For this reason, an experimental simulation of the particle-substrate reactions at the particle impingement was developed. This simulation is based on original filter impact experiments from laser shock acceleration of plates/foils (fliers). These were applied to the Cu-Al metallurgically-reactive system to simulate Cu cold-sprayed onto Al. The velocity of the plate was selected in the range of actual cold spray velocities. Relevant Cu-Al interaction phenomena were featured and studied as a function of filter impact conditions, i.e., primarily, shearing, plastic deformation, phase transformation (including rapid melting/solidification and formation of intermetallics). These phenomena were shown to be similar to those involved in cold spray. This was ascertained by a parallel study of cold-sprayed Cu coating of Al using SEM, TEM, EPMA, and an energy balance and diffusion calculations. In addition, this simulation can be used to feed FE modeling of cold spray particle impingement on the substrate. Preliminary results are discussed from modeling using the “RADIOSS®” code. More generally, laser shock flier impact experiments were demonstrated to result in a powerful tool capable of simulating cold spray coating-substrate interface mechanisms. Major assets rest on their high significance, reproducibility, flexibility and potential for substituting for direct laborious cold spray optimization testing.

To address drawbacks with conventional destructive adhesion tests, two advanced nondestructive methods were developed to characterize the acoustic response of coating-substrate bonding. These new tests, immersion ultrasonic testing and laser shock adhesion testing, are discussed in this contribution. The paper describes the test process and results as compared to traditional destructive testing. The advantages and drawbacks of the techniques are addressed.

The Cold Gas Dynamic Spray Method (CGDS) requires high-kinetic energy particles to obtain dense coatings. The aim of this study is to characterize some properties of CGDS coatings and compare them to the bulk materials. Pure nickel and nickel-base alloys (NiCrAlY, CoNiCrAlY, and Hastelloy C) are sprayed on 316L steel substrates. Coating thickness is about 700 µm. The particle velocity at impact is measured using an imaging technique based on a fast-shutter CCD camera and a high-power diode laser. The original powder characterization involves particle size, density, chemical composition and hardness, and coating analysis includes micro hardness, nano hardness (performed in the first 60 µm of the coating), Young’s modulus determination and porosity level. The hardness test results make it possible to determine effects of this specific property on the sprayability with this process.

The Plazjet system usually works with a binary gas mixture of nitrogen and hydrogen for the deposition of a thick TBC (NiCrAlY as a bond coat and Zirconia as a top coat). In order to improve the performances of our spraying device and ensure good quality coating, different experiments were conducted. The substitution of N 2 or the classical binary mixture N 2 /H 2 respectively by a binary N 2 /He, and a ternary gas composition N 2 /H 2 /He leads to an evolution of the deposition efficiency and quality coating. In order to optimise the various ratio in the gas mixture, the evolution of experimental parameters such as voltage were analysed.

The authors carried out in 1999 a multiclient market research covering the Thermal Coatings business in Europe. This work has allowed to obtain detailed business facts relative to the industry and has provided an in-depth understanding of applications, markets, competition, key factors for success and industry structure. Thermal coatings are defined here as coating parts by hardfacing (e.g. MIG, TIG, PTA, laser...) or thermal spray (flame, arc, plasma, HVOF...). This study also provided a further opportunity to investigate about present business issues and to provide a fresh look into growth opportunities. This presentation intends to provide the scientific community with a summary of this business analysis and to stress business issues and factors found to constrain business growth today. We do expect that a more carefully focused teamwork between independent R&D and the supply chain could significantly accelerate the growth of the Thermal Coatings business in the future.

Substrates protected by thermal spray coatings are usually found intact after use, making them viable candidates for recycling and reuse. The key is to remove the coating without damaging the component. This requires a process that minimizes the development of residual stresses and the associated distortion. The purpose of this work is to determine the optimal descaling technique for Ni-base sheets with a thermal barrier coating. Test specimens were produced following industry procedures. Thin sheets (<3 mm) of Ni-base superalloy were plasma sprayed with a NiCrAlY bond coat and a Y203-stabilized ZrO2 topcoat. The coating layers were then removed using different methods, including pickling, shot blasting, and water jet descaling, and the substrates were assessed based on X-ray diffraction and chord width measurements. The findings of the study show that water jetting removes all surface materials, particularly the bond coat, without damaging the underlying surface. It also produces the least amount of stress and deformation and is relatively easy to automate.

This paper presents the comparison of a TBC coating obtained by a conventional and a high power plasma system. It aims to analyze the benefits of the Plazjet in terms of high productivity and high quality. The first part of this paper consists of a technical review of the spraying torches: a classical 40 kW APS is compared with the 250 kW HPPS Plazjet. The second part consists of a description of the spraying tests conditions: material substrate, powders, and qualitative and quantitative characteristics of the coatings. An additional study of the economic features is conducted to analyze the industrial point of view. Paper includes a German-language abstract.