Static mechanical properties such as Young's Modulus, Yield Stress and Ultimate Tensile Strength and especially fatigue behavior are important material properties for thermal spray coatings and their industrial application in automotive and aerospace industry. The static and dynamic mechanical properties of Al-Si, Al-Sn, Fe-Cr and Fe-Cr-B based coating materials deposited by APS, TWAS and HVOF were investigated by nanoindentation and in a three point bending test using DMA (Dynamic Mechanical Analysis). This method permits the determination of pure coating material static and dynamic mechanical properties without substrate influence over a wide temperature range. In this investigation all measurements were carried out at room temperature. The DMA method was verified by comparison of Young's modulus to those obtained by nanoindentation.

The application of metallic foam core sandwich structures in engineering components has been of particular interest in recent years because of their unique mechanical and thermal properties. Thermal spraying of the skin on the foam structure has recently been employed as a novel cost-efficient method for fabrication of these structures from refractory materials with complex shapes that could not otherwise be easily fabricated. The mechanical behavior of these structures under flexural loading is important in most applications. Previous studies have suggested that heat treatment of the thermally sprayed sandwich structures could improve the ductility of the skins and so affect the failure mode. In the present study the mechanical behavior of sandwich beams prepared from arc sprayed alloy 625 skin on 40 ppi nickel foam was characterized under four point bending. The ductility of the arc sprayed alloy 625 coatings was improved after heat treatment at 1100ºC and 900ºC while the yield point was reduced. Heat treatment of the sandwich beams reduced the danger of catastrophic failure.

In this study, in-situ shot-peening approach was introduced by mixing large stainless steel (SS) shots with diameters over 150 μm with IN718 spray powders to aim at developing a novel approach to achieve dense coating. Effect of mixed stainless steel shot content on the microstructure and mechanical properties of the IN718 coating was examined. Results show that IN718 coating can be deposited without any shot peening particle inclusions for their relatively low velocity. It was revealed that the deposition efficiency of the IN 718 powders is improved by the in-situ shot peening effect. With increasing shot fraction in the powder mixture from 0% to 50 vol.%, the coating porosity decreased from 5.6% to 0.2% only by using N2 accelerating gas. Remarkable work hardening induced by impact of the shot peening particles was detected.

In this study, ethylene methacrylic acid copolymer (EMAA) was used as the matrix to produce EMAA/Al2O3 and EMAA/NiCr composite coatings from dry-blended powder mixtures. This work was conducted to determine processing concerns when using similar sized reinforcement particles of different density in a flame-spray process. This work has utility for applications that require a reduction in mechanical wear and/or to confer upon a polymeric deposit a certain functional property by the introduction of value-added powder. Free-standing coatings were produced to test the mechanical properties of the sprayed deposit. The effects of the filler content on the secant modulus, yield stress, and tensile strength are discussed. The differences in deposition efficiencies among the EMAA, Al2O3, and NiCr are highlighted with respect to particle size and density.

Three different coatings were deposited using the Detonation Gun Spraying (DGS) technology from steel powders alone, and steel powers mixed with Fe3C and SiC particles, respectively. The microstructural characteristics of these coatings were examined and the hardness of each type of coating was studied. The morphology and structure of the feedstock powders were affected by the exposure to high temperature during the spraying process and rapid solidification of steel powders that resulted in the formation of an amorphous structure. The unreinforced steel coating had the highest hardness among the three types of coatings, possibly due to a higher degree of amorphization in the coating compared to the other two samples. The microstructural observation confirmed the formation of dense coatings with a layered structure with good connectivity between layers with minimum defects and porosities in the interfacial regions.

Beams of a hardenable aluminium foam were coated using electric arc spraying. AlSi6 and XCr13 were sprayed using compressed air or nitrogen. Subsequently the aluminium foam – coating - composites were post treated. The post treatment comprised of a heat treatment, suitable for hardening of the foam, grinding, shot-peening and / or sealing of the coating. Young’s moduli of the composites were non-destructively measured by resonant frequency. The dynamic properties of the composites were investigated by four-point-bending fatigue tests. The influence of the different post treatments on the bending stiffness and the fatigue behaviour was analysed using a statistical approach.

A high velocity oxy-fuel spraying system using liquid fuel (HVOLF) has produced Stellite 6 (CoCrWC) and NiCoCrAlY coatings from gas atomised powders of both alloys. Comparative coatings were prepared by weld 0verlay (Stellite 6) and vacuum plasma spraying (VPS) of NiCoCrAlY. The original powders and coatings were characterised by Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD). The presence or absence of cored dendritic microstructures in etched surfaces was used to interpret the degree of melting which took place during spraying, i.e. >80% in VPS and <20% in HVOLF. Low levels of oxide were formed in HVOLF coatings due to the reduced level of thermal transfer during the short heating cycle involved in spraying. For the same reason less melting occurred which permitted sufficient plastic deformation of the solid fraction to occur, reducing voidage between particles and then allowing the liquid fraction to weld them together. This pattern of short cycle heating with both NiCoCrAlY and Stellite 6 particles influenced second phase formation. In NiCoCrAlY coatings the β (Co Ni Al) phase remained as relatively coarse precipitates in the as - sprayed condition whilst in Stellite 6 little carbide eutectic formed. HVOLF spraying can produce coatings with different hardness values when compared with VPS coatings and weld overlays. This may widen the range of coating applications as well as reduce costs.

The cermet coatings constituted by a metallic phase mixed with a ceramic one allows obtaining coating properties with a wide range of variations. This is particularly interesting for graded coatings produced by APS technique with two different injection ports devoted to each kind of powder. By monitoring the powder feed rates independently it is relatively easy to obtain the requested composition and also the gradient as a function of the coating thickness. In the present work 600 ìm graded coatings were produced with 5 or 6 layers, each one with a specific composition. The hardness properties of the whole coating were evaluated by the Knoop technique. Also each layer was produced separately and characterized as well. These coatings were devoted to thermo-mechanical applications. In this work the metallic phase is always NiCr 80/20 wt% and the ceramic phase is zirconia doped with yttria or ceria as well as Al 2 TiO 5 . The powders used as a standard have a size range included between 40 and 10 µm. Smaller size ranges were evaluated to produce NiCr / ZrO 2 , Y 2 O 3 graded coatings and were compared to those obtained with the standard powder. In this last part a post heat treatment of the coating was evaluated against the mechanical properties.

Amorphous PEEK coating was prepared on Al substrate, employing flame spraying technology. The amorphous coating was subjected to annealing treatments under different conditions. Both differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD) analysis revealed that the isothermally treated coating exhibited semi-crystalline structure. Coexistence of double crystal entities in semi-crystalline PEEK coating was deduced from the results obtained by DSC and WAXD measurements. Annealing temperature and holding time under this temperature affect the morphology of the minor crystal entity which is metastable. The mechanical properties of the isothermally treated coating were investigated considering coating microhardness and friction and wear properties. The variations of the coating mechanical properties were correlated with the modifications in the coating structure induced by the different annealing conditions.

Nanostructured and conventional titania (TiO 2 ) powders were thermally sprayed using APS and HVOF processes. The fatigue and mechanical properties of the coatings investigated. Coatings were characterized using SEM to investigate the microstructural features and Vickers indentation to determine the hardness. SEM analyses were also carried out on the fracture surfaces of fatigue-tested samples to assess crack nucleation and to study the mechanisms of deformations. The fatigue strength of coatings deposited onto low-carbon steel (AISI 1018) showed that the nanostructured titania coated specimens exhibited significantly higher fatigue strength compared to the conventional titania

Alumina and stabilized Zirconia were plasma sprayed in air using the water-stabilized plasma torch. In the case of Alumina two different stand-off distances were applied at spraying. Nd-YAG laser was then used for additional treatment of plasma sprayed coatings. The laser was maintained in a quasi-continual regime and defocused from the surface to increase the treated coating's area. Energy density was varied together with the laser scanning velocity to ensure variance in thermal history of the treated surfaces. Microhardness, surface roughness and slurry abrasion resistance (SAR) were measured before and after the laser treatment. Results vary in dependence on the laser treatment's parameters. When the treatment results in substantial changes of the structure (up to a complete re-melting of the surface), enhancement of all measured properties was proven. It is demonstrated that the extent of change of mechanical properties can be correlated with optical properties of coating materials at the laser wavelength. Microstructural aspects of the laser treatment are discussed as well, especially at the boundary between the laser-annealed layer and the basic coating's microstructure. It is pointed out that laser overheating due to use of an extremely high energy density can cause delaminating of the coatings.

Indentation tests were provided with various applied loads and indentors’ profiles to determine the mechanical properties of selected HVOF coatings. The four well-known wear resistant coatings, WC-17%Co, Cr 3 C 2 -25%NiCr, NiCrSiB and AISI 316L, sprayed by TAFA JP-5000, were tested. Besides the common indentation tests (e.g. coatings surface hardness and microhardness), the indentation fracture toughness (IFT) and Young modulus of elasticity (E) were measured using Vickers and Knoops indentors profiles, resp. From the Vickers indentation results, the IFT was evaluated in terms of 18 models for KIc determination. The big differences between results of used models were found. For evaluation of E, the Knoop indentation in three different orientations was used. The measurement results show the anisotropic behavior of sprayed coatings. Based on the measured data, the relation between coatings properties with respect to the coating unique microstructure was proved.

Cold spraying is quite a new process, which is an effective method to deposit dense and pure coatings. The aim of this study was to investigate microstructures and mechanical properties (hardness and adhesion) of the cold sprayed coatings. The coating materials were aluminium, copper, nickel and zinc. The substrate materials were carbon steel and copper. Influence of heat treatments on mechanical properties was studied, especially different heat treatment times and temperatures. The hardness of the cold sprayed coatings was higher than that thermally sprayed coatings and bulk materials. During heat treatment, the hardness of the cold sprayed coatings decreased and the ductility increased. Corrosion resistance of cold sprayed coatings was also studied. The corrosion resistance was tested with salt spray (fog) testing and open cell potential measurements. The corrosion tests showed some through-porosity but some parts of the cold sprayed coatings appeared to be fully dense, which showed their potential for corrosion protection.

Cold sprayed copper coatings have been widely studied but the effect of substrate properties and spraying conditions on the bond strength still needs further investigations. Using nanoindentation, it is possible to compare the effect of spray parameters on the change in hardness of the coating due to the difference in size distribution of the powder. Deposition of 2 copper powders on aluminium and Ta6V substrates has been done at different stagnation temperatures and pressures using nitrogen as process gas. Hardness profiles show how the speed of the particles induces shot peening effects on the surface. The interaction between the hot gas jet and the surface may modify the hardness profiles. The effect on the substrate hardness has also been investigated.

HVOF thermal spraying has been developed to deposit dense ceramic coatings with improved protective properties for various applications. Even though HVOF coatings are much denser as compared to ordinary plasma sprayed coatings, the coating properties are inferior as compared to bulk ceramics because of pores and microcracks, which influence adversely the coating properties, i.e. toughness, hardness and wear resistance. One strategy to improve the properties of the coatings is to decrease the grain size of the ceramic phase and to add toughening elements to the microstructure. Nanocrystalline coatings have been found to offer better thermal shock resistance, lower thermal conductivity and better wear resistance than their conventional counterparts. In this paper we describe the development of nanocrystalline ceramic composite coatings, where the grain size of ceramic has been decreased and a few percents of alloying element has been added in order to toughen the coating. Dense nanostructured alumina coatings alloyed with Ni and ZrO 2 nanosized particles were manufactured by HVOF spraying by using HV2000 spray gun. Mechanical properties, especially elastic modulus and relative fracture toughness were studied. Used techniques were instrumented nanoindentation and KIC evaluation. As a result coatings with nearly 100% improvements in relative fracture toughness were produced for nanoreinforced alumina composite coating. Results are compared with the microstructure, hardness and abrasive wear resistance of the coatings.

In laser-assisted air plasma spraying (LAAPS), a laser beam interacts simultaneously with the coating surface during plasma spraying in order to increase the coating surface temperature and possibly remelt the coating surface. As a result, the microstructure is partially densified and macrocracks can be inhibited. In this paper, LAAPS was performed to improve the mechanical properties of ZrO 2 – 8 wt.% Y 2 O 3 coatings. The coating microstructure was characterized by optical microscopy, SEM and X-ray diffraction. The mechanical characterization was done by hardness measurements, thermal shock resistance and erosive wear tests. Results showed that laser assistance may induce: (1) a decrease of the amount of microcracks and interlamellar pores, (2) a columnar dendritic structure in the coating splats and (3) an improvement of the thermal shock resistance. LAAPS did not affect the hardness or the erosive wear resistance of yttria partially stabilized zirconia coatings.

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, Al 2 O 3 -TiO 2 , Al 2 O 3 , and Cr 2 O 3 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.

Twelve commercially available WC-Co powders with different average carbide sizes (0.2, 2, and 6 µm) and cobalt contents (8, 12, 17 and 25 wt.%) were sprayed on carbon steel substrates using High Velocity Oxy-Fuel (HVOF) spraying Characterization of the coatings showed that the average carbide sizes and carbide volume contents in the coatings were lower than those of feedstock powders. Hardness and fracture toughness of the coatings were investigated using indentation techniques. Young’s modulus was measured by an ultrasonic technique. The hardness and Young’s modulus decreased with increasing cobalt content, while fracture toughness slightly increased. The effect of carbide size on the hardness showed no specific trend. These behaviors were discussed with the help of microstructure observations of the coatings by scanning electron microscopy, X-ray diffraction and chemical analysis. Using an improved HVOF process with a gas shroud could result in less decomposition of the powder and higher fracture toughness.

Elastic properties of 20 and 40 µm thick deposits of yttria fully stabilized zirconia (YSZ), fabricated by vacuum plasma spraying (VPS) and air plasma spraying (APS) with modified injection system were investigated at room temperature by nanoindentation, and 4 point flexion test and at 800°C by 4 point bend test. The data was correlated with structural analysis of different YSZ deposits. At room temperature, E values of VPS YSZ deposit decreased from 237 ± 6 to 105 ± 5 GPa on increasing nanoindentation load from 1 mN to 450 mN. The results indicated change from intrinsic to defect-dependent E values with increasing load. Despite lower porosity of VPS deposit (6 ± 1%) compared to that of APS (24 ± 1%), E values, measured by flexion test at room temperature and at 800°C, of former were 35 ± 1 and 16 ± 1 and of latter were 55 ± 1 and 18 ± 1 GPa respectively. The interlamellar sliding, parallel to applied load, was considered as prime reason of lower rigidity of deposits.

Mechanical properties of thermal-sprayed ceramic coatings were investigated. Al 2 O 3 and Y 2 O 3 -stabilized ZrO 2 (YSZ) coatings were deposited on plate substrates. Stainless steel plates and aluminum plates, of different thermal expansion coefficients, were used as substrates. The coatings were prepared at two different thicknesses. During deposition of each sample, the history of substrate temperature was recorded. Four-point bending tests were carried out, while strains at the coating surface and the substrate surface were measured with strain gages. The apparent Young's modulus of the coating was determined using the composite beam theory. In addition, the rupture strain of the coating was measured by three-point bending test. The relationship between the results of these tests and the temperature of each substrate during deposition is discussed.