Michel Jeandin

Effect of heat treatment on high pressure plasma sprayed hydroxyapatite coatings

Abstract This paper reports the characteristics and properties of two different sets of hydroxyapatite (HA) coatings obtained by thermal spraying two different HA powders, spray dried HA (SDHA) and spheroidisided HA (SHA), at various chamber pressures. The evaluation of the coatings following post-spray treatment at 800°C is also included. Comparisons to the results from the as sprayed coatings were made to show the effects of post-spray heat treatment. The median particle sizes for SDHA and SHA were 35 and 47 μm, respectively. The main difference between the powders is their density and morphology. The SHA powder provides higher density and spherical morphology, and a more porous and rough surface is present in the SDHA powders. These two powders were sprayed using a controlled atmosphere plasma spraying (CAPS) system in the inert plasma spray (IPS) and high pressure plasma spray (HPPS) modes. Four different pressures of 100, 150, 200, and 250 kPa were applied in an argon atmosphere. Post-spray heat treatment was performed to increase the crystallinity of the coatings, to homogenise their structure, and to convert other calcium phosphate phases to HA. Different techniques were used to characterise these coatings. Scanning electron microscopy (SEM) was used to observe surface and cross-section morphology of both powder and sprayed coatings. The phase and chemical characteristics of the samples were evaluated by X-ray diffraction (XRD) and Fourier transform infrared spectrometry (FTIR). Finally, in order to have a qualitative measure of the integrity of the coatings, Vickers hardness testing was performed on polished cross-sections of the coatings.

Laser-Assisted Cold Spray (LACS)

Resume du livre : nDiscovered almost fifty years ago at Bell Labs (1964), the Nd:YAG laser has undergone an enormous evolution in the years, being now widely used in both basic research and technological applications. Nd:YAG Laser covers a wide range of topics, from new systems (diode pumping, short pulse generation) and components (a new semiorganic nonlinear crystal) to applications in material processing (coating, welding, polishing, drilling, processing of metallic thin films), medicine (treatment, drug administration) and other various fields (semiconductor nanotechnology, plasma spectroscopy, laser induced breakdown spectroscopy).

Residual Stress Analysis of Laser-Drilled Thermal Barrier Coatings Involving Various Bond Coats

The gas turbine combustion chamber of aero-engines requires a thermal barrier coating (TBC) by thermal spraying. Further heat protection is achieved by laser drilling of cooling holes. The residual stresses play an important role in the mechanical behaviour of TBC. It could also affect the TBC response to delamination during laser drilling. In this work, studies of the cracking behaviour after laser drilling and residual stress distribution have been achieved for different bond coats by plasma spray or cold spray. From interface crack length measured pulse-by-pulse after laser percussion drilling at 20° angle, the role of the various bond coats on crack initiation and propagation are investigated. It is shown that the bond coat drastically influences the cracking behaviour. The residual stresses profiles were also determined by the incremental hole-drilling method involving speckle interferometry. An original method was also developed to measure the residual stress profiles around a pre-drilled zone with a laser beam at 90°. The results are discussed to highlight the influence of TBCs interfaces on the resulting residual stresses distribution before laser drilling, and also to investigate the modification around the hole after laser drilling. It is shown that laser drilling could affect the residual stress state.

Cold spray under the banner of thermal spray in the whirlwind of additive manufacturing

Additive manufacturing does obey the generalised Godwin’s Law in any materials science and engineering forum since all the technological roads seem to lead to it. In that sense, additive manufactur...

An Artistic Approach to Thermal Spray

“Art is everywhere” to quote Ben, a renowned French contemporary artist. However, there are some areas in which art is more prevalent. Thermal spray is one of them, as this presentation seeks to demonstrate. For this, each of the arts (according to their official classification) is shown to correspond to a specific key point of the thermal spray process for coating: e.g., coating build-up, additive manufacturing, deposition onto brittle and/or temperature sensitive materials (glass, wood, fabrics, polymers), powder optimization, and adhesion. Both modeling and experimental aspects are discussed, focusing on the study of particle-to-particle or particle-to-substrate interfaces, shock phenomena and advanced investigation techniques such as X-ray microtomography or high-speed instrumentation. Plasma spray and cold spray provide the relevant examples that this contribution elaborates. They relate to different industrial sectors such as aircraft-aerospace, luxury, biomedical and the automotive industry. Beyond anecdotal evidence, the discussion aims to show that an artistic approach to thermal spray does help to understand better this powerful coating process.

On the interaction of the particles of tantalum with a substrate of copper in the cold spray bonding process

Cold gas spraying is a relatively new deposition process in which coatings can be produced without significant heating of the sprayed powder. In contrast to the well-known thermal spray processes such as spray flame and plasma, in cold spray there is no melting of particles prior to impact on the substrate. The adhesion in this process is due solely to the kinetic energy upon the impact. The adhesion usually occurs for particles between 5 and 100u2005µm diameter sprayed at supersonic velocities, typically between 300 and 1500u2005m/s [1]. Experimental investigations show that successful bonding is achieved only above a critical velocity that depends on the temperature and physical properties of the sprayed material. For the study of Particle/substrate interaction in the cold-spray bonding process, an experimental simulation of the particlesubstrate reactions at the particle impingement was developed. This simulation is based on laser shock experiments. We used a system of cameras to visualize the state of the interface tantalum/copper in different times.Cold gas spraying is a relatively new deposition process in which coatings can be produced without significant heating of the sprayed powder. In contrast to the well-known thermal spray processes such as spray flame and plasma, in cold spray there is no melting of particles prior to impact on the substrate. The adhesion in this process is due solely to the kinetic energy upon the impact. The adhesion usually occurs for particles between 5 and 100u2005µm diameter sprayed at supersonic velocities, typically between 300 and 1500u2005m/s [1]. Experimental investigations show that successful bonding is achieved only above a critical velocity that depends on the temperature and physical properties of the sprayed material. For the study of Particle/substrate interaction in the cold-spray bonding process, an experimental simulation of the particlesubstrate reactions at the particle impingement was developed. This simulation is based on laser shock experiments. We used a system of cameras to visualize the state of the int...

New advances for laser adhesion test (lasat): From thick to thin coatings

This paper present recent developments in LAser Adhesion Test. This technique sollicitates material interfaces with laser driven shock wave. Results show the ability of the technique to do a quantitative adhesion test for wide range of material and configuration. Edge effect principle and ultra-short shock wave give perspectives for new applications for thick and thin coatings. Fundamental principles are evidenced through experiments on bulk ductile materials before demonstrating their application to coated systems.This paper present recent developments in LAser Adhesion Test. This technique sollicitates material interfaces with laser driven shock wave. Results show the ability of the technique to do a quantitative adhesion test for wide range of material and configuration. Edge effect principle and ultra-short shock wave give perspectives for new applications for thick and thin coatings. Fundamental principles are evidenced through experiments on bulk ductile materials before demonstrating their application to coated systems.

2D effect during the propagation of schock wave induced by laser plasma : Application for laser adherence test (LASAT)

Using numerical simulations (RADIOSS), 2D mechanical effects induced at laser spot edges have been studied. Results show that during the propagation in material, tensile lateral waves are generated behind the main compressive shock. The main shock wave is attenuated and/or the interface coating-substrate can be debonded by this tensile wave. Experimental validation has be done using pure Al target and Cu thermal spraying coating on Al substrate. Free rear velocity profiles measured by Doppler Velocimetry technique are in rather good agreement in both configurations. New perspectives are open with the 2D-LASAT test for massive target and so, new industrial applications.Using numerical simulations (RADIOSS), 2D mechanical effects induced at laser spot edges have been studied. Results show that during the propagation in material, tensile lateral waves are generated behind the main compressive shock. The main shock wave is attenuated and/or the interface coating-substrate can be debonded by this tensile wave. Experimental validation has be done using pure Al target and Cu thermal spraying coating on Al substrate. Free rear velocity profiles measured by Doppler Velocimetry technique are in rather good agreement in both configurations. New perspectives are open with the 2D-LASAT test for massive target and so, new industrial applications.