Abstract: In the present study, the residual stress state and macroscopic deformation of automotive rack bar semi-products were examined. The rack bars were taken from the original production line after induction hardening, burnishing and polishing. Induction hardening was performed at 860°C, 880°C and 900°C and the polishing step was performed with standard and increased polishing force. Thus, the effect quenching temperature and polishing force are described. Non-destructive residual stress mapping was performed after which macroscopic deformation measurements were carried out on the same rods. It was shown that the variation of quenching temperature had no effect on the residual stress state and deformation of the components. The increased polishing force did not change the average stress state of the rods, however, it resulted in higher stress asymmetry and deformation of the rods. Stress asymmetry was shown to be the cause of bending of the rods.
Abstract: This study presents the production of silver doped bioactive calcium-phosphate (CaP) coatings on commonly used orthopaedic implant materials (Ti6Al4V). The deposition process was performed by pulse current technique from electrolyte containing the appropriate amount of Ca(NO3)2 and NH4H2PO4 components at 70 °C. In order to modify the CaP layer, Ag+ ions were added to the base electrolyte. The electrochemical behaviour of the coatings was investigated by potentiodynamic polarization method in conventional Ringer’s solution in a three-electrode open cell. The corrosion properties of samples prepared with different parameters were compared. During immersion, the coating comes into contact with the electrolyte and corrosion occurs. Due to the potential difference between layer and the metallic substrate, discrete anodic and cathodic areas can be formed, which result in the release of silver and calcium ions. For antimicrobial applications of the modified CaP coated implant alloys, it is important to maintain a continuous release of silver ions, while the bioactive CaP layer enhance the biocompatibility properties of the layer by fostering the bone cell growth. The morphology and grain size of coatings as deposited have been investigated and confirmed by different methods such as Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray (EDX) analysis.
Abstract: The effect of different plastic deformation methods on the phase composition, lattice defect structure and hardness in 316L stainless steel was studied. The initial coarse-grained γ-austenite was deformed by cold rolling (CR) or high-pressure torsion (HPT). It was found that the two methods yielded very different phase compositions and microstructures. Martensitic phase transformation was not observed during CR with a thickness reduction of 20%. In γ-austenite phase in addition to the high dislocation density (~10 × 1014 m-2) a significant amount of twin-faults was detected due to the low stacking fault energy. On the other hand, γ-austenite was gradually transformed into ε and α’-martensites with transformation sequences γ→ε→α’ during HPT deformation. A large dislocation density (~133 × 1014 m-2) was detected in the main phase (α’-martensite) at the periphery of the disk after 10 turns of HPT. The high defect density is accompanied by a very small grain size of ~45 nm in the HPT-processed sample, resulting in an very large hardness of 6130 MPa.
Abstract: The improvement of interfacial adhesion between multiwalled carbon nanotubes (MWCNTs) and epoxy resin (EP) was investigated in nanocomposites with the addition of an ionic liquid (IL, 1-Ethyl-3-methyl imidazolium tetrafluoroborate - EMIM BF4) as interfacial adhesion promoter. MWCNT (0, 0.3 and 0.5 weight%) was dispersed in EP through diluting an MWCNT-rich masterbatch prepared in presence and absence of IL. Three point bending and compact tension (CT) fracture mechanical tests were performed on specimens with different MWCNT contents with and without IL surfactant. IL addition resulted in easier dispersion of MWCNT in the EP masterbatch. With the addition of the IL the three point bending strength, the bending modulus of elasticity and the critical force required for crack propagation have increased significantly at the optimal, 0.3 weight% MWCNT content. Scanning electron microscopic (SEM) investigation of the fracture surfaces of the CT specimens revealed that incorporation of MWCNTs and its IL-assisted dispersion produced rougher surfaces suggesting higher fracture toughness than the reference EP.
Abstract: The automotive industry always had a determining role in the whole economy. In sheet metal forming both the material and the technological developments are strongly affected by the development tendencies in car manufacturing. One of the main trends in today’s car manufacturing is to apply light weight construction principles to meet the increased customers’ demand and legal requirements. In this respect, application of high strength steels is regarded as one of the most promising possibilities. Applying high strength steels has a very positive response for many requirements: increasing strength results in the application of thinner sheets leading to significant mass reduction and simultaneously to lower consumption and less harmful emissions however it also leads to formability problems. Hot press forming is one of the most successful solutions to overcome these difficulties. In this paper, a general overview of hot press forming processes will be summarised.
Abstract: Melamine-formaldehyde (PMF) coated microcapsules were produced with liquid pentaerythritol-tetrakis (3-merkaptopropionate) (PETMP) and UV-sensitive indicator colored PETMP cores. Capsules with an average diameter of 43 μm formed due to the adjustments on magnetic stirring, compound ratios, acidity and reaction time. Reproducible recipe was found to produce colored PETMP filled capsules with yields of 1-10%. Optical microscopic investigations were conducted to follow the formation of the particles, and scanning electron-microscope (SEM) was used to verify that the capsules did not break up as an effect of the brittle failure of the epoxy matrix specimens. Improvement of the shell-matrix adhesion was attempted with silane compounds and investigated with X-ray photoelectron spectroscopy (XPS) and SEM.
Abstract: Blending polymers is an effective method to develop novel materials, tailoring the properties of the components. However, different morphology structures can be formed during the preparation, which could result in a wide diversity of mechanical and physical properties. The properties of polymer blends are most significantly influenced by the emerging range of phase inversion, which depends on the composition ratio and the viscosity ratio. In this paper various blends were prepared, utilizing polyethylene terephthalate (PET), polystyrene (PS) and two high density polyethylenes (HDPE), which differ in flowability. After preliminary homogenization by twin screw extruder, standard injection moulded specimen were prepared in order to present the effects of phase inversion on tensile properties, shrinkage and burning characteristics in binary polymer blends.
Abstract: It is a well-known fact that thermoelectric currents, reaching even the scale of ampere, develop during chip formation in the workpiece-tool-chip-machine system. The impact of these currents on tool wear in continuous cutting was examined with a qualitative mathematical model, in which wear is described by an autonomous non-linear differential equation.The constants of the model were tailored to wear curves determined by experiments conducted with a P20 carbide tool on a C45 quality steel workpiece. The differences among the tool isolation measurement results obtained by various researchers may be justified by simulation calculations.According to the model, the thermoelectric system behaves in a chaotic way in certain cases. Further research is necessary to decide if this is only a special characteristic of the model or the model shows the actual processes.
Abstract: Understanding of the incorporation of actinides in borosilicate matrix used for nuclear waste storage is of a great importance for radioactive waste immobilization. This study carried out on matrix glasses doped respectively with 30wt% UO3 and CeO2, Nd2O3 used for chemical modelling of the actinides. Neutron and X-ray diffraction measurements and Reverse Monte Carlo (RMC) simulations were performed. For several glasses, it was found that the basic network structure consists of tetrahedral SiO4 units and of mixed trigonal BO3 and tetrahedral BO4. The BO3 and BO4 units are linked to SiO4, forming mixed Si-O-B and Si-O-B bond-linkages. From significant second neighbour atomic pair correlations have been revealed that U, Ce, Nd accommodates in both silicate and borate site.