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Effect of recasting on the thickness of metal-ceramic interface of nickel-chromium and cobalt-chromium alloys  [PDF]
Mirkovi? Nemanja,Draganjac Miroslav,Stamenkovi? Dragoslav,Risti? Ljubi?a
Vojnosanitetski Pregled , 2008, DOI: 10.2298/vsp0805365m
Abstract: Introduction/Aim. This research was done to establish recasting effects of nickel-chromium and cobalt-chromium alloys on the thickness of their metal-ceramic interface in making fixed partial dentures. Metal-ceramic interface determines their functional integrity and prevents damages on ceramics during mastication. Investigation of metal-ceramic samples is supposed to show if base metal alloys for metalceramics are successfully recycled without any risk of reduction of metal-ceramic interface thickness. Methods. The research was performed as an experimental study. Per six metal-ceramic samples of nickel-chromium alloy (Wiron99) and cobalt-chromium alloy (Wirobond C) were made each. Alloy residues were recycled through twelve casting generations with the addition of 50% of new alloy on the occasion of every recasting. Analysis Energy Dispersive X-ray (EDX) (Oxford Instruments) and Scanning Electon Microscop (SEM) analysis (JEOL) were used to determine thickness of metal-ceramic interface together with PC Software for quantification of visual information's (KVI POPOVAC). Results. Results of this research introduced significant differences between thickness of metal-ceramic interface in every examined recycle generation. Recasting had negative effect on thickness of metal-ceramic interface of the examined alloys. This research showed almost linear reduction of elastic modulus up to the 12th generation of recycling. Conclusion. Recasting of nickel-chromium and cobaltchromium alloys is not recommended because of reduced thickness of metal-ceramic interface of these alloys. Instead of recycling, the alloy residues should be returned to the manufacturers.
Effect of recasting on the elastic modulus of metal-ceramic systems from nickel-chromium and cobalt-chromium alloys  [PDF]
Mirkovi? Nemanja
Vojnosanitetski Pregled , 2007, DOI: 10.2298/vsp0707469m
Abstract: Background/Aim. Elastic modulus of metal-ceramic systems determines their flexural strength and prevents damages on ceramics during mastication. Recycling of basic alloys is often a clinical practice, despite the possible effects on the quality of the future metal-ceramic dentures. This research was done to establish recasting effects of nickel-chromium and cobalt-chromium alloys on the elastic modulus of metalceramic systems in making fixed partial dentures. Methods. The research was performed as an experimental study. Six metal-ceramic samples of nickel-chromium alloy (Wiron 99) and cobalt-chromium alloy (Wirobond C) were made. Alloy residues were recycled through twelve casting generations with the addition of 50% of new alloy on the occasion of every recasting. Three- point bending test was used to determine elastic modulus, recommended by the standard ISO 9693:1999. Fracture load for damaging ceramic layer was recorded on the universal testing machine (Zwick, type 1464), with the speed of 0,05 mm/min. Results. The results of this research revealed significant differences between elasticity modules of metal-ceramic samples in every examined recycle generation. Recasting had negative effect on the elastic modulus of the examined alloys. This research showed the slight linear reduction of elastic modulus up to the 6th generation of recycling. After the 6th recycling there was a sudden fall of elastic modulus. Conclusion. Recasting of nickelchromium and cobalt-chromium alloys is not recommended because of the reduced elastic modulus of these alloys. Instead of reusing previously recasted alloys, the alloy residues should be returned to the manufacturer. .
Nickel-Containing Alloys for Medical Application Obtained by Methods of Mechanochemistry and Powder Metallurgy  [PDF]
D. D. Radev
ISRN Metallurgy , 2012, DOI: 10.5402/2012/464089
Abstract: The methods of mechanochemistry, in combination with cold pressing and pressureless sintering, were used to obtain the most popular nickel-based and nickel-containing alloys used in dentistry and implantology. It was shown that the intense mechanical treatment of Ni, Ti, and Cr powders used as reagents, and the application of the above-mentioned simple powder metallurgical technique for densification allows obtaining NiCr and NiTi alloys with controlled structural properties. The nickel-based dental alloys obtained by mechanically activated sintering possess excellent mechanical, technological, and aesthetic properties. These alloys are suitable as dental restorative materials and for production of porcelain veneered constructions like crowns and bridges using the so-called metal-to-ceramic dental technique. It was shown that the method of mechanically assisted synthesis allows obtaining nanosized NiTi alloy at significantly lower temperature in comparison with the traditional high-temperature alloying. It was also shown that after 40 hours intense mechanical treatment of reagents, a direct synthesis of NiTi alloy proceeds. The product has excellent sinterability which enables to produce bodies with controlled porosity appropriate for application in implantology. 1. Introduction The range of traditional application of nickel-based alloys covers different areas that require high performance at elevated temperatures. The formation of continuous matrix austenitic phase, that usually contains various percentages of Cr, Mo, W, Fe, and Co, the presence of coherently precipitating phases, and carbide or boride grain boundary segregates gives possibilities to form variety of alloys working at extremely high temperatures subjected to a combination of mechanical stresses and thermal shocks. The large number of Ni-based superalloys and the multiplicity of their properties and areas of application are a good example in this respect. Due to the attractive combination of good mechanical properties, chemical resistivity and biocompatibility Ni-based alloys also find a broad application in the fields of dentistry and implantology. Nickel-chromium and nickel-titanium alloys are the most popular representatives in these two medical branches. 1.1. Nickel-Chromium Dental Alloys Dental alloys could be categorized as noble, containing as a main element gold or palladium and base nickel or cobalt metal alloys [1]. The significant increases of the noble metals price since 1960s stimulate the development of nonprecious nickel-based dental alloys. Nowadays Ni-based alloys used
Bond strength of three dental porcelains to Ni-Cr and Co-Cr-Ti alloys
Fernandes Neto, Alfredo Julio;Panzeri, Heitor;Neves, Flavio Domingues;Prado, Ricardo Alves do;Mendon?a, Gustavo;
Brazilian Dental Journal , 2006, DOI: 10.1590/S0103-64402006000100006
Abstract: ceramometal bond strength has played an important role for the replacement of gold alloys by nickel-chromium alloys in dentistry. this study evaluated the metal/porcelain bond strength of three ceramic systems (vita vmk 88, williams and duceram) associated with three nickel-chromium alloys (durabond, lite cast b and resistal p) and one experimental cobalt-chromium-titanium alloy. thirty cast cylinder specimens (15 mm in height; 6 mm in diameter) were obtained for each alloy, in away that 10 specimens of each alloy were tested with each porcelain. bond strength was measured with an emic screw-driven mechanical testing machine by applying parallel shear forces to the specimens until fracture. kruskal-wallis and mann-whitney u tests were used for statistical analysis of the alloy/ceramic combinations (p<0.05). resistal p/duceram had significantly higher bond strength (44.38±9.12 mpa) (p<0.05) than the other combinations, except for co-cr-ti alloy/vita vmk 88 (38.41±12.64 mpa). the association of the experimental co-cr-ti alloy with williams porcelain had significantly higher bond strength (28.20±3.86 mpa) than the combination of other alloys with the same porcelain (p<0.05). based of these results and within the limitations of an in vitro study, it may be concluded that the bond strength of the three ceramic systems to the ni-cr and co-cr-ti alloys varied significantly, indicating that metal/ceramic compatibility was very important to the bond strength.
Studies on the Codeposition of SiC Nanopowder with Nickel, Cobalt, and Co-Ni Alloys  [PDF]
Ewa Rudnik,S?awomir Syrek
Journal of Coatings , 2014, DOI: 10.1155/2014/659697
Abstract: Electrodeposition of SiC nanopowder (approximately 120?nm) with nickel, cobalt, and Co-Ni alloy matrix was studied. It was found that particles suspended in the bath affect slightly the reduction of metallic ions. Incorporation of the ceramic particles was governed mainly by the morphology of the matrix surface, while no strict correlation between the amount of cobalt ions adsorbed on the powder and the SiC content in the composites was found. Microhardness of nickel deposits was ?HV, while for cobalt-rich coatings (84–95?wt.% Co) the values were in the range of 260–290?HV, independently of the SiC content in the coatings. Fine-grained nickel deposits were characterized by good corrosion resistance, while cobalt and Co-Ni alloys showed high corrosion current densities. 1. Introduction Electrodeposited composite coatings consist of intentionally joined together two or more components (i.e., matrix and reinforcement) with different properties receiving a new unique and macroscopically monolithic material exhibiting desirable, better, or different characteristics in comparison with each individual component or only mixed together. Properties of the composites are determined not only by a kind of matrix (metal or alloy), but also by the type and size of the incorporated particles. Various metal-particle combinations have been developed [1, 2]. Among them nickel matrix composites seem to be the most investigated systems [1–6], while composite coatings based on cobalt [1, 7–9] and Co-Ni alloys [10–13] were studied in a lesser extent. Coatings are reinforced usually with ceramic particles as carbides, oxides, nitrides, borides, and so forth. Such materials show high hardness and strength, but a decrease in the properties at elevated temperatures can occur in some cases [14]. A series of our previous studies on the codeposition of the composites was carried out using micron-sized SiC particles. The percentage of ceramic phase in the electrodeposited Ni, Co, and Co-Ni alloy matrix composites as well as some properties of the layers determined in the dependence on the powder concentration in the plating bath, current density, and the presence of some additives were reported [14–19]. The present paper is focused on understanding the influence of the electrolyte composition and the presence of SiC nanoparticles in the plating bath on the course of the cathodic reactions as well as composition, morphology, and some properties of the deposits. It is known that behavior of nanoparticles during electrodeposition differs seriously from that observed for the particles
Thermal Expansion Behaviour of Ternary Nickel-Based, Cobalt-Based, and Iron-Based Alloys Containing Very High Fractions of Carbides  [PDF]
Patrice Berthod,Lionel Aranda
ISRN Metallurgy , 2012, DOI: 10.5402/2012/750914
Abstract: Some of the wear-resistant pieces or coatings, constituted of a metallic matrix and of carbides present in high fractions, are a mix, in similar quantities, of two materials displaying greatly different levels of hardness but also of thermal expansion coefficient. When temperature increases, the second difference of property may lead to particular geometrical behaviours. To study these differences, nine nickel-based, cobalt-based, and iron-based alloys containing very high quantities of carbides were elaborated by foundry. In their as-cast conditions, the microstructures of these alloys were characterized; their hardness and thermal expansion until 1200°C were measured and analysed, with regard to the evolution of the structures predicted by thermodynamic calculations. The hardness of the alloys is high (nickel alloys) or very high (cobalt and iron alloys, 600?Hv and more) while the thermal expansion is greatly influenced by carbides, notably when temperature has become very high. Some of the variations of thickness at the end of heating or during an isothermal stage at 1200°C, essentially contraction, directly result from the mechanical interaction between matrix and carbides which was accumulated during the heating. 1. Introduction Refractory metallic alloys containing significant quantities of carbides are of a great importance for high temperature applications [1, 2], even if they are less common than the -type superalloys, solid-solution strengthened cobalt-based superalloys, or heat-resistant steels. Many of the carbides-strengthened alloys are based on nickel, cobalt, or iron and elaborated by foundry. They generally contain great quantities (several tens percents in weight) of chromium, which is a carbide-former element promoting, in presence of carbon, the formation of Cr7C3 or Cr23C6 carbides. The chromium-rich cast nickel-based alloys are used for numerous applications, notably for turbine blades in aeronautics, for which chromium brings to the alloys a good resistance against high temperature oxidation [3, 4]. Carbon can be added to the (Ni, Cr-) based alloys in order to obtain high levels of mechanical resistance and an example of hardness [5–8]. Cobalt-based alloys rich in chromium are also considered for hot parts in aeronautic turbines and power generation machines, as well as for other applications like some of the fiberizing tools used in the glass industry [9]. Generally several tens of weight percents of chromium are added to cobalt to allow the alloy sufficiently resisting hot corrosion by various molten substances (salts, glasses,
Shear bond strength of dental porcelains to nickel-chromium alloys
Prado, Ricardo Alves do;Panzeri, Heitor;Fernandes Neto, Alfredo Julio;Neves, Flávio Domingues das;Silva, Marlete Ribeiro da;Mendon?a, Gustavo;
Brazilian Dental Journal , 2005, DOI: 10.1590/S0103-64402005000300006
Abstract: the continuous technological advance and increasing availability of new base metal alloys and ceramic systems in the market, coupled to the demands of daily clinical practice, have made the constant evaluation of the bond strength of metal/porcelain combinations necessary. this study evaluated the metal/porcelain shear bond strength of three ceramic systems (duceram, williams and noritake) in combination with three nickel-chromium (ni-cr) alloys (durabond, verabond and viron). thirty cast cylinder specimens (15 mm high; 6 mm in diameter) were obtained for each alloy, in a way that 10 specimens of each alloy were tested with each porcelain. bond strength was measured with an emic screw-driven mechanical testing machine by applying parallel shear forces to the specimens until fracture. shear strength was calculated using the ratio of the force applied to a demarcated area of the opaque layer. mann-whitney u test was used for statistical analysis of the alloy/ceramic combinations (p<0.05). viron/noritake had the highest shear bond sregnth means (32.93 mpa), while verabond/duceram (16.31 mpa) presented the lowest means. viron/noritake differed statistically from other combinations (p<0.05). viron/duceram had statistically significant higher bond strengths than verabond/duceram, verabond/williams and durabond/noritake (p<0.05). it was also found significant difference (p<0.05) between verabond/noritake, verabond/duceram and durabond/noritake. no statistically significant difference (p>0.05) were observed among the other combinations. in conclusion, the noritake ceramic system used together with viron alloy presented the highest resistance to shear forces, while duceram bonded to verabond presented the lowest bond strength. viron/duceram and verabond/noritake provided intermediate results. the combinations between the williams ceramic system and ni-cr alloys had similar shear strengths among each other.
Contact sensitivity to metals (chromium, cobalt and nickel) in childhood
Brand?o, Marilda Helena Toledo;Gontijo, Bernardo;
Anais Brasileiros de Dermatologia , 2012, DOI: 10.1590/S0365-05962012000200012
Abstract: metals, especially nickel, are the most common contact allergens in children. recent data has shown increased incidence of allergy in industrialized countries. sensitization can occur at any age, even in neonates. costume jewelry, particularly earrings, is linked to increased sensitization to nickel. sensitization to cobalt often occurs by the use of costume jewelry. the most common source of sensitization to chromium is leather. due to the absence of a specific therapy, the main treatment is to identify and avoid the responsible allergens. this article presents an updated view on the epidemiological and clinical aspects of contact allergy to metals, focusing on prevention strategies and risk factors, and warns about possible and new sources of contact.
Effect of Heat Treatment on the Corrosion Behavior of Nickel Chromium (Wiron 99) Alloys  [PDF]
Supreetha SN,Ravindra K,Murali H
Indian Journal of Dental Advancements , 2010,
Abstract: The purpose of this study was to evaluate the corrosion behavior of Nickel chromium alloys (Wiron 99) in the as-cast condition and when subjected to different firing temperatures. This information is important as the firing porcelain on the metal substructure of a restoration may produce changes in corrosion behavior that could influence an alloy behavior during long term use. This study was also designed to study comprehensively the clinical serviceability of these Nickel chromium alloys.
Use of base metal casting alloys for implant framework: marginal accuracy analysis
Kano, Stefania Carvalho;Bonfante, Gerson;Hussne, Raquel;Siqueira, Aline F.;
Journal of Applied Oral Science , 2004, DOI: 10.1590/S1678-77572004000400016
Abstract: the original protocol for implant prosthesis recommends the use of a gold framework for acrylic and ceramic prosthesis. however, due to its high cost, the use of alternative alloys is desired. this study compares the marginal accuracy of pre-made cylinders versus plastic cylinders cast with two different base metal casting alloys. five samples each of (1) plastic cylinder cast in cobalt-chromium alloy, (2) plastic cylinder cast in nickel-chromium alloy, and (3) silver-palladium pre-made cylinder (control) were examined for marginal accuracy according to: (a) vertical gap; (b) horizontal gap and (c) horizontal gap depth at the abutment/cylinder interface. data were submitted to statistical analysis (anova and student-newman keuls, p<0.05). mean values for vertical, horizontal and gap depth were 4.13μm, 14.5μm and 6.93μm for pre-made cylinder, 23.18μm, 33.2μm and 88μm for ni-cr cast cylinder and 25.6μm, 51.8μm and 114.54μm for co-cr cast cylinder. no statistically significant differences were found between cast groups (1 and 2), but significant better fit was obtained with pre-made metal cylinders when compared to cast cylinders with ni-cr and co-cr alloys, for all analyses.
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