TY - JOUR A1 - Tezel, Tugce A1 - Schultheiss, Ulrich A1 - Hornberger, Helga A1 - Kovan, Volkan T1 - Operational wear behaviour of 3D-printed lightweight metal gears: EDS and oil analysis comparison JF - Materials Testing N2 - Additive manufacturing (AM) has come to the fore in recent years among manufacturing techniques. This technique, which has different advantages than traditional ones such as casting, forging and machining, is expected to be widely used in producing machine parts like gears in the coming years. Therefore, experimental data on AM parameters for lightweight metal gears are important for industrial production. In this study, a wear test was applied to AlSi10Mg and Ti6Al4V gears under operational conditions, and the wear behaviour of conventionally and additively manufactured gears was compared. The amount of abrasion elements was determined by analysing the oil in the gearbox. In addition, gear surfaces were analysed using scanning electron microscopy and an energy-dispersive spectrometer before and after wear. Thus, the wear behaviour of gears produced by conventional and AM under service conditions was demonstrated comparatively. KW - additive manufacturing KW - titanium KW - aluminium KW - gear KW - wear Y1 - 2024 U6 - https://doi.org/10.1515/mt-2023-0222 SN - 0025-5300 VL - 66 IS - 6 SP - 830 EP - 834 PB - de Gruyter ER - TY - JOUR A1 - Reich, Sven A1 - Hornberger, Helga T1 - The effect of multicolored machinable ceramics on the esthetics of all-ceramic crowns JF - Journal of Prosthetic Dentistry N2 - Statement of problems: Computer-aided design/computer-assisted machining systems offer the possibility of fabricating restorations from one machinable ceramic block. Whether multishaded blocks improve esthetic results and are a viable alternative to individually stained ceramics has not been fully determined. Purpose: The aim of this investigation was to examine the effect of multishaded blocks on the esthetic appearance of all-ceramic CEREC crowns and compare these crowns with single-shade and stained restorations. Material and methods: Ten subjects were included in this study. For each subject, 6 different crowns were milled with the use of a CEREC machine. One crown was milled from each of the following machinable ceramic materials: CEREC Vitablocs Mark II in classic colors; Vitablocs Mark II in 3D-Master colors; Vitablocs Mark II in either classic or 3D-Master colors, with additional staining; Megadenta Bloxx multishaded; Mark II experimental multilayer; and an experimental multilayer leucite ceramic. Three independent examiners assessed the esthetic appearance of crowns fabricated to match each subject's anterior tooth shade. A scale of 1 to 6 was used to score the shade match and esthetic adaptation of each crown, with 1 representing excellent characteristics and 3.5 serving as the threshold for clinical acceptability. The examiners' scores were averaged, and the mean values were analyzed with the Wilcoxon signed rank test (P=40 MPa as measured according to ISO 6 872; said second material is an organic material which at least partly fills the pores of said porous matrix; and said composite material has a modulus of elasticity, E, of >=25 GPa as measured according to ISO 10 477. Y1 - 2001 UR - https://depatisnet.dpma.de/DepatisNet/depatisnet?action=bibdat&docid=US020090001623A1 ER - TY - PAT A1 - Muerrle, Ulrich A1 - Hornberger, Helga T1 - Method of making a ceramic restoration N2 - Production of a dental reconstruction comprises: (a) forming a mold (12) from a model (10); (b) using (12) to make an isotropically heat-expandable replica from a ceramic precursor (14); (c) oxidizing (14) to produce an enlarged ceramic replica; (d) forming a silicone mold from this replica; (e) using (d) to make a second ceramic replica; and (f) sintering the second replica with volume reduction to form a replica identical to (10). T2 - Verfahren zur Herstellung einer Zahnrestauration aus Keramik Y1 - 2003 UR - https://depatisnet.dpma.de/DepatisNet/depatisnet?action=bibdat&docid=EP000001346702A1 ER - TY - JOUR A1 - Hornberger, Helga A1 - Marquis, Peter M. A1 - Franks, J. T1 - The impact of diamond-like coatings on the strength of dental ceramics JF - Journal of Dental Research Y1 - 1995 VL - 74 SP - 522 ER - TY - JOUR A1 - Hornberger, Helga A1 - Marquis, Peter M. T1 - Mechanical properties and microstructure of In-Ceram BT - a ceramic-glass composite for dental crowns JF - Glastechnische Berichte - Glass Science and Technology Y1 - 1995 VL - 68 IS - 6 SP - 188 EP - 194 ER - TY - JOUR A1 - Kloiber, Jessica A1 - Anetsberger, Viktoria A1 - Schultheiß, Ulrich A1 - Hornberger, Helga T1 - High quality surfaces of magnesium alloy AZ31 by adjusting appropriate electropolishing parameters JF - Electrochimica Acta Y1 - 2025 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:898-opus4-79298 N1 - Corresponding author der OTH Regensburg: Jessica Kloiber VL - 513 PB - Elsevier ER - TY - JOUR A1 - Kloiber, Jessica A1 - Schultheiß, Ulrich A1 - Hornberger, Helga T1 - Impact of heat treatment on the surface quality of electropolished WE43 alloy JF - Materials Letters N2 - In this study, the Mg alloy WE43 was solution annealed and precipitation hardened prior to electropolishing to evaluate the effects of different microstructures on the electropolishing result. While coarsely distributed precipitates led to surfaces showing wavy structures and dents after electropolishing, a uniform microstructure resulted in an even finish of the surface. The homogenization and refinement of the microstructure by heat treatment is a method to ensure improved electropolished surfaces of Mg materials Y1 - 2025 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:898-opus4-83512 SN - 0167-577X N1 - Corresponding author der OTH Regensburg: Jessica Kloiber VL - 397 PB - Elsevier BV ER - TY - JOUR A1 - Manaranche, Claire A1 - Hornberger, Helga T1 - A proposal for the classification of precious dental alloys according to their resistance to corrosion based on the iso 10271 standard JF - European Cells and Materials N2 - A lot of dental alloys are available on the market. Among these alloys, there are the conventional alloys, the so called casting alloys used without ceramics, the bonding alloys used with high fusing ceramics and the universal alloys used without or with low fusing ceramics. It is im portant to know the physical and mechanical properties of these materials but also their biocompatibility and their resistance to corrosion. Dental alloys are generally placed in the mouth for many years, they must not induce adverse biological reactions such as gingival swelling and erythema, mucosal pain and lichenoid reactions. Although these troubles are often caused not by the materials itself (1, 2), they can be induced by the metallic ions released during their corrosion. In order to decrease the risks to the health, it is necessary to study the corrosion of the dental alloys. Currently, the ISO 10271 Standard (3), describes 3 different corrosion tests: a static immersion test (chemical corrosion), an electrochemic al test and a tarnish test. However, there are no indications yet about the possible interpretation of test results. In this paper, we propose a method to compare and classify the dental alloys in relation to their chemical and electrochemical corrosion results. METHODS: The material tested are pure metals such as gold, palladium, silver, copper and zinc as well as dental alloys which are commercially sold (see Table 1). 54 different materials have been tested. A minimum of four samples of each material were tested by electrochemic al corrosio n and a minimum of three in chemical test. The samples were cast and prepared as indicated by the manufacturer and by the ISO 10271. For the electrochemical test, the samples are in the form of disks 11 mm in diameter. They are tested with a potentiostat/galvanostat Voltalab Model 21. For the chemical test, the samples are rectangular with the dimensions 35X10X1.7 mm. The solution used and the operating conditions are described in the ISO 10271. The concentration of metallic ions released is measured by Induced Coupled Plasma Y1 - 2003 UR - https://www.researchgate.net/publication/242728857_A_proposal_for_the_classification_of_precious_dental_alloys_according_to_their_resistance_to_corrosion_based_on_the_ISO_10271_standard VL - 5 IS - SUPPL. 1 SP - 34 EP - 36 PB - Univ. of Wales CY - Aberystwyth, Wales ER - TY - JOUR A1 - Schultheiß, Ulrich A1 - Hornberger, Helga T1 - Comparison of etchants for corrosion-resistant stainless steels in medical engineering JF - Practical Metallography N2 - Corrosion-resistant stainless steels are widely used in medical engineering. Today, additive manufacturing techniques are also used for this purpose, in particular for implant steels. Additively processed materials sometimes react differently to etching than conventionally processed ones. The use of etchants for contrasting the microstructure must therefore be adapted. Chemical etching using V2A etchant, Murakami, and anhydrous Kalling solutions, as well as electrochemical etching using nitric acid, sodium hydroxide, and oxalic acid were performed. Etched samples made of conventionally processed X2CrNi-Mo17-12-2 were compared to samples manufactured using selective laser melting and sintering, and the optimal contrast was developed in each case. It can be shown that the different etchants reveal different microstructural constituents and that etchants must therefore be selected as a function of the application. N2 - Korrosionsbeständige Edelstähle werden vielfältig in der Medizintechnik eingesetzt. Dabei werden insbesondere bei Implantat-Stählen heute auch additive Fertigungstechniken angewandt. Additiv verarbeitete Materialien reagieren teilweise anders beim Ätzen als konventionell verarbeitete, weshalb der Einsatz von Ätzmitteln zur Gefüge-Kontrastierung adaptiert werden muss. Es wurde sowohl chemisch mit V2A-Beize, Murakami- und wasserfreier Kalling-Lösung geätzt, als auch elektrochemisch mit Salpetersäure, Natronlauge und Oxalsäure. Geätzte Proben aus konventionell verarbeitetem X2CrNiMo17-12-2 wurden mit Proben verglichen, die mittels selektivem Laserschmelzen und -sintern hergestellt wurden, und die jeweils optimale Kontrastierung entwickelt. Es kann gezeigt werden, dass die unterschiedlichen Ätzmittel verschiedene Gefügebestandteile hervorheben und somit je nach Anwendungsfall das jeweilige Ätzmittel ausgewählt werden muss. Y1 - 2024 U6 - https://doi.org/10.1515/pm-2024-0094 VL - 62 IS - 1 SP - 19 EP - 30 PB - de Gruyter ER - TY - INPR A1 - Kloiber, Jessica A1 - Anetsberger, Viktoria A1 - Schultheiss, Ulrich A1 - Hornberger, Helga T1 - Electropolishing of Magnesium Alloy Az31 with Varying Electrolyte Concentrations and Applied Potentials N2 - Magnesium alloy AZ31 is a light material with a good mechanical stability and is used in various engineering applications. Although its tendency to localized corrosion is a limiting factor in its use. Electropolishing is a widely used process for improving the surface roughness and corrosion behavior of metals. However, there is a lack of knowledge about the electropolishing of magnesium and its alloys. In this study, an optimal electropolishing process for AZ31 was developed to improve the surface properties by varying the electrolyte concentration and the applied potential. The electrolyte composition was a mixture of phosphoric acid, ethanol and deionized water. The applied potentials were selected based on measured current density potential curves. Thereby, electropolishing was performed up to an electric charge of 18 As. The experimental results indicate that the electropolishing process should be carried out at a low current density to avoid bubble evolution and surface defects. Therefore, the concentration of the electropolishing electrolyte should have an appropriate low conductivity, and the applied potential should be in the transient or passive region of the polarization curve recorded prior to electropolishing. It could be shown that an optimized electropolishing process improved the surface of AZ31 by providing a bright and mirror-like surface and a lower roughness compared to a mechanically ground surface. KW - magnesium alloy KW - AZ31 KW - electropolishing KW - electrolyte KW - surface characterization KW - polarization curve Y1 - 2024 U6 - https://doi.org/10.2139/ssrn.4991311 PB - SSRN ER - TY - JOUR A1 - Tezel, Tugce A1 - Schultheiss, Ulrich A1 - Hornberger, Helga A1 - Kovan, Volkan T1 - Operational wear behaviour of 3D-printed lightweight metal gears: EDS and oil analysis comparison JF - Materials Testing N2 - Additive manufacturing (AM) has come to the fore in recent years among manufacturing techniques. This technique, which has different advantages than traditional ones such as casting, forging and machining, is expected to be widely used in producing machine parts like gears in the coming years. Therefore, experimental data on AM parameters for lightweight metal gears are important for industrial production. In this study, a wear test was applied to AlSi10Mg and Ti6Al4V gears under operational conditions, and the wear behaviour of conventionally and additively manufactured gears was compared. The amount of abrasion elements was determined by analysing the oil in the gearbox. In addition, gear surfaces were analysed using scanning electron microscopy and an energy-dispersive spectrometer before and after wear. Thus, the wear behaviour of gears produced by conventional and AM under service conditions was demonstrated comparatively. KW - gear KW - wear KW - additive manufacturing KW - titanium KW - aluminium Y1 - 2024 U6 - https://doi.org/10.1515/mt-2023-0222 SN - 2195-8572 VL - 66 IS - 6 SP - 830 EP - 834 PB - de Gruyter ER - TY - JOUR A1 - Hornberger, Helga A1 - Weissmann, R. A1 - Lutz, N. T1 - Machining of silica glasses using excimer laser radiation JF - Glastechnische Berichte - Glass Science and Technology Y1 - 1996 VL - 69 IS - 2 SP - 44 EP - 49 ER - TY - JOUR A1 - Hornberger, Helga A1 - Marquis, Peter M. A1 - Christiansen, Silke H. A1 - Albrecht, Manuel A1 - Strunk, Horst P. A1 - Franks, J. T1 - Microstructure of a high strength alumina-glass composite combined with a diamond like carbon coating JF - Electron Microscopy and Analysis N2 - We investigate the mechanical and microstructural properties of a diamond-like carbon coating (DLC) which is deposited by plasma enhanced chemical vapor deposition (PECVD) onto an alumina/aluminosilicate glass composite used for biomedical applications. Ball-on-ring tests yield a fracture strength that is essentially influenced by the surface topology/roughness. The surface topology of the coating is investigated by atomic force microscopy (AFM). Tribology tests and nanoindentation represent the wear resistance and hardness; these are properties that are mainly influenced by the microstructural properties of the DLC coating. This microstructure is investigated by transmission electron microscopy (TEM) and analyzed by parallel electron energy loss spectroscopy (PEELS). For the general applicability of the coated composite, the interfacial adhesion of the DLC coating on the comparably rough substrate (roughness amplitudes and wavelengths are in the micrometer range) is important. Therefore, we focus on TEM investigations that show the interface to be free of gaps and pores that we, together with a characteristic microstructure adjacent to the interface, relate to the excellent adhesion. The interlayer consists of a high density of SiC grains, part of them directly bound to the substrate, and part of them bound to other SiC grains. This interlayer is followed by an essentially different region of the coating as concerns the microstructure; this region consists of nanocrystalline diamond particles embedded in an amorphous carbon matrix. It is this heterogeneous microstructure to which we attribute (i) the good adhesion based upon the interface stabilizing SiC grains, and (ii) the high hardness and wear resistance based upon the diamond nanocrystals in the coating. Y1 - 1995 U6 - https://doi.org/10.1557/JMR.1996.0244 SP - 559 EP - 562 ER - TY - JOUR A1 - Christiansen, Silke H. A1 - Albrecht, Manuel A1 - Strunk, Horst P. A1 - Hornberger, Helga A1 - Marquis, Peter M. A1 - Franks, J. T1 - Mechanical properties and microstructural analysis of a diamond-like carbon coating on an alumina/glass composite JF - Journal of Materials Research N2 - We investigate the mechanical and microstructural properties of a diamond-like carbon coating (DLC) which is deposited by plasma enhanced chemical vapor deposition (PECVD) onto an alumina/aluminosilicate glass composite used for biomedical applications. Ball-on-ring tests yield a fracture strength that is essentially influenced by the surface topology/roughness. The surface topology of the coating is investigated by atomic force microscopy (AFM). Tribology tests and nanoindentation represent the wear resistance and hardness; these are properties that are mainly influenced by the microstructural properties of the DLC coating. This microstructure is investigated by transmission electron microscopy (TEM) and analyzed by parallel electron energy loss spectroscopy (PEELS). For the general applicability of the coated composite, the interfacial adhesion of the DLC coating on the comparably rough substrate (roughness amplitudes and wavelengths are in the micrometer range) is important. Therefore, we focus on TEM investigations that show the interface to be free of gaps and pores that we, together with a characteristic microstructure adjacent to the interface, relate to the excellent adhesion. The interlayer consists of a high density of SiC grains, part of them directly bound to the substrate, and part of them bound to other SiC grains. This interlayer is followed by an essentially different region of the coating as concerns the microstructure; this region consists of nanocrystalline diamond particles embedded in an amorphous carbon matrix. It is this heterogeneous microstructure to which we attribute (i) the good adhesion based upon the interface stabilizing SiC grains, and (ii) the high hardness and wear resistance based upon the diamond nanocrystals in the coating. Y1 - 1996 U6 - https://doi.org/10.1557/JMR.1996.0244 VL - 11 IS - 8 SP - 1934 EP - 1942 ER - TY - JOUR A1 - Kloiber, Jessica A1 - Schultheiß, Ulrich A1 - Sotelo, Lamborghini A1 - Sarau, George A1 - Christiansen, Silke H. A1 - Gavras, Sarkis A1 - Hort, Norbert A1 - Hornberger, Helga T1 - Corrosion behaviour of electropolished magnesium materials JF - Materials Today Communications N2 - Although magnesium and its alloys are promising candidates as biodegradable implant materials, the tendency for localized corrosion mechanism in physiological environment limit their biomedical application. Electropolishing is an attractive strategy for improving the corrosion behaviour of metals, but it is still largely unexplored in magnesium materials. In this study, the characterization of electropolished surfaces of AM50 and pure magnesium was performed, focussing on their in vitro degradation behaviour in cell medium. Corrosion rates were evaluated using potentiodynamic polarisation. The surface morphology before and after the onset of corrosion was investigated by scanning electron microscopy and confocal laser scanning microscopy. The presented electropolishing process led to improved surface performances, observable by significantly lower corrosion rates (0.08 mm·year-1 in Dulbecco's modified Eagle's medium), lower arithmetical mean height (0.05 µm), lower water contact angle (25-35°) and lower micro hardness (35-50 HV 0.1) compared to mechanically and chemically treated surfaces. MgO/Mg(OH)2 could be detected on electropolished surfaces. The localized corrosion mode could be reduced, but not entirely prevented. Electropolishing shows great potential as post-treatment of magnesium-based components, but detailed tests of the long-term corrosion behaviour are an important area of future research. KW - biomedical application KW - corrosion behaviour KW - electropolishing KW - magnesium alloy KW - pure magnesium KW - surface characterization Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:898-opus4-68254 N1 - Corresponding author: Helga Hornberger PB - Elsevier ET - Journal Pre-proof ER -