SURFACE SEGREGATION STUDIES OF SELENIUM ON FeSiAl ALLOY RAZISKAVE POVR[INSKE SEGREGACIJE SELENA NA FeSiAl ZLITINI

Surface segregation of selenium in a polycrystalline FeSiAl alloy with 0.05% Se was investigated by high resolution Auger Electron Spectroscopy and X-ray Photoelectron Spectroscopy. Surface segregation measurements of selenium and impurities e.g. carbon, phosphorus and sulfur, were performed in situ under UHV conditions in the temperature range from 200 to 900°C. In the low temperature range, 200<T<550°C, carbon segregated due to its high diffusion and segregation enthalpy. Carbon segregated in the form of graphite clusters. At higher temperature T>850°C sulfur and selenium segregated. The selenium segregation rate was low, probably due to its low solubility in αFe and its high vapor pressure. The grain boundary segregation of selenium was negligible. The fracture facets were practically transgranular, only on some areas intergranular decohesion was noticed. Key words: equilibrium segregation, cosegregation, diffusion, surface precipitates, selenium, HR AES, XPS Povr{insko segregacijo selena na polikristalini~ni zlitini FeSiAl legirani z 0,05% Se, smo raziskali z visokolo~ljivo spektroskopijo Augerjevih elektronov na poljsko emisijo (HR AES) in z rentgensko fotoelektronsko spektroskopijo (XPS). Meritve povr{inske segregacije selena in elementov ne~isto~ kot so ogljik, fosfor in 'veplo so potekale v temperaturnem podro~ju od 200 do 900°C in situ v ultravisokem vakuumu. V nizko temperaturnem podro~ju 200<T<550°C, ogljik segregira na povr{ini zaradi visokega difuzijskega koeficienta in entalpije segregacije. Ogljik je na povr{ini segregiral kot grafit v oto~kih. Pri v i{jih temperaturah T>850°C sta na povr{ini segregirala 'veplo in selen. Stopnja sergegacije selena je bila nizka, predvidevamo da je vzrok temu nizka topnost selena v αFe in visok parni tlak. Segregacija selena po mejah zrn je zanemarljivo majhna. Skoraj vse prelomljene facete so bile transkristalne, le nekaj je bilo interkristalnih prelomov. Klju~ne besede: povr{inska segregacija, segregacija po mejah zrn, povr{inski precipitati, kosegregacija selen, HR AES, XP

PACVD duplex prevlake za toplo kovanje visoko čvrstih čelika za automobilsku primjenu

The tribological load is the load on forging tools resulting from the relative motions between the plastically deformed workpiece and the die. In comparison to many other forming processes hot die forging has an especially disadvantageous tribological system. The advantages of the application of hard coatings, which are well known for cutting tools, are to a much lesser extent explored for casting, extrusion, moulding and forging tools. Increasing the lifetime of these tools is an important task in surface engineering because of the complex loading conditions and often complicated tool geometry. The plasma-assisted chemical-vapour- deposition (PACVD) technique is well suited to depositing hard coatings onto large dies and moulds. The aim of this study is to present and discuss results obtained on a duplex PACVD hard coating in an industrial application such as hot forging of automotive parts. The results presented here are from a preliminary investigation. The experimental results indicate that introduction of a proper duplex PACVD hard coating will lead to improved wear resistance and longer lifetime for hot-forging dies. Furthermore, by using a hard, lowfriction coating excellent anti-sticking property can be obtained. At this stage of the investigation it is also necessary to carry out pilot trials to determine the wear resistance and tool life in practice.Tribološko opterećenje je opterećenje na alatu za kovanje koje je rezultat kretanja između plastično deformiranog dijela i alata. U usporedbi s mnogim drugim postupcima oblikovanja, kod kovanja u toplom postoji nepovoljan specifičan tribološki sistem. Prednosti primjene tvrdih prevlaka, koje su poznate za alate za rezanje, manje su izražene za ljevačke, ekstruzijske i kovačke alate. Povećanje radnog vijeka tih alata je važan zadatak u inženjerstvu površina zbog složenih uvjeta opterećenja i često komplicirane geometrije alata. Plazmom potpomognuto taloženje u parnoj fazi kemijskim postupkom (PACVD) je vrlo prikladno za taloženje tvrdih prevlaka na velike kalupe. Cilj ovog istraživanja je predstaviti i prodiskutirati dobivene rezultate na duplex PACVD tvrdim prevlakama u industrijskoj primjeni kao što je kovanje automobilskih dijelova. Predstavljeni rezultati dobiveni su uvodnim istraživanjima. Eksperimentalni rezultati navode da će uvođenje prikladne duplex PACVD tvrde prevlake dovesti do poboljšanja otpornosti na trošenje i na produljenje životnog vijeka alata za kovanje. Nadalje, korištenjem tvrde prevlake s malim trenjem mogu se postići izvrsna svojstva ne-lijepljenja. U ovoj fazi istraživanja također je nužno iznijeti početne pokušaje (pilote) za određivanje otpornosti na trošenje i određivanje životnog vijeka alata u praksi

Characterisation of NiTi Orthodontic Archwires Surface after the Simulation of Mechanical Loading in CACO2-2 Cell Culture

Nickel-titanium (NiTi) orthodontic archwires are crucial in the initial stages of orthodontic therapy when the movement of teeth and deflection of the archwire are the largest. Their great mechanical properties come with their main disadvantage-the leakage of nickel. Various in vitro studies measured nickel leakage from archwires that were only immersed in the medium with little or minimal simulation of all stress and deflection forces that affect them. This study aims to overcome that by simulating deflection forces that those archwires are exposed to inside the mouth of a patient. NiTi orthodontic archwires were immersed in CACO2-2 cell culture medium and then immediately loaded while using a simulator of multiaxial stress for 24 h. After the experiment, the surface of the NiTi orthodontic archwires were analysed while using scanning electron microscopy (SEM) and auger electron spectroscopy (AES). The observations showed significant microstructural and compositional changes within the first 51 nm thickness of the archwire surface. Furthermore, the released nickel and titanium concentrations in the CACO2-2 cell culture medium were measured while using Inductively Coupled Plasma Mass Spectroscopy (ICP-MS). It was found out that the level of released nickel ions was 1.310 mu g/L, which can be assigned as statistically significant results. These data represent the first mention of the already detectable release of Ni ions after 24 h during the simulation of mechanical loading in the CACO2-2 cell culture medium, which is important for clinical orthodontic praxis

Smjerovna ovisnost izdvajanja antimona na površinama legura FeSi

The antimony surface segregation was investigated on surfaces of a polycrystalline Fe-Si alloy with 0.05 wt. % Sb, under UHV conditions, in the temperature range from 450 to 950 °C. The grain boundary segregation in experimental alloys was negligible. It was concluded that the texture formation results from orientation-dependent effects of antimony on the surface energy and through them on grain boundaries. Controlled surface segregation promotes the selective grain growth.Proučavano je površinsko izdvajanje antimona na površinama polikristalne legure FeSi sa 0.05 tež.%, u ultravakuumu i na temperaturama od 450 do 950 ◦C. Izdvajanje na granicama zrna je zanemarivo. Ustanovljeno je da je nastajanje teksture posljedica smjerovno–ovisnih učinaka antimona na površinsku energiju pa stoga i na granice zrna. Upravljavano površinsko izdvajanje potiče poseban rast zrna

Hydroxyapatite coatings on cp-titanium grade-2 surfaces prepared with plasma spraying

Thin hydroxyapatite coatings were produced on Cp-Titanium Grade-2 samples, with new high-voltage pulse-power equipment PJ-100 (Plasma Jet, Serbia) in order to get a more stable implant structure appropriate for further clinical applications. A comparative analysis of differently prepared surfaces of the Cp-Titanium Grade-2 samples was done before the hydroxyapatite was applied. Microstructural observation of the modified hydroxyapatite/implant surface was done using scanning-electron-microscopy imaging and Auger electron spectroscopy, with the aim of detecting the morphology and the elements contained in the new surfaces of the samples. The results confirmed that the surface of Cp-Titanium Grade-2 modified with hydroxyapatite is very similar to the bone structure

Vpliv bakra na razogljičenje in rekristaizacijo zlitin Fe-Si-Al

The decarburization and recrystallization of Fe-Si-Al alloys containing copper was investigated. The decarburization annealing of non-oriented electrical steel sheets produced from Fe-Si-Al alloys depends on the chemical reactions between the gas mixture and the carbon at the steel\u27s surface. The carbon diffusion, the temperature of decarburization annealing, the composition of the gas mixture and the chemical composition of the steel are the influencing parameters that determine the kinetics and the mechanism of decarburization. The decarburization of Fe-Si-Al alloy with the mass fraction of 0.24% and 0.43% of copper was compared with the decarburization of an Fe-Si-Al alloy with a very small amount of copper (0.01%). The decarburization annealing was performed in a H2-H2O gas mixture at 840 °C. The residual carbon content was determined by analytical chemical method. The alloys were also recrystallized in hydrogen at 980 °C. Microstructure of samples after decarburization and recrystallization annealing was investigated with optical microscopy.Preučevali smo razogljičenje in rekristalizacijo modelnih zlitin Fe-Si-Al z različno vsebnostjo bakra. Razogljičenje neorientiranih elektropločevin, ki jih lahko izdelujemo iz zlitin Fe-Si-Al, je odvisno od kemijskih reakcij med ogljikom, ki difundira na površino jekla, ter plinsko mešanico. Vplivni parametri, ki določajo kinetiko in mehanizem razogljičenja, so: površinska segregacija ogljika, temperatura razogljičevalnega žarjenja, sestava plinske mešanice in kemijska sestava jekla. Razogljičenje smo merili v zlitinah Fe-Si-Al z vsebnostjo masnega deleža bakra 0,24 % in 0,43 % ter ga primerjali s tistim v zlitini z zelo nizko vsebnostjo bakra, 0,01 %. Zlitine smo razogljičili pri temperaturi 840 °C v plinski mešanici H2-H2O. Preostali delež ogljika po razogljičenju smo določili s kemijsko analizo vzorcev. Zlitine smo tudi rekristalizacijsko žarili v suhem vodiku pri 980 °C. Mikrostrukturo vzorcev po žarjenju za razogljičenje in rekristalizacijo smo analizirali s svetlobno mikroskopijo