Advanced Materials Research Vol. 445

Abstract: This paper focuses on the coupled structural/thermal response of a cylindrical part of multi-layered composite vessel. Uniform and parabolic temperature distributions are chosen for the structural loads. In this work, an analytical model is proposed in which the laminate composite is assumed to be an anisotropic purely elastic material. Assuming that the interface between the core and skin are perfectly bound, continuity conditions for the displacement and stress, the suggested analytical model provides an exact solution for stresses and strains on the cylindrical section of the vessel solution submitted hygrothermal loading coupled with internal pressure with end effect.

Abstract: In the present investigation, the surface of a commercially pure titanium (CP-Ti) substrate was modified to Ti/SiC nanocomposite layer employing friction stir processing technique; nanosized SiC powder was introduced into the stir zone provided by a rotating and advancing tool. The fabricated nanocomposite surface layer exhibited a micro hardness value of ~535HV which is much greater than 160HV of the substrate material using Vickers micro hardness testing. In addition, the un-treated CP-Ti substrate showed sever wear regime in the pin-on-disc test against the hardened AISI 52100 steel. It suffers extensive typical adhesive wear dominated by plastic deformation as evidenced by scanning electron microscopy. Also, deep grooves were formed, i.e. evidence of abrasive wear. Contrary to this, enhanced wear properties were detected for the Ti/SiC nanocomposite surface layer, i.e. lower coefficient of friction and weight loss. The nanocomposite surface layer was found to be adherent to the underlying substrate during the pin-on-disc test. The superior wear behavior of the nanocomposite surface layer is attributed to its improved micro hardness value due to the presence of hard nanosize SiC particles in a refined titanium matrix.

Abstract: With an industrial era characterized by new regulations aiming at protecting costumers and the global environment, manufacturers have to be more effective in delivering products that meet customers requirement but also, they have to be apt to dispose of the products properly whenever customers decide to return them. The traditional role of material selection and process design are challenged to take these issues into consideration and provide more effective solutions for the entire (closed-loop) supply chain. We aim at studying the impact of material and process selection decisions in the design of the reverse supply chain. We present an integrated approach that consolidates these design frameworks, and also a total cost approach to be used to set products end of life management decisions.

Abstract: Fluid flow through a bone scaffold structure is an important factor in its ability to build up a living tissue. Permeability is often used as a measure of a structure’s ability to allow for flow of nutrients and waste products related to the growth of new tissue. These structures also need to meet conflicting mechanical strength requirements to allow for load bearing. In this work, the effect of different bone structure morphologies on permeability were examined both numerically and experimentally. Cubic and hexagonal based three dimensional scaffold structures were produced via stereolithography and 3D printing techniques. In particular, porosity percentage, pore size, and pore geometry were examined. Porosity content was varied from 30% to 70% and pore size from 0.34 mm to 3 mm. An adapted Kozeny-Carmen numerical method was applied for calculation of permeability through these structures and an experimental validation of these results was performed via a standard permeability experimental testing set-up. From the results it was determined that increased permeability was provided with the cubic rather than hexagonal structure as well as by utilizing the larger pore size and higher levels of porosity. Stereolithography was found to be the better processing technique, not only for improved micrometer scale dimensional accuracy reasons, but also due to the increase wettability found on the produced surfaces. The appropriate model constants determined in this work will allow for analysis of new alternate structure designs on the permeability of rapid prototyped synthetic bone structures.

Abstract: In the present study laser nitriding of titanium alloy surface is carried out and fracture toughness of the resulting surface is measured using the micro-indentation method. The fracture toughness is then related to the microstructure of the laser treated surface. It is found that laser gas assisted nitriding lowers the fracture toughness of the surface due to the micro-stress formed at the surface region during the high cooling rates.

Abstract: In the present study, two layer HVOF coatings of carbon steel is carried out. The microstructural changes in the coating layers and fracture toughness of the coated surface are examined. The micro indentation method is incorporated for the fracture toughness measurements, while optical and scanning electron microscopy are used for the microstructural analysis. It is found that the fracture toughness of the coating surface produced by the tungsten carbide blended powders is less than that of the coating produced by corrosion resistance powders. Key words: HVOF, Diamalloy 2002, Diamalloy 4010, Fracture toughness.

Abstract: nternal heating of hollow cylinders with moving periodic heat source is examined in relation to surface treatment applications. This study includes three different cylinder materials, namely aluminum, nickel and titanium. Effective stresses in the cylinder wall are found to be mainly attributed to longitudinal temperature gradients. The aluminum cylinder shows sharper longitudinal temperature gradients as compared to the nickel and the titanium cylinders, which is due to the high value of the aluminum specific heat capacity. However, the larger Eα (elasticity modulus × thermal expansion coefficient) values for nickel cylinder result in higher levels of stress although nickel and titanium cylinders exhibit similar longitudinal temperature profiles. During dwelling time for the heating source at a certain spot, titanium cylinder exhibits lower levels of temperature increase as compared to aluminum and nickel cylinders, due to its lower value of thermal conductivity.

Abstract: Friction Stir Processing (FSP) is an innovative solid-state processing technology, which is being currently used to enhance locally the mechanical properties of conventional materials. In this work, 1 and 3 mm-thick copper-DHP plates were processed with the aim of simulating surface (SFSP) and bulk (VFSP) processing. The influence of the processing conditions on the microstructure and mechanical properties of the processed materials was analyzed. It was found that the tool geometry, which has a close relation with the plastic deformation and dynamic recrystallization kinetics inside the stirred volume, the processing parameters and the heat exchange conditions, which determine the extent of dynamic recrystallization and annealing phenomenon, are determinant in FSP.

Abstract: In this study, zirconium oxide coatings were formed on pure zirconium by microarc oxidation technique with the electrolytes containing KOH and different amounts of sodium silicate (0-40 gr/lt) for the same coating duration of 2 hours. The microstructure, surface roughness, phase content and chemical composition of the coatings were characterized by using scanning electron microscopy, profilometery and X-ray diffractometry. It was found that the coatings on surface of zirconium consist of monoclinic ZrO₂ (m-ZrO₂) and tetragonal ZrO₂ (t-ZrO₂) phases and the addition and increasing sodium silicate concentration in the electrolyte increases amount of t-ZrO₂ phase. The coatings were well adhered to Zr substrate with some cracks and porosities in the coating for all concentrations of sodium silicate. The coating thickness and surface roughness increased with sodium silicate concentration in the electrolyte. A glaze like Si rich structure and its increase with Si rate was evident in the outermost region of the coating.

Abstract: In the present study, the wear and friction behaviour of vanadium nitride coated AISI 52100 steel against hardened AISI D2 steel disc was studied using ball-on-disc arrangement. Vanadium nitride coating treatment was performed on pre-nitrided AISI 52100 steel balls using thermo-reactive diffusion techniques. The presence of VN and V₂N phases in the coating layer was confirmed by X-ray diffraction analysis. Friction and wear tests were carried out at dry test conditions under 2.5 N, 5 N and 10 N loads at 0.1 m/s, 0.2 m/s and 0.3 m/s sliding speeds. The results showed that the friction coefficient values of vanadium nitride coated AISI 52100 steel balls against hardened AISI D2 steel disc are changing between 0.49 and 0.71, depending on test conditions. The wear rates of the vanadium nitride coated AISI 52100 steel is ranging from 6.704×10⁴ mm³/m to 2.619 × 10⁶ mm³/N m. In general, the wear rate increased with the increase in load and sliding speed.