Volume 57, Issue 5

TiAlN films with thicknesses of 250, 500 and 750 nm were deposited on 4140 steel using the reactive direct current co-unbalanced magnetron sputtering method. The effects of the film thickness on the microstructure were revealed using a field emission scanning electron microscope, an image analyzer and X-ray diffraction. The results showed that grain size apparently increased when the film was at greater thicknesses whereas porosity, lattice strain and dislocation density decreased. Meanwhile, the results of anodic polarization tests in air-saturated 3.5 wt.-% NaCl solution at pH levels of 2, 7 and 10 and at 25 °C showed lower corrosion potential in thicker film, attributed to a lower ratio of grain boundary area to individual grain area. However, a more stable passive film with higher pitting potential was formed. By analyzing using X-ray absorption spectromicroscopy, oxidation of Ti into TiO 2 was found on the corroded surface of TiAlN film.

To improve the biocompatibility and operational safety of titanium implants made of Ti6Al4V alloy, anodizing is applied. The anodizing process allows adjustment of the highly biocompatible oxide level on the metallic surface. However, little attention is paid to the influence of the layer thickness on the considered material corrosion resistance. Electrochemical polarization and open circuit potential tests as well as scanning electron microscope, laser confocal microscope and energy-dispersive X-ray studies were performed on as-received samples. Taking all experimental investigations into account, the following conclusions can be formulated: 1. Anodizing of Ti6Al4V alloy results in improvement of its corrosive characteristics. 2. In general, the higher the anodizing voltage is, the worse the anticorrosive properties exhibited by the material. 3. Despite the observed corrosion characteristics, the titanium oxide films obtained by means of the anodizing technique can be severely corroded in 0.9 wt.-% NaCl aqueous solution.

Three dimensional porosity analysis was conducted using computed tomography for Al-Si alloy castings. Statistical analysis was performed to compare the porosities of the castings at high and low cooling rates. It was observed that the cooling rates strongly affect the formation of pores for both small and large pores. The incidence of small pores measuring 0.00003 mm 3 to 0.0004 mm 3 can be up to six times higher in castings formed at low cooling rates. For large pores measuring 300 μm to 360 μm, it was observed that lower cooling rates give rise to larger pores, which are known to be detrimental to castings as potential failure initiation sites.

Nanosilica modified potassium silicate conversion coatings were deposited on the surface of 2024 aluminum alloy by the dip immersion method, and the effect of the immersion time was studied on anticorrosion behavior of coatings. The corrosion behavior of coatings was examined by means of electrochemical impedance spectroscopy, potentiodynamic polarization and surface analyzing techniques. The coated samples showed a significant decrease in corrosion rate. The experimental results indicated that the increase in silica ratio led to an increasing in the corrosion resistance of aluminum. Immersion time in potassium silicate solution showed a significant effect on silicate conversion coating and higher corrosion resistance was obtained with 400 s immersion. This behavior can be related to increasing the silicate coating continuity which formed on the surface. The coating performance evaluated in acidic and basic NaCl solution as well as the results showed the corresponding stability of nanosilica modified silicate conversion coating in these solutions.

A corrosion exposure test was performed on a commercially available Haynes® 556® Fe-Ni-Cr-Co alloy sample to investigate its solid/gas reaction behavior in integrated coal gasification combined cycle pilot plant facilities affiliated with the Institute for Advanced Engineering (2.005 MPa and 160–300 °C). Thermodynamic Ellingham-Pourbaix stability diagrams were constructed and the post-exposure samples were examined ex-situ by morphological and microstructural SEM and EDS analyses on the external surfaces to obtain information on the corrosion scale and provide insight into the mechanism of the observed corrosion behavior in the piping materials connecting the particulate removal unit and water scrubber of the integrated coal gasification combined cycle pilot plant. Uniform material thinning was observed after 46 hours of operation, and a preliminary corrosion mechanism was suggested. The observed material wastage and corrosion behavior of the Haynes® 556® Fe-Ni-Cr-Co alloy sample cut off from the coal syngas IGCC plant were explained by the formation of discontinuous (complex) oxide phases and subsequent chlorine-induced active oxidation under the predominantly reducing environment encountered.

AlN plates were fabricated by hot pressing AlN-Y 2 O 3 and AlN-Y 2 O 3 -Al 2 O 3 powder mixtures at 1700–1900 °C using yttria and alumina (Al 2 O 3 particle sizes of 3 and 10 μm) powders as sintering additives. The physical and mechanical properties of the hot-pressed AlN ceramics were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The density, thermal conductivity, transverse rupture strength, and grain size were measured. The thermal conductivity of the hot–pressed AlN ceramics ranged between 83–92.7 W × (m × K) −1 and decreased with the addition of Al 2 O 3 , whereas the mechanical properties improved with the addition of Al 2 O 3 , which is known to have a beneficial effect of grain size refinement. The measured density values of 3.31 to 3.34 g × cm −3 were slightly higher than the theoretical density of 3.26 g × cm −3 . This result was attributed to the use of a carbon mold under N 2 atmosphere, which effectively removed oxygen atoms from the yttrium-aluminate phase that is expected to form at 1100 °C.

Kurzfassung In dieser Arbeit wurden Kopplungsfaktor und Lebensdauer von auf Federstahl mit Epoxykleber geklebten Piezoflächenwandlern unter Einflussgrößen wie Oberflächenrauigkeit und Klebschichtdicke mit einem Ansatz aus der Schwingungslehre experimentell untersucht. Verschiedene Proben mit variierten Klebschichtdicken wurden mit bestimmten Vorgangseinrichtungen erstellt und beklebt. Analytische Berechnungen wurden durchgeführt, um den Einfluss der Klebschichtdicke und Oberflächenrauigkeit auf den elektromechanischen Kopplungsfaktor sowie die Zuverlässigkeit zu betrachten. Der Einfluss der Klebschichtdicke auf den Kopplungsfaktor wurde dem der Fertigungstoleranzen und der Materialstreuung gegenübergestellt. Das Ermüdungsverhalten in Abhängigkeit von Klebschichtdicke wurde in Langzeitversuchen ausgewertet und verglichen. Die Ergebnisse zeigen keinen nennenswerten Einfluss der Klebschichtdicke auf Kopplungsfaktor und Lebensdauer bei Applikationen von Piezoflächenwandlern mit Epoxykleber.

A Ni-P coating with low phosphorus content has been deposited onto an AISI 1020 plain carbon steel. The effect of temperature on the structure of coating was determined by DSC and XRD analysis. To determine the effect of heat treatment on the hardness and wear properties, some of the coated specimens were heat treated at different temperatures as isothermal for 1 h. Pin-on-disc wear tests were carried out on the specimens under loads of 20, 40 and 60 N, respectively. It has been determined that hardness and wear resistance of electroless Ni-P coating increased with the heat treatment. Maximum hardness and wear resistance were obtained for samples heat treated at 400 °C.

Properties of steel can be enhanced by surface treatments such as coating. In some cases, further treatments such as nitriding can also be used in order to get even better results. In order to investigate the properties of nitride layer on hard Cr coated AISI 1010 steel, substrates were electroplated to form hard Cr coatings. Then hard Cr coatings were plasma nitrided at 700 °C for 3 h, 5 h and 7 h and nitride phases on the coatings were investigated by X-ray diffraction analysis. The layer thickness and surface properties of nitride films were investigated by scanning electron microscopy. The hardness and adhesion properties of Cr-N phases were examined using nano indentation and Daimler-Benz Rockwell C adhesion tests. The highest measured hardness was 24.1 GPa and all the three samples exhibited poor adhesion.

In order to investigate the different Cr-N formation characteristics of plasma nitrided hard Cr coatings, Cr was electrodeposited on AISI 1010 steel and plasma nitrided at 600, 700 and 800 °C for 3 h, 5 h and 7 h, respectively. Phase analyses of resulting Cr-N phases and grain size of Cr layer before and after nitriding process were calculated by X-ray diffraction analysis. Structure of nitride layer and its thickness were analyzed using scanning electron microscopy micrographs. The micrographs indicated that samples consisted of three distinctive layers. In order to distinguish these layers, scanning electron microscopy and energy dispersive spectroscopy (EDX) analysis were used as well as elemental distribution versus depth was plotted. The Cr-N diffusion was investigated by layer thickness measurements, and diffusion coefficient as well as activation energies were calculated.

A finite element model has been developed based on molecular mechanics to predict the mechanical properties of single wall carbon nanotubes (SWCNT). In addition, the mechanical properties of nanocomposite were investigated analytically and experimentally. This work consists of three parts; the first part is prediction of Young's modulus of single wall carbon nanotubes by molecular mechanics based finite element modeling. The second part describes the experimental work. The third part deals with the validation of the analytical part and the experimental work. The mechanical properties of SWCNT were obtained from FE. The mechanical properties of neat epoxy were experimentally determined. Both of them were used to estimate the mechanical properties of SWCNT/epoxy nanocomposite analytically. A comparison between the analytical and experimental results of SWCNT/epoxy nanocomposite has been done. The modeling and analysis of (SWCNT) were carried out using FEM by MATLAB and ANSYS software. However, in the experimental work the epoxy resin was modified by adding SWCNT with different ratio, i. e. 0, 0.1, 0.3, 0.5 and 0.7 wt.-%, respectively. The materials were characterized in tension to obtain the mechanical properties of SWCNT/epoxy nanocomposite experimentally. The results from the FE model were compared with the results in the literature and good agreement was achieved. The FE approach is a valuable tool for studying the mechanical behavior of carbon nanotubes. The results show that a nanotube weight percent of 0.3 wt.-% of SWCNT improves all mechanical properties such as tensile strength, modulus of elasticity and toughness. The weight percent greater than 0.5 wt.-% SWCNT should be avoided. To predict the mechanical properties of the composite materials analytically, it is worth considering the conventional rule of mixtures using the reasonable nanotube volume fractions and exact value of the efficiency parameter.

An effective joining between polypropylene (PP) and polybutylene terephthalate (PBT) is closely related to bonding between PP and PBT. The objective of this study is to improve the bonding between PBT and PP with a compatibilizer application between joints as tie-layer at various concentrations. Flexural strength, lap-shear strength and interlaminar shear strength of joined parts were determined to determine the adhesive bonding performance. The fracture behavior of the bonds was also investigated. It was found that using compatibilizers in a PP/PBT joining system improved the mechanical characteristics. Improved results were obtained with increasing ratios of compatibilizers in tie-layer and maximum mechanical results were achieved for 100 % compatibilizer usage in PP-PBT system.

In the present study, seam welding process parameters were optimized for joining 306 stainless steel plates. Welding pressure, welding speed and welding temperature combinations were carefully selected with the objective of producing a weld joint with maximum impact strength and hardness. Taguchi technique was applied for optimizing the selected welding parameters. The factors used in this study consisted of pressure, welding speed and welding temperature, each of which had three levels in the study. L 27 orthogonal array and corresponding levels were selected according to the aforementioned factors and experimental tests were performed. Signal-to-noise (S/N) ratio was used to evaluate the experimental results. The results indicate that the welding speed has the greatest influence on impact strength, followed by welding pressure and temperature. Experiments have also been conducted to validate the optimized parameters.

In this study, the AISI 304 steel specimens were boronized with nanoboron of the size of 10–50 nm and commercial Ekabor 3 powders (<1400 μm) at 950 °C to 1000 °C for 2 h and 4 h. Boronized steel specimens were characterized via SEM, microhardness and XRD analyses. Abrasive wear behavior of the specimens, boronized at different temperatures and treatment durations, were examined. The fixed ball micro-abrasion tests were carried out using the abrasive slurry, prepared with different SiC powder particle sizes on the boronized specimens at different rotational speeds. The specimens boronized with nanoboron powders exhibited a higher hardness and abrasive wear resistance than the samples boronized with the Ekabor 3 powders.

This study presents optimum buckling design of axially layered graded uniform columns. Firstly, characteristic equations for determining critical buckling loads for all end conditions are obtained using the transfer matrix method and for each case, square of this equation is selected as a fitness function. Due to the explicitly unavailable objective function for the critical buckling loads as a function of volume fraction and length of the column, initially, prescribed value is assumed for it and then the design variables satisfying constraints are determined. Different boundary conditions are considered. Among them, maximum increment up to 19 % of the critical buckling load is attained for the simply supported case. Finally, the strongest column configurations are determined.