Effect Of Interstitial Carbon Research Articles

Effect of interstitial carbon and nitrogen on corrosion of FeCoCrNi multi-principal element alloys made by selective laser melting

The corrosion behaviors of selective laser melted (SLMed) FeCoCrNi multi-principal element alloys (MPEAs) with carbon or nitrogen addition in 0.5 M H2SO4 solution were investigated. Both C and N addition refined the grains and introduced a heterogeneous structure in SLMed FeCoCrNi MPEA, but they had opposite effects on the corrosion behavior. The doped carbon participated as nano-sized carbides in SLMed MPEA, and localized galvanic corrosion occurred, degrading the corrosion resistance. The doped nitrogen was gathered with chromium and formed CrN chemical clusters in SLMed MPEA, and a protective passive film with a higher Cr2O3/Cr(OH)3 ratio formed, which improved corrosion resistance.

First-Principles Investigation on Work Function of Martensitic Carbon Steels: Effect of Interstitial Carbon on Anodic Dissolution Resistance

The effect of interstitial carbon on the work function and the dissolution resistance of martensitic carbon steels was investigated. Ultraviolet photoelectron spectroscopy measurements of 0.001%C, 0.44%C, and 0.88%C specimens showed that the work function of steels increased with the amount of interstitial carbon. In addition, first-principles calculations indicated that the presence of interstitial carbon clearly increased the work function on both the (110) and (100) orientation surfaces. The immersion tests and potentiodynamic polarization measurements of the specimens were conducted in 50 mM C 8 H 5 KO 4 at pH 4.0, and it was clarified that the anodic dissolution reaction was suppressed as the amount of interstitial carbon increased. The improvement in work function appeared to be related to the superior anodic dissolution resistance.

Effect of interstitial carbon on the evolution of early-stage irradiation damage in equi-atomic FeMnNiCoCr high-entropy alloys

Owing to their excellent radiation tolerance, some of the high-entropy alloys (HEAs) are considered as potential candidates for structural materials in extreme conditions. In order to shed light on the early-stage irradiation damage in HEAs, we performed positron annihilation spectroscopy on hydrogen implanted equiatomic FeMnNiCoCr and interstitial carbon-containing FeMnNiCoCr HEAs. We reveal primary damage as monovacancies in low dose irradiated HEAs. The enhancement of Frenkel pair recombination by C addition is observed in C-containing HEAs. In addition, the C interstitials suppress the vacancy cluster formation in high dose irradiated HEAs.

The Effect of Heat-Treatments on Corrosion Resistance of Martensitic Stainless Steel

Martensitic stainless steels are widely used in industries because of their high strength and corrosion resistance. However, pitting corrosion sometimes occurs in chloride environments. It is known that pitting corrosion is usually initiated at MnS inclusions. The pit initiation at the MnS inclusions in Type 304 stainless steels was found to be inhibited by interstitial carbon. However, the effect of interstitial carbon on pit initiation of martensitic stainless steels is still unknown. In this research, in order to change the amount of interstitial carbon, the specimens were heart-treated by different tempering conditions, and potentiodynamic polarization curves were measured. A commercial Type 420J2 (13Cr-0.3C) martensitic stainless steel (low S) and re-sulfurized Type 420J2 martensitic stainless steel (high S) were used. After solution treatment at 1273 K (5 h, air-cooling), the specimens were tempered at various temperature (from 473 to 1023 K, 2h, air-cooling). After these heat-treatments, the surfaces of the specimens were successively polished with a diamond paste down to 1 µm. With the exception of the electrode area, the surfaces of the specimens were covered with a resin. Figure 1 shows the macroscopic anodic polarization curves of low-sulfur and re-sulfurized Type 420J2 stainless steels in boric-borate buffer solution with 10 mM NaCl (pH 8.0). The electrode area was 1.0 cm2. In the case of low sulfur steels, pitting potentials decreased with increasing tempering-temperature (473-773 K), but the pitting potential of the specimen tempered at 1023 K was higher than that of non-tempered specimen. It is supposed that tempering at 1023 K improves pitting corrosion resistance. For high sulfur steels, pitting potential decreased with tempering-temperature. Because the amount of interstitial carbon decreased with tempering-temperature, these results suggests that interstitial carbon inhibits pit initiation. Figure 1

The Effect of Interstitial Carbon on Pitting Corrosion Resistance of Martensitic Carbon Steels

Ultra-high strength steels with excellent ductility are required to reduce the weight of automobiles and other transportation vehicles. While martensite including high amount of interstitial carbon is favored for strengthening steels, the ductility is relatively low. To optimize the balance between ductility and strength, tempering is conducted. In the case of carbon steels, the precipitation of carbides occurs, and the amount of interstitial carbon decreases during tempering. Although tempering provides the balance between the strength and the ductility, it was reported that the pitting corrosion resistance tends to decrease by tempering.1 To achieve a balance between pitting corrosion resistance and mechanical properties, it is important to determine the quantitative effect of tempering on the pitting corrosion resistance. The specimens were AISI 1045 carbon steel (0.47%C, 0.19%Si, 0.85%Mn, 0.015%P, 0.015%S, 0.02%Ni, 0.18%Cr, 0.01%Mo, 0.01%Cu, <0.001%Ti, <0.002%Nb, 0.024%Al, 0.005%N, 0.002%O). The specimens were heat-treated at 1123 K for 3.6 ks and then quenched in water to form a full martensitic structure. To obtain a tempered martensitic structure, the as-quenched specimens were heated to 873 K and kept at this temperature for 0.1, 1, 10, 15, and 20 h in an Ar atmosphere. The metallographic inspection was performed to ascertain the characteristics of the microstructures of the as-quenched and tempered specimens by using FE-SEM. In tempered martensitic specimens, many small white dots were observed. This is evidence of the carbides formed by tempering. The sizes of the carbides increased with tempering time, meaning that the interstitial carbon decreased. The micro-scale anodic polarization measurements of the as-quenched and tempered specimens were conducted in a boric-borate buffer solution with 500 mM NaCl (pH 8.0) under naturally aerated conditions at 298 K. A small area without non-metallic inclusions was selected for the working electrode. The polarization measurements started at -0.1 V to eliminate the influence of active dissolution on pitting corrosion initiation. For 20 h tempered specimen, a stable pit was initiated immediately after immersion. The pitting potential of 20 h tempered specimen was thought to be less than -0.1 V. In the case of 15 h tempered specimen, the sharp increase in current density was observed at 0.05 V due to the pit initiation. In contrast, no pit was initiated on the as-quenched specimen and the specimens tempered for less than or equal to 10 h. It was found that the pitting corrosion resistance of the martensite tempered for less than or equal to 10 h was higher than that of the martensite tempered for more than or equal to 15 h. Pitting corrosion resistance of martensite decreased with tempering time. To clarify the role of the interstitial carbon on the pitting corrosion resistance, the macro-scale anodic polarization curves of as-quenched, 10 h tempered, and 20 h tempered specimens in a boric-borate buffer solution with 1 mM NaCl (pH 8.0) were measured. The polarization started at -1.0 V after a cathodic treatment (-1.2 V, 600s). For the macro-scale polarization, the region of active dissolution appeared on all specimens in the potential region from -0.7 to -0.6 V. The dissolution current density for 20 h tempered specimen was certainly higher than that of other two specimens. It is suggested that the higher pitting corrosion resistance of the as-quenched and short-time tempered specimens was due to the low dissolution rate of those specimens. It is proposed that the inhibition of the active dissolution rate of these specimens is because of the existence of interstitial carbon, and interstitial carbon improves the pitting corrosion resistance. Short-time tempering is one of the answers for striking an optimal balance between pitting corrosion resistance. References; 1. M. Kadowaki, I. Muto, Y. Sugawara, T. Doi, K. Kawano, and N. Hara, J. Electrochem. Soc., 164, C962 (2017).

First-principles prediction of interstitial carbon, nitrogen, and oxygen effects on the helium behavior in nickel

The effects of interstitial carbon, nitrogen, and oxygen (C/N/O) on the helium behavior in nickel are studied by using first-principles calculations. The interstitial C/N/O changes the occupying priority of helium to the first nearest neighbor Oct-site, which is related to local strain effect and chemical bonding between helium and its adjacent atoms. Both binding energy calculation and diffusion property analysis confirm that the interstitial C/N/O can trap helium in nickel. Moreover, with lower binding energy and larger trapping radii to helium, the interstitial oxygen has significant effect on helium trapping compared with that of nitrogen and carbon. With more helium aggregating at vacancy, the C/N/O would also trap smaller helium clusters and repel larger ones, indicating that the interstitial C/N/O could disperse helium bubbles and further inhibit their growth in nickel. This work helps to understand the helium embrittlement resistant mechanisms of the initial nucleation sites for second phase nanoparticles in nickel-based alloys.

The effect of interstitial carbon on the mechanical properties and dislocation substructure evolution in Fe40.4Ni11.3Mn34.8Al7.5Cr6 high entropy alloys

A systematic study of the effects of up to 1.1 at. % carbon on the mechanical properties and evolution of the dislocation substructure in a series of a high entropy alloys (HEA) based on Fe40.4Ni11.3Mn34.8Al7.5Cr6 is presented. Transmission electron microscopy (TEM), synchrotron X-ray diffraction (XRD) and atom probe tomography (APT) were used to show that all the alloys are single-phase f.c.c. random solid solutions. The lattice constant, determined from synchrotron XRD measurements, increases linearly with increasing carbon concentration, which leads to a linear relationship between the yield strength and the carbon concentration. The dislocation substructures, as determined by a TEM, show a transition from wavy slip to planar slip and, at higher strains, and from cell-forming structure (dislocations cells, cell blocks and dense dislocation walls) to non-cell forming structure (Taylor lattice, microbands and domain boundaries) with the addition of carbon, features related to the increase in lattice friction stress. The stacking fault energy (measured via weak-beam imaging of the separation of dislocation partials) decreases with increasing carbon content, which also contributes to the transition from wavy slip to planar slip. The formation of non-cell forming structure induced by carbon leads to a high degree of strain hardening and a substantial increase in the ultimate tensile strength. The consequent postponement of necking due to the high strain hardening, along with the plasticity accommodation arising from the formation of microbands and domain boundaries, result in an increase of ductility due to the carbon addition.

Helium Behaviour in Fe-Base Materials: Thermal Desorption and Nuclear Reaction Analyses

Polycrystalline Fe 99.95 and 99.5 samples were implanted with helium at 8 keV and 3 MeV. Thermal Desorption Spectroscopy (TDS) and Nuclear Reaction Analysis (NRA) provided a complementary set of techniques to characterize helium-materials interactions within two different implantation depths, respectively close to the surface and in the bulk. Using TDS, it was possible to get information about the nature and the states of the structures where helium was trapped in radiation damaged Fe specimens. Activation energies for every trapping site (mono-vacancies, clusters) have been determined from conventional reaction model. The effect of interstitial carbon was also discussed, and compared with previous ab-initio studies. Moreover, the helium bulk diffusion constants in radiation damaged structures could be derived from non destructive 3He depth profiling. Preliminary observations highlighted that a few part of He remained trapped while helium bubbles migrated in the bulk.

The effect of interstitial carbon on the initiation of plastic deformation of steels

Abstract Pop-in behavior in nanoindentation was studied as a mechanism for the initiation of plastic deformation in two kinds of steels with different interstitial carbon contents; interstitial free (IF) and ultra low carbon (ULC) steels. The critical load P c at which the pop-in occurs is higher in ULC than in IF, and the P c decreases with decreasing loading rate, indicating that the pop-in mechanism is based on a thermal activation process. The interstitial carbon is thought to yield higher friction stress against dislocation movement and have an influence on the critical stress for the activation of the dislocation source formed underneath the indenter.

Carbon in copper and silver: diffusion and mechanical properties

The effects of interstitial carbon on the diffusion and mechanical properties of copper and silver are studied theoretically. Semiempirical methodology, atomistic simulations, and first-principles density functional schemes are combined to extract some understanding of the diffusion process and lattice reconstruction in extremely dilute interstitial Cu–C and Ag–C alloys. It is demonstrated that carbon inclusion in the host matrix leads to sufficient non-uniform dilatation of the lattice. We also show that an account of static displacements is important in the calculations of the activation energy for the diffusion of the interstitial atoms. The “embedded” cluster scheme is suggested to simulate the relaxation in extremely dilute alloys. High-resolution scanning electron microscopy results are presented, which demonstrate the existence of a solid solution zone at the Cu–C interface.

Interstitial carbon in copper: Electronic and mechanical properties

The effects of interstitial carbon on the electronic and mechanical properties of copper are studied theoretically. Semiempirical methodology, atomistic simulations and first-principles density-functional embedded-cluster schemes are combined to extract some understanding of the diffusion process and related degradation of Cu-C composite materials under extremes of temperature and stress. High-resolution scanning electron microscopy results are presented, which demonstrate the existence of a solid solution zone at the Cu-C interface.

Structural and magnetic behaviour of the series Th 2Fe 17C x ( x=0 to 1.25)

The crystal properties of the Th 2Fe 17C x series with x=0, 0.3, 0.6, 0.9, 1.2, 1.25, have been determined from neutron powder diffraction. The effects of interstitial carbon on the structure and the magnetization have been studied both at 2 and 300 K. As in the structurally related rare earth intermetallics, carbon is found statistically to occupy a distorted octahedral site shared by two thorium and four iron atoms. The interatomic distances are compared with those previously reported and discussed with reference to some binary carbides.

Interstitial Ordering of Carbon in Tantalum

AbstractThe effect of interstitial carbon on the structure of tantalum was investigated by transmission electron microscopy and diffraction. Interstitial ordering was found, and the ordered structure was determined from computation and comparison with electron diffraction data. The superlattice structure is tetragonal, with a c/a ratio of 1.128, and an ideal composition of Ta64C. Since the superlattice was determined from thin foils, it was necessary to compare the thin foil results with bulk specimens, alloyed to correspond to Ta64C. Microscopic examination of bulk specimens showed many domain boundaries, separating regions in which the tetragonality associated with ordering was oriented in different directions. An analysis of these domain boundaries indicates that there are three possible types: coherent, semicoherent, and antiphase.