Bond Strength Of Coatings Research Articles

Laser-Induced Surface Texturing of Metal or Organic Substrates for Structural Adhesive Bonding

Laser-matter interaction is commonly described regarding three main factors: laser beam, materials and environment. Conversion of absorbed energy via collision process into heat is the most important effect that occurs during laser interaction. Short-pulsed laser beam induces fast transition from the overheated liquid to a mixture of vapor and drops which allows the ablation of micrometric layers. Specific patterns can then be achieved using scanning and automation technology also called laser texturing. New materials with specific properties such as endurance life and/or lower environmental impact attract emerging technologies such as thermal spraying. However, adhesive bond strengths have to be high enough to play a key role in surface properties. A clean surface to enhance mechanical interlocking is a key element. Mechanical and physico-chemical bond strength for thick coatings elaborated by thermal spray process can then be developed using laser. The aim of the present paper is to show the potential of such emerging treatments through new results using various thermal spray processes (thermal spraying as well as cold spraying). Metal or organic materials were investigated implementing various powders.

Structures and Properties of Laser-Assisted Cold-Sprayed Aluminum Coatings

In the cold spray process, solid particles impact on a surface with high kinetic energy, deform plastically and form a coating. This enables the formation of pure and dense coating structures. Even more, coating performance and deposition efficiency can be improved by assisting the process with a laser. Laser-assisted cold spraying (LACS) has shown its potential to improve coating properties compared with traditional cold spraying. In this study, coating quality improvement was obtained by using a co-axial laser spray (COLA) process which offers a new, cost-effective laser-assisted cold spray technique, for high-quality deposition and repair. In the COLA process, the sprayed surface is laser heated while particles hit the surface. This assists the better bonding between particles and substrate and leads to the formation of tight coating structures. This study focuses on the evaluation of the microstructural characteristics and mechanical properties (e.g., hardness and bond strength) of LACS metallic coatings.

The bond strength of Al + Al2O3 cermet coatings deposited by low-pressure cold spraying

This article presents the bond strength of composite coatings built by cold spraying method. The composite Al–Al2O3 coatings were made with the use of low pressure cold spraying (LPCS) equipment. The main aim of the study was to analyze the influence of thickness, roughness and waviness on the adhesive and cohesive properties of composite coatings. The experiments were performed at constant spraying parameters for different coating thicknesses within the range from 250μm to 3000μm. The use of manipulator allowed the uniform deposition of coatings. The coatings bond strength amounted up to 61MPa. A significant effect of coating thickness on the nature of the failure was observed. Machining process influenced the coatings failure nature as well as bond strength value. What is more coating failure changed from adhesive into cohesive with increasing coating thickness.

Interface bonding of NiCrAlY coating on laser modified H13 tool steel surface

Bonding strength of thermal spray coatings depends on the interfacial adhesion between bond coat and substrate material. In this paper, NiCrAlY (Ni-164/211 Ni22 %Cr10 %Al1.0 %Y) coatings were developed on laser modified H13 tool steel surface using atmospheric plasma spray (APS). Different laser peak power, Pp, and duty cycle, DC, were investigated in order to improve the mechanical properties of H13 tool steel surface. The APS spraying parameters setting for coatings were set constant. The coating microstructure near the interface was analyzed using IM7000 inverted optical microscope. Interface bonding of NiCrAlY was investigated by interfacial indentation test (IIT) method using MMT-X7 Matsuzawa Hardness Tester Machine with Vickers indenter. Diffusion of atoms along NiCrAlY coating, laser modified and substrate layers was investigated by energy-dispersive X-ray spectroscopy (EDXS) using Hitachi Tabletop Microscope TM3030 Plus. Based on IIT method results, average interfacial toughness, Kavg, for reference sample was 2.15 MPa m1/2 compared to sample L1 range of Kavg from 6.02 to 6.96 MPa m1/2 and sample L2 range of Kavg from 2.47 to 3.46 MPa m1/2. Hence, according to Kavg, sample L1 has the highest interface bonding and is being laser modified at lower laser peak power, Pp, and higher duty cycle, DC, prior to coating. The EDXS analysis indicated the presence of Fe in the NiCrAlY coating layer and increased Ni and Cr composition in the laser modified layer. Atomic diffusion occurred in both coating and laser modified layers involved in Fe, Ni and Cr elements. These findings introduce enhancement of coating system by substrate surface modification to allow atomic diffusion.

Fabrication and properties of Al2O3–TiB2–TiC/Al metal matrix composite coatings by atmospheric plasma spraying of SHS powders

The Al2O3–TiB2–TiC/Al metal matrix composite coatings were deposited onto MB26 magnesium alloy substrates by atmospheric plasma spraying (APS) using the powders produced by self-propagation high-temperature synthesis (SHS). Phase composition and microstructure of the SHS powders and APS coatings were characterized by XRD and SEM. Microhardness, bond strength and wear resistance of the composite coatings were investigated by using a Vickers hardness tester, pull-off tester and pin-on-desk tribometer. The APS composite coatings mainly consisted of TiB2, TiC, excess Al and two types of alumina. The coatings bonded well to the substrate. Microhardness and wear resistance of the coatings increased significantly in comparison with that of the MB26 substrate. The applied load and the fraction of Al content were found to be the most effective factors on the wear rate of the coatings.

The Structure and Bond Strength of Composite Carbide Coatings (WC-Co + Ni) Deposited on Ductile Cast Iron by Thermal Spraying

An investigation was conducted to determine the role of Ni particles in the WC-Co coating produced with the supersonic method on microstructure, mechanical, and wear properties in a system of type: WC-Co coating/ductile cast iron. The microstructure of the thermal-sprayed WC-Co + Ni coating was characterized by scanning electron and transmission electron microscopes as well as the analysis of chemical and phase composition in microareas (EDS, XRD). The microstructure of the WC-Co + Ni coating consisted of large, partially molten Ni particles and very fine grains of WC embedded in cobalt matrix, coming to the size of nanocrystalline. Moreover, the results were discussed in reference to examination of bending strength considering cracking and delamination in the system of (WC-Co + Ni)/ductile cast iron as well as hardness and wear resistance of the coating. It was found that the addition of Ni particles was significantly increase resistance to cracking and wear behavior in the studied system.

Influence of Process Parameter on Grit Blasting as a Pretreatment Process for Thermal Spraying

In thermal spraying, uncoated substrates usually require roughening. As the most common roughening method, grit blasting increases the surface area and produces undercuts in almost all cases, which facilitate mechanical interlocking and thus promote the bonding between the substrate and coating. The effects of grit blasting parameters, i.e., the particle size, the blasting angle, the stand-off distance, and the pressure, on the resulting surface topography are investigated. Furthermore, the efficiency and wear behavior of the blasting media are analyzed. Influences of three different blasting media, corundum, alumina zirconia, and steel shot, on the surface roughening, are compared. By varying adjusted blasting parameters, different initial conditions (surface topography) are created. Subsequently, the substrate is coated, and the coating bond strength is measured. One of the main results of this publication is that alumina zirconia and steel grit show a longer lifetime than pure alumina as a blasting media. Moreover, it has been shown that the blasting parameters such as grain size, working pressure, and history (wear status) of the abrasive particles have a significant effect on the resulting surface topography. Additionally, systematical analysis in this study shows that the blasting parameters such as stand-off distance and blasting angle have a small influence on the results of the blasting process. Another important conclusion of this study is that the conventional surface parameters that have been analyzed in this study did not turn out to be suitable for describing the relationship between the surface topography of the substrate and resulting bond strength.

Simulation of damage and failure processes of thermal barrier coatings subjected to a uniaxial tensile load

Abstract The tensile bond strength of thermal barrier coatings (TBCs) is an important criterion in evaluating the quality of coatings, which depends significantly on the coatings' complex microstructures. In the current study, a three-dimensional (3D) microscopic structural model reflecting the actual interface morphology and pore distribution of TBCs is built using microcomputer tomography (micro-CT). The model is then applied to investigate the 3D spatial evolution processes of damage and failure under uniaxial tension using FE techniques. To validate the numerical simulation results, the tensile responses of the TBCs are measured and a follow-up quantitative description of the tensile fracture morphology is obtained with a 3D surface profiler. The simulation results are in good agreement with the experimental data. Our simulation results show that the local stress concentration induces two types of crack sources located either at the top coat (TC)/bond coat (BC) interface or along the pore boundaries; as the load increases, only the microcracks at the interface amalgamate and begin to form a primary crack; then the primary crack propagates rapidly horizontally along the interface, eventually inducing an undulating fracture morphology.

Method and Apparatus for Measuring the Strength of Weak Binding Coating Interface<sup></sup>

For the difficulty of coating weak bonding strength measurement, we proposed coating weak bonding strength measurement method and apparatus based on laser-induced shock wave. This apparatus contained the laser, the beam splitter, the photodiode, the convex lens, acoustic emission sensors and the oscilloscope. First the distance of the focus and the circular area was calculated by the interaction of laser-induced shock wave and the measurement object. The acoustic emission sensor was moved to the same distance, which was used to measure the shock wave propagation time under the same power laser beam. Finally, coating weak bonding strength is calculated by the laser-induced shock wave propagation equation. The experimental results showed that the present method and apparatus can measure weak binding strength of the coating, which provides an important reference for the coating bond strength measurement.

Effects of Slurry Fused Ni60 Interlayer on Bond Strength of Cermet Coating to GH202 Substrate

effects of slurry fused Ni60 interlayer on bond strength of cermet coating to GH202 substrate were studied. A compact NiCrBSi interlayer was prepared by slurry fused method and the NiCr-HfB2 cermet coating was fabricated on the interlayer. Surface morphology of the NiCrBSi interlayer and NiCr-HfB2 cermet coating and cross-sectional morphology of samples with the NiCrBSi interlayer were examined by means of SEM. The bond strength of the NiCr-HfB2 cermet coating to GH202 substrate with and without the NiCrBSi interlayer was measured by pulling apart tests. And thermal shock resistance of the cermet coating with and without the intermediate layer was measured. The results show that the NiCrBSi interlayer effectively enhance the bond strength of the NiCr-HfB2 cermet coating to GH202 substrate and the thermal shock resistance of the cermet coating .

Sealing of cracks in the rhenium coating on C/C composites by alloying with cobalt

Thermal stress cracks of the rhenium coating on C/C composites have severely limited its applications. In the present work, rhenium coatings were prepared on C/C composites by chemical vapor deposition (CVD) and modified by alloying with cobalt. The results showed that the as-prepared rhenium coating consisted of monolayer columnar grains with significantly <002> preferred orientation, which led to lower ductility and mechanical strength in the coating. After modification, the cracks of the rhenium coating were sealed by rhenium–cobalt alloys and the ductility and mechanical strength of the coating had a remarkable improvement. Moreover, tensile and shear bond strength of the as-modified rhenium coatings with C/C substrates had a considerable reduction. The cobalt-modified rhenium coatings free of cracks were acquired on C/C composites ultimately.

Influence of metal surface preparation on its surface profile, contact angle, surface energy and adhesion with glass fibre prepreg

Surface preparation of metal plays a vital role to enhance the adhesion of polymer coatings in ensuring the desired performance of metal infrastructure for the oil and gas industry. In this study, a range of techniques for the surface preparation of mild steel were evaluated which included garnet grit blasting, disk sanding, needle gun, flap wheel, strip wheel and wire brush. The surface profile and apparent surface energy parameters such as apparent surface energy, work of adhesion, Lifshitz-van der Waals acid–base components were measured from these trials correlation made with these properties to the metal to polymer coating bond strength and bond failure mode.The dolly pull-off strength was used to quantify the bond strength while the laminate failure area (%) was used to assess the bond failure mode. Based on the testing results, it was found that irrespective of the surface preparation technique used, the dolly pull-off strength and laminate failure area increased with increasing surface profile up to a value of approximately 21µm and both of these properties followed a plateau up to 24μm and then decreased above this surface profile value. The dolly pull-off strength was also seen to increase with the increase of surface energy and work of adhesion and decrease of contact angle. It was found that the maximum adhesion could be attained with three of the four grit sizes of the garnet grit blasting technique which appeared to have achieved the most favourable properties amongst all the surface properties studied here. Wenzel model was found to be in agreement with the values of the surface profile of different surface preparation techniques.

Accepted Practice to Test Bond Strength of Thermal Spray Coatings

Abstract This article describes a new document on methods to test the bond strength of thermal spray coatings that was developed and released by the ASM Thermal Spray Society Accepted Practices Committee on Metallography. This practice clarifies details of ASTM C633 requirements and provides examples of best practices confirmed by hundreds of tests performed wordwide

Rhenium used as an interlayer between carbon–carbon composites and iridium coating: Adhesion and wettability

Iridium (Ir) is one of the most promising materials as a protective coating on carbon/carbon (C/C) composites for very high temperature applications. However, the poor adhesion and thermal stress induced by thermal expansion mismatch between Ir coating and C/C substrate restrict their application. Rhenium (Re) has been selected as the interlayer material between the Ir coating and C/C substrate which can improve the adhesion of Ir coating and relieve the thermal stress. The Re coating was prepared on the C/C substrate by chemical vapor deposition (CVD). The Ir coating was electrodeposited on the C/C and Re/C/C substrates in molten salt. The morphology and microstructure of the Re and Ir coatings were studied by SEM and XRD. The bond strength of the coatings on C/C substrate was measured by coating-pull-off test. The molten salt wettability on the C/C and Re/C/C substrates was determined by drop shape method. The results showed that the CVD Re coating on the C/C substrate had a preferential orientation of <002> with many fine regular cracks. The bond strength between the Re coating and C/C substrate was higher than 15MPa before and after annealing treatment. The contact angles of molten salt on C/C and Re/C/C substrates at 500°C were 128.5° and 43.4°, respectively. The bond strength of as-deposited coatings increased from 3.2MPa for Ir/C/C to 7.9MPa for Ir/Re/C/C. After high temperature annealing treatment, however, the bond strength has been reduced by ~50%, probably due to the infiltration of molten salt into the C/C substrate.

Effect of Vacuum Annealing on the Characteristics of Plasma Sprayed Al2O3-13wt.%TiO2 Coatings

Adhesion strength is one of the critical properties for plasma-sprayed coating. In this study, the plasma-sprayed Al2O3-13wt.%TiO2/NiCrAl coatings were annealed at 300-900 °C for 6 h in vacuum. The tensile bond strength and porosity of the coatings were investigated. The microstructure and the fracture were studied using optical microscopy, scanning electron spectroscopy, and x-ray diffraction. It was found that the tensile bond strength of coatings increased with the increase of annealing temperature until 500 °C, reaching the maximum value of 41.2 MPa, and then decreased as the annealing temperature continues to increase. All coatings presented a brittle fracture and the fracture occurred inside the ceramic coatings except for the coating annealed at 500 °C, which had a brittle-ductile mixed fracture and the fracture occurred at the interface of bond coating and the substrate.

Study of the characteristics of plasma spray sealing aluminum silicon-polyester coatings

This study shows the homologation of the plasma spray parameters of soft abrasive AlSi - Polyester seals so that they can be applied on the TV2 - 117A compressor engines. The research has aimed at substituting existing sealants with a new class of materials in order to increase the sealing effect under the highest levels of pressure and to provide the air flow temperature of 100-125°C through the compressor. The Metco 601NS material and plasma spray technology were applied on the air labyrinth ring as a part of the TV2-117A turbojet engine compressor in order to obtain soft sealing. The deposit parameters were carefully selected in order to obtain coatings with the best characteristics depending on their application.The flow of helium was taken as a basic parameter in the parameter selection procedure. The coating with the best mechanical and structural properties was deposited on the air labyrinth ring to examine the effect of the coating application in an assembly. The microstructures of deposited layers were estimated with a light microscope and a (SEM) Scanning Electron Microscope. The microstructural analysis of deposited layers was performed according to the Pratt - Whitney standard. The assessment of the mechanical properties of the coatings was done by examining the macrohardness of the sealing layers with the HR15Y method. The coating bond strength was tested by tensile testing. The effect of the air labyrinth ring sealing was tested inside the TV2-117A engine compressor on the test station for a period of 42 hour.

TiAlNb intermetallic compound coating prepared by high velocity oxy-fuel spraying

Ti28.35Al63.4Nb8.25 (at.%) intermetallic compound coatings were sprayed onto 316L stainless steel substrates by HVOF processes using various parameters. By varying the grit blasting pressure between 0.11 and 0.55MPa, the effects of substrate roughness on the adhesion of TiAlNb thermal sprayed coatings were investigated. The microstructure, porosity and microhardness of the coatings were characterized by SEM, XRD, Image Analysis and Vickers hardness analysis. The tensile adhesion test (TAT) specified by ASTM C 633-79 was used to measure the tensile bonding strength of the coating. The results show that the coatings with substrate roughness of 8.33μm displayed the best combined strength. TiAlNb coatings had a lamellar microstructure with different spraying parameters. The porosity, bonding strength, microhardness of coatings were assessed in relation to the spraying processes. The thickness of bond coat on the bond strength of coatings was also discussed.

Microstructure and Properties of Mo&lt;sub&gt;2&lt;/sub&gt;FeB&lt;sub&gt;2&lt;/sub&gt; Cermet Coating by Induction Heating

Mo2FeB2 Cermet Coating was deposited on Fe substrate by react flame spraying (RFS) process. Three different groups of specimens were prepared according to the change of induction heating treatment time. Comparative study of phase composition, microstructure, interfacial microstructure and bond strength of Mo2FeB2 Coating was carried out. X-ray diffractometry (XRD) and Scanning electron microscopy (SEM) were used to characterize the Mo2FeB2 coating. The bond strength between the coatings and Fe substrates was measured with the pull-off test method according to the corresponding GB 8642-88 standard. Results indicated that the time of induction heating treatment greatly affected the microstructure, interfacial microstructure and bond strength of Mo2FeB2 coating. 13 seconds of induction heating treatment favoured the formation of a compact Mo2FeB2 Coating with the highest bond strength of approximately 60 MPa.

FEM Analysis and Experimental Study for Bond Strength of High-Strength Coating by Wedged Load Test Method

A wedged load test method is used to evaluate the adhesion strength of high-strength coatings, which have been processed with various sintering parameters. In this test, for stress concentration at cut tip, cracks are always induced and expanded rapidly cross the interface between coating and substrate. Macro-fracture and SEM image of coating interface of high-strength coating are characterized using optical microscope and scanning electron microscopy (SEM), respectively. In order to evaluate the bonding properties between coating and substrate effectively, corresponding finite element (FE) analysis has been conducted to evaluate the adhesion strength of high-strength coating. And stress distributions cross the interface of high-strength coating are obtained. The stress analysis can help to evaluate the bond strength of high-strength coating. Because of small specimen and contact relationship between wedged pressure head and wedged cuts, complex stress state is affected by many factors resulting from interface, and also by the thickness of coating.

The influence of ceramic particles on bond strength of cold spray composite coatings on AZ91 alloy substrate

Abstract Al–Al 2 O 3 composite coatings were produced on AZ91D magnesium alloy substrates using kinetic metallization (KM), which is a special type of cold spray using a convergent barrel nozzle to attain sonic velocity. The effect of the volume fraction of Al 2 O 3 particles and KM spray temperatures on the microstructure, hardness of the composite coatings, the deposition efficiency, and the bond strength between the coating and substrate was studied. Results show that addition of Al 2 O 3 particles not only significantly improves the density of the coating, but also enhances the deposition efficiency to an optimum value. The bond strength of the composite coatings with the substrate was found to be much stronger than the coating itself, measured using a specially designed lug shear method. Furthermore, based on bond strength data and SEM analysis, higher Al 2 O 3 content resulted in a failure mode transition from adhesive failure to cohesive failure. This is considered a result of a competition between the strengthening of the ceramic reinforcing particles at the coating/substrate interface, and the weakening of coating cohesive strength due to an increase in the proportion of weaker Al–Al 2 O 3 bonds compared with stronger Al–Al bonds. Characterisation of the composite coating in terms of hardness, porosity and microstructure was also conducted.