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Age-hardening characteristics of a dental low-carat gold alloy with dual hardener system of In and Cu
Hyo-Joung Seol,Seong-Woo Kweon,Su-Yeon Cho,Gwang-Young Lee,Yong Hoon Kwon,Hyung-Il Kim
Gold Bulletin , 2011, DOI: 10.1007/s13404-011-0034-5
Abstract: The age-hardening characteristics of a dental low carat gold alloy with a dual hardener system of indium (In) and Cu (33.9 Au–26.2 Ag–20.28 Cu–9.8 Pd–7.8 In–2 Zn (at%)) were examined by observing the age hardenability and related phase transformation, microstructural changes and elemental distribution during the aging process at 400°C. The dual hardener system by the use of both In and Cu provided more powerful hardening effect compared to a single-hardener system of In or Cu, without the formation of a AuCu type ordered phase. The alloy showed apparent initial hardening, which was attributed to the pre-precipitation or zone formation by the help of quenched in excess vacancies. During the constant increase in hardness, the single parent phase separated into three phases, Au–Ag-based phase, Au–Cu-based phase containing Pd and In, and InPd-based phase, through a metastable state. Indium which was added as one of the hardeners induced initial grain boundary precipitation, followed by an expansion of the lamellar structure, which was responsible for softening. The alternative lamellar structure was composed of a Cu-rich layer (Au–Cu-based phase containing Pd and In) and an Ag-rich layer (Au–Ag-based phase) replaced partly by the InPd-based phase. Separation of the Ag-rich layer from the Cu-rich layer is based on the miscibility limit of Ag and Cu due to their eutectic property.
Age-hardening and overaging mechanisms related to the metastable phase formation by the decomposition of Ag and Cu in a dental Au–Ag–Cu–Pd–Zn alloy
Sang-Hwa Lee,In-Sook Lim,Mi-Hyang Cho,Ae-Ri Pyo,Yong Hoon Kwon,Hyo-Joung Seol,Hyung-Il Kim
Gold Bulletin , 2011, DOI: 10.1007/s13404-011-0021-x
Abstract: The age-hardening and overaging mechanisms related to the metastable phase formation by the decomposition of Ag and Cu in a dental casting gold alloy composed of 56Au–25Ag–11.8Cu–5Pd–1.7Zn–0.4Pt–0.1Ir (wt.%) were elucidated by characterizing the age-hardening behaviour, phase transformations, changes in microstructure and changes in element distribution. The fast and apparent increase in hardness at the initial stage of the aging process at 400°C was caused by the nucleation and growth of the metastable Ag–Au-rich phase and the Cu–Au-rich phase by the miscibility limit of Ag and Cu. The transformation of the metastable Ag–Au-rich phase into the stable Ag–Au-rich phase progressed concurrently with the ordering of the Cu–Au-rich phase into the AuCu I phase through the metastable state, which resulted in the subsequent increase in hardness. The further increase in hardness was restrained before complete decomposition of the parent α0 phase due to the initiation of the lamellar-forming grain boundary reaction. The progress of the lamellar-forming grain boundary reaction was not directly connected with the phase transformation of the metastable phases into the final product phases. The heterogeneous expansion of the lamellar structure from the grain boundary caused greater softening than the subsequent further coarsening of the lamellar structure. The lamellar structure was composed of the Ag–Au-rich layer which was Cu-, Pd- and Zn-depleted and the AuCu I layer containing Pd and Zn.
Age-hardening by grain interior and grain boundary precipitation in an Au-Ag-Pt-Zn-In alloy for multipurpose dental use
Joo-Hee Park,Mi-Hyang Cho,Mi-Gyoung Park,Yong Hoon Kwon,Hyung-Il Kim,Hyo-Joung Seol
Gold Bulletin , 2010, DOI: 10.1007/BF03215001
Abstract: The complex precipitation mechanisms related to the age-hardening of Cu-free Au-Ag-Pt-Zn-In alloy for multipurpose dental use was studied by means of hardness test, X-ray diffraction (XRD) studies, field emission scanning electron microscopic (FE-SEM) observations, energy dispersive spectrometer (EDS) analysis, and electron probe microanalysis (EPMA). The early diffusion and then clustering of the In-concentrated phase in the grain interior, together with the early diffusion and then ordering of the PtZn phase in the grain boundary, introduced the internal strains in the Au-Ag-rich α1 matrix, resulting in the hardening process. As the Au-Ag-rich α 1 ’ and PtZn β lamellarforming grain boundary reaction progressed, the phase boundaries between the solute-depleted face-centered cubic (FCC) α 1 ’ matrix and the face-centered tetragonal (FCT) PtZn β precipitate reduced, resulting in softening. In the particlelike structures composed of the major Pt-Au-rich α2 phase and the minor Pt-Zn-rich α3 phase, the separation of In and Zn progressed producing the In-increased Pt-Au-rich α 2 ’ phase and the Zn-increased PtZn α3′ phase with aging time without restraining the softening. The miscibility limit by complex systems of Au-Pt, Ag-Pt, Au-In and In-Zn resulted in the phase transformation and related microstructural changes.
Tarnish and corrosion behaviour of dental gold alloys
Leon W. Laub,John W. Stanford
Gold Bulletin , 1981, DOI: 10.1007/BF03216554
Abstract: For many years the specification of alloy composition, particularly high gold and platinum contents, was considered sufficient to guarantee the stability of dental prostheses in the oral environment. This article reveals a considerably more complex situation and stresses the need for extensive laboratory and clinical testing of new alloy formulations before these may be unreservedly recommended to practitioners.
Age-hardening and related phase transformations in dental gold alloys
Katsuhiro Yasuda
Gold Bulletin , 1987, DOI: 10.1007/BF03214661
Abstract: Gold alloys that can be hardened by thermal ageing play an important role in dentistry. But the ordering and precipitation phenomena responsible for hardening are complex and not fully understood. In this comprehensive survey of the field, the author shows that transmission electron microscopy coupled with electron diffraction measurements is a powerful tool for studying age-hardening mechanisms in dental gold alloys.
Hardening of gold-based dental casting alloys
Jean-Jacques Labarge,Daniel Tréheux,Pierre Guiraldenq
Gold Bulletin , 1979, DOI: 10.1007/BF03216539
Abstract: The ordering and precipitation phenomena responsible for hardening of gold-based alloys used in jewellery and in dentistry are complex and by no means fully understood. The authors of this article review these effects and present evidence which indicates that separation of gold-zinc intermetallic phases may contribute to such hardening in certain alloys.
Effect of age hardening on corrosion resistance and hardness of CoCrMo alloys used in dental engineering  [PDF]
L.A. Dobrzański,?. Reimann,C. Krawczyk
Archives of Materials Science and Engineering , 2012,
Abstract: Purpose: The goal of the study is to research the effect of various time of ageing on corrosion resistance, hardness and structures of Remanium 2000+ Co-Cr-Mo alloys used in prosthodontia.Design/methodology/approach: To investigation was prepared mould, cast in 1430°C and realized the heat treatment: solutioning in 1250°C by 3 hours and then ageing in 850°C by 4, 8, 16 and 24 hours. Electrochemical corrosion examination were made in water center which simulated artificial saliva environment. The evaluation of breakdown potential was realized by recording of anodic polarization curves with use the potentiodynamic methods. Corrosion resistance test were carried out at room temperature and use of the VoltaLab PGP201 system for electrochemical tests. Hardness test were obtained by use the microhardness FM ARS 9000 FUTURE TECH with load 1 kg. Structure observation was made after surface preparation: grinding, polishing and etching by light microscope LEICA MEF4A with the magnification 500x.Findings: The age hardening for Co-Cr-Mo alloys is one of the possible method which effect in forming the hardness. The highest value of hardness were obtain for specimen which was ageing with the longer time. Research alloy characterized dendritic crystals in structure for all realized heat treated process. At specimen after the longer ageing was observed the most of discontinuous precipitation and stacking faults in compare with specimen ageing by 4 hours. The age hardening doesn’t influenced much on electrochemical results and only the open circuit potential changed by decreased while increased ageing time. The values of breakdown potential and repassivation potential kept at a constant level.Practical implications: Research material is used on dentures so it’s demand that their characterized corrosion resistance and result of this work make up an information on what heat treatment parameters may be pay attention for CoCrMo alloys.Originality/value: The paper present effect of age hardening especially the ageing time, on the most important criteria of CoCrMo alloys use in dental engineering.
Gold alloys for porcelain-fused-to-metal dental restorations
Randall M. German
Gold Bulletin , 1980, DOI: 10.1007/BF03215454
Abstract: The age-hardenable dental alloys that have been developed specifically for use with porcelain veneers rely on high gold contents to ensure biocompatibility and on palladium and platinum additions to raise their melting range. Base metals such as iron, cobalt, nickel and copper are used to promote hardness and to give these alloys an age hardening potential. This study shows that age hardening results from the ordering of an FePt-type compound, a reaction which is insensitive to variations in porcelain firing cycles.
Age-hardenability and related microstructural changes during and after phase transformation in an Au-Ag-Cu-based dental alloy
Kim, Hyung-Il;Kim, Tae-Wan;Kim, Young-Oh;Cho, Su-Yeon;Lee, Gwang-Young;Kwon, Yong Hoon;Seol, Hyo-Joung;
Materials Research , 2013, DOI: 10.1590/S1516-14392012005000169
Abstract: the aim of this study was to clarify how the microstructural changes during and after phase transformation determine the age-hardenability of an au-ag-cu-based dental alloy. the rapid increase in hardness in the initial stage was the result of rapid atomic diffusion by spinodal decomposition into metastable ag-rich' and cu-rich' phases. the constant hardening after apparent initial hardening was the result of a subsequent transformation of the metastable ag-rich' and cu-rich' phases to the stable ag-rich α1phase and aucu i phase through the metastable aucu i' phase. during the increase in hardness, fine block-like structure with high coherency formed in the grain interior, which changed to a fine cross-hatched structure. a relatively coarse lamellar structure composed of ag-rich α1and aucu i phases grew from the grain boundaries, initiating softening before the grain interior reached its maximum hardness. as a result, the spinodal decomposition attributed to rapid hardening by forming the fine block-like structure, and the subsequent ordering into aucu i, which is a famous hardening mechanism, weakened its hardening effect by accelerating the lamellar-forming grain boundary reaction.
Characteristic of intermetallic phases in cast dental CoCrMo alloy  [PDF]
M. Podrez-Radziszewska,K. Haimann,W. Dudziński,M. Morawska-So?tysik
Archives of Foundry Engineering , 2010,
Abstract: Apart from chromium and molybdenum, casting alloys of cobalt usually contain also up to 0.35 % of carbon. With significant content ofcarbon, presence of carbide-forming alloying elements results in creating carbide phases. These alloys are characterised by dendriticstructure of solid solution of chromium and molybdenum in cobalt with interdendritically precipitated carbides. Because of high chromiumcontent, dominating are M23C6-type carbides, but chromium-rich carbides can be also of M7C3 and M3C2-types. The other elements inthe alloy result in creating M6C and MC-type carbides. In the case of low carbon content, creating carbides and forming intermetallicphases based on the alloying elements and cobalt become limited.The presented research was aimed at characterising structure of the cobalt-based dental alloy containing trace quantity of carbon.Characterised were intermetallic phases hardening the alloy. Microscopic examinations using light microscopy, SEM and TEM werecarried out. Chemical microanalysis of the precipitates using X-ray analyser EDS was performed, as well as phase analysis using selectedarea electron diffraction.
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