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.
•Dry sliding wear behavior of cobalt-based hardfacings at different temperatures.•Relationship between crystal structure and friction coefficient evolutions.•Alloying elements influence on mechanisms of plasticity.•Plasticity achieved by perfect dislocation gliding or by phase transformation.•Surface texturing with basal planes oriented nearly parallel to sliding surface.
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.
Aeronautic forging dies are subjected to very high loads and temperatures for a long contact time between the pre-heated parts and dies. Cobalt-based hardfacings are commonly deposited on dies and ...their main wear mechanism is large plastic deformation of the die radii.
This paper deals with the wear damage mechanisms of three different cobalt-based hardfacings: Stellite 21 deposited by a MIG process, Stellite 21 and Stellite 6 deposited by a LASER process. The tribological tests are carried out on a high load Ring on Disc tribometer at room temperature. The post-mortem investigations are undertaken by SEM observations, micro-hardness measurements as well as by X-ray diffraction analyses.
Results show that the increase of the hardness, in order to improve the wear behaviour, can be achieved by a higher carbon content and by a lesser iron dilution that depends on the deposition process. A very important work-hardening, up to 90%, is also observed under sliding conditions and a relationship is established between the increase of the micro-hardness and the plastic strain level. Two different plastic strain mechanisms are observed. For high (MIG) or low (LASER) iron dilution levels, the plastic strain causes respectively a reorientation of grains or a FCC to HCP phase transformation; the latter being associated with a lower friction coefficient.
A step by step algorithm for air-sea CO
2
flux (F(CO
2
)) calculation from satellite parameters is presented in this study. Parameters used for F(CO
2
) calculation are: (1) sea surface temperature ...(SST) and chlorophyll-a (chl-a) from Moderate Resolution Imaging Spectroradiometer Aqua (MODIS Aqua), (2) sea surface salinity (SSS) estimated from MODIS Aqua SST using multiple linear regression, (3) seawater CO
2
fugacity (f(CO
)) estimated by MODIS Aqua SST and chl-a using feedforward neural networks, (4) atmospheric CO
2
fugacity (f(CO
)) from the Cape Grim station, and (5) wind speed from the Quick and Advanced Scatterometer (QSCAT and ASCAT). In situ data provided by (1) the Surveillance de l'Océan Austral - Monitoring the Southern Ocean (SURVOSTRAL) project, (2) the Integrated Marine Observed System (IMOS) project, and (3) Mesures à l'INterface Eau-aiR de la Variabilité des échanges de CO
2
(MINERVE) project collected on the research vessel L'Astrolabe, are used to establish and validate the models. These models are then tested using remote sensing data. This work focus on the southern ocean from the south of Australia to the Antarctica coasts (between 43.5° S and 67° S), on the period of spring and Austral summer (from October to March, between 2002/2003 and 2014/2015). In each step, the result's precision of experiments was determined by the root mean square error (RMSE). Results show (1) an improvement of satellite SSS estimation with a precision of ±0.16 using SST and latitude, (2) an estimation of f(CO
) by satellite data with a good accuracy of ±9.45 µatm (0.96 Pa), and (3) a calculation of F(CO
2
) using satellite data with a global RMSE of about ±3 mmol CO
2
m
-2
day
-1
. The interpolated F(CO
2
) shows that, in the period of austral spring and summer, this region absorbs the atmospheric CO
2
, and becomes a stronger sink of CO
2
throughout the years (from an overall average absorption of about 2 mmol CO
2
m
-2
day
-1
in 2002/2003 to about 7 mmol CO
2
m
-2
day
-1
in 2014/2015).
The most active deep convection area in the western Mediterranean Sea is located in the Gulf of Lions. Recent studies in this area provides some insights on the complexity of the physical dynamics of ...convective regions, but very little is known about their impacts on the biogeochemical properties. The CASCADE (CAscading, Surge, Convection, Advection and Downwelling Events) cruise, planed in winter 2011, give us the opportunity to compare vertical profiles of properties sampled either during stratified conditions or after/during a convection event. In the present study, we focus on the distributions of the carbonate system properties (mainly total alkalinity, AT; and total dissolved inorganic carbon, CT) because, in the context of the climate change, deep convection areas are suspected to significantly increase the sequestration of anthropogenic CO2 (CANT). Given its limited size, the impact of the Mediterranean Sea on the global carbon budget is probably minor but this marginal sea can be used as a laboratory to better understand carbon sequestration and its transfer to the basin interior by deep convection processes. Distributions of AT and CT, both measured from bottle samples, and that of CANT (estimated with the TrOCA approach) are first analyzed in the light of other key properties (salinity, temperature, and dissolved oxygen). An objective interpolation procedure is then applied to estimate CT and AT from CTD measured properties. With this procedure, the vertical resolution goes from a maximum of 32 samples per station to one property estimate every meter (more detailed distributions are obtained). Results provide arguments to conclude that CANT is rapidly transferred to the deepest layer due to deep convection events. During deep convection events, the increase of CANT in the water column is positively correlated to that of potential density and oxygen content. The challenge of quantifying the amount of sequestered carbon is however not resolved due to the complexity and the highly dynamical nature of the convective regions. Deep convection in the Gulf of Lions, in parallel with cascading along the continental slope, could thus potentially explain the very high levels of both CANT and acidification estimated in the deep layers of the western Mediterranean Sea.
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.
The Southern Ocean is thought to play an important role in the context of global warming and anthropogenic emissions of CO2 due to its high sensitivity to both climate change and changes in the ...carbon cycle. Assessing the penetration of anthropogenic CO2 (Cant) into the Southern Ocean is therefore highly relevant to reduce the uncertainties attached to both the present knowledge of anthropogenic carbon inventories and predictions made by current ocean carbon models. This study compares different data‐based approaches for estimating the distribution of Cant in the ocean: a recently developed method based on the composite Tracer Combining Oxygen, Inorganic Carbon, and Total Alkalinity (TrOCA) and the “historical” back‐calculation methods (the so‐called ΔC* and preformed dissolved inorganic carbon methods). Note that the back‐calculation technique requires special care when used in the Southern Ocean, where surface oxygen can significantly deviate from equilibrium with the atmosphere. All three methods were applied to data collected at the Indian‐Atlantic boundary (WOCE line I6), where significant transient tracer concentrations were observed in deep and bottom waters. North of 50°S, distribution and inventories of Cant are coherent with previous data‐based and model estimates, but we found larger storage of Cant south of 50°S as compared to the midlatitude region. In that, our results disagree with most previous estimates and suggest that the global inventory of anthropogenic CO2 in the Southern Ocean could be much larger than what is currently believed.
The aim of the MINERVE project (Mesures à l’INterface Eau-aiR de la Variabilité des Échanges de CO2) is to observe and understand the seasonal and interannual variability of the partial pressure of ...CO2 (pCO2) in surface waters using hydrological and biogeochemical data in the Southern Ocean south of Australia. Logistics routes of the RV Astrolabe provide access to scarcely studied areas, thus allowing us to understand the different processes acting in this area of the Antarctic Ocean. The surface area covered by these cruises, however, is tiny compared with the total surface area of the Antarctic Ocean. Correlations between in situ surface temperature and salinity data were applied to satellite images of sea surface temperature to map ocean surface salinity over a much wider area than under the cruise tracks. Comparisons with salinity data from satellites which provide ~100 km resolution and 0.1 accuracy indicate that we are able to map salinity at 4 km resolution and almost the same accuracy of ± 0.1.
We present results of the CO2/carbonate system from the BIOSOPE cruise in the Eastern South Pacific Ocean, in an area not sampled previously. In particular, we present estimates of the anthropogenic ...carbon (C>TrOCAant) distribution in the upper 1000 m of this region using the TrOCA method. The highest concentrations of CTrOCAant found around 13° S, 132° W and 32° S, 91° W, are higher than 80 μmol.kg−1 and 70 μmol.kg−1, respectively. The lowest concentrations are observed below 800 m depth (≤2 μmol.kg−1) and within the Oxygen Minimum Zone (OMZ), mainly around 140° W (<11 μmol.kg−1). As a result of the anthropogenic carbon penetration there has been decrease in pH by over 0.1 on an average in the upper 200 m. This work further improves our understanding on the penetration of anthropogenic carbon in the Eastern Pacific Ocean.
A compilation of data from several cruises between 1998 and 2013 was used to derive polynomial fits that estimate total alkalinity (AT) and total dissolved inorganic carbon (CT) from measurements of ...salinity and temperature in the Mediterranean Sea surface waters. The optimal equations were chosen based on the 10-fold cross-validation results and revealed that second- and third-order polynomials fit the AT and CT data respectively. The AT surface fit yielded a root mean square error (RMSE) of ± 10.6 μmol kg−1, and salinity and temperature contribute to 96 % of the variability. Furthermore, we present the first annual mean CT parameterization for the Mediterranean Sea surface waters with a RMSE of ± 14.3 μmol kg−1. Excluding the marginal seas of the Adriatic and the Aegean, these equations can be used to estimate AT and CT in case of the lack of measurements. The identified empirical equations were applied on the 0.25° climatologies of temperature and salinity, available from the World Ocean Atlas 2013. The 7-year averages (2005–2012) showed that AT and CT have similar patterns with an increasing eastward gradient. The variability is influenced by the inflow of cold Atlantic waters through the Strait of Gibraltar and by the oligotrophic and thermohaline gradient that characterize the Mediterranean Sea. The summer–winter seasonality was also mapped and showed different patterns for AT and CT. During the winter, the AT and CT concentrations were higher in the western than in the eastern basin. The opposite was observed in the summer where the eastern basin was marked by higher AT and CT concentrations than in winter. The strong evaporation that takes place in this season along with the ultra-oligotrophy of the eastern basin determines the increase of both AT and CT concentrations.
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