Solubility Limit Of Carbon Research Articles

The effect of oxygen, nitrogen and carbon on the microstructure and compression properties of titanium foams

Abstract

Dynamic simulation of impurity transport and chemical reactions in a Bridgman furnace for directional solidification of multi-crystalline silicon

Numerical results from a dynamic simulation of impurity transport and reactions in a Bridgman furnace for directional solidification of multi-crystalline silicon are presented and compared to experimental results. The simulation includes the calculation of the thermal field, melt and gas flow velocity field, transport and chemical reactions of oxygen and carbon impurities for the entire process based on heating, melting and solidification phases. Carbon and oxygen distribution in the ingot is analyzed experimentally by means of FT-IR spectroscopy and LECO combustion method, the CO development by means of an μ-GC gas analyzer.The simulated impurity distribution in the ingot and the CO development above the free melt surface are in good agreement with the experimental results. Furthermore the results indicate that the carbon solubility limit is already reached at the stage of melting and SiC precipitates are likely to form at the early stage of growth.

In-Situ observation of the carburization of solid iron by graphite

The carburization of solid iron by graphite was investigated by using confocal laser scanning microscopy to understand the initial carburization reaction mechanism of solid iron by solid carbon at high temperatures. As the carburization was initiated, a liquid layer was formed at the interface and grew parallel to the interface after an incubating period for the liquid phase formation. This required incubation time decreased with an increasing temperature due to the decrease in the solubility limit of carbon in γ-Fe. A moving interface model was used to interpret the carburization and melting behavior of solid iron by solid carbon with consideration for the diffusion of carbon in both solid and liquid phases. Using the moving interface model, the diffusion coefficient of carbon in the liquid Fe-C alloys was obtained. $$D_L (m^2 /s) = 5.1 \times 10^{ - 7} \exp \left( { - \frac{{53.9 \times 10^3 }} {{RT}}} \right)\{ 1458 - 1623K\} $$ The rate of carburization in the solid and liquid phases was evaluated. As the liquid phase was formed, the contribution of solid phase in the carburization decreased from 9.5% at 1.3 s to 5.4% by 20 s.

High‐Interstitial Stainless Austenitic Steel Castings

AbstractInterstitial atoms are most effective in strengthening austenitic steels. In stainless grades, chromium strongly reduces the solubility limit of carbon. High‐nitrogen contents require costly pressure or powder metallurgy to dissolve N in the melt. The combination of both elements comes with a high‐interstitial solubility at normal pressure of air. Sand casting with 18 mass% Cr and Mn each and 0.85 mass% (C + N) were industrially produced. The investigation revealed: proof strength Rp0.2 = 457 [MPa], true fracture strength R = 1714 [MPa], fracture elongation A = 44%, notch impact toughness KV = 290 J combined with a DBTT of −94°C, an impact wear resistance comparable to Hadfield steel X120Mn12 but combined with a good corrosion resistance. Deep freezing and cold working does not effect the low relative magnetic permeability. This unique combination of properties offers advantages in application.

Graphene synthesis from graphite/Ni composite films grown by sputtering

Graphite/Ni composite films have been deposited on SiO2/Si (100) wafers by varying their graphite concentration (nG) and thickness (t) from 2 to 12 wt% and 40 to 400 nm, respectively, in a RF sputtering system, subsequently annealed at 900 °C for 4 min, and then slowly cooled to room temperature to form graphene layers on Ni surfaces. Several structural-analysis techniques reveal the optimum nG (∼8 wt%) and t (∼160 nm) of the composite films for the synthesis of fewest-layer, defect-minimized graphene. At the annealing temperature, carbon atoms diffuse out from the composite film, followed by their precipitation as graphene on the Ni layer as the carbon solubility limit in Ni is reached during the cooling period. Based on this mechanism, the optimum conditions are explained. Our approach provides an advantage in that the number of layers can be simply tuned by varying nG and t of the composite films.

Influence of substitutional atoms on the solubility limit of carbon in bcc iron

The influence of substitutional atoms (Mn, Cr, Si, P, and Al) on the solubility limit of C in body-centered cubic iron in equilibrium with cementite was investigated in low-carbon steels at a temperature of 700 °C. The C solubility limit was determined from internal friction measurements combined with infrared analysis of C using a high-frequency combustion technique. Experiments clarified that Mn, Cr and Al hardly change the C solubility limit, whereas P and Si increase it.

Influence of a High Magnetic Field on the Solubility of Ferrite and the Amount of Pearlite

AbstractThrough microstructural analysis of a high purity Fe‐0.027%C alloy after continuously cooling transformation under a magnetic field, it is found that the amount of pearlite of the alloy decreases with the increase of the strength of the magnetic field. Under a 12 Tesla magnetic field, no pearlite appears. The result indicates that the carbon solubility limit of ferrite is enlarged by the magnetic field.

Impurity segregation in directional solidified multi-crystalline silicon

In this paper numerical results on the impurity segregation in directional solidified multi-crystalline silicon are presented and compared with experimental results. A solute transport model has been established to predict the final segregation pattern of impurities in the ingot. The segregation is analyzed experimentally on the basis of Fourier transform infrared (FTIR) spectroscopy and glow-discharge mass spectrometry (GDMS). Precipitates were located by IR-transmission microscopy (IRM). Qualitative agreement between simulation and experiment is found. It is demonstrated how the flow pattern can influence the final solute distribution. The simulation also shows that the solubility limit of carbon and nitrogen is reached locally in the ingot and SiC and Si 3N 4 precipitates are likely to form.

Solute Concentration and Carbides Formation for Steel Milling Rolls

The selection and the formation of carbide govern quality and the service life of hot steel milling rolls. Thus the microsegregation and the formation of the carbides and the graphite during the solidification have been investigated for high speed steel type cast iron and Ni-hard type cast iron. The crystallization of high speed steel type cast iron proceeds in the order of primary austenite (γ), γ+MC and γ+M2C eutectic. On the other hand, in Ni-hard type cast iron, eutectic graphite flakes can crystallize after the formation of primary γ, and γ+M3C eutectic by controlling the content of Ni and Si in spite of containing strong carbide formers such as Cr. As γ+carbide eutectic grows, the residual liquid among eutectic cells becomes rich or poor in carbide formers according the partition coefficient between residual liquid and eutectic cell. It is realized that the change of composition of carbide formers during the solidification is estimated with Scheil–Gulliver equation and computed phase diagrams in both of cast irons. The graphite forming tendency is also evaluated by applying the parameter, which expresses the solubility limit of carbon to the molten iron for Ni-hard type cast iron.

The effect of reactive nanostructured carbon on the superconducting properties of mechanically alloyedMgB2

Polycrystalline samples of MgB2 doped with reactive nanostructured carbon were synthesized by pressure assisted sinteringof mechanically alloyed precursors. Varying the nominal carbon concentration fromx = 0 to 0.316,the effects of carbon doping on the lattice parameter, lattice strain, actual amount of incorporated carbon(xactual), grain size, normalstate resistivity (ρ), connectivity, superconducting transition(Tc), criticalfields (Birr andBc2) and critical currentdensity (Jc) as well asthe pinning force (Fp) were evaluated. An evident solubility limit of carbon within theMgB2 matrix,forming MgB2−xCx with an xactual≈0.125, was observed. In addition to the carbon saturation the superconducting properties,e.g. Tc, Bc2 andJc, alsoreflect saturation effects with respect to the actual carbon concentration. Improved electron scatteringin MgB2−xCx seems responsible for the observed enhancement ofBc2 to11.4 T at 20 K. On the other hand, calculations of the flux-pinning forces show a dramatic decreaseof Fp,max with increasing carbon concentration. Therefore we conclude theobserved improvement in critical current density at applied fields>6 T to result mainly from the raised upper critical field.

Structure and magnetic properties of Fe1−x C x , solid solution prepared by mechanical alloying

Supersaturated solid solutions Fe1−x C x (0⩽x⩽0.9) of wide composition range have been prepared by mechanical alloying process. Nanocrystalline phase was formed for 0⩽x⩽0.67 and a large grain phase for 0.75⩽x⩽0.9. The large fraction of graphite volume puts off formation of nanocrystalline phase for high carbon content. In the large grain phase, magnetization follows simple magnetic dilution, and coercivity H c is mainly due to dissolution of carbon at grain boundaries. In the nanocrystalline phase the alloying effect of carbon is revealed by a distinct reduction of average magnetic moment. The increasing lattice constant with increasing carbon content is observed for a;$0.5, suggesting that the high carbon concentration may enhance diffusion of carbon into the Fe lattice. It shows a discontinuity in the H c variation with a grain size D of nanocrystalline phase. For small grain D below the critical value, H c increases with D. For a large grain D, H c decreases with increasing D. The solubility limit of carbon in a-Fe extended by nanocrystalline phase formation is discussed.

Preparation and magnetic properties for supersaturated Fe–C solid solution with nanocrystalline structure

The supersaturated solid solutions Fe 1− x C x ( 0 ⩽ x ⩽ 0.9 ) have been prepared by mechanical alloying process. The nanocrystalline phase was formed for 0 ⩽ x ⩽ 0.67 and the large grain phase for 0.75 ⩽ x ⩽ 0.9 . The large fraction of graphite volume puts off the formation of nanocrystalline phase for high carbon content. In the large grain phase, magnetization follows the simple magnetic dilution and the coercivity H c is mainly due to the dissolution of carbon in the grain boundaries. In the nanocrystalline phase, the alloying effect of carbon is revealed by a distinct reduction of average magnetic moment. The increasing lattice constant with increasing carbon content is observed for x ⩽ 0.5 , which suggests that the high carbon concentration enhances the diffusion of carbon into the Fe lattice. It is observed the dependence of grain size on the coercivity H c. The decrease in the mean moment per Fe atom is probably linear with the increasing carbon content for nanocrystalline phase x ⩽ 0.5 . The solubility limit of carbon in α-Fe extended by nanocrystalline phase formation is also discussed in this paper.

Critical analysis and determination of the solubility limit of carbon in ferrite

In spite of an extensive bibliography available, the solubility limit of carbon in ferrite is still uncertain (between 50 and 100 ppm at 600°C for example), and this is not sufficient for the improvement of steel processing. Therefore we have tried to establish as accurately as possible the solubility of carbon between 500 and 750°C in a low carbon aluminium killed steel using a thermoelectric power protocol, which enables to calculate the amount of free interstitials in a ferritic matrix from the amount of interstitials that segregate on dislocations after strain. The solubility limit has been determined at ± 2 ppm between 550 and 730°C, and described by the relation: C(%wt) = 6.63 exp(-11.8 kcal/mol/RT). At a time when metallurgical phenomena are more and more simulated, we believe that a similar procedure should be used for other experimental studies providing basic data for modelling.

Transition from amorphous boron carbide to hexagonal boron carbon nitride thin films induced by nitrogen ion assistance

Boron carbon nitride films (BCN) were grown by B4C evaporation under concurrent N2 ion beam assistance. The films were characterized by x-ray absorption near-edge spectroscopy, infrared and Raman spectroscopies, and high-resolution transmission electron microscopy. The bonding structure and film composition correlate with the momentum transfer per incoming atom during deposition. As the momentum transfer is increased, the film structure evolves from an amorphous boron carbide network towards a hexagonal ternary compound (h–BCN) with standing basal planes. The growth of h–BCN takes place for momentum transfer in the window between 80 and 250 (eV×amu)1/2. The characteristic vibrational features of the h–BCN compounds have also been studied. Finally, the solubility limit of carbon in the hexagonal BN structure, under the working conditions of this article, is found to be ∼15 at. %.

Relationships between interstitial content, microstructure and mechanical properties in fully lamellar Ti–48Al alloys, with special reference to carbon

Carbon effects on microstructural and mechanical properties of Ti–48Al fully lamellar alloy are studied for increasing concentrations from 20 to 6000 wt.ppm. The lamellar structure is obtained for alloys slowly cooled (35 °C/mn) from 1350 °C. Carbon in solid solution increases lattice parameters of the α 2 phase. In the experimental conditions of this study, the solubility limit of carbon is 3000 wt.ppm. For higher carbon contents, Ti 2AlC (H phase) precipitates in the γ phase, leading to grain size decrease. Carbon in solid solution increases the α 2 volume fraction, microhardness, yield stress and decreases the minimum creep rate. Precipitation of the H phase does not modify these parameters except yield stress which increases still further. Comparison is made with previous results obtained from alloys with similar contents of either oxygen or nitrogen. Emphasis is put on the importance of α 2 phase hardening by solute interstitial elements on the mechanical properties of lamellar alloy.

Effect of Heat Treatment on Caustic Stress Corrosion Cracking Behavior of Alloy 600

Abstract Constant elongation rate tests (CERT) were conducted to evaluate the effect of heat treatment on intergranular stress corrosion cracking (IGSCC) susceptibility of alloy 600 (UNS N06600) in 140°C and 50% caustic solution at −900 mV vs saturated calomel electrode (SCE). Results showed: — Heat treatment at low temperature for a long time (600°C for 260 h) led to a material that was not susceptible to caustic intergranular (IG) cracking. Increase in heat treatment temperature enhanced IG cracking susceptibility. Caustic IGSCC susceptibility was at maximum near the carbon solubility limit. However, when the heat treatment temperature was higher than the carbon solubility limit, a significant decrease in crack growth rate was observed. — Grain boundaries acted as a preferential crack path when grain boundary carbon segregation was likely. Thermodynamic considerations suggested that severe caustic IGSCC susceptibility near the carbon solubility limit could be explained in terms of carbon segregation at ...

Structure Degradation of 25Cr35Ni Heat-Resistant Tube Associated with Surface Coking and Internal Carburization

Microstructures of 25Cr35Ni heat-resistant cracking tube after service were investigated and degradation mechanism of tube material was discussed. Results reveal that three distinguished zones, that is, internal oxide, carbide free, and internally carburized zones, will gradually develop in the inner wall of a cracking tube during service. Carbide free and internally carburized zones are formed primarily in relation to the periodic spalling and regeneration of surface oxide scale, and diffusion velocity of carbon and carbide forming elements in matrix and the solubility limit of carbon in alloy. The formation and growth of filament coke can aggravate structure degradation of the inner wall of the cracking tube, while deposition of lamellar and spheroidal coke may slow structure degradation to some extent. Surface coking and decoking cycles strongly aggravate the structure degradation of tube material and damage the service life of the cracking tube.

Saturation of hole concentration in carbon-doped GaAs grown by metalorganic chemical vapor deposition

The behavior of hole concentration in carbon-doped GaAs grown by metalorganic chemical vapor deposition (MOCVD) is investigated using carbon tetrabromide (CBr4) as a C source. The hole concentration tends to saturate at higher CBr4 flow rates in the heavily doped region regardless of growth temperature, V/III ratio and Ga source. This tendency is found to be due to the saturation of C incorporation efficiency, not the deactivation of C acceptors. It is also found that the saturation concentration, which is far lower than the value reported for metalorganic molecular beam epitaxy (MOMBE), is nearly independent of the growth conditions. These results suggest that an additional mechanism other than the solubility limit of carbon into GaAs must be considered to explain the saturation tendency of hole concentration in C-doped GaAs grown by MOCVD.

Substitutional carbon in Si1−yCy alloys as measured with infrared absorption and Raman spectroscopy

We present a study of the infrared absorption and Raman scattering intensity of the local carbon mode in Si1−yCy alloys grown by direct carbon implantation followed by different recrystallization procedures. For the case of laser-induced recrystallization, the integrated infrared absorbances are found to agree with an extrapolation of the calibration curve previously determined for very low substitutional carbon concentrations in Si. We argue that this finding provides strong evidence for the achievement of nearly perfect substitutionality in laser-recrystallized films, even though their carbon concentrations are three orders of magnitude beyond the solubility limit of carbon in Si. This conclusion is found to be consistent with measurements of the intensity of defect-induced Si Raman scattering relative to the Raman intensity of the local carbon mode. The Raman intensity of the local carbon mode at 605 cm−1 relative to the first-order Si Raman line at 521 cm−1 provides an ideal spectroscopic tool for the determination of substitutional carbon concentrations. By correlating Raman and infrared measurements, we find that for laser excitation at 488 nm the intensity ratio is given by I605/I521=(3.7±0.2)ysub.

Interactions between SiC fibers and a titanium alloy during infrared liquid infiltration

The rapid interaction between SiC fibers (SCS-0) and a liquid titanium alloy has been investigated using an infrared processing technique. Experimental results revealed that disso-lution of the fibers in the alloy occurred within seconds without forming a continuous layer of reaction products at the interface. Thermodynamic analysis indicated that SiC is unstable in the presence of liquid titanium and dissociates into Si and C in the metal. With increasing carbon concentration, TiC will form when the carbon solubility limit in Ti is exceeded. The Ti-rich corner of the Ti-Si-C phase diagram with supercooled liquid Ti at 1300 °C was used to illustrate the tendency of TiC formation in this system. The fiber-matrix interface comprised two distinct morphologies: uniform dissolution fronts and scalloped dissolution fronts. The uniformly dis-solved domains are believed to be caused by an isothermal dissolution mechanism controlled by a zeroth-order chemical reaction, whereas the scalloped interfaces are believed to be caused by an accelerated dissolution mechanism resulting from localized heating. A model employing heat balance and reaction kinetics indicates that the conditions for accelerated dissolution are satisfied by the observed dissolution rates in the scalloped domains.