Cyclic, mechanical fatigue testing of coated materials has increased with the wider use of thermal spray coatings on components experiencing fatigue loading. Fatigue testing of coated specimens presents all of the difficulties associated with fatigue testing of uncoated specimens and several difficulties that do not arise when testing uncoated specimens. A summary of fatigue test methods and test specimen geometries for both coated and uncoated specimens is presented. Issues of specimen standardization, geometry, substrate preparation, and post-spray surface finishing are discussed. Several specimen configurations are described.

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.

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.

Light weight design offers a lot of interesting manufacturing and operation aspects in mechanical engineering, e.g. concerning production and material cost or energy consumption. By means of protective coatings, light metal components can also be used under extreme wear and corrosion conditions. Of tribological interest are coating systems with low friction and wear coefficients. If traditional liquid lubricants cannot be used, the tribological functions must be taken over by material surfaces with solid lubricant capability. Very promising tribological results under dry and mixed friction are obtained by thermally sprayed TiO 2 coatings. The paper presents a general overview about the tribological and mechanical properties of APS and HVOF sprayed TiO 2 coatings on different light metal materials.

Fatigue and delamination resistance of overlay coatings is critical to their performance in tribological applications involving Hertzian loading. This study addresses the influence of coating thickness and contact stress fields on the fatigue/delamination resistance of thermal spray (WC-12%Co) coatings, deposited by a JP-5000 system. These coatings were deposited in three different thicknesses on the surface of 440-C steel substrate cones. Fatigue tests were conducted using a modified four-ball machine under various tribological conditions of contact stress and configuration. Results are discussed in terms of Hertzian contact stress fields, coating thickness and Scanning Electron Microscope (SEM) observations to comprehend the performance and ascertain the fatigue failure modes of coated rolling elements. These results indicate that by appropriate control of coating thickness and tribological conditions, it is possible to achieve a fatigue life in excess of 70 million stress cycles without failure. Further studies in this field can thus trigger an area of new novel applications of thermal spray coatings.

To improve the bonding strength of HA coating, several HA-based composite coatings (HA/Ti, HA/ZrO 2 HA/ZrO 2 SiO 2 and HA/NiCr composite coatings) have been fabricated via atmospheric plasma spraying. The bonding strengths of fabricated specimens were tested by ASTM C-633 method. The bioactivity of composite coatings was evaluated by examining carbonate-containing apatite formation on their surfaces in simulated body fluid (SBF). In vitro cell cultures were carried out to examine the biocompatibihty of composite coatings. The results obtained revealed that the addition of metal or ceramics in HA improved the bonding strength of coating significantly except HA/ZrO 2 -SiO 2 composite coating. In SBF test, all of these four coatings were covered by carbonate-containing apatite after immersed in SBF, indicating good bioactivity for composite coatings. The results of cell cultures produced the testimony of excellent biocompatibihty for the coatings except that HA/NiCr composite coating possessed cytotoxicity. By comprehensive survey of bonding strength, bioactivity and biocompatibihty, HA/Ti and HA/ZrO 2 composite coatings were candidates of prospective biocoatings.

Fatigue strength and fracture mechanism of a medium carbon steel having carbon content of 0.35%C with gas flame thermally sprayed Co-based alloy coatings were investigated by rotating bending tests. After fusing treatment, machining was done to make three kinds of specimens having 0.3mm, 0.5mm and 1.0mm in coating thickness. The fatigue strength of all coated specimens was much higher than that of the substrate and that of the grit blasted ones. Especially, it was found that the fatigue strength of the specimens with 1.0mm coating was remarkably higher compared to those with 0.3mm and 0.5mm coatings. That is, fatigue characteristics depend on coating thickness, and fatigue strength increases with the increase of coating thickness. The result showed that at lower stress levels, the fatigue cracks were initiated only inside the substrate of 0.3mm and 0.5mm coated specimens (Internal failure in the substrate). At higher stress levels the fatigue cracks were initiated at the coating layer, originated from the porosity located in coating layer of all coated specimens (Coated layer failure). But no fracture mode transition was noticed for the case of 1.0mm coated specimen. The cause of the fracture mode transition depending on the coating thickness was discussed on the basis of the results from calculation of the stress at the location where the fatigue fracture was initiated.

In recent years, the thermal spray technique has emerged as the most useful method for developing a wide variety of coatings which enhance the performance and durability of engineering components exposed to diverse forms of wear. Among the thermal spray techniques, detonation spray coating (DSC) has retained its position as one of the best available techniques for obtaining dense, wear-resistant coatings. Notwithstanding the advantages of the DSC technology over other thermal spray variants, the understanding of the fundamental aspects of this technology is still extremely limited. In view of the above, a major programme has been undertaken in this laboratory to assess the parametric impact of the key DSC process variables (oxy-fuel ratio, spray distance, powder feed rate and shot frequency) on the mechanism of coating formation and the properties of the resulting coating. As a part of the above exercise, the key DSC process variables have been varied systematically employing a statistical design and the properties of the WC-12Co coatings so obtained have been evaluated. The results of such a study are presented in this paper. In particular, it has been demonstrated that useful conclusions regarding the influence of process parameters on the properties of the WC-12Co coating cannot be reached unless the scatter in the experimentally measured coating property data is also simultaneously taken into account.

In a fusion reactor (i.e. ITER), the use of a ceramic coating on structural material (SS3I6LN-IG) has been considered as electrical insulator. Al 2 O 3 including TiO 2 (Al 2 O 3 -TiO 2 ) is one of most promising materials as coating from a point of high electrical resistivity and so on. However, crack and peeling occur by difference of thermal expansion between substrate material and coating material. Therefore, 80Ni-20Cr was selected as the undercoating between SS316LN-IG substrate and Al 2 O 3 -TiO 2 coating. In this characterization, Al 2 O 3 -3%TiO 2 and Al 2 O 3 -13%TiO 2 were used as ceramic coating material. 80Ni-20Cr undercoating was fabricated by atmospheric plasma spray method. The thickness of 80Ni-20Cr was 50µm. Al 2 O 3 -3%TiO 2 and Al 2 O 3 -13%TiO 2 were fabricated by atmospheric plasma spray method. Thickness of these ceramic coatings are 200 and 500µm. From the results of out-of-pile test, it was clear that Al 2 O 3 -3%TiO 2 and Al 2 O 3 -13%TiO 2 coating had a good mechanical and electrical properties.

Yttria partially stabilized zirconia (YSZ) was atmosphere plasma sprayed on to mild steel substrates. The spray parameters were varied to determine their effects on the elastic modulus of the coating. The parameters were (i) continuous spray vs. paused spray, (ii) bond coat vs. no bond coat, and (iii) cooled vs. not-cooled. The elastic modulus was measured using laser ultrasonics and Knoop Indentation. Using indentation, the continuous/ paused spray exhibited the greatest effect with the paused spray samples having a lower elastic modulus value regardless of the condition of the other parameters. The other parameters did not reveal any statistically significant effect. The laser ultrasonics measurements showed that cooling and no-cooling had a greater effect on elastic modulus, with the other parameters having little effect. Laser ultrasonics detected parameters whose influence can be detected near the surface (in this work the cooling and no-cooling), but did not detect those parameters that influence the properties throughout the coating. Indentation detected the parameters that influence the properties throughout the coating, in this work continuous and paused spraying.