Band 111, Heft 8

In this study, hydroxyapatite-reinforced ZK60 Mg alloybased composites were fabricated via a powder metallurgy route. The mechanical properties of these composites were studied by compressive tests and hardness tests. The in-vitro corrosion behavior was also investigated using immersion testing and electrochemical measurement. The influence of hydroxyapatite content on the mechanical properties and invitro corrosion behavior was evaluated. The microstructure and corrosion morphology were characterized by means of X-ray diffraction, optical and scanning electron microscopy. The results showed that the composite materials with 10 wt.% hydroxyapatite exhibited a better combination of mechanical strength and corrosion resistance. Compared with ZK60 alloy, the addition of 10 wt.% hydroxyapatite resulted in an increase in corrosion resistance by 38.6%.

In this study, AA6061 matrix composites reinforced with multilayer graphene and MoS 2 were analyzed. The composites were prepared by powder metallurgy using the spark plasma sintering and spark plasma texturing methods. Microstructure, physical and mechanical properties were investigated and compared with unreinforced AA6061 sinter and AA6061 sheet plate. The results showed that the application of spark plasma texturing positively influences the relative density and compressive yield strength of AA6061 matrix composites. Moreover, in composites with MoS 2 , significant differences in compressive yield strength between the centre and the edge of the sintered compacts were noticed. These differences are related to the formation of the MoAl 12 phase as a result of the temperature gradient generated in the graphite die during sintering by the spark plasma texturing.

In the present study, Al6061/zirconium carbide surface composites have been developed using the friction stir processing method. The volume fraction of the zirconium carbide particles was varied as 3%, 6% and 9%. The developed composites were characterized using optical microscopy, X-ray diffraction and scanning electron microscopy. Micrographs revealed uniform distribution of zirconium carbide particles, and addition of zirconium carbide particles was found to improve hardness and tensile properties of Al6061 alloy. Corresponding strengthening mechanisms have been discussed and associated with the microstructural studies. Fractographic analysis was found to show a reduction in ductility with increase in addition of zirconium carbide particles.

The microstructural evolution and mechanical properties of hot rolled Mg-12Gd-1Zn-0.5Zr-0.5Ag (in wt.%) (MGZKA) alloys, with and without Al and Li additions, were investigated in this study. The Al and Li-containing alloys achieved excellent overall mechanical properties, especially MGZKA-6Al5Li alloy with a high elastic modulus of 52.2 GPa and a good plasticity of 15%. Compared with Al and Li-free MGZKA alloy, the fragmented Al 2 Gd and nanoscale Al 2 Li 3 phases with high modulus are observed in Al and Li-containing MGZKA-4Al 3 Li and MGZKA-6Al5Li alloys, which contribute to the overall elastic modulus of the alloys. The dynamic recrystallization regions of Al and Li-containing alloys increased while c/a ratio reduced, leading to the weakened texture. The activation of non-basal slip in Al and Li-containing alloys is closely related to the fine grains and weakened texture, which jointly promote the plasticity of Al and Li-containing alloys.

Ti-6Al-4V components were developed in different orientations (horizontal and vertical) using an additive manufacturing technique called direct metal laser sintering and heat treated under three different procedures. Anodizing (18- 22 V) the vertically built heat treated-2 specimen yields an optimum combination of mechanical properties and corrosion resistance tested in an acidic environment. The anodized (18- 22 V) heat treated-1 specimen built in horizontal orientation performed better in terms of combined mechanical properties and corrosion resistance tested in ringer solution.

The present study aims to establish a comparison of corrosion resistance between four (non-commercial) high manganese steel models in relation to 9% nickel steel in an aqueous solution of H 2 SO 4 . High manganese steels have emerged as an alternative material for the manufacture of equipment for the storage and transportation of liquefied petroleum gas due to their mechanical properties and mainly for the lower cost compared to 9% nickel steel. The electrochemical techniques used were open circuit potential, linear polarization and electrochemical impedance spectroscopy. The results obtained by these techniques have helped to understand the phenomena that produce a lower corrosion resistance of high manganese steels when compared to 9% nickel steel in aqueous solutions.

Although thermomechanical processing has been widely used in grain boundary engineering, the relationship between thermomechanical parameters and grain boundary character distribution is still not well understood. In the present study, electron backscatter diffraction was used to study the grain boundary character distribution in pure copper after lowstrain thermomechanical treatments. It was found that the low-R coincidence site lattice frequency and grain size decreases in the following sequence, 10% compression > 15% compression > 5% compression, except for 700 0 C. During thermomechanical treatments of copper, strain-induced grain boundary migration and grain growth may occur during annealing of 5% compressed copper, and recrystallization dominates during annealing of 15% compressed copper, while the annealing mechanism of 10% compressed copper changes from strain-induced grain boundary migration and grain growth to recrystallization when the annealing temperature exceeds 600 0 C. The results indicated that during single-step low-strain thermomechanical treatments, straininduced grain boundary migration and grain growth would gradually change to recrystallization with the increase of pre-deformation level and annealing temperature. Among the three mechanisms, strain-induced grain boundary migration seems to be more effective than recrystallization and grain growth in the optimization of grain boundary character distribution, and it is suggested that this is due to the high boundary migration rate of strain-induced grain boundary migration.

Two-step annealing after cold rolling is proposed for the optimization of the annealing process of AISI 316L austenitic stainless steel toward more intense grain refinement. It was revealed that the first step of the annealing process at lower temperatures (i. e. 750 0 C) can be used for the reversion of strain-induced martensite to austenite without uninhibited grain growth and recrystallization of the retained austenite. Afterwards, the primary recrystallization of the retained austenite takes place in the second step of the annealing process at higher temperatures (in the range of 850 to 950 0 C). Carefully controlling the second annealing step resulted in a finer grain size and better mechanical response compared to those of a conventional one-step annealing approach.

The Fe 2 CrSi nanostructured Heusler alloy was prepared by mechanical alloying followed by heat treatment. The structure, microstructure, and magnetic properties of the samples were studied by the following analysis methods: X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectrometry, transmission electron microscopy, and a vibrating sample magnetometer. The a-Fe (Si, Cr) solid solution with a disordered body centered cubic (bcc) crystal structure was obtained after 24 h of milling. An example of the sample milled for 32 h with a disordered crystal structure a-Fe(Si, Cr) was chosen to investigate the transformation with temperature using differential scanning calorimetry. The effect of annealing temperatures on the structural, microstructural, and magnetic properties of the ordered Fe 2 CrSi Heusler phase for the sample milled for 32 h was investigated.

In this study, we focus on the experimental determination of damping expressed by logarithmic decrement, damping ratio, and loss factor of particulate, continuous- and discontinuous- fibre reinforced, hybrid, and sandwich composites using the free vibration decay effect evaluated using the logarithmic decrement and half-power bandwidth methods. Composite materials with damping properties of magnitude several orders higher than that of traditional engineering materials are well known. However, in one study, we present different types of composite materials with different damping properties depending on various parameters such as ply angle, volume fraction, material configuration, reinforcement geometry, temperature, etc., which provide varied options to design the material arrangement of dynamically loaded components to maximize damping. Moreover, in this study, we determine typical time and frequency domain curves for individual types of analysed composites.

The effects of radiation damage on bcc tungsten with preexisting helium and hydrogen clusters have been investigated in a high-energy environment via a comprehensive molecular dynamics simulation study. This research determines the interactions of displacement cascades with helium and hydrogen clusters integrated into a tungsten crystal generating point defect statistics. Helium or hydrogen clusters of atoms~0.1% of the total number of atoms have been randomly distributed within the simulation model and primary knock-on-atom (PKA) energies of 2.5, 5, 7.5 and 10 keV have been used to generate displacement cascades. The simulations quantify the extent of radiation damage during a simulated irradiation cycle using the Wigner-Seitz point defect identification technique. The generated point defects in crystals with and without pre-existing helium/hydrogen defects exhibit a power relationship with applied PKA energy. The point defects are classified by their atom type, defect type, and distribution within the irradiated model. The presence of pre-existing helium and hydrogen clusters significantly increases the defects (5 - 15 times versus pure tungsten models). The vacancy composition is primarily tungsten (e. g., ~70% at 2.5 keV) in models with pre-existing helium, but the interstitials are primarily He (e. g., ~89% at 10 keV). On the other hand, models with pre-existing hydrogen have a vacancy composition that is primarily tungsten (more than 90% irrespective of PKA energy), and the interstitial composition is more balanced between tungsten (average 46%) and hydrogen (average 54%) interstitials across the PKA range. The distribution of the atoms reveals that the tungsten point defects prefer to reside close to the position of cascade initiation, but helium or hydrogen defects reside close to the positions where clusters are built.