Carbon Diffusion In Iron Research Articles

Diamond Deposition on Iron and Steel Substrates: A Review.

This article presents an overview of the research in chemical vapor deposition (CVD) diamond films on steel substrates. Since the steels are the most commonly used and cost-effective structural materials in modern industry, CVD coating diamond films on steel substrates are extremely important, combining the unique surface properties of diamond with the superior toughness and strength of the core steel substrates, and will open up many new applications in the industry. However, CVD diamond deposition on steel substrates continues to be a persistent problem. We go through the most relevant results of the last two and a half decades, including recent advances in our group. This review discusses the essential reason of the thick catalytic graphite interlayer formed on steel substrates before diamond deposition. The high carbon diffusion in iron would induce severe internal carburization, and then voluminous graphite precipitated from the substrate. In order to hinder the catalytic graphite formation, various methods have been applied for the adherent diamond film deposition, such as pre-imposed various interlayers or multi-interlayers, special controls of the deposition process, the approaches of substrate alloying and so on. We found that adherent diamond films can be directly deposited on Al alloying steel substrates, and then the role of Al alloying element was examined. That is a thin dense amorphous alumina sublayer in situ formed on the alloying substrate, which played a critical role in preventing the formation of graphite phase and consequently enhancing diamond growth and adhesion. The mechanism of Al alloying suggests that the way used to improve hot corrosion resistance is also applicable. Then, some of the hot corrosion resistance methods, such as aluminizing, siliconizing, and so on, which have been used by some researchers examining CVD diamond films on steel substrates, are reviewed. Another way is to prepare diamond-like carbon (DLC) films on steel substrates at low temperature, and then the precipitated graphite from the internal carburization can be effectively avoided. In addition, based on some new findings, the understanding of the diamond nucleation and metastable growth is discussed.

Magnetic and electronic properties of Fe/C multilayers: Interfacial effects

Fe/C multilayers with different Fe thicknesses (tFe) were prepared using triode sputtering with a fixed C layer thickness of 20 Å, while the Fe film thickness was changed from 30 to 300 Å. The magnetization strongly decreases with decreasing tFe when tFe was smaller than 60 Å. This is attributed to the existence of a magnetically dead layer due to the presence of Fe1−xCx alloys at the Fe/C interface due to the diffusion of carbon in iron. First-principles calculations based on Density Functional Theory (DFT) were performed to investigate the magnetic and electronic structures of the interfacial Fe1−xCx alloys. It is shown that the C insertion reduces the magnetization, which becomes significant with increasing C content. In addition, the influence of pressure by changing volume on the magnetic properties was investigated as well, where the pressure reduces significantly the interfacial magnetization.

Effect of quenching medium on microstructure and hardness of as sintered Fe-Cr-Mo-0.6C and Fe-Mo-0.6C alloy steel

In the present investigation prealloyed Fe-Cr-Mo and Fe-Mo alloy steel with 0.6 wt.% graphiteaddition are processedvia conventional sintering technique followed by their study of physical and mechanical properties. Powder mixtures are compacted at 600 MPa pressure and sintered in an atmosphere of N2-H2at 1200°C held for one hour with 6.0°C/minute cooling rate. Relative density (>90%)is achieved for both the alloys. XRD pattern revealed the major peaks of ferrite and iron carbide phases. SEM micrographs of as sintered Fe-Cr-Mo-0.6C and Fe-Mo-0.6C alloy reveal the presence of ferrite, pearlite and bainite structurewith some carbide at the boundaries.SEM micrographs of as sintered oil quenched Fe-Cr-Mo-0.6C and Fe-Mo-0.6C alloy reveal the presence of martensite structure. EDS confirmed Cr, Mo, Fe and carbon elements in sintered samples with respect to their compositions. As sintered Fe-Mo-0.6C alloy hardness is higher than Fe-Cr-Mo-0.6C alloy, reason attributes to it is the presence of dominant bainitic structure in as sintered Fe-Mo-0.6C alloy resulted in high hardness value (195HV5) in comparison of Fe-Cr-Mo-0.6C alloy. Whereas sintered Fe-Cr-Mo-0.6C alloy resulted in high hardness value than Fe-Mo-0.6C alloy on quenching in water and oil medium, reason being presence of Cr more resist the diffusion of carbon in iron in faster cooling medium resulting in high hardness of sample in water and oil.

Diffusion properties of Fe–C systems studied by using kinetic activation–relaxation technique

Diffusion of carbon in iron is associated with processes such as carburization and the production of steels. In this work, the kinetic activation–relaxation technique (k-ART) – an off-lattice self-learning kinetic Monte Carlo (KMC) algorithm – is used to study this phenomenon over long time scales. Coupling the open-ended ART nouveau technique to generate on-the-fly activated events and NAUTY, a topological classification for cataloging, k-ART reaches timescales that range from microseconds to seconds while fully taking into account long-range elastic effects and complex events, characterizing in details the energy landscape in a way that cannot be done with standard molecular dynamics (MD) or KMC. The diffusion mechanisms and pathways for one to four carbon interstitials, and a single vacancy coupled with one to several carbons are studied. In bulk Fe, k-ART predicts correctly the 0.815eV barrier for a single C-interstitial as well as the stressed induced energy-barrier distribution around this value for 2 and 4 C interstitials. For vacancy–carbon complex, simulations recover the DFT-predicted ground state. K-ART also identifies a trapping mechanism for the vacancy through the formation of a dynamical complex, involving C and neighboring Fe atoms, characterized by hops over barriers ranging from ∼0.41 to ∼0.72eV that correspond, at room temperature, to trapping time of hours. At high temperatures, this complex can be broken by crossing a 1.5eV barrier, leading to a state ∼0.8eV higher than the ground state, allowing diffusion of the vacancy. A less stable complex is formed when a second C is added, characterized by a large number of bound excited states that occupy two cells. It can be broken into a V–C complex and a single free C through a 1.11eV barrier.

Deformation and fracture of Ti/439 stainless steel clad composite at intermediate temperatures

Deformation and fracture of Ti/439 stainless steel (STS) were studied. Activation energy for elongation minimum in Ti/STS 439 is close to that of carbon diffusion in iron, suggesting ductility loss is caused by dynamic strain aging in STS 439. Wavy surface in Ti-layer is caused by multiple necking in titanium.

“Conjugate Channeling” Effect in Dislocation Core Diffusion: Carbon Transport in Dislocated BCC Iron

Dislocation pipe diffusion seems to be a well-established phenomenon. Here we demonstrate an unexpected effect, that the migration of interstitials such as carbon in iron may be accelerated not in the dislocation line direction , but in a conjugate diffusion direction. This accelerated random walk arises from a simple crystallographic channeling effect. is a function of the Burgers vector b, but not , thus a dislocation loop possesses the same everywhere. Using molecular dynamics and accelerated dynamics simulations, we further show that such dislocation-core-coupled carbon diffusion in iron has temperature-dependent activation enthalpy like a fragile glass. The 71° mixed dislocation is the only case in which we see straightforward pipe diffusion that does not depend on dislocation mobility.

Diffusion of carbon in iron under magnetic fields

This study was conducted with the aim of investigating the effect of magnetic fields on the carbon diffusion in pure iron. The Fe/Fe-0.87 mass% C diffusion couples prepared by explosive welding were annealed at temperatures from 850 to 1200 K without and with a uniform magnetic field up to 6 T and with a magnetic-field gradient of 45 T/m. We evaluated the carbon diffusivity in iron from the penetration profiles of carbon into iron measured by secondary ionization mass spectroscopy. The diffusivity of carbon in $\ensuremath{\alpha}$-Fe decreased under a magnetic field, while it increased by twice under a magnetic-field gradient.

1017 鉄中炭素挙動と炭素が鉄の力学的特性に与える影響の原子レベル解析(OS10. 電子・原子・マルチシミュレーションに基づく材料特性評価,OS11. 材料の組織・強度に関するマルチスケールアナリシス 合同ポスターセッション,オーガナイズドセッション講演)

1017 鉄中炭素挙動と炭素が鉄の力学的特性に与える影響の原子レベル解析(OS10. 電子・原子・マルチシミュレーションに基づく材料特性評価,OS11. 材料の組織・強度に関するマルチスケールアナリシス 合同ポスターセッション,オーガナイズドセッション講演)

Transformation Mechanism from Carbon Nanotubes to n-diamond

Nanocrystal n-diamond particles were synthesized after a pyrogenation of carbon nanotubes and colloidal Fe(OH)3 at atmospheric pressure. The product was investigated with x-ray diffraction, transmission electron microscopy, thermal gravimetric analysis, and differential thermal analysis. The results indicate that the n-diamond can be synthesized with the carbon nanotubes as carbon source. The formation mechanism of the n-diamond is suggested in this paper. With the increase of temperature and hence the carbon diffusion in iron, the phase sequence is from Fe(OH)3 into Fe2O3, α–Fe, γ–Fe, and then liquid iron. When carbon in the liquid iron is saturated, graphite separated out of the liquid iron. With the decrease of temperature, the carbon in γ–Fe is separated out, and the n-diamond nuclei form and grow.

Formation mechanism of diamond nanocrystal from catalysed carbon black

Recently, our group has synthesized nanocrystal n-diamond and diamond-likecarbon (DLC) from catalysed carbon black. Based on the results of XRD, TGAand DTA, a formation mechanism has been proposed to explain the phasetransformation from carbon black to diamond nanocrystal. With the increase oftemperature and hence the carbon diffusion in iron, the phase sequence is fromFe(OH)3 intoFe2O3,α-Fe,γ-Fe, then liquid iron. When the carbon in the liquid iron is saturated, DLC or graphiteseparates out of the liquid iron. With decrease of temperature, the carbon inγ-Fe is separated out, and n-diamond nuclei form and grow.

Effect of microadditions on the structure and properties of powder carbon steel

1. Additions of alkali metals accelerate the diffusion of carbon in iron, particularly at low sintering temperatures, increase the carbon concentration of the steel, improve the strength properties at all temperatures studied, and produce a more uniform and stable structure. 2. Increasing the amount of alkali metal produces some increase in strength if sodium or potassium are added, but no change if lithium is added. Increase in the diffusional mobility of carbon with increase in the amount of alkali metal added is not observed.

Diffusitivity of carbon in Fe-V alloys

Tracer diffusion of carbon in iron—vanadium alloys containing 2.45, 0.5 and 0.1 at% vanadium has been measured in a temperature range from 900 to 1325 K. No effect of magnetic transforms is observed on the C14 diffusivity in the α-stabilized Fe-2.4 at% V alloy, as has been reported for α-iron. Trapping behaviour of vanadium in slowing down the carbon diffusivity in iron shows a reasonable fit with the model predicted by Koiwa. However, the effect of these traps appears not to be felt during lowtemperature internal friction measurements in Fe-2.4 at% V alloy.

Carbon deposition from propylene on polycrystalline and single crystal iron

The kinetics and morphology of the deposition of carbon from propylene on polycrystalline and single crystal iron have been studied over the temperature range 400–700 °C. The dependence of the rate of carbon formation on temperature shows a pronounced maximum at ca. 600 °C. Below this temperature, single crystals and polycrystalline iron foils behave similarly. On fresh samples, carbon deposition appears to be rate controlled by the diffusion of carbon in iron. After the deposition of some carbon it is suggested that the rate is controlled by the carbide-catalyzed production of carbon from propylene. Above ca. 600 °C, carbon formation is considered to be rate controlled by the surface decomposition of propylene. On fresh samples, the rate was affected by the geometry of the surface with carbon formation decreasing in the order (100) ∼ foils > (110). On used catalysts, where the active surface is probably iron carbide, geometric effects were not observed. Encapsulation of the surface by carbon was important at these higher temperatures, and this reaction was independent of the surface geometry.

Kinetics of carbon precipitation in irradiated iron

Iron containing approximately 0.01 wt.% carbon was irradiated in the BNL reactor at different times and temperatures, and the amount of carbon in solution was measured by torsion pendulum internal friction. Isothermal annealings after irradiation for 12 days at 200°K showed that the irradiation accelerated the disappearance of carbon from solution by about three orders of magnitude over the thermal rate. The extent of the accelerated decay is a function of irradiation time, and after 12 days irradiation the peak decayed to background level. The decay curves are all second order with an activation energy of the diffusion of carbon in iron. After a 4 hr irradiation at 57°C, however, the decay was accelerated by only about one order of magnitude and the decay rate is not affected by further irradiation.

Peculiarities of the diffusion of carbon in iron

1. Diffusion of carbon inα andγ-irons is non-uniform: at 550 to 950°C, carbon enriches preferentially the grain boundaries; the diffusivity of carbon along grain boundaries of ferrite is three to four higher than inside the grain. An enrichment with carbon of theα-solid solution is also observed in regions adjoining the grain boundaries. 2. The diffusion rate and the distribution of carbon within a single grain are changed by alloying. Addition of substantial amounts of certain elements curtailing theγ loop considerably increases the penetration depth of carbon on account of boundary diffusion developing inγ-iron. The concentration gradient of carbon between boundary and interior of a grain is less in alloyed than in unalloyed iron.