Utjecaj lantanida na viskoznost stakla RE-Si-Mg-O-N

Compressive creep behavior of RE-Si-Mg-O-N glasses (RE = La, Yb, Sm and Lu) was investigated to determine temperature dependency of their viscosity in temperature range from 770 °C up to 895 °C. Viscosity and heat transfer through the glass (Tg) were increased by > 10 times and by 26 °C, when La is replaced with Lu in the corresponding glasses. Assuming valence Z = +3 and coordination number CN = 6 of the RE ions, Tg depends approximately linearly on cationic field strength except Yb. Tg of Yb-containing glass also falls on linear dependence provided CN = 8 in the case of Yb. Lanthanides seem to modify the structure of the corresponding glasses and bond strength rather than the mechanisms of deformation.Ispitivano je puzanje stakla RE-Si-Mg-O-N (RE=La, Yb, Sm i Lu) pod tlakom radi određivanja ovisnosti viskoznosti o temperaturi u temperaturnom području od 770 °C - 895 °C. Viskoznost i prijenos topline kroz staklo (Tg) povećane Si za > 10 puta i za 26 °C kad je La zamijenjen s Lu u odgovarajućim staklima. Ako pretpostavimo da je valentnost Z = +3, a koordinacijski broj CN = 6 RE iona, Tg ovisi približno linearno o čvrstoći kationskog polja, osim za Yb. Tg stakla koja sadrže Yb također se svode na linearnu ovisnost pod uvjetom daje CN = 8 a u slučaju Yb. Čini se da lantanidi modificiraju strukturu odgovarajućih stakala i čvrstinu veze a ne mehanizmi deformacije

Superplastična deformacija Al-Al4C3 kompozita

Deformation of the Al-Al4C3 composites with different volume fraction of Al-Al4C3 phase was investigated at different temperatures (293 - 723 K) and different strain rates (2,5 * 10-5 s-1 do 1,0 * 10-1 s-1). At temperatures 673 - 723 K and at the highest strain rate of 1,0 * 10-1 s-1, a significant ductility increase was observed. TEM analysis suggests the onset of superplasticity may be the result of dynamic grain polygonization, grain slip and rotation, partial recrystallization and dislocation creep in the tested system, which is known as strain induced dynamic recovery. Increase of the volume fraction of secondary phase in the studied composite resulted in a shift from slip on grain boundaries controlled mechanism to the grain rotation controlled deformation mechanism.Istraživana je deformacija Al-Al4C3 kompozita različitog volumnog udjela Al-Al4C3 faze kod različitih temperatura (od 293 do 723 K) i brzina deformacije (od 2,5 * 10-5 s-1 do 1,0 * 10-1 s-1). Kod temperatura od 673 do 723 K i najviše brzine deformacije od 1,0 * 10-1 s-1 zapaženo je značajno povećanje kovkosti. TEM analiza ukazuje da početak superplastičnosti može biti rezultat dinamičke poligonizacije zrna, klizanja i rotacije zrna, djelomične rekristalizacije i puzanja dislokacija u istraživanom sustavu, što je poznato kao deformacijom inducirano dinamičko oporavljanje. Porast volumnog udjela sekundarne faze u istraživanom kompozitu rezultirao je promjenom kontrolnog mehanizma deformacije od klizanja po granicama zrna do rotacije zrna

Electrical Resistivity of CrN Thin Films

The work is focused on the measurements of electrical resistivity of CrN thin films deposited on glass substrates by DC-magnetron sputtering in Ar+$N_{2}$ atmosphere. The studied samples reveal semiconducting behaviour of electrical resistivity in the whole range of tested preparation parameters (such as pressure and composition of Ar-$N_{2}$ mixture), whereas the electrical transport regime is strongly influenced by parameters of preparation. Numerical analysis of the experimental data showed that electrical transport can be adequately described in terms of variable-range hopping conduction in selected temperature intervals. Moreover, S-shaped anomaly in ρ(T) dependence, being expected to be a consequence of phase transition to a low-temperature antiferromagnetic orthorhombic phase, has been observed for sample with the highest concentration of $N_{2}$ in the temperature interval of 220-250 K. The obtained results indicate that technology processes typically used for preparation of CrN coatings represent a promising potential to develop also high sensitivity cryogenic sensors for high magnetic fields applications

Tribological behavior of hydrogenated W-C/a-C:H coatings deposited by three different sputtering techniques

Abstract The evolution of structure, mechanical properties and friction behavior of DC magnetron sputtered (DCMS), high power impulse magnetron sputtered (HiPIMS) and high target utilization sputtered (HiTUS) W-C:H coatings was investigated as a function of the addition of acetylene and hydrogen into Ar atmosphere. The gradual addition of reactive gases caused a transition from PVD toward hybrid PVD-PECVD and even PECVD dominant processes. The coating structure evolved from nanocrystalline toward nanocomposite and amorphous structure with the increase of acetylene addition. Deposition rates in all techniques increased linearly with the increase of acetylene flow until certain saturation limit due to the limited energy available for acetylene fragmentation during hybrid PVD-PECVD deposition. Hardness and coefficient of friction in DCMS and HiTUS W-C:H coatings deposited in this regime followed standard congruent tendencies whereas PECVD dominated deposition process produced coatings with different dependencies. In contrary, HiPIMS W-C:H coatings showed low sensitivity to the influence of acetylene and hydrogen additions. Lower coefficients of friction (<0.1) and moderate hardness (around 20 GPa) of HiPIMS W-C:H coatings over a wide range of acetylene additions seem to be a principal advantage of HiPIMS compared to DCMS and HiTUS techniques in this class of coatings

TEM and AES study of changes in the micro-structure of alumina during creep

Translated from Slovak (Kovove Mater. 1997 (4) p. 247-256)SIGLEAvailable from British Library Document Supply Centre-DSC:9023.19000(VR-Trans--8610)T / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Structure and rheological properties of the RE-Si-Mg-O-N (RE = Sc, Y, La, Nd, Sm, Gd, Yb and Lu) glasses

International audienceStructure, viscosity, glass transition temperature, Littleton temperature and elastic moduli were investigated by MAS-NMR spectroscopy, compressive creep, dilatometry and ultrasound velocity experiments, in order to reveal the effects of rare earth elements and nitrogen on the behavior of RE-Si-Mg-O-N glasses (RE = Sc, Y, La, Nd, Sm, Gd, Yb and L) with different nitrogen contents. NMR showed that nitrogen modifies the glass structure depending on RE type via increasing content of SiO3N(+Q(1)) units at the expense of Q(2) units and Lu seems to be more effective in their formation than La. Despite that, the effects of rare-earth modifiers and nitrogen as network former are independent, additive and a synergy effect was not observed. Approximately linear dependencies of most properties on molar volume (and ionic radii) suggest that glass network is tightened proportionally to ionic radius of corresponding modifier and cross-linking is proportional to nitrogen content. However, the mechanism involved in lanthanide effect is different from that of Sc and Y additives, although they result in properties similar to those of Lu-containing glasses. Irregularities found for Yb and Sm additives at elevated temperatures may be related to the change of valence state. (C) 2004 Published by Elsevier B.V