Microstructures, Hardness and Corrosion Behaviours in a Neutral Artificial Saliva of a Series of {Cobalt-Chromium}-Based Alloys; Influence of the Presence and Contents of the Minor Elements W, Mo and Si

International audienceDental cobalt alloys devoted to the constitution of frameworks strengthening fixed partial dentures may be based on cobalt and chromium. Such alloys generally contain also other elements such as tungsten, molybdenum and silicon, for example. These minor elements may be added for mechanical reasons. In contrast with the alloys of the High Noble and Noble categories which are rich in gold or platinum, these cheaper alloys may be threatened by corrosion. When it happens this phenomenon may cause health problems, allergic diseases typically. The topic of this work is to characterize the electrochemical behavior of six alloys based on cobalt and containing 25 wt.%Cr, in a NaCl 9g/L aqueous solution rated at pH=7.4 and T=37°C

Corrosion Behavior in a Neutral Artificial Saliva of Several Binary Co-Cr Alloys with Various Chromium Contents

International audienceSubstitution of too expensive alloys rich in noble metals by alloys based on nickel or chromium is often considered in prosthetic dentistry. When containing chromium in quantities high enough the corrosion performances of the “predominantly base” alloys very interesting, as well as their mechanical properties. Such alloys are generally rather complex because of the presence of other elements such as molybdenum, tungsten, silicon and other, which may be active during corrosion and mask the importance of the chromium content. In this work it was chosen to look for a critical chromium content over which the corrosion behaviour is acceptable or very good, by working with simple binary Co-xCr alloys (x varying from 0 to 30 wt.% by slices of 5 wt.%) especially prepared by casting, by avoiding any interference of other elements classically present (Mo, W, Si…). Electrochemical investigations were carried out in a neutral 37°C-heated 9 g/L NaCl solution, classically used in such studies. Follow-up of open circuit potential, application of the Stern-Geary and Tafel methods, and cyclic polarizations allowed identifying 25 wt.% as being a threshold to respect for being certain to benefit from the highest corrosion resistance

High temperature properties of several families of TiC-reinforced cast Superalloys

Some poly-crystalline superalloys synthesized by classical foundry can be very refractory and offer unexpectedly high properties at elevated temperature. This is for example the case of some cobalt-based alloys strengthened by tantalum carbides or hafnium carbides. Besides, cast alloys based on Co, Ni or Fe, and containing other types of MC carbides may be also envisaged for high temperature applications. In this study this is the titanium carbide phase which is under consideration. Several Ni-based, Co-based and Fe-based alloys of the {M-25Cr-xC-yTi}-type (x=0.25 or 0.50, y=1 or 2, in wt.%) were synthesized by casting using a high frequency induction furnace under pure argon. Their microstructures were characterized by electron microscopy and energy dispersion spectrometry. Especially prepared samples were subjected to DTA control of the melting range, to {1200°C, 20MPa}-flexural creep tests and to oxidation in synthetic air at 1200°C. The as-cast microstructures are composed of equi-axed dendrites of matrix and of eutectic script-like TiC carbides, mixed with matrix, placed in the interdendritic spaces. The obtained temperatures of melting start are generally higher than 1300°C. The high temperature creep resistance and the behavior in oxidation by air both strongly depend on the base element. At 1200°C the best mechanical properties were obtained for the cobalt-based alloys and the best oxidation resistance was obtained for the nickel-based ones. Please click Additional Files below to see the full abstract

Influence of Titanium on the High Temperature Oxidation and Chromia Volatilization of Ternary Ni–Cr–C Alloys

International audienceTwo ternary alloys, Ni-25Cr-0.25C and Ni-25Cr-0.50C (wt.%) and three versions containing also titanium (1 and 2 wt.%) were cast and submitted to oxidation in dry synthetic air at 1200°C to observe the effects of titanium on the behaviors of the nickel-based alloys belonging to this category. The mass gains are wholly parabolic in all cases and the values of the parabolic and chromia-volatilization constants are typical of a chromia-forming behavior. The mass gains of the Ti-containing alloys are faster than for the Ni-Cr-C alloys, and these kinetic differences are consistent with the differences in chromia thickness and in Cr-impoverishment of the subsurface. In addition the presence of Ti led to the development of thin a TiO2 outer scale isolating chromia from hot air, but without benefit for the protection of Cr2O3 against volatilization. The obtained results also suggest that Ti may perturb the Cr diffusion in volume but also delay the oxide spallation during cooling

Search for Scalar Diphoton Resonances in the Mass Range 65−60065-600 GeV with the ATLAS Detector in pppp Collision Data at s\sqrt{s} = 8 TeVTeV

A search for scalar particles decaying via narrow resonances into two photons in the mass range 65–600 GeV is performed using $20.3\text{}\text{}{\mathrm{fb}}^{-1}$ of $\sqrt{s}=8\text{}\text{}\mathrm{TeV}$ $pp$ collision data collected with the ATLAS detector at the Large Hadron Collider. The recently discovered Higgs boson is treated as a background. No significant evidence for an additional signal is observed. The results are presented as limits at the 95% confidence level on the production cross section of a scalar boson times branching ratio into two photons, in a fiducial volume where the reconstruction efficiency is approximately independent of the event topology. The upper limits set extend over a considerably wider mass range than previous searches

Search for Higgs and ZZ Boson Decays to J/ψγJ/\psi\gamma and Υ(nS)γ\Upsilon(nS)\gamma with the ATLAS Detector

A search for the decays of the Higgs and $Z$ bosons to $J/\psi\gamma$ and $\Upsilon(nS)\gamma$ ($n=1,2,3$) is performed with $pp$ collision data samples corresponding to integrated luminosities of up to $20.3\mathrm{fb}^{-1}$ collected at $\sqrt{s}=8\mathrm{TeV}$ with the ATLAS detector at the CERN Large Hadron Collider. No significant excess of events is observed above expected backgrounds and 95% CL upper limits are placed on the branching fractions. In the $J/\psi\gamma$ final state the limits are $1.5\times10^{-3}$ and $2.6\times10^{-6}$ for the Higgs and $Z$ bosons, respectively, while in the $\Upsilon(1S,2S,3S)\,\gamma$ final states the limits are $(1.3,1.9,1.3)\times10^{-3}$ and $(3.4,6.5,5.4)\times10^{-6}$, respectively

Measurements of the Total and Differential Higgs Boson Production Cross Sections Combining the H??????? and H???ZZ*???4??? Decay Channels at s\sqrt{s}=8??????TeV with the ATLAS Detector

Measurements of the total and differential cross sections of Higgs boson production are performed using 20.3~fb$^{-1}$ of $pp$ collisions produced by the Large Hadron Collider at a center-of-mass energy of $\sqrt{s} = 8$ TeV and recorded by the ATLAS detector. Cross sections are obtained from measured $H \rightarrow \gamma \gamma$ and $H \rightarrow ZZ ^{*}\rightarrow 4\ell$ event yields, which are combined accounting for detector efficiencies, fiducial acceptances and branching fractions. Differential cross sections are reported as a function of Higgs boson transverse momentum, Higgs boson rapidity, number of jets in the event, and transverse momentum of the leading jet. The total production cross section is determined to be $\sigma_{pp \to H} = 33.0 \pm 5.3 \, ({\rm stat}) \pm 1.6 \, ({\rm sys}) \mathrm{pb}$. The measurements are compared to state-of-the-art predictions.Measurements of the total and differential cross sections of Higgs boson production are performed using 20.3  fb-1 of pp collisions produced by the Large Hadron Collider at a center-of-mass energy of s=8  TeV and recorded by the ATLAS detector. Cross sections are obtained from measured H→γγ and H→ZZ*→4ℓ event yields, which are combined accounting for detector efficiencies, fiducial acceptances, and branching fractions. Differential cross sections are reported as a function of Higgs boson transverse momentum, Higgs boson rapidity, number of jets in the event, and transverse momentum of the leading jet. The total production cross section is determined to be σpp→H=33.0±5.3 (stat)±1.6 (syst)  pb. The measurements are compared to state-of-the-art predictions.Measurements of the total and differential cross sections of Higgs boson production are performed using 20.3 fb$^{-1}$ of $pp$ collisions produced by the Large Hadron Collider at a center-of-mass energy of $\sqrt{s} = 8$ TeV and recorded by the ATLAS detector. Cross sections are obtained from measured $H \rightarrow \gamma \gamma$ and $H \rightarrow ZZ ^{*}\rightarrow 4\ell$ event yields, which are combined accounting for detector efficiencies, fiducial acceptances and branching fractions. Differential cross sections are reported as a function of Higgs boson transverse momentum, Higgs boson rapidity, number of jets in the event, and transverse momentum of the leading jet. The total production cross section is determined to be $\sigma_{pp \to H} = 33.0 \pm 5.3 \, ({\rm stat}) \pm 1.6 \, ({\rm sys}) \mathrm{pb}$. The measurements are compared to state-of-the-art predictions