Key Engineering Materials Vols. 592-593

Abstract: Fluidized bed technology has been used for surface engineering applications in the deposition of hard and/or corrosion resistant layers e.g. aluminizing, chromizing, nitriding, carburizing, boronizing. In the present paper we used fluidized bed technology (FBT) to deposit silicide coatings on steels. The silicide coatings are well known for their excellent corrosion resistance. Siliconizing in fluidized bed is a promising method to improve the corrosion resistance of steel without altering its other properties. The asproduced silicide coatings are uniform all over the steel substrate, with good thickness, adequate adherence and consisted only from the phase FeSiC.

Abstract: The widespread use of thermal barrier coatings (TBC) in gas turbines stresses the importance of accurate life prediction models for TBCs. During service, the TBC may fail due to thermal fatigue or through the formation of thermally grown oxides (TGOs). The current paper presents a Thermo-Calc/Dictra-based approach to life prediction of isothermally oxidised atmospheric plasma sprayed (APS) TBCs. The β-phase depletion of the coating was predicted and compared to life prediction criteria based on TGO thickness and Al content in the coating. All tried life models underestimated the life of the coating where the β-depletion-based model was the most conservative.

Abstract: The structure of interest is a thin, metallic coating of fcc copper, of thickness down to a few nanometers only, resting on a stiffer substrate. The elastic and plastic properties of the thin coating using nanoindentation under different geometrical features such as size of the indenter and coating thickness are determined. The force-displacement curve is monitored during indentation and the precise conditions for the occurrence of so called pop-ins during loading are investigated. To simulate the nanoindentation process, a molecular dynamics approach is used, where an infinitely stiff indenter is pushed into the coating under displacement control. The coating is modeled as a thin rectangular plate, with the bottom atom layers locked from movement, simulating the stiffer substrate, and periodic boundary conditions in the plane of the plate are applied.

Abstract: Low pressure plasma spraying (LPPS) is one of the most advanced processes of an MCrAlY bond coat formation. It ensures the forming of metallic coatings free of oxides which can act as an bond coat for thermal barrier coatings used, among others, for protection of turbine blade surface. The paper presents results of tests into microstructure of coatings made from AMDRY 997 powder on the base of type Inconel 617 heat-resistant nickel alloy. The tests were carried out using light and scanning electron microscopy. Evaluated was the influence of spraying conditions on microstructure, porosity and thickness of the obtained coating. Test results show that the LPPS method allows to form coatings of low porosity and free of oxides which can be used as an bond coat in thermal barrier coatings.

Abstract: The aims of this study are to fabricate Ti/APC-2 hybrid composite laminates with and without (W/WO) nanoparticles and investigate the mechanical properties of laminates with single-edged cracks due to both tensile and cyclic tests. The mechanical properties such as ultimate tensile strength and longitudinal stiffness of original composite laminates W/WO nanoparticles were first obtained from the static tensile tests. However, the load-displacement diagrams were plotted for the crack laminates. The constant stress amplitude tension-tension cyclic tests were conducted to receive the S-N curves and fatigue data. The ultimate strengths for both Ti/APC-2 composite laminates W/WO nanoparticles were very close at varied crack length. Ti/APC-2 cross-ply nanocomposite laminates had better fatigue resistance than that of laminates without nanoparticles. The longer the crack length is, the more their properties are reduced. Also, the values of fracture toughness of both hybrid cracked laminates W/WO nanoparticles were obtained by rule of mixtures and found acceptable. Finally, in predicting crack growth rate and residual life, instead of commonly used Paris Law for metals, the modified method was adopted for hybrid cracked laminates. The prediction is not satisfactorily acceptable, even if most results are in good agreement with empirical data.

Abstract: The present paper is focused on scanning electron microscopy investigation of surface relief developed in cyclically strained specimens at high temperature. Symmetrical fatigue tests without hold times and with tensile or compressive hold times were used in strain control regime. The gauge length of specimens was analyzed after cyclic straining in a wide range of total strain amplitudes. Experimental temperature was 800 °C and selected hold time was 10 minutes.Surface relief is developed during the cyclic straining in localized plastic strain areas. Developed surface relief strongly depends on the type of fatigue test and a value of total strain amplitude. Well-developed surface persistent slip markings were observed after cyclic loading without hold times. Another group of observed slip markings with perpendicular orientation to stress axis exhibits irregular and wavy morphology. Similar markings were also observed on specimen surfaces after fatigue tests with tensile hold times as well as compressive hold times. Third group, named imperfect persistent slip markings, was observed after cyclic straining with tensile holds. In some suitably oriented grains, areas with high density of well-developed markings with irregular morphology were found.

Abstract: This paper describes the effect of solution treatment on the fatigue properties of AlSi9Cu3 cast alloy. The heat treatment consisted of a solution treatment at two different temperatures 515°C and 525°C, a holding time of 4 hours; water quenching at 40°C and natural aging at room temperature for 24 hours. Thus prepared samples were subjected to fatigue test with a rotating bending loading (testing machine ROTOFLEX operating at 30 Hz, load ratio R = -1). The fatigue fracture surfaces were observed using a scanning electron microscope (SEM) after the fatigue test. The results showed that the existence of casting defects (8.4 % of micro-shrinkage) has considerable influence on fatigue properties and can be considered as fatigue crack initiators in what leads to final fatigue damage. Apart from cast defects, the morphology of eutectic silicon and intermetallic phases (Fe- and Cu-rich phases) are also important factors which have an influence on the fatigue properties of Al-Si cast components. The solution treatment used (at 525°C/4hours) has increased fatigue properties (the fatigue lifetime increased from 49 to 76 MPa), thanks to Si particles, morphology changes, and cast defects area reduction as well as reduction Fe-rich phases.

Abstract: The duplex treatment consisted of a plasma nitriding at 470 °C for 4 h and subsequent coating with TiN layer was applied on AISI 304L stainless steel. The article is concerned to a study of the chemical composition and mechanical properties of duplex system. GDOES method, laser confocal microscopy, nanohardness and indentation test were employed to characterize the chemical composition, depth profiles, surface morphology, hardness, adhesion. The results show that the duplex surface system possesses a desirable combination of properties especially hardness. Adhesion of PVD coating was increased on nitrided surface.

Abstract: Local defects, as micro-fractures, precipitates and other material inhomogeneities in solar cell structure, evidently modify electrical and photoelectrical behavior of the latter. To improve the efficiency and lifetime of existing solar cells, it is important to localize these defects which influence the p-n properties, and assign them corresponding electrical characteristics. Although the electric breakdown can be evident in current-voltage plot, the localization of local defects in the sample, that generate this breakdown, is not so easy task. It has to be done by microscopic investigations and measurement of light emission from defects under electrical bias conditions. Thus to contribute to this end, the structure of defects is microscopically investigated and consequently, the defects can be removed by focused ion beam milling. The experimental results obtained from samples before and after milling are also discussed.

Abstract: In recent years, particle reinforced composites are widely used due their mechanical properties as construction materials, high-performance engineering materials or protective organic coatings. The paper was mainly focused on the estimating of the interactions of the micro-crack and the particles in the particulate polymer composites. A non-linear material behavior of the matrix was obtained from the experiment and it was used to investigation by means of the finite element method - using ANSYS software. A two-dimensional numerical model was developed and a micro-crack propagation direction was calculated based on the assumption of the linear elastic fracture mechanics. The results indicated that the presence of the interphase between particle and matrix can improve the fracture toughness of the polymer particle composites through debonding process. The paper can contribute to a better understanding of the behavior and failure of the composites with the polymer matrix reinforced by the rigid particles.