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WOM 2019 - 22nd International Conference on Wear of Materials, 14-18 April 2019, Hyatt Regency Miami, Miami, FL, USA; International audience; This paper deals with the influence of the mechanisms of plasticity on the evolution of the friction coefficient in cobalt-based hardfacings. Particularly depending on the alloying element content and so on the stacking fault energy, plasticity in Co-based alloys may occur through mechanisms involving either perfect dislocations gliding and/or partial dislocation gliding. As the coalescence of stacking faults by partial dislocations promotes the phase transformation of the Co, this study focus on the impact of this phase transformation on the evolution of the friction coefficient.Stellite 21 (Co-27Cr-5Mo-0.25C) hardfacings deposited on a steel substrate by two different processes, namely metal inert gas (MIG) and laser, are studied. The tribological properties are evaluated with a ring on disc tribometer under high load (800 daN) and continuous sliding (5 mm/s) at room and high temperatures (450 °C and 600 °C). The wear volume is characterized by confocal microscope. From micro-hardness measurements and SEM observations the work-hardening and the plastic strain of the Tribological Transformations of Surfaces are identified in relationship with chemical analysis (by EDS). Moreover X-rays diffraction and EBSD reveal the crystal structure evolution.As-deposited Co-based hardfacings have a face-centered cubic (FCC) structure. Meanwhile depending on the process of deposition on the steel substrate, the nominal composition of the Stellite 21 can be modified due to dilution effect. So, the iron content is found to be higher in the MIG hardfacing than in the laser one, leading to different mechanisms of plasticity, respectively by perfect dislocations gliding and by phase transformation (FCC to hexagonal closed-packed (HCP)). Moreover, a significant influence of the phase transformation on the friction coefficient has been evidenced: without phase transformation the cobalt remains in the FCC structure and the friction coefficient is stable during the test, while a decrease of its value occurs during the FCC to HCP phase transformation.

The creep behaviour of MC2 single crystal superalloy has been studied at 1150°C/80 MPa, with an applied load along [001] axis. The resulting dislocation microstructures were examined by transmission electron microscopy. The occurrence of a[010] type dislocations (with a zero Schmid factor) within the ordered γ' precipitates is often observed. It is shown that those dislocations moved by a climb process, based on a mechanism involving two dislocation systems and vacancy exchanges, as proposed in the literature. We calculate the vacancy fluxes associated with such a mechanism and show that the vacancy transportation can be easily insured by a simple diffusion process. This calculation shows that the diffusion and climbing steps do not seem to be the creep rate controlling mechanisms for those situations in MC2 alloy.

Issu de : ICTMP 2014 - 6th International Conference on Tribology in Manufacturing Processes & joining by plastic deformation, Darmstadt, GERMANY, June 22-24, 2014; International audience; High temperature forging tools are highly damaged by wear shearing under cyclic loading which reduces the life of tools. In real conditions, depending upon the tool areas, the level of wear can change. The surfaces of tools can be treated by cobalt-based hardfacing using different welding processes. This study focuses on tribological damages of Stellite 21 deposited by MIG process. Wear tests are carried out at room and high temperature on a ring on disc tribometer under high normal load. Different testing conditions are examined. The surface plastic strain due to the friction shear stresses is demonstrated by different methods like SEM observations, micro-hardness measurements and XRD analyses. More particularly, it is shown that the initial (200) crystallographic preferred orientation due to the welding process is modified into (111) crystallographic preferred orientation due to shear stresses regardless the loading. Moreover, a relationship between the gradient of the plastic shear strain at the friction subsurface and the level of the micro-hardness measurement has been established. In regard of the results, when the shear strain exceeds a threshold, the micro-hardness measurement is stabilised. The ultimate value could be induced by the stacking fault energy that is considered as weak in Stellites.

Since anthropogenic CO2 concentrations in the ocean cannot be measured, it is very difficult to assess the accuracy of the various estimates. Until now, only comparisons among the various approaches and hypotheses have been used to estimate the uncertainties of the results. Here we use three measured anthropogenic tracers (CFC-11, Δ14C and 3H) to assess the relevance of three estimates of anthropogenic CO2 distributions based upon very different hypotheses. In order to focus this work on the correlations among tracers and estimates of anthropogenic CO2 concentrations in the ocean, we chose as an example the data set from the WOCE I1 cruise (Indian Ocean; 1995), since it included data from the three tracers as well as data of the carbonate/CO2 properties. This choice further allows us to use the published results of anthropogenic CO2 concentrations using both the ΔC* and MIX approaches. Using four properties (total dissolved inorganic carbon, total alkalinity, dissolved oxygen and potential temperature) of this data set, we also estimated the distribution of anthropogenic CO2 using the recent TrOCA approach. The results of correlations of anthropogenic CO2 concentrations with the anthropogenic tracers 3H, CFC-11 and Δ14C, indicate that these correlations are significantly higher when anthropogenic CO2 is estimated using either the MIX or the TrOCA approaches than using the ΔC* approach. Based upon these results and the easiness to use the simple TrOCA approach we propose to use this method to unravel the distribution of anthropogenic carbon in the Ocean.DOI: 10.1111/j.1600-0889.2006.00247.x

13 páginas, 6 figuras, 1 tabla., Five of the most recent observational methods to estimate anthropogenic CO2 (Cant) are applied to a high-quality dataset from five representative sections of the Atlantic Ocean extending from the Arctic to the Antarctic. Between latitudes 60° N–40° S all methods give similar spatial distributions and magnitude of Cant. However, discrepancies are found in some regions, in particular in the Southern Ocean and Nordic Seas. The differences in the Southern Ocean have a significant impact on the anthropogenic carbon inventories. The calculated total inventories of Cant for the Atlantic referred to 1994 vary from 48 to 67 Pg (1015 g) of carbon, with an average of 54±8 Pg C, which is higher than previous estimates. These results, both the detailed Cant distributions and extrapolated inventories, will help to evaluate biogeochemical ocean models and coupled climate-carbon models., This work was developed and funded by the European Commission within the 6th Framework Programme (EU FP6 CARBOOCEAN Integrated Project, Contract no. 511176). Marcos Vázquez-Rodríguez is funded by Consejo Superior de Investigaciones Científicas (CSIC) I3P predoctoral grant program REF. I3P-BPD2005.

[1] Regional air-sea fluxes, ocean transport, and storage of anthropogenic carbon () are quantified. Observation-based data from the ocean interior are assimilated into the Bern3D dynamic ocean model using an Ensemble Kalman Filter. Global uptake of is estimated to be 131 ± 18 GtC over the period 1770 to 2000. Uncertainties from systematic biases in the reconstruction of are assessed by assimilating data from four global and six Atlantic reconstructions and found to be comparable or larger than uncertainties from ocean transport. Aggregated fluxes for the southern high-latitude, tropical and midlatitude, and northern high-latitude ocean agree within 0.11 GtC a−1 for the two reconstructions with the highest skill score, whereas regional uptake rates are up to a factor of three different. Results indicate that uptake and regional partitioning of anthropogenic carbon in the Southern Ocean remains uncertain.

One of the main challenges we face today is to determine the evolution of the penetration of anthropogenic CO 2 into the Indian Ocean and its impacts on marine and human life. Anthropogenic CO 2 reaches the ocean via air-sea interactions as well as riverine inputs. It is then stored in the ocean and follows the oceanic circulation. As the carbon dioxide from the atmosphere penetrates into the sea, it reacts with water and acidifies the ocean. Consequently, the whole marine ecosystem is perturbed, thus potentially affecting the food web, which has, in turn, a direct impact on seafood supply for humans. Naturally, this will mainly affect the growing number of people living in coastal areas. Although anthropogenic CO 2 in the ocean is identical with natural CO 2 and therefore cannot be detected alone, many approaches are available today to estimate it. Since most of the results of these methods are globally in agreement, here we chose one of these methods, the tracer using oxygen, total inorganic carbon, and total alkalinity (TrOCA) approach, to compute the 3-D distribution of the anthropogenic CO 2 concentrations throughout the Indian Ocean. The results of this distribution clearly illustrate the contrast between the Arabian Sea and the Bay of Bengal. They further show the importance of the southern part of this ocean that carries some anthropogenic CO 2 at great depths. In order to determine the future anthropogenic impacts on the Indian Ocean, it is urgent and necessary to understand the present state. As the seawater temperature increases, how and how fast will the ocean circulation change? What will the impacts on seawater properties be? Many people are living on the bordering coasts, how will they be affected?

We present results from the BIOSOPE cruise in the eastern South Pacific Ocean. In particular, we present estimates of the anthropogenic carbon CantTrOCA distribution in this area using the TrOCA method recently developed by Touratier and Goyet (2004a, b) and Touratier et al. (2007). We study the distribution of this anthropogenic carbon taking into account of the hydrodynamic characteristics of this region. We then compare these results with earlier estimates in nearby areas of the anthropogenic carbon as well as other anthropogenic tracer (CFC-11). The highest concentrations of CantTrOCA are located around 13° S 132° W and 32° S 91° W, and their concentrations are larger than 80 μmol kg−1 and 70 μmol kg−1, respectively. The lowest concentrations were observed below 800 m depths (≤2 μ mol kg−1) and at the Oxygen Minimum Zones (OMZ), mainly around 140° W (

The subtropical Indian Ocean along 32° S was for the first time simultaneously sampled in 2002 for inorganic carbon and transient tracers. The vertical distribution and inventory of anthropogenic carbon (CANT) from five different methods: four data-base methods (ΔC*, TrOCA, TTD and IPSL) and a simulation from the OCCAM model are compared and discussed along with the observed CFC-12 and CCl4 distributions. In the surface layer, where carbon-based methods are uncertain, TTD and OCCAM yield the same result (7±0.2 molC m−2), helping to specify the surface CANT inventory. Below the mixed-layer, the comparison suggests that CANT penetrates deeper and more uniformly into the Antarctic Intermediate Water layer limit than estimated from the much utilized ΔC* method. Significant CFC-12 and CCl4 values are detected in bottom waters, associated with Antarctic Bottom Water. In this layer, except for ΔC* and OCCAM, the other methods detect significant CANT values. Consequently, the lowest inventory is calculated using the ΔC* method (24±2 molC m−2) or OCCAM (24.4±2.8 molC m−2) while TrOCA, TTD, and IPSL lead to higher inventories (28.1±2.2, 28.9±2.3 and 30.8±2.5 molC m−2 respectively). Overall and despite the uncertainties each method is evaluated using its relationship with tracers and the knowledge about water masses in the subtropical Indian Ocean. Along 32° S our best estimate for the mean CANT specific inventory is 28±2 molC m−2. Comparison exercises for data-based CANT methods along with time-series or repeat sections analysis should help to identify strengths and caveats in the CANT methods and to better constrain model simulations.

The Ross Sea is an area of dense water formation within the Southern Ocean, hence it potentially plays an important role for anthropogenic CO2 sequestration. In order to estimate the penetration of anthropogenic carbon in the Ross Sea from total inorganic carbon (TCO2) measurements carried out in 2002–03 Antarctic Italian Expedition, we applied two independent models. Anthropogenic carbon was present throughout the water column. The highest concentrations were associated with the recently ventilated shelf waters, namely High Salinity Shelf Water (HSSW) and Ice Shelf Water (ISW), due to their recent contact with the atmosphere. The lowest concentrations were observed for Circumpolar Deep Water (CDW), due to its relatively older ventilation age. This water mass intrudes onto the shelf in some parts of the Ross Sea and hence is observed in the sampled section, where it is recognizable for its low O2 and high TCO2 concentrations. The overflow of the dense High Salinity Shelf Water out of the continental slope was observed in the area off Cape Adare. Since this recently formed shelf water contributes to the formation of the Antarctic Bottom Water (AABW), this process represents a pathway for anthropogenic carbon export down to the deep ocean.