Fe 3C Research Articles

Effects of Ti- and Zr-based interlayer coatings on the hot filament chemical vapour deposition of diamond on high speed steel

The prospect of obtaining good adhesion of diamond films onto steel substrates is highly exciting because the achievement of this objective will open up applications in the cutting and drilling industry. However, a major problem with depositing diamond onto steel is high diffusion of carbon into steel at chemical vapour deposition (CVD) temperatures leading to very low nucleation density and cementite (Fe 3C) formation. Therefore, the study of the nucleation and growth processes is timely and will yield data that can be utilised to get a better understanding of how adhesion can be improved. This work focuses on investigating the adhesion of thin diamond films on high speed steel previously coated with various interlayers such as ZrN, ZrC, TiC and TiC/Ti(C,N)/TiN. The role of seeding on nucleation density and the effect of diamond film thickness on stress development and adhesion has been investigated using SEM, XRD and Raman spectroscopy. The main emphasis in this study is the TiC interlayer which for the first time proved to be a suitable layer for diamond CVD on high speed steel (HSS). In contrast from other interlayer materials investigated here, no delamination was observed even after 3 h of CVD at 650 °C only when TiC was employed. Nevertheless, the increase of diamond film thickness on TiC coated HSS substrates led to the delamination of small areas in various regions of the substrate. This occurrence suggests that there was a distribution of adhesive toughness values at the diamond/TiC interface with stress development being dependent on film thickness.

Oxidation of 1018 carbon steel in borate medium by in situ EC-STM: Surface morphology of the oxidized ferrite and pearlite phases

Microstructures of low carbon steel are ferrite (Fe-α) and pearlite (alternate mixture of Fe-α and Fe 3C) and each one has its own oxidation mechanism. These two phases were identified using in situ electrochemical scanning tunneling microscopy (EC-STM). Real time images were obtained during the immersion of 1018 carbon steel probes in 0.642 M H 3BO 3 and 0.1 M NaOH, pH 7.8. Two different corrosion mechanisms (oxide characteristics) were identified and correlated with the observed surface changes.

Effect of pressure application on microstructure evolution in a composite of Fe–Al alloy and CrMo steel

The effect of pressure applied by hot isostatic press (HIP) on microstructure evolution during diffusion bonding was studied using a couple composed of an Fe–Al alloy (Fe–Al) and CrMo steel (CrMo). Columnar grains are formed from the joint interface to the CrMo side irrespective of pressure application. The average length of the columnar grains of the couple bonded with pressure was shorter than that of the couple bonded without pressure. For the couple bonded with pressure, the microstructure of the CrMo side beyond the columnar grains exhibits fine facets with acicular precipitates of Fe 3C. Further, strong hardening is found in this region. The application of pressure retards the aluminum diffusion from Fe–Al to CrMo. The growth rate of the columnar grain with respect to bonding time deviated from the parabolic law. These effects of the pressure application on the microstructure evolution are due to the suppression of aluminum diffusion and retardation of transformation during bonding.

Surface melting of nodular cast iron by Nd-YAG laser and TIG

The effect of surface melting and rapid solidification on the structure and hardness of nodular cast iron has been investigated. Two heat sources were used for surface melting mainly, laser beam (LB) and electric arc generated between the tungsten electrode and the specimen (i.e. TIG). Optical microscope, scanning electron microscope and X-ray diffraction were used to describe the microstructure and identify the phases in the melted zone. Results showed that surface melting has led to a complete dissolution of the graphite nodules and re-solidification of a dendritic structure. The specimen melted by TIG showed dendrites of transformed austenite in a matrix of eutectic consisting of transformed austenite γ and Fe 3C while the laser-melted zone exhibited finer dendrites of retained austenite surrounded by a continuous network of Fe 3C; some needles of martensite within the dendrites are observed. The retained austenite dendrites have a preferred growth direction and contained a high concentration of dissolved carbon. The microhardness of the nodular cast iron was found to be significantly increased after melting.

Production and characterization of in situ Fe–Fe 3C composite produced by mechanical alloying

In this study, mechanical alloying (MA) of elemental iron powders containing 1 wt% carbon was carried out under Ar atmosphere by using a high-energy ball mill for various milling time. In order to compare and determine the effect of MA on properties the same amount of powders were mixed by a conventional mixer up to 5 h. Particle size, shape and compressibility of the alloyed powders depending on the milling time were characterized. Powders were compacted at 1000 MPa to produce standard transverse rupture strength specimens. Specimens were then sintered at various temperatures for 2 h under Ar atmosphere in a tube furnace. Optical and SEM studies were conducted in order to determine the effect of temperature and MA durations on the degree Fe 3C transformation on sintered specimen. Transverse rupture strength and hardness tests were carried out to find the mechanical properties of specimens. The results showed that the hardness, transverse rupture strength and microstructure of sintered compact specimens were affected by mechanical alloying time and sintering temperature.

The significance of impeded reactions in solid state electrochemistry

While one usually looks for reversible reactions, in reality, many of the reactions are impeded. This turns out to yield interesting results. In particular, certain reaction routes that would seem impossible become possible, as certain a priory competing and thermodynamically more favorable routes are blocked. We review here few cases that were recently discussed in the field of solid state electrochemistry. Yet, the first example is a chemical reaction (formation of Fe 3C) recently considered, which serves as an introduction. The other impeded reactions discussed are those that show up in a single chamber or mixed gas solid oxide fuel cell, in the electro-catalytic enhancement of reactions, NEMCA, when the reaction cell is based on an oxygen ion conductor (YSZ) and finally, the catalytic activity (enhancement and retardation of reactions) of certain metallic electrodes in cells based on the proton conductor Nafion.

Thermal transitions in Fe–Ti–Cr–C quaternary system used as precursor during laser in situ carbide coating

The temperature range of thermal transitions within the quaternary system (Fe, Ti, Cr, and C) and the thermal stability of the evolved phases were studied with the help of differential scanning calorimetry (DSC). DSC studies indicated that the major exothermic reactions (formation of carbides) take place within 850–1150 °C. The evolved phases (TiC, M 7C 3, Fe–Cr, and Fe 3C) were characterized using X-ray diffraction (XRD). This multicomponent powder mixture was used as a precursor for synthesizing a composite coating on the surface of steel via laser surface engineering (LSE). The intended wear applications of the coating made thermal stability investigations vital. Experimental evaluation of thermal stability of the phases formed was done.

Orientation relationship between a ferritic matrix and κ-phase (Fe 3AlC x) precipitates formed during metal dusting of Fe-15Al

An Fe-15 at.% Al alloy has been exposed to a strongly carburising CO–H 2–H 2O gas mixture under metal dusting conditions. Cementite (Fe 3C) was detected to be present only in the coke which is a reaction product of the high-temperature corrosion metal dusting. Needle- or plate-like κ-phase (Fe 3AlC x ) precipitates close to the surface were identified by means of electron back-scattered diffraction (EBSD). EBSD analyses of several precipitates and neighboured matrix areas indicate a Nishiyama–Wassermann orientation relationship between the κ-phase precipitates and the α-Fe(Al) matrix.

Paramagnetic susceptibility of ferrite and cementite obtained from ab initio calculations

Paramagnetic susceptibility of BCC ferrite ( α -Fe) and of cementite (Fe 3C), was calculated in a temperature range above the Curie point, using a density functional-based method in conjunction with statistical approximations. The electronic structure and the magnetic energy of both systems were calculated using the full potential linear augmented plane wave (FPLAPW) method as implemented in the Wien2k Code. The temperature effect was captured by introducing the Boltzmann statistical distribution to describe the orientation perturbation of the magnetic moments caused by thermal agitation. The magnetic moment was calculated in the temperature range from 1045 to 1175 K for alpha-iron and from 540 to 640 K for cementite. The modeling was performed for applied magnetic fields ranging from 1–2 T. The main assumption was that the effect of temperature and that of the applied magnetic field can be decoupled and, consequently, be treated separately. The calculated moments were used to estimate the paramagnetic susceptibility according to the linear relation χ = M / B well established for paramagnetic systems. The calculated values were compared with published experimental measurements for iron and with values obtained from the Curie–Weiss law for cementite.

High yield synthesis of multi-walled carbon nanotubes by catalytic decomposition of ethane over iron supported on alumina catalyst

Ethane was successfully used as an active and efficient carbon source in a large scale synthesis of high quality carbon nanotubes by chemical vapour deposition (CVD) over Fe/Al 2O 3 catalyst with an iron loading of 20 wt.%. The multi-walled carbon nanotubes yield approaching 50 g per gram of catalyst per hour at 750 °C, which was among the highest yield reported today in the open literature. The active phase for growing carbon nanotubes is a mixture of a metastable iron carbide (Fe 3C) and α-Fe which were formed in situ by the ethane dissociation followed by carbon diffusion through the starting α-Fe phase. The reaction products only contained multi-walled carbon nanotubes with very homogeneous diameters of around 30 nm and lengths up to several hundred nanometers without any trace of other impurities such as nanoparticles or amorphous soot. According to the observed results ethane is an active carbon source for growing multi-walled carbon nanotubes with high yield and selectivity. The reaction temperature should be keep ≤750 °C as synthesis carried out at 800 °C under similar reaction conditions led to the formation of amorphous soot and carbon nanoparticles mixed with nanotubes.

An investigation of a thin metal film covering on HPHT as-grown diamond from Fe–Ni–C system

Scanning Raman spectroscopy, scanning auger microprobe, electron probe microanalysis, X-ray powder diffraction and transmission electron microscopy were used to investigate a thin metal film covering on HPHT as-grown diamond from Fe–Ni–C system. In different regions of the film, the fine structure of carbon and iron atoms are different. It is clear that the microstructure and composition in the inner part of the film near diamond are different from those in other regions of the film. The fine structures of carbon and iron atoms have been greatly transformed. Crystalline graphite and amorphous carbon were not found in the inner part near diamond. The diamond formation should be directly associated with carbide. There exist parallel relationships between the crystal faces of (Fe,Ni) and Fe 3C. We suggest that graphite could not be directly catalyzed into diamond structure in the molten film, and the carbon for diamond growth may be related to the decomposition of Fe 3C under the effect of (Fe,Ni) phases in the inner part, which can play an important role under diamond growth at high temperature and high pressure.

Reactive laser synthesis of carbides and nitrides

Carbides and nitrides play an important role for technological applications. Here, we present a new promising technique for a direct laser synthesis of carbides and nitrides by pulsed laser irradiation in reactive atmospheres, e.g. methane and nitrogen. A number of laser types have been used (excimer laser, Nd:YAG, Ti:sapphire, free electron laser) and a number of different nitrides and carbides have been produced (e.g. TiN, AlN, Fe 3C, SiC). The mechanisms and examples will be presented and it will be shown that also the lateral and in depth structuring can be modified from nanoscale to mesoscale. The dependence of phase formation and resulting properties are given in relation to the laser treatment parameters, such as laser type, pulse duration, material and reactive gas pressure. This reactive laser synthesis can also be used for the improvement of steel surfaces. For example, the irradiation of pure iron in methane atmosphere at low pressures or low number of laser pulses results in the formation of an amorphous carbon surface layer and hexagonal ɛ -Fe 1−xC x, which is more and more transformed into cementite when increasing the number of pulses or the gas pressure.

Electronic structure and geometry optimization of nanoparticles Fe 2C, FeC 2, Fe 3C, FeC 3 and Fe 2C 2

The geometry optimization of the beginning of the row of Fe n C m nanoparticles was carried out using the DFT based DMol 3 method. For FeC 2 and Fe 2C the triangular configurations are found to have the lowest binding energy. The most stable planar structures for FeC 3 and Fe 2C 2 are favored over the three-dimensional isomers, whereas for Fe 3C the pyramidal configuration appeared to be the ground state. The effective charges and total spin densities on the atoms were calculated using integral and Mulliken schemes incorporated in DVM and Hirshfeld procedure of DMol 3. The most reasonable values were obtained with the use of integral method.

Non-stoichiometric cementite by rapid solidification of cast iron

This paper deals with rapidly solidified binary Fe–C alloys containing 3.8 wt% and 4.3 wt% C. Their microstructure reveals that, as an effect of undercooling, the conventional eutectics have been suppressed and there is occurrence of the ferrite–cementite eutectic. Both phases are metastable: ferrite is supersaturated in C and cementite has a C deficiency. This is demonstrated by means of determination of phase fractions in metallographic sections and of lattice parameters via Rietveld refinement of X-ray diffraction patterns. A major consequence of non-stoichiometricity of cementite is the reduced value of the Curie temperature (up to 17 °C) with respect to that of the equilibrium compound. The maximum C deficiency in Fe 3C 1− x is estimated as x = 0.02. The free energy of defective cementite has been computed by means of the two sublattice model and compared with that of ferrite and austenite obtained from an assessed phase diagram. It is shown that the non-stoichiometric phase is close in energy to the equilibrium one for a composition range of several atomic per cent. It is suggested that this helps in explaining the mechanism of cementite dissolution by heavy deformation of ferrous alloys, and the ease of cementite nucleation in castings.

C 2H 6 as an active carbon source for a large scale synthesis of carbon nanotubes by chemical vapour deposition

Ethane was successfully used as an active and efficient carbon source in a large scale synthesis of high quality carbon nanotubes by chemical vapour deposition (CVD) over Fe/Al 2O 3 catalyst with an iron loading of 20 wt.%. The carbon nanotubes yield of 20 g per gram of catalyst per hour was obtained at a synthesis temperature of 660 °C. The active phase for growing carbon nanotubes is a mixture of a metastable iron carbide (Fe 3C) and α-Fe which were formed in situ by the ethane dissociation followed by carbon diffusion through the starting α-Fe phase similarly to that reported in the literature. The reaction products only contained multi-walled carbon nanotubes with very homogeneous diameters between 20 and 40 nm and lengths up to several hundred nanometers without any trace of other impurities such as nanoparticles or amorphous soot. The high yield of the MWNT significantly decreases the amount of the catalyst in the final product and the product can be used directly without need for post-synthesis treatment in order to remove the catalyst. Ethane is an active carbon source for growing MWNTs with high yield and selectivity. The reaction temperature should be keep ≤750 °C as synthesis carried out at 800 °C under similar reaction conditions led to the formation of amorphous soot and carbon nanoparticles mixed with nanotubes.

Characterization of copper–cementite nanocomposite produced by mechanical alloying

A copper–iron carbide nanocomposite has been synthesized by high-energy milling of elemental powders (Cu 69–Fe 23–C 8), followed by annealing at 873 K. Phase identification and microstructure characterization have been carried out by transmission electron microscopy and energy dispersive spectroscopy. The carbide phase found in the as-milled material has been identified as Fe 3C and/or Fe 7C 3, but clearly only Fe 3C was present after annealing. Overall, grain sizes ranged from 10 to 50 nm in the as-milled condition and from 30 to 160 nm after annealing, with the carbide phase presenting a higher growth rate than copper. Stacking faults and a dispersion of Cu nanoparticles (5–10 nm) have been detected in annealed cementite while copper grains exhibited twins on {1 1 1} planes. Cementite growth could be evaluated in terms of precipitate growth theory. The remarkable thermal stability of the copper matrix is proposed to be related to solute drag effects.

Reengineering of heat-treatment system for axle-shaft of racing cars

The system of heat-treatment operations, involved in the manufacture of alloy-steel axle-shafts, is reengineered and standardized to ensure quality-consistency as per international standards. The quality-engineering tool of Cause-and-Effect diagram/analysis is also applied in the reengineering technique. The heat-treatment temperatures and time-duration parameters are readjusted by their relationship to their mechanical properties. The Fe–Fe 3C phase diagram was extensively referred in reengineering of the austenising temperature. The required hardness values were successfully achieved in the heat-treated axle-shafts as a result of this reengineering research and development.

A quartz crystal microbalance study of the adsorption of quaternary ammonium derivates on iron and cementite

The adsorption of alkyl trimethyl ammonium bromide with alkyl groups from C 10 to C 16 onto solid surfaces (iron and cementite (Fe 3C)) is investigated with and without NaCl. For the first time the adsorption of these surface active compounds onto model carbon steel compounds are measured directly by the use of a quartz crystal microbalance (QCM). The adsorption increases steeply around the critical micelle concentration (cmc) in bulk which was also determined for the homologous series. The adsorption of the higher homologues shows rather rigid surface structures while a detailed interpretation of the isotherms for the lowest homologues is disturbed by high bulk viscosities. Based on the obtained results, and in comparison with similar adsorbents on hydrophilic oxide surfaces, it is concluded that the surfactant is adsorbed patchwise in similar structures as in bulk. Finally, the possibilities for close-packing of the surfactant film are discussed.

Failure analysis of a heat-exchanger serpentine

The failure analysis of a ASTM A 178 grade A steel serpentine, belonging to a vertical heat-exchanger, has been carried out. Parallel transversal wedge cracks were observed in the concave region of the outer serpentine after just two years of use. The results indicated that the cracking was caused by thermal fatigue (corrosion-fatigue) due to thermal cycling. The presence of graphite nodules and spherodised Fe 3C particles (dominant) indicates a localised overheating of the outer serpentine in temperatures between 550 and 650 °C, which further catalysed the thermal fatigue mechanism. The overheating can be explained by the local presence of a thick deposit (rich in S and Mg) on the internal surface the serpentine, composed of hematite, magnetite and iron sulphide. Finally, the results did not show evidences of the action of a creep mechanism associated to the failure.

Microstructural characterisation of Fe–Cr–P–C powder mixture prepared by ball milling

In an attempt to prepare amorphous Fe 77Cr 4P 8C 11 alloy by mechanical alloying, powder mixtures of Fe, Cr, P and C (activated carbon) with a purity of 99.9% have been ball milled, under argon atmosphere for several periods up to 90 h, in a planetary ball mill (Fritsch P7). The structure and microstructure of the milled powders have been characterised, as a function of milling time, by X-ray diffraction and Mössbauer spectrometry. During the first stage of milling (up to 12 h), detailed analyses of the diffraction patterns and the Mössbauer spectra reveal a complete dissolution of the elemental powders and the formation of Fe x P (1 < x < 2), Fe 3P phosphides and Fe 3C carbide in addition to α-(Fe,Cr) phase. The amorphous like state is reached after 32 h of milling. Further milling leads to the appearance of new carbides such as (Fe,Cr) 7C 3 and ɛ′-Fe 2.2C with the phosphide (Fe,Cr) 3P type phase embedded in the amorphous matrix.