Olga Bláhová

Mechanical properties of thin film–substrate systems

Abstract This paper is devoted to a study of the mechanical properties of thin film–substrate systems using indentation methods. The magnitude of the load used for indentation, the properties of the system thin film–substrate and the thickness of the thin film, determine the type of material properties which can be analyzed such as microhardness (nanohardness), adhesive and cohesive behavior, fracture properties and wear resistance. Nanoindentor Shimadzu DUH2, scratch tester CSEM Revetest and common hardness tester Ernst were used for the investigation of mechanical properties. Useful indentation methods and the magnitudes of the load are discussed for each mechanical property.

The Instrumented Indentation Study of HVOF-Sprayed Hardmetal Coatings

Elastic-plastic properties, namely, hardness and Young’s modulus, of four HVOF-sprayed hardmetal coatings were measured by instrumented indentation using Oliver-Pharr method Nanoindenter XP MTS with a continuous stiffness measurement (CSM) module. The results show that with sufficient number of CSM measurements, one can distinguish between indents made in the hard particles and indents made in the binder material. This can be accomplished by analyzing the plots of hardness and Young’s modulus versus load (or versus indentation depth). Further development of the dependence curves enables the load (or indentation depth) to be set to correspond to the point of transition from a single structure component to the composite material and to determine the properties of both. Comparison of results of CSM measurement with the results of single indentation measurement at a defined load reveals a new perspective on the origin of the indentation size effect in hardmetal coatings. The measurements show that the increase in both the hardness and Young’s modulus with decreasing load is caused mainly by the predominant influence of hard particles in the coatings.

The Influence of Spraying Parameters on Stresses and Mechanical Properties of HVOF-Sprayed Co-Cr-W-C Coatings

Stellite 6 Co-Cr-W-C coatings were sprayed by HVOF while systematically varying the spraying parameters, namely the equivalent ratio and combustion pressure. During spraying, the in-flight particle temperature and velocity were measured. Deposition, thermal and residual stresses were determined by in-situ curvature monitoring of the sprayed samples. Youngs moduli and hardness of the coatings were determined by instrumented indentation. The relationship between spraying parameters, in-flight particle characteristics and mechanical properties is discussed.

Deterioration of Local Mechanical Properties of HVOF-Sprayed Stellite 6 after Exposure to High-Temperature Corrosion

Coating properties determine its behavior in operation. The simulation of future operational conditions is therefore the best quality test. The evaluation during operation is usually not possible to perform, and the coatings are therefore frequently characterized by their physical or mechanical properties. This text deals with the high temperature corrosion of HVOF sprayed Stellite 6 coating and with changes of its local mechanical properties before and after the corrosion testing. High temperature corrosion is defined as a corrosion in the presence of molten salts. In this case, the mixture of salts in composition of 59% Na2(SO)4 with 34.5% KCl and 6.5% NaCl was used. Two exposure temperatures 525 °C and 575 °C were selected and the tests for both temperatures were performed in the time interval of 168h in the autoclave. The coating with salt mixture layer was analyzed using scanning electron microscopy and nanoindentation. The high temperature resistance of Stellite 6 coating was evaluated according to the changes in the coating surface and by the occurrence of individual phases formed on the coating surface during the test. Generally, it can be said that the Stellite 6 alloys deposited by HVOF technology show selective oxidation under the salt film. This fact was also proved in this study. Furthermore, the nanoindentation measurements of Stellite 6 coating were performed before and after the corrosion testing. These measurements were used to evaluate the change of local mechanical coating properties.

Mechanical Properties of HVOF Sprayed, Flame and Laser Remelted NiCrBSi Coatings

The influence of thermal post-treatment by means of flame and laser energy on the mechanical properties of NiCrBSi coating was studied. The evaluation was done in terms of microstructure, surface hardness, microhardness and instrumented indentation. The microstructure evaluation showed an increase of coatings inner cohesion, together with the creation of metallurgical bond between the coating and the substrate material. In the the case of laser remelted coating, the creation of thick transition layer responsible for lower measured microhardness and hardness value was proved.

Influence of Hydrogen Content on Microstructure and Mechanical Properties of Zr1Nb Fuel Cladding after High-Temperature Oxidation

The aim of this study is to investigate the influence of hydrogen on the microstructure and mechanical properties of Zr1Nb fuel cladding after high-temperature oxidation. As-received or pre-hydrided materials were tested. The influence of different cooling rates was examined as well. The microstructure was observed using of light microscopy. Oxygen distribution was measured using X-ray microanalysis. Local mechanical properties were determined by the microhardness and nanohardness measurements. Ring compression testing (RCT) was employed with the aim to obtain the macroscopic mechanical properties. Fractographic analysis was performed after the RCT. The experimental results confirmed that hydrogen as well as the cooling rate substantially influenced the microstructure and affected both local and macroscopic mechanical properties.

Influence of Hot Corrosion on Local Mechanical Properties of HVOF Sprayed Coating Based on NiCrBSi Alloy

Ongoing increase in demands on efficiency of power plants and other facilities leads to increased interest of new progressive materials and technologies. One of the modern methods which lead to enhancement of surface properties is application of coatings on surface of components composed of less quality materials. Commonly used methods protecting components are based on some form of heat treatment. The current pressure on increasing operating temperatures for enhanced performance of steam turbines caused elevation of operating temperature at limit of the applicability of commonly used protections. From this reasons the demand for using an alternative technologies which would provide such a desired protection rises rapidly. One of the key areas of protection in such environment is protection against hot temperature corrosion. Possible solution can be found in application of coatings based on alloys and cermets prepared by HVOF technology. This paper examines local mechanical and microstructural properties of NiCrBSi coating after exposition to extremely severe hot corrosion environment. Furthermore, the nanoindentation measurements of NiCrBSi coating were performed before and after the corrosion test. In this case the mixture of salts composed from 59% Na2(SO)4 with 34.5% KCl and 6.5% NaCl was used. Temperature of test was set on 525°C and 575°C. Duration of exposition to hot corrosion environment was 168 hours in autoclave.

The Variation of Mechanical Properties of WC-Based HVOF Sprayed Coatings with Respect to the Co Content

The indentation methods (HR15N, HV0.3, HIT, EIT) were used to evaluate differences between the WC-based coatings with 12, 17 and 25% of Co binder. The two sets of WC-12%Co coatings with two different sets of parameters were sprayed to evaluate the influence of spraying parameters. The measured mechanical characteristic were correlated to the to the wear resistance of the coatings evaluated by dry sand/rubber wheel test according to ASTM G-65 and pin-on disc according to ASTM G-99. The measured results showed that there is almost no difference between the abrasive wear resistance of WC-Co coating with 12 and 17% of Co binder, while the wear of coating with 25% of Co binder is significantly higher. The importance of the spraying parameters on the WC-12%Co coatings properties has been found to be comparable to the importance of binder content influence.

Local Mechanical Properties of Au Thin Films on Polyethylene

Mechanical properties and surface morphology of metallized and grafted PE samples were studied upon their surface modification (plasma exposure and grafting) and subsequent metallization (Au sputtering).

Gold Nanolayers Prepared on Poly(ethyleneterephtalate)

Ablation, water etching and gold coating were studied on poly(ethyleneterephtalate) (PET) exposed to DC Ar plasma for 240 s at 8.3 W power. Au layers were sputtered on pristine and modified PET and their adhesion and topography were investigated. The roughness and changes of topography after plasma treatment, subsequent water etching and gold coating were followed using AFM microscopy. The thicknesses of ablated layer and water dissolved layer were determined using gravimetry. A nanoindentor was used to perform microstratch tests of sputtered layers. Water dissolving of thin layer after plasma treatment was confirmed by FTIR spectroscopy. We have found that under the present experimental conditions ca 30 nm thick layer of PET is plasma ablated. The surface topography changes dramatically and surface roughness increases. Another ca 16 nm thick layer was removed under present laboratory conditions after 24hour water etching. Subsequent coating with 50 nm thick gold layer increases surface roughness in all cases of surface modification.