Materials Science Forum Vol. 729

Abstract: Examination of three findings (a hammer axe from the Bronze Age, a bracelet of Aunjetitz, and a pick with neck-disc) from the Bronze Age was performed by the Research Group on Archeometallurgy of the University of Miskolc. The chemical composition, the phase constituents and the microstructure of the findings was examined. Beyond the common analysis of chemical composition features of the microstructure was examined, and data from the production process were collected (metallurgical processes, casting, cold and hot deformation). It was stated that the bracelet is produced by casting; the hammer axe and the pick give the final shapes by hammering after casting. Not only the annealed and hammered microstructure, but the casted primer microstructures were analyzed by application of different etching techniques. The chemical compositions and structures of inclusions were analyzed by SEM-EDS technique. The amount, shape and ordering was examined of the inclusion on micrographs. The aforementioned results gives a detailed study of producing process of the findings which was compared the newest technological knowledge.

Abstract: The Rákóczi Museum of the Hungarian National Museum revealed a cannon casting foundry in the territory of the castle of Sárospatak. The excavation started in the summer of 2006. A great amount of findings were revealed from the metallurgical, alloying and casting processes of the foundry. The Archeometallurgical Research Group of the University of Miskolc examines the microstructure and the chemical composition of these findings. The aim of this research work is to complete the knowledge of the contemporary literature and reconstruct the technological processes of the foundry. In this article the current status of the examination is introduced.

Abstract: Nitriding is one of the most important processes among surface technologies. The purpose of this process is to produce a wear resistant layer on the surface of components, to meet the complex requirements. Ferritic nitrocarburising was carried out at three different temperatures (520, 570 and 620°C) and with five different process times, to study the effects on process parameters . The experiments proved that in case of ferritic nitrocarburising, it is possible to produce larger diffusion zone during the same time. If the temperature is higher than the iron-nitrogen eutectoid temperature, the diffusion is deeper, but we should consider the softening of the core.

Abstract: The wettability of graphite by the Ag-M based (M: Cd, In Sn, Sb) liquid alloys was measured using the sessile drop method at a temperature interval of 1273 1473 K. Except the Ag-Cd alloys, the investigated systems exhibit worse wettability than that of Ag (host metal) melt, within the investigated temperature range. The compositional and concentration dependence of contact angle (Θ) exhibits similar trends, than the residual resistivity change measured in the same alloys in solid state. Nevertheless, the measured segregation effects during the solidification are not significant.

Abstract: Hydroxyapatite, (Ca₁₀(PO₄)₆(OH)₂ is chemically similar to the mineral component of bones and teeth. HAp is among of the few materials that are classified as bioactive, meaning that it will support bone ingrowth and osseointegration when used in orthopaedic, dental and maxillofacial applications. Hydroxyapatite may be employed in forms such as powders, porous blocks and hybrid composites to fill bone defects or voids. These may arise when large sections of bone have had to be removed or when bone augmentations are required (e.g. dental applications). In this work, nanohydroxyapatite (nanoHAp) was successfully produced by using recycled eggshell and phosphoric acid by mechanochemical activation method (e.g. attrition milling). nanoHAp bioactivity was evaluated in animal (rabbit) models. Sixteen 4-month-old New Zealand white rabbits with an average weight of 2.8kg were used in experiments. After bilateral parietal bony defects formation (diameter: 8.0mm), nanoHAp was grafted. The control was unfilled defect. The bone regeneration was evaluated by micro-computerized tomograms (μCT) and histomorphometric analysis at 4 and 8 weeks. In conclusion, nanoHAp from eggshell showed much more bone formation compared to unfilled control group in both μCT analysis and histomorphometric analysis. Considering that the eggshell is easily available and cheap, nanoHAp from the eggshell can be good calcium source in tissue engineering.

Abstract: Multiwall carbon nanotubes were dispersed with a concentration of 3wt% in silicon nitride ceramic host. A high efficiency attritor mill has been used for an effective dispersion of the filler phase in the matrix. In this work we have developed a spark plasma sintering process (SPS) suitable to consolidate and tailor the microstructure of CNT-reinforced silicon nitride-based ceramic composites. Mechanical measurements, micro-indentation investigations of the hardness and fracture toughness have been performed. Scanning electron microscopy has been involved in order to reveal the microstructure of the resulting composites.

Abstract: Using our local equilibrium model of the martensitic transformation [ the elastic energy contributions, as the function of martensite volume fraction, ξ, in the phase transformation of single crystalline Cu-11.5wt%Al-5.0wt%Ni shape memory alloy were calculated from our measurements published earlier [. The derivative of the elastic energy δE/δξ=e (E is the total elastic energy stored/released during the austenite to martensite (AM) as well as MA transformation) could be calculated only irrespectively of the ST₀ term (T₀ is the equilibrium transformation temperature and S is the entropy change of phase transformation). But, since ST₀ is independent of ξ, the functions obtained reflect the ξ dependence of e as well as E quantities. From the DSC curves measured at zero uniaxial stress (σ = 0) [, the ξ-T hysteric loop was constructed. Then the e (ξ) curves at fix σ as well as fix T were calculated. The E values obtained from the integral of e (ξ), fit well to the E(σ) as well as E(T) curves calculated from the strain-temperature and stress-temperature curves measured in [.

Abstract: To obtain advance hetero-modulus and hetero-viscous complex materials with extreme high dynamic strength, wear and thermal shock resistances a novel approach was applied by the authors. The developed new hetero-modulus and hetero-viscous composites were reinforced with nanoparticles and submicron fibers and whiskers of Si₂ON₂, SiAlON, AlN, Si₃N₄ as well as with special additives, which had turned into amorphous phases during sintering. These types of materials have several Youngs modulus and viscosities simultaneously and have high damage tolerance and ability to absorb and dissipate the elastic energy during crack propagation. Understanding the energy engorgement of high speed collision processes, the material structures and rheological properties of such a complex hetero-modulus and hetero-viscous material the authors could mathematically describe the mechanical shear stresses in these complex materials. Analytical methods applied in this research were scanning electron microscopy (SEM), X-ray diffraction, and energy dispersive spectrometry, digital image analysis was applied to microscopy results, to enhance the results of transformations.

Abstract: The influence of the consolidation conditions on the microstructure and plastic behavior of ultrafine-grained Ni and Al sintered from nanopowders was studied. It was found that the smaller initial Ni powder particle size yielded a smaller grain size and a larger oxide content in the as-consolidated sample resulting in a higher strength and lower ductility. When the Ni nanopowder was in contact with air (instead of an inert atmosphere) during the short handling time before sintering, the oxide content increased without a considerable change of the grain size that also decreased the ductility. The reduced time and temperature in Spark Plasma Sintering compared to Hot Isostatic Pressing led to a smaller grain size that resulted in a higher strength of Ni. In the case of an Al nanopowder processed by Hot Isostatic Pressing at 450 °C, the consolidation was hindered by the strongly limited diffusion due to the presence of a rigid amorphous layer on the surface of particles. However, at the sintering temperature of 550 °C, the crystallization and the fragmentation of the layer occurred that yielded a better densification.