Literatura científica selecionada sobre o tema "Alpha brasses"

Cu–Zn–Pb brasses are popular materials, from which numerous industrially and commercially used components are fabricated. These alloys are typically subjected to multiple-step processing—involving casting, extrusion, hot forming, and machining—which can introduce various defects to the final product. The present study focuses on the detailed characterization of the structure of a brass fitting—i.e., a pre-shaped medical gas valve, produced by hot die forging—and attempts to assess the factors beyond local cracking occurring during processing. The analyses involved characterization of plastic flow via optical microscopy, and investigations of the phenomena in the vicinity of the crack, for which we used scanning and transmission electron microscopy. Numerical simulation was implemented not only to characterize the plastic flow more in detail, but primarily to investigate the probability of the occurrence of cracking based on the presence of stress. Last, but not least, microhardness in specific locations of the fitting were examined. The results reveal that the cracking occurring in the location with the highest probability of the occurrence of defects was most likely induced by differences in the chemical composition; the location the crack in which developed exhibited local changes not only in chemical composition—which manifested as the presence of brittle precipitates—but also in beta phase depletion. Moreover, as a result of the presence of oxidic precipitates and the hard and brittle alpha phase, the vicinity of the crack exhibited an increase in microhardness, which contributed to local brittleness.

By searching a database of expressed sequences, we identified a member of the signal transducers and activators of transcription (Stat) family of proteins. Human and murine full-length cDNA clones were obtained and sequenced. The sequence of the human cDNA was identical to the recently published sequence for interleukin-4 (IL-4)-Stat (J. Hou, U. Schindler, W.J. Henzel, T.C. Ho, M. Brasseur, and S. L. McKnight, Science 265:1701-1706, 1994), while the murine Stat6 amino acid and nucleotide sequences were 83 and 84% identical to the human sequences, respectively. Using Stat6-specific antiserum, we demonstrated that Stat6 is rapidly tyrosine phosphorylated following stimulation of appropriate cell lines with IL-4 or IL-3 but is not detectably phosphorylated following stimulation with IL-2, IL-12, or erythropoietin. In contrast, IL-2, IL-3, and erythropoietin induce the tyrosine phosphorylation of Stat5 while IL-12 uniquely induces the tyrosine phosphorylation of Stat4. Inducible tyrosine phosphorylation of Stat6 requires the membrane-distal region of the IL-4 receptor alpha chain. This region of the receptor is not required for cell growth, demonstrating that Stat6 tyrosine phosphorylation does not contribute to mitogenesis.

Ce travail présente l'étude de la sensibilité à la fragilisation par les métaux liquides (FML) à température ambiante de laitons alpha contenant différents taux de zinc par l'eutectique liquide In-Ga (EGaIn). Le liquide EGaIn mouille le cuivre pur de manière partielle avec un angle de contact relativement faible de 49 ± 5 °. Cet angle est plus faible pour les laitons alpha et décroit avec le pourcentage en zinc. Il est de 36 ± 5 ° pour le laiton Cu-30%Zn. De plus, l'intermétallique CuGa2 se forme dès le contact avec le liquide EGaIn avec le cuivre et les laitons alpha, indépendamment de la teneur en zinc. Les essais de flexion 3 points montrent que la sensibilité à la FML par l'EGaIn augmente pour des vitesses de déformation élevées, des taux de zinc plus élévés et des duretés plus importantes. Dans les cas de FML, le liquide EGaIn n'affecte pas la phase d'initiation de la fissure mais seulement la propagation de la fissuration. En effet, les faciès de rupture présentent toujours une initiation ductile de la fissure puis une rupture fragile. L'intermétallique CuGa2 empêche l'initiation d'une rupture fragile en limitant le contact entre le métal liquide et le laiton dans les premières phases de l'essai mécanique. Puis l'intermétallique se fissure et ainsi, le liquide EGaIn rentre en contact avec le laiton rendant possible la FML à condition de déformations plastiques suffisamment importantes du laiton. A cause de l'initiation d'une rupture ductile, le laiton Cu-30%Zn ne présente pas de sensibilité à la FML lorsque il est testé par le small punch test (SPT) standard. Cependant l'utilisation d'échantillons de SPT pré-entaillés permet l'observation pour ce laiton de la FML en contact avec l'EGaIn liquide. De plus, du fait de l'initiation d'une rupture ductile, il est impossible à partir des résultats des essais de SPT et de flexion de déterminer une ténacité en présence de métal liquide. C'est pourquoi, des micro-essais de flexion avec observations in-situ et présence d'une couche fine protectrice de W ont été mis en oeuvre. Ils ont permis de déterminer en présence d'EGaIn liquide une ténacité de 1,57 ± 0.08 MPa m1/2 pour le laiton Cu-30%Zn
This work presents a study of the liquid metal embrittlement (LME) phenomenon at room temperature on alpha brasses with different Zn content in contact with the liquid eutectic Ga-In (EGaIn). The liquid EGaIn wets pure Cu partially with a relatively low contact angle of 49 ± 5 °, which is lower for the alpha brasses and decreases with the Zn content alloy down to 36 ± 5 ° for the Cu-30%Zn alloy. Moreover, the CuGa2 intermetallic forms whenever the liquid EGaIn is in contact with Cu and the alpha brasses, independently of the Zn content. Testing with the 3-point bending test showed that the LME sensitivity by the EGaIn increases at higher strain rates, higher Zn content, and higher hardness. Whenever there is LME, the liquid EGaIn does not affect the fracture initiation but the fracture propagation; hence the samples systematically presented a ductile fracture initiation followed by a brittle intergranular fracture propagation. The CuGa2 intermetallic impedes the brittle fracture initiation by blocking the contact between the EGaIn and the alpha brasses from the early stages of the test. Later, when the intermetallic breaks, the liquid EGaIn comes into contact with the alpha brass making the LME possible if the brass is under sufficient plastic deformation. Due to the ductile fracture initiation, the Cu-30%Zn alloy does not present LME when tested using the standard Small Punch Test (SPT). In contrast, using pre-notched SPT samples enables the observation of this alloy's embrittlement in contact with the liquid EGaIn. Furthermore, due to the ductile fracture initiation, it is impossible to use the bending tests or the SPT to measure the fracture toughness related to the LME phenomenon. In contrast, in-situ micro-bending tests with a W protective layer were suitable for the fracture toughness measurement of Cu-30%Zn in contact with the EGaIn; for instance, a fracture toughness value of 1.57 ± 0.08 MPa m1/2 was measured with the double clamped beam test

The uniaxial creep and creep fracture properties of α/β brass in air, have been determined over the stress range 9MPa - 185MPa at 523-673 K, using high precision constant stress creep testing machines. In the majority of cases, normal creep curves were recorded however, under certain conditions, due to the interactions of the two constituent phases some curves exhibited two areas of primary creep. Traditional Power Law analysis was carried out, and was found to be in agreement with published data. An alternative approach, known as the θ Projection Concept accurately described the accumulation of strain with time. Creep fracture was found to occur as a result of the accumulation of damage, primarily at α-β interfaces. To investigate the effect of varying stress states, biaxial creep testing was carried out at an effective stress of 140MPa at 523K. Using uniaxial and multiaxial test data, the θ Projection Concept was further developed to critically evaluate the damage processes occurring and their dependence on stress state. It was found that a damage at failure parameter, ω, decreased with increasing maximum principal stress.

Le travail présenté vise à améliorer la compréhension des mécanismes d'oxydation des laitons industriels exposés à un plasma d'oxygène basse pression, et la détermination des paramètres du réacteur contrôlant la cinétique d'oxydation de ces matériaux. La spectroscopie d'émission complétée par des mesures de température des laitons-cible, ont permis d'accéder aux paramètres de fonctionnement du réacteur qui contrôlent la réactivité du plasma et de déterminer à l'interface plasma-surface, la nature chimique des espèces gazeuses susceptibles d'induire l'oxydation du substrat. L'analyse par des méthodes optiques (IRTF et UV-VIS-PIR), électrochimiques (voltampérométrie en régime purement diffusionnel) et par diffraction X des laitons traités par plasma d'oxygène pur ont permis de mettre en évidence l'influence du titre en zinc et du mode de préparation de surface sur l'évolution des films d'oxydes en composition et structure. Lors d'un décapage chimique, les mécanismes d'oxydation conduisent à la formation majoritaire des oxydes de cuivre par rapport à ZnO et une organisation en pavage de ces oxydes. Le polissage mécanique favorise le développement de l'oxyde de zinc et ce phénomène est d'autant plus accentué que la teneur en zinc est plus importante. La formation de l'oxyde de zinc apparait dès lors comme l'un des paramètres conditionnant les mécanismes d'oxydation d'un laiton alpha.

According to the hydrophile-lipophile balance (HLB) theory and the evaluation results of friction, wear and lubrication using a four-ball tribometer, a novel oil-in-water emulsion was developed for the hot rolling process of hard brass (single phase alpha-brass, CuZn32 (ASTM C26200) and CuZn30 (ASTM C26000)) by controlling the composition of the emulsion, such as emulsifying, antiwear, extreme pressure, antirust and so on. In the actual hot rolling process, the roller material was the welded-stainless steel ASTM 420 (HRC34-44), in which the lubrication mechanism of brushing grease discontinuously was replaced by emulsion jet directly to the hot roller surface. The actual hot rolling results proved that it was easy to control the accuracy and size of the brass sheet with the emulsion jet. This new process increased the antiwear and anti-galling abilities of the rollers, and improved the surface quality of the brass sheet. For example, the formation of deep, dark streaks in the hot rolled copper sheet is prevented, galling and roughening of the roller surfaces during hot rolling is reduced and it also saved labor, and increased production efficiency and the service life of the hot roller greatly.