The microstructure, mechanical and electrochemical properties of 3D printed alloys with reusing powders

CoCrMo and Ti6Al4V are widely used in medical, dental and 3D printing technology, allowing the accurate fabrication of geometrically complicated structures. In order to reduce the costs of printed objects, the reuse of powder is common daily practice. AQ1 When using 3D printing technology, the direct impact of elevated temperatures and the influence of the laser beam may change the properties of the powder when it is reused, thus affecting the final properties of the printed object. The main aim of the present study was to investigate the impact of reused powder on the mechanical, microstructural and electrochemical properties of 3D printed objects. 3D printed objects fabricated from virgin and reused powder of both alloys were analyzed by metallographic observation, computed tomography, XRD and electrochemical methods. The main finding of the study was that the use of reused powder (recycled 3 times) does not detrimentally affect the mechanical and corrosion integrity of 3D printed CoCr and Ti6Al4V alloys, especially for the purpose of applications in dentistry

Corrosion characterization and ion release in SLM-manufactured and wrought Ti6Al4V alloy in an oral environment

As-produced and heat-treated TiAlV samples were prepared by selective laser melting and compared to wrought samples of identical chemical composition. Microstructural, corrosion, and spectroscopic studies of additively manufactured samples in artificial saliva at 37 °C, with NaF and at pH 2.3 were as a novelty combined with metal ion release during 42 days immersion. In artificial saliva higher amount of ions was released on SLM specimen when compared to wrought alloy. The total amount of ions released from SLM specimen in AS containing NaF was 10-times higher than in AS, while in AS with lactic acid it was 100-times higher

The corrosion resistance of dental Ti6Al4V with differing microstructures in oral environments

The impact of the microstructural properties of a Ti6Al4V alloy on its electrochemical properties, as well as the effect of the α- and β-phases present within it, is still unclear. With the introduction of new, emerging technologies, such as selective laser melting and post heat treatments, the effect of the microstructure on an alloy\u27s corrosion properties has become increasingly interesting from a scientific perspective. When these alloys are produced through different methods, despite an identical chemical composition they have diverse microstructures, and consequently display varying resistance to corrosion. In the present research study, Ti–6Al–4V alloy specimens produced by three different processes, leading to the formation of three different microstructures were investigated: heat treated specimen fabricated by selective laser melting, wrought and cast specimens. The impact of the microstructure of these alloys when immersed in artificial saliva was studied through the use of various electrochemical techniques, by microscopical examinations, and time-of-flight secondary ion mass spectrometry. Corrosion properties were investigated by the measurement of open circuit potential, linear polarization, and potentiodynamic curve measurements followed by microscopical examinations, and time-of-flight secondary ion mass spectrometry examination was conducted to reveal spatial distribution of alloying species on oxide film. It was found that the difference between specimens containing an α+β microstructure was small and not dependent on the aspect ratio of the β-phase, alloy grain size, and vanadium partitioning coefficient, but rather on the size, shape, and content of this phase

Ocena korozijskih lastnosti titanovih dentalnihzlitin, izdelanih s SLM postopkom

Titanium alloys are known for their excellent biocompatible properties. The development of additive-manufacturing technologies has increased the interest in the use of Ti-6Al-4V, produced by selective laser melting (SLM) method, also in dentistry, i.e., prosthodontics and orthodontics. In the present paper, the effect of laser printing parameters in the selective laser melting (SLM) process on the porosity and corrosion behavior of Ti-6Al-4V dental alloy was metallographically and electrochemically studied. All the tests were performed in artificial saliva at 37 °C. Different forms of Ti-6Al-4V alloy were selected: a reference sample, i.e., pre-fabricated milling disc in wrought condition and four different 3D-printed samples made from Ti-6Al-4V powder using the SLM method, one being heat treated. Electrochemical, spectroscopic and hardness measurements were employed in the study. It was shown that the SLM-produced Ti-6Al-4V samples with different printing parameters have similar microstructural and electrochemical properties, while the electrochemical properties of a reference and thermally treated 3D-printed sample were different, most probably due to the change in the microstructure of the alloys. The corrosion properties were related to the microstructural properties as well as to the pore density.Titanove zlitine so znane po odličnih biokompatibilnih lastnostih. Razvoj aditivnih tehnologij je povečal zanimanje za uporabo Ti-6Al-4V, proizvedenega z metodo selektivnega laserskega taljenja (SLM) v zobozdravstvu - tako v protetiki kot v ortodontiji. V prispevku smo metalografsko in elektrokemijsko proučili vpliv parametrov laserskega tiska pri procesu selektivnega laserskega taljenja (SLM) na poroznost in korozijsko obnašanje dentalne zlitine Ti-6Al-4V. Vsi testi so bili opravljeni v umetni slini pri telesni temperaturi 37 °C. Izbrane so bile različne oblike zlitine Ti-6Al-4V: referenčni vzorec (v obliki diska za rezkanje v kovanem stanju) in štirje različni 3D natisnjeni vzorci iz prahu Ti-6Al-4V po metodi selektivnega laserskega taljenja (SLM), pri čemer je eden toplotno obdelan. Pri raziskavi so bile uporabljene elektrokemijske, spektroskopske metode in meritve trdote. Pokazalo se je, da imajo vzorci Ti-6Al-4V, izdelani s postopkom SLM, z različnimi parametri, podobne mikrostrukturne in elektrokemijske lastnosti, medtem ko so bile elektrokemijske lastnosti referenčnega in termično obdelanega 3D natisnjenega vzorca različne, najverjetneje zaradi različne mikrostrukture te zlitine. Korozijske lastnosti so bile povezane z mikrostrukturnimi lastnostmi, pa tudi z gostoto por

An assessment of the damage to ropeway clips and an analysis of the source of the damage

Vrvna prižemka je nosilni, dinamično obremenjen konstrukcijski element, ki povezuje sedežno obešalo s transportno vrvjo sedežnice. V lanskem letu smo sistematično vizuelno in defektoskopsko pregledali večje število prižemk in ostalih vitalnih konstrukcijskih elementov sedežnic. Osnovni cilj preiskav je bil oceniti njihovo stanje, detektirati obstoječe razpoke in ostale poškodbe, ki bi lahko vodile do nenadnih lomov ter določili obseg teh poškodb. Ultrazvočna metoda s posebej prirejeno površinsko sondo se je pokazala kot najprimernejša in izredno zanesljiva metoda za določanje razpok na prižemkah. Rezultati preiskav so pokazali, da ima material prižemk in nekaterih drugih konstrukcijskih elementov zelo nizko žilavost in grobo zrnato feritno - perlitno mikrostrukturo, ki je posledica neustrezne toplotne obdelave. Konstrukcijski elementi iz materiala s tako strukturo ne zagotavljajo zadostne odpornosti proti krhkemu lomu.A ropeway clip is an important dynamically loaded construction element that fastens together the hanger bar and the rope. During the last year, we were involved in systematic non-destructive testing of a range of ropeway clips and some other important construction elements. The main goal of the research was to detect the existance of cracks and other types of the damage that can lead to unexpected fracture, and an evaluation of the condition of the ropeway clips. The ultrasound method, accompanied by a specially arranged ultrasound surface beam-probe proved to be the most suitable, precise and reliable method for the cracks detection on the clips. In addition, several laboratory investigations were carried out in order to find causes for the initiation and propagation of cracks in the clips. Results of laboratory examinations revealed that the material of the clips, and also of the other construction elements, had very low toughness and a coarse-grain pearlite-ferritic microstructure, which is a result of improper heat treatment. It was concluded that the construction elements made from material with this kind of structure and mechanical properties would not ensure sufficient resistance to brittle fracture

Comparison between simultaneously performed measurements of electrochemical noise and mechanical parameters during stress-corrosion processes

Namen našega dela je bil določiti značilnosti elektrokemijskega šuma, povzročenega z napetostno-korozijskim pokanjem. Želeli smo predvsem ugotoviti poveznanost značilnih elektrokemijskih fluktuacij z mehanskimi spremembami zaradi procesov pokanja ter tako posredno tudi oceniti primernost te metode za detekcijo in študij različnih oblik pokanja. Elektrokemijski šum smo merili med počasnim enakomernim nateznim obremenjevanjem delovne elektrode (modificiran Slow Strain Rate Test), izdelane iz nerjavnega avstenitnega jekla tipa AISI 304 v žarjenem ter toplotno neobdelanem stanju. Izrazite nenadne fluktuacije napetostnega in tokovnega šuma smo opazili po preseženi napetosti tečenja. Vse se časovno popolnoma ujemajo z nenadnimi spremembami raztezka natezno obremenjene elektrode, kar dokazuje zanesljivo možnost detekcije pokanja. Iz izmerjenih sprememb raztezka smo določili hitrost rasti razpok ter jih primerjali z amplitudami fluktuacij elektrokemijskega šuma. Dokazali smo, da obstaja med vrednostmi teh dveh količin linearna odvisnost. Poudariti je treba, da samo poznanje elektrokemijskih razmer ter spremljanje mehanskih sprememb, povzročenih s pokanjem, še ni dovolj za ovrednotenje mehanizmov napetostno-korozijskega pokanja, pač pa bo za to v prihodnosti treba vključiti še fraktografsko analizo prelomnih površin.The main aim of the research work was to asses basic characteristics of electrochemical noise generated by stress-corrosion cracking, and especially to find a correlation between the electrochemical and mehanical quantities. Electrochemical noise was measured during slow constant increasing of stress (modified Slow Strain Rate Test) on tensile tube made from austenitic stainless steel of the type AISI 304, in sensitized and nonsensitized condition. One of the objectives of this research was to investigate the possibility of electrochemical noise method for studying stress-corrosion processes. After the reaching yielding point, voltage and current spikes, as well as elongation transients, all appearing at the same time, were detected. Afterwards, the cracking velocities were determined from the time series of elongation, and compared to characteristic parameters of the measured electrochemical noise. The results of the comparision indicated that the amplitudes of the electrochemical noise spikes are lineary dependent upon cracking velocity. It has to be pointed out, that the knowledge of elecrochemical conditions and mechanical changes generated by cracking processes by themselves, cannot form revalant information concering the cracking mechanisms. In order to get better overview to this problem additional fractographic inspections of cracking surfaces has to be performed

Primerjava korozijskih lastnosti CoCrMo dentalnih zlitin v umetni slini

CoCrMo alloys are known for their biocompatible properties, which, together with their favorable mechanical properties, mean they can be efficiently used in dentistry. With the development of selective laser melting for the fabrication of 3D-printed ob - jects, interest in the corrosion properties of this alloy has risen in the field of prosthodontics. In the study, CoCrMoW dental al - loys were studied in artificial saliva at body temperature, i.e., 37 °C. Different forms of CoCrMoW alloy were selected: a refer - ence sample, i.e., original material as received from the supplier, a cast sample acquired from an ordinary procedure in a dental laboratory, and two 3D-printed samples made from CoCrMoW powder using the selective laser melting (SLM) method. Electro - chemical, spectroscopic and hardness measurements were conducted. It was shown that the reference and cast samples have similar microstructural and electrochemical properties, while the electrochemical properties of the 3D-printed samples differ, most probably due to the effect of the higher micro porosity and chemical composition of the alloys.CoCrMo-zlitine so znane po svojih biokompatibilnih lastnostih, ki jih zaradi ugodnih mehanskih lastnosti vse pogosteje uporabljamo v zobozdravstvu. Z razvojem selektivnega laserskega taljenja (SLT) se je zanimanje za izdelavo 3D tiskanih predmetov in preučevanje korozijskih lastnosti teh zlitin povečalo tudi v stomatološki protetiki. V študiji je bila preučevana CoCrMoW-zlitina v umetni slini pri telesni temperaturi 37 °C. Izbrane so bile različne oblike zlitin CoCrMoW: originalni referenčni vzorec dostavljen od dobavitelja, kovinski ulitek, pridobljen z ustaljenim postopkom v zobotehničnem laboratoriju in dva 3D vzorca iz prahu CoCrMoW, ki sta bila izdelana z uporabo metode selektivnega laserskega taljenja. Izvedene so bile elektrokemijske in metalografske preiskave z merjenjem trdote. Ugotovljeno je bilo, da imata referenčni in ulit material podobne mikrostrukturne in elektrokemijske lastnosti, medtem ko imajo vzorci 3D tiska različne elektrokemijske lastnosti, najverjetneje zaradi učinka večje mikro poroznosti in kemijske sestave zlitin

Comparison of cycling high temperature corrosion at 650°C in the presence of NaCl of various austenitic stainless steels

The high temperature corrosion at 650°C in the presence of NaCl at atmospheric pressure of AISI 304L, AISI 309, AISI 310S, AISI 314 and AISI 321 austenitic stainless steel was studied. The specimens were cyclically heated in the furnace and immersed in a 3.5% aqueous NaCl solution after cooling for 15 min. After each cycle, the change in mass of the samples was measured. The corroded samples were analysed by SEM /EDX, and the corrosion products were analysed by XRD. The chloride ions react with the steel surface to form porous and poorly adherent oxides and metal chlorides. After the mass increase during the first exposure cycles, spalling of the oxides occurred. The high temperature austenitic stainless steels (AISI 309, AISI 310S, AISI 314) showed less mass loss than conventional austenitic steels (AISI 304L). Surprisingly, the stainless steel AISI 321 showed a similar low weight loss after the cyclic test as AISI 309, but a detailed analysis of the exposed surfaces after the test showed a similar corrosion attack as for AISI 304. After the cyclic test at high temperature in the presence of NaCl, a higher concentration of Cr and Ni definitely improves the corrosion resistance under the present conditions, but a certain addition of Si is even more obvious

Analysis of electrochemical noise generated by different corrosion processes

Analizirali smo elektrokemijski šum, ki ga povzročijo korozijski procesi na površini elektrod. Tokovni in napetostni šum, ki skupaj sestavljata elektrokemijski šum, sta bila merjena med tremi vzporedno postavljenimi elektrodami iz nerjavnega jekla AISI 302. Srednja - skupna elektroda, ki je bila z ostalima dvema povezana v tokovni in napetostni vir, je bila obremenjena s konstantno natezno silo. Elektrokemijski šum smo merili v vodnih raztopinah z različnimi koncentracijami NaCl in HCI. Med meritvami smo z računalniškim vizualizacijskim sistemom posneli spremembe na površini elektrod, ter jih primerjali s posameznimi fluktuacijami elektrokemijskega šuma. Za karakterizacijo izmerjenih signalov, predvsem pa, da bi razločili med posameznimi tipi korozije, smo uporabili različne matematične metode v frekvenčnem (analiza spektralne gostote moči) in faznem prostoru (rekonstrukcija atraktorjev, določitev fraktalne dimenzije in maksimalnega Ljapunovega eksponenta). Raziskava je pokazala, da z merjenjem elektrokemijskega šuma in njegovo analizo lahko ločimo med splošno korozijo, ter različnimi tipi lokalne korozije. Pri lokalnih oblikah korozije detektiramo preboje pasivnega filma, njegovo repasivacijo in rast jamic. Odkrijemo lahko tudi začetek napetostno - korozijskega pokanja, ne moremo pa oceniti hitrosti propagacije posameznih razpok, oziroma napovedati pretrga preskušancaIn the present study the characteristics of electrochemical noise generated by different types of corrosion have been examined. The potential and current noise have been measured between three identical electrodes made from the same material (AISI 302) in aqueous solutions with different concentration of chlorides and/or additions of acid at the higher temperature. The common electrode was under tensile load. The optical microscope supported by a computer visualization technique was used simultaneously during the tests and compared with signals of electrochemical noise generated at the same time. In order to characterise the measured signals, and especially to distinguish between the signals of electrochemical noise generated by pitting corrosion, stress-corrosion cracking and uniform corrosion, various parameters known from the fractal theory and theory of chaos were estimated. It is concluded that the electrochemical noise measurements and analysis can distinguish between uniform corrosion and different types of localised corrosion. We can detect breakdown of passive film, repassivation and growth of stable pitts. We can also detect the initiation of cracks, but we still cannot follow to the propagation of crack

Differences between 3-D printed and traditionally milled CoCr dental alloy from casted block in oral environment

The aim of this study was to compare corrosion resistance and ion release in CoCr dental alloys with identical chemical compositions produced using different technologies (SLM – selective laser melting and milling from cast blocks) and heat treatment (SLM parts only). The corrosion properties were tested in artificial saliva, artificial saliva with fluoride ions, and artificial saliva with added lactic acid to simulate inflammations. The study included electrochemical tests, microstructural investigation and ion release tests in the three different environments for a total of 42 days. The best performance of CoCr as a result of potentiodynamic polarization was observed in the artificial saliva with added lactic acid, which is in contradiction with the highest ion release measured from all the materials tested and electrochemical impedance spectroscopy that showed a deterioration of the passive layer in an acidic environment. Microstructural investigation revealed that different phases precipitated by heat treatment trigger increased release of Mo and W ions. The printing method does not raise critically ion release from CoCr alloy, while the state of the surface greatly impacts the extent of the ion release. This study demonstrates the importance of an interdisciplinary approach to the study of corrosion and biocompatibility in dental alloys