Grain Boundary Segregation Of Sulfur Research Articles

Reducing sulfur to improve thermal embrittlement in electrodeposited nickel using citric acid

Electrodeposited nickel usage has been limited owing to thermal embrittlement at high temperatures. Electrodeposited nickel generally contains sulfur, and the grain boundary segregation of sulfur leads to thermal embrittlement. As the main source of sulfur, saccharin (C7H5NO3S) has been suspected to primarily cause thermal embrittlement. In this study, electrodeposited nickel with improved ductility and high heat resistance was fabricated using citric acid instead of saccharin. Using citric acid, a strong (100) plane-preferred orientation parallel to a substrate was obtained over a wide current density range, similar to the case of using saccharin. Therefore, high ductility is expected in as-deposited electrodeposits obtained from electrolyte using citric acid over a wide current density range. The sulfur content in the samples significantly decreased from 0.025 to 0.007wt% using citric acid instead of saccharin sodium. Specimens obtained from the electrolyte using citric acid achieved an elongation to failure of 7.4% even when annealed at 300°C for 24h, whereas specimens obtained from electrolyte using saccharin were brittle and exhibited no plastic deformation at an annealed state.

First-Principles Investigation of Intergranular Fracture in Copper by Grain Boundary Segregation of Sulfur

Grain boundary (GB) embrittlement by sulfur in fcc CuΣ5(012)[100] symmetrical tilt grain boundary (STGB) is simulated by first-principles calculations. The surface and grain boundary segregation energies are estimated by progressively placing solute atoms in the potential segregation sites in the boundaries. Based on the calculated segregation energies, the cohesive energy of the grain boundary is evaluated as a function of the sulfur atoms concentration. It is found that, when a two atomic layers’ concentration is attained, the cohesive energy is reduced by one order of magnitude compared to its value for the clean grain boundary.

Reduction in sulfur content of electrodeposited bulk nanocrystalline Fe–Ni alloys using manganese chloride

A method for reducing the sulfur content of electrodeposited bulk nanocrystalline Fe–Ni alloys was developed to improve the tensile ductility of the materials and prevent thermal embrittlement caused by the grain boundary segregation of sulfur. Bulk nanocrystalline Fe–Ni alloys were prepared using electrolytes that primarily consisted of iron sulfate and nickel sulfamate combined with manganese chloride (MnCl2). The addition of MnCl2 in the deposition bath did not produce any significant changes in the Ni content and grain sizes of the electrodeposited alloys. In contrast, the sulfur content in the materials decreased from 840 to 620atppm. The bulk nanocrystalline Fe–Ni alloys with low sulfur content exhibited a higher tensile elongation of 16–19% compared to the materials with high sulfur content. Furthermore, after annealing at 200°C for 3h, The bulk nanocrystalline Fe–Ni alloys with low sulfur content exhibited a high tensile elongation of 9–10%, whereas the elongation of the materials with high sulfur content was 3%. The results indicate that the plastic elongation of electrodeposited bulk nanocrystalline Fe–Ni alloys can be improved by reducing the amount of sulfur in the materials.

The Mechanism of Hot Ductility Loss and Recovery in Nb-Bearing Low Alloy Steels

In low alloy steels containing Nb, the poor hot ductility is basically due to the austenite grain boundary segregation of sulfur and the additional matrix strengthening of Nb(C,N) precipitates, both of which decrease the equicohesive temperature. The recovery of hot ductility is therefore attributed to not only the clean grain boundaries that the segregated sulfur is scavenged through the MnS reaction but also the matrix softening by the coarse Nb(C,N) precipitates.

In situ observations of crack propagation and role of grain boundary microstructure in nickel embrittled by sulfur

In situ observations of crack propagation in sulfur-doped coarse-grained nickel were performed for the specimens with grain boundary microstructure pre-determined by SEM/EBSD analysis. The role of grain boundary microstructure was studied in the crack propagation in nickel embrittled by grain boundary segregation of sulfur. It was found that the main crack tends to predominantly propagate along random boundaries, and the crack propagation rate can be locally accelerated at the grain boundary network with a high connectivity of random boundaries. On the other hand, the cracks can propagated along fracture-resistant low-Σ coincidence site lattice (CSL) boundary only when the trace of the grain boundary is arranged being almost parallel to slip bands in the adjacent grains. The local crack propagation rate was found to become lower when a crack propagated along low-Σ CSL boundaries. Moreover, when the crack propagation is inhibited by low-Σ CSL boundaries, the branching of propagating crack occurs at partially cracked triple junctions. The crack propagation can locally slow down due to the occurrence of crack branching. The optimum grain boundary microstructure for the control of sulfur segregation-induced brittle fracture is discussed on the basis of new findings obtained from the in situ observations on crack propagation and fracture processes in polycrystalline nickel.

Nonequilibrium Grain Boundary Segregation of Sulfur and Its Effect on Intergranular Corrosion for 304 Stainless Steel

The data obtained by bending tests for intergranular embrittlement after 45 h and 450 h exposure to Strauss solution have been reported for 304 stainless steel. The results show that an embrittlement peak appears at 650 °C for all samples quenched from 1260 °C and then sensitized for 150 h at 480, 565, 650, 730, 815 and 900 °C respectively. The temperature corresponding to the embrittlement peak is decreased to 565 °C when the sensitizing time is prolonged to 1500 h. In this paper, these data are analyzed with an isothermal kinetic model of nonequilibrium grain boundary segregation, indicating that the embrittlement peak is related to the critical time for nonequilibrium grain boundary segregation of sulfur.

Study on Non-Equilibrium Grain-Boundary Segregation of Sulfur among Hastelloy X

Sulfur is the main element which caused Nickel-based alloy embrittlement. In this study, the sulfur in Hastelloy X superalloy was determinated with Auger Electron Spectroscopy (AES) for samples quenched from 1180 °C and aged at 500 °C for different time. Experiments results confirmed the non-equilibrium segregation characteristics of sulfur. The results showed that a segregation peak of sulfur is at about 20 min during ageing. This peak was satisfactorily elucidated by the theory of non-equilibrium grain-boundary segregation. By theoretical calculation, the critical time constant of impurities sulfur atom in the Hastelloy X δs= 357. At the same time, the result provides a theoretical basis for sulfur segregation mechanism.

Intermediate-temperature embrittlement induced by non-equilibrium grain-boundary segregation of sulfur in Ni–Cr–Fe alloy

Intermediate-temperature embrittlement (ITE) for a Ni–Cr–Fe alloy has been experimentally studied by Auger electron spectroscopy and elevated-temperature tension tests. Results show both the grain boundary concentration of sulfur and the degree of embrittlement reach maxima at 500°C. The peak of the grain boundary concentration of sulfur during aging at 500°C occurs at about 20 min, which is close to the holding time prior to the start of tension at the test temperature. It can be concluded from these results that ITE of this alloy is induced by non-equilibrium grain-boundary segregation of sulfur.

Effect of manganese on grain boundary segregation of sulfur in iron

The ASED-MO theory was used to study the electronic effects of S and the S–Mn couple upon the chemical embrittlement of Fe grain boundaries. The results obtained for S alone in a model of grain boundary (GB) are consistent with its observed behavior as a chemical embrittling agent. It was found that the total energy of the cluster decreases when the S atom is located at the GB. When S segregate at the Fe GB containing Mn, the embrittlement process was modified. The crystal orbital overlap population (COOP) curves gives a measure of Fe–Fe bond weakening due to the segregated atoms at the GB. Our calculations show that Mn behaves as a weak embrittler on the Fe GB. The Fe–Mn bonds were strengthened, while Fe–Fe bonds of the capped trigonal prism of the GB (CTP) were weakened. On the other hand, when S segregate at the Mn/Fe cluster, some metallic bonds were resistant to chemical embrittlement.

Ｎｉ‐５８ｍａｓｓ％Ｆｅ合金めっき皮膜の機械的性質に及ぼす熱処理の影響

The authors investigated the mechanical properties of Ni-58mass%Fe alloy electrodeposits, which are expected to be used as low thermal expansion materials, before and after heat treatment for one hour at 400 to 600°C.For the Ni-58mass%Fe alloy electrodeposits without heat treatment, ultimate tensile strength (UTS) was 1610MPa, elongation (&delta) was 7%, and hardness was 430HV. After heat treatment for one hour at 400, 500, and 600°C to stabilize the liner expansion coefficient of the Ni-58mass%Fe alloy electrodeposits, the alloy electrodeposits had a UTS of 830MPa, a &delta of 9%, and a hardness of 270HV at 400°C ; a UTS of 720MPa , a &delta of 17%, and a hardness of 240HV at 500°C ; and a UTS of 640MPa, a &delta of 22%, and a hardness of 220HV at 600°C. After heat treatment for one hour at 400 to 600°C, the mechanical properties of the Ni-58mass%Fe alloy electrodeposits were comparable to those of melted Ni-58mass%Fe alloys for IC leadframes.Though a reduction in the ductility of the Ni-58mass%Fe alloy electrodeposits after heat treatment for one hour at 400 to 600°C by grain boundary segregation of sulfur was expected because the alloy electrodeposits contained 0.04mass% sulfur, ductility of the alloy electrodeposits was not reduced after heat treatment in this temperature range. It was considered that since sulfur dispersed as granular Fe-Ni-S compounds in the Ni-58mass%Fe alloy electrodeposits after heat treatment for one hour at 400 to 600°C, embrittlement originating from sulfur segregation to grain boundaries of the alloy electrodeposits was able to be prevented.

Dynamic embrittlement in an age-hardenable copper-chromium alloy

Copper containing up to {approximately}1 weight % chromium is a precipitation hardening alloy exhibiting good room temperature strength, ductility and high electrical and thermal conductivity. Age-hardenable Cu-Cr alloys have been found to suffer from embrittlement in the temperature range 400--800 K. Grain boundary segregation of sulfur has been suggested to be the cause. Minor additions of Zr and Ti have been found to significantly improve the hot ductility of these alloys and this has been attributed to scavenging of grain boundary sulfur as zirconium sulfide. The mechanism of embrittlement during hot deformation processing of Cu-Cr alloy and other copper-based alloys is far from understood and efforts are continuing to understand the embrittlement process in these alloys.

Environmentally Assisted Cracking of Nickel Strip in LiAlCl4 / SOCl2

Constant extension rate tests (CERT) were used to evaluate the susceptibility of two cold‐rolled nickel strip materials to environmentally assisted cracking (EAC) in 1.5M . One strip material was made by a powder metallurgy (PM) process that started with carbonyl nickel. The other was cast and wrought (C&W). Both were 0.05 mm thick and cold‐rolled to the three‐quarter hard condition. The bulk impurity concentrations, grain structures, and mechanical properties of these two materials were similar. However, the C&W alloy was distinguished by a substantially higher bulk manganese content and oxygen‐rich inclusions, a large fraction of which also contained sulfur. EAC of the PM alloy, manifested principally as intergranular fracture, occurred in samples that were polarized to −50, 0, and +200 mV , but not in ones that were freely corroding at +3.65 V . These results are consistent with EAC being caused by a mechanism involving zero‐valent lithium, proposed by Scully et al1. In marked contrast to the PM alloy, the C&W alloy exhibited no susceptibility to Li‐assisted cracking. In ancillary experiments, performed with samples that were cathodically charged with hydrogen, only the PM alloy exhibited a high susceptibility to intergranular cracking. The present results indicate that subtle microstructural differences may affect the reliability of cells. Although the existing evidence is circumstantial, the results also suggest that lithium‐assisted and hydrogen‐assisted intergranular cracking have analogous sensitivities to grain boundary segregation of sulfur.

純鉄における酸化物によるイオウの粒界偏析と粒界脆性破壊の抑制

純鉄における酸化物によるイオウの粒界偏析と粒界脆性破壊の抑制

Grain boundary segregation of sulfur and antimony in iron alloys

A correlation between sulfur and antimony grain boundary segregation has been observed on inter-granular surfaces of iron by Auger electron spectroscopy (AES). The slope of a plot of S/Sb indicated a ratio of two antimony atoms per sulfur atom arriving at the grain boundary, while the ratio for the total S/Sb at the grain boundary was about 1.2. These results were obtained with Fe, Fe + 0.07Mn, Fe + 0.03Sb, Fe + 0.1Mn + 0.02Sb, and Fe + 0.1Mn + 0.05Sb (at. pct) alloys. Possible expla-nations for this correlated segregation, such as cosegregation of sulfur and antimony, precipitation of a thin layer of antimony sulfide, and compctitive segregation with carbon and nitrogen, were evalu-ated using AES, X-ray photoelectron spectroscopy (XPS), and scanning transmission electron mi-croscopy with energy-dispersive X-ray (STEM-EDS). The results of these analyses indicated that there was no resolvable antimony sulfide phase in the grain boundary and that S and Sb were not chemically bound at the grain boundary in a two-dimensional phase. The S was shown to be strongly bound to the iron in a chemical state close to that of an iron sulfide, but the Sb was in the elemental state. Nor could this correlated segregation be satisfactorily explained by a cosegregation process nor by compctitive segregation with other elements. The most plausible explanation appears to involve the effect of sulfur on the activity/solubility of antimony or antimony on the activity/solubility of sul-fur, as explained by an increase in the ratioXc/XCo in the Brunauer-Emmett-Teller (BET) adsorption isotherm adapted for equilibrium segregation in solids.

Surface and grain boundary segregation of sulfur and boron in nickel

Auger Electron Spectroscopy and Secondary Ion Mass Spectrometry were used to study surface and grain boundary segregation of B and S in Ni. Sulfur segregation was not influenced by the presence of boron and resulted in a uniform monolayer surface and grain boundary coverage. Segregation of boron differed from that of sulfur and resulted in the precipitation of Ni 3B in the near surface layer. At temperature analysis showed that bondes dissolved into the matrix at temperatures above 923 K and precipitated during cooling. This process did not affect the segregation of sulfur, which covered the bondes and matrix uniformly. Grain boundary segregation of boron, its effect on the co-segregation of sulfur and on the tendency for intergranular fracture were studied using hydrogen charged in situ fractured samples. Addition of boron to Ni reduced the tendency for intergranular fracture. A small amount of boron was found at the grain boundaries, together with sulfur and carbon; the sulfur and carbon levels were about 20% smaller than in the boron-free sample. These results suggest that boron has a beneficial effect on the strength of the grain boundaries and also reduces the negative effect of sulfur segregation on the boundary properties.

Effect of carbon on grain boundary segregation of sulfur in iron

Effect of carbon on grain boundary segregation of sulfur in iron

Site competition between sulfur and carbon at grain boundaries and their effects on the grain boundary cohesion in iron

Grain boundary segregation in iron-sulfur-carbon alloys containing up to 100 wt ppm sulfur and up to 90 wt ppm carbon has been investigated with Auger electron spectroscopy (AES). The results show the site compctition on grain boundaries between the segregation of sulfur and carbon. The segregation energy of sulfur is estimated to be 75 kJ/mol. Impact tests of these alloys were carried out. Iron-sulfur alloys with less than 20 wt ppm carbon fractured by the intergranular mode with high ductile-brittle transition temperatures (DBTT’s). Addition of up to 90 wt ppm carbon to the binary alloys prevented the intergranular fracture caused by the grain boundary segregation of sulfur, and decreased the DBTT. Carbon, when segregated to grain boundaries, drives sulfur away from the boundaries and also increases the grain boundary cohesion. The DBTT values of the iron-sulfur-carbon alloys are analyzed in terms of the degree of grain boundary segregation of sulfur and carbon. It is shown that sulfur decreases the grain boundary cohesion of iron more severely than phosphorus if compared at the same degree of grain boundary segregation.

Grain boundary segregation of sulfur in iron

This paper reports a study of grain boundary segregation of sulfur in iron. The results show that if the amount of sulfur in the alloy is greater than the solubility limit, the amount of segregation increases with increasing ageing temperature. When the temperature is raised above the point where all sulfur goes into solution, the amount of segregation decreases with increasing temperature. These results can be explained quite straightforwardly by McLean's model for segregation. However, at high bulk concentrations. Auger analysis may be difficult because the signal obtained from a grain boundary facet will arise from a combination of segregated sulfur and precipitated sulfur.

Grain boundary segregation of sulfur and nitrogen in sintered molybdenum

Working of sintered polycrystalline, powder-metallurgy molybden is necessary to increase its strength, ductility, and fracture resistance. A portion of a study that determined the partitioning of impurities between the grain boundaries and the grain interior in powder-metallurgy molybenum is summarized. It was determined that sulfur and nitrogen segregate to the grain boundaries. Both carbon and oxygen were detected but it is believed that they were contamination from the residual atmosphere. (FS)

Grain Boundary Segregation of Sulfur, Nitrogen, and Carbon in α‐Iron

AbstractThe segregation of sulfur, nitrogen, and carbon at surfaces and grain boundaries of α‐iron was studied by Auger Electron Spectroscopy (AES). Specimens of pure iron, doped with nitrogen or carbon by equilibria with gas mixtures were introduced into the UHV‐chamber and fractured by impact at about −130°C. Enrichment of nitrogen, carbon, or sulfur was observed on the intergranular fracture surfaces. Displacement equilibria exist between nitrogen or carbon and sulfur, which was present in the bulk material only as a trace impurity. The presence of sulfur decreases the cohesion of the grain boundaries, so that mainly intergranular fracture occurs. Obviously nitrogen or carbon reinforce the cohesion of grain boundaries, so that transgranular fracture prevails.