Increasing Silicon Content Research Articles

酸化物超伝導体の合成と特性 シリコンを含むＰ／Ｍ二相ステンレス鋼の機械的性質と耐食性

Influence of the addition of silicon on mechanical properties and corrosion resistances of P/M austenitic stainless steels was investigated by means of microstructual examinations, calorimetric analysis and X-ray analysis. Silicon addition to P/M austenitic stainless steels makes the sintering in the duplex structure of austenite(γ) and ferrite(α) possible by the liquid phase sintering with a eutectic liquid. For example, addition of 4mass% Si results in the formation of about 40vol% of ferrite. Tensile strength of sintered steels increases with increased silicon content, and the maximum strength (940MPa) was obtained in the steel with 4mass%Si which was sintered for 3.6ks at 1623K. On the other hand, elongation of sintered steels tends to increase with rising sintering temperature. The maximum elongation (47.5%) was obtained in the steel with 2mass%Si which was sintered for 3.6ks at 1673K. The sintered steel with 2mass%Si was found to have excellent corrosion resistance in a boiling solution of 65% HNO3 : The corrosion rate of the steel was very small in comparison with the sintered SUS304L steel, but it was three times larger than that of a SUS304L steel produced by ingot metallurgy. However, further addition of silicon causes a decline in corrosion resistance probably due to a decrease in the green density.

A study of the 500 to 900°C tensile deformation behaviour of spheroidal graphite cast iron

The general characteristics of the 500 to 900°C tensile deformation behaviour of spheroidal graphite cast iron are reported. The effects of silicon content and strain rate are also included. Three SG cast irons (3.5 wt%C) with 2.1 wt%Si, 2.8wt%Si and 3.9 wt%Si were used to perform the tensile tests. The strain rates were chosen within the same range from 3.3 × 10−4 to 2.7 × 10−2 s−1.At temperatures below 700°C, the flow stress decreases and the elongation increases with temperature. Because of the solid solution strengthening effect, the flow stress increases while the elongation decreases with silicon content. At temperatures above 700°C, there is a reversion of temperature dependence for the flow stress, and the elongation then deteriorates. The temperature of reversion increases with increasing silicon content, a result which can be attributed to the increase in the eutectoid transformation temperature. Because of the higher eutectoid transformation temperature, 3.9%Si alloy has shown good ductility. From the wavy flow in the flow curves and the recrystallization structure, dynamic recrystallization takes place at the temperatures above 700°C. Furthermore, the strain rate sensitivity m value increases with temperature, and has a maximum near the eutectoid transformation temperature. The specimens of higher silicon content have higher m values when deformed at higher temperatures.

Grain boundary segregation and intergranular fracture in Ferrite containing Mo, Si or Al

Roles of molybdenum, silicon or aluminum in ferrite on grain boundary segregation and hence on intergranular fracture have been investigated by using Auger electron spectroscopy (AES) and tensile test. Competitive segregation between sulfur and carbon or nitrogen, which caused the decrease below 700°C of sulfur content at the grain boundaries, was observed in the pure iron. The intergranular brittleness of the pure iron was caused by sulfur at the grain boundaries. When molybdenum was added to the pure iron, the sulfur contents at the grain boundaries were lowered in comparison to those in the pure iron. The molybdenum-bearing alloy showed higher fracture strength than that of the pure iron, and fractured mostly in the transgranular mode. This arises from the intrinsic effect of molybdenum on the grain boundaries as well as the decrease in sulfur content. Tn the 3.37 wt.%Si alloy, silicon and carbon or nitrogen competitively segregated to the grain boundaries, and such a competitive segregation was also observed between sulfur and carbon or nitrogen. The sulfur content at the grain boundaries decreased with increasing silicon content. The fracture modes in the 3.37- and 4.26 wt.%Si alloys were transgranular in the rolling direction, but were mostly intergranular in the transverse direction and in the as-rolled condition. The intergranular characteristic in the fracture behavior may be attributed to the detrimental effect of silicon as well as sulfur on the intergranular cohesion. Carbon and aluminum only were found at the grain boundaries of the aluminum-bearing alloy. This suggests that aluminum is a strong repulser of sulfur or nitrogen at the grain boundaries. Additionally, it was found that aluminum has a detrimental effect on grain boundary strength of ferrite.

浸炭鋼の疲れ特性に及ぼすＳｉ，Ｖの影響

Influence of silicon and vanadium contents on fatigue properties of carburized steels have been investigated. The rolling con;tact fatigue strength and rotating bending fatigue strength increase with addition of silicon and vanadium. The L10 life of 1.5%Si-0.3%V steel is five times longer than that of SCr420 steel. The microstructural changes induced by rolling contact load have been observed below the raceway surface of the tested specimens by the optical microscopy. These microstructural changes are affected by silicon and vanadium contents and for that reason the rolling contact fatigue life increases with an increase of silicon and vanadium content.

A magnetic, neutron-diffraction, and Mössbauer spectral study of the Ce2Fe17−xSix solid solutions

The magnetic properties of a series of Ce2Fe17−xSix solid solutions with x equal to 0.0, 0.23, 0.4, 0.6, 0.8, 1.02, 1.98, and 3.20 have been studied by magnetic measurements, neutron diffraction, and Mössbauer spectroscopy. An x-ray-diffraction study indicates that the compounds adopt the rhombohedral Th2Zn17-type structure. The substitution of silicon for iron in Ce2Fe17 leads to a contraction of the a axis by 0.2%, an expansion of the c axis by 0.2%, and a consequent reduction of the unit-cell volume by about 0.2% per substituted silicon. Magnetization studies indicate that the Curie temperature increases uniformly from 238 K for Ce2Fe17 to 455 K for Ce2Fe14Si2. Powder neutron-diffraction results, obtained at 295 K, indicate both that the silicon atoms preferentially occupy the 18h sites and that the iron moments increase with increasing silicon content, an increase which is related to the increase in Curie temperature. The Mössbauer spectra have been fit with a binomial distribution of the near-neighbor environments in terms of a maximum hyperfine field Hmax for an iron with zero silicon near neighbors, and a decremental field ΔH per silicon near neighbor. The compositional independence of both the weighted average maximum hyperfine field and of the decremental field indicates that the silicon acts as a magnetic hole, a hole which does not perturb the magnetic moments at the iron sites. The compositional dependence of the weighted average isomer shift is explained in terms of an interband mixing of the iron 4s and silicon 2p bands, due to the reduction of the iron 18h bond lengths. This interband mixing affects the charge but not the spin distribution at the iron sites.

The Effects of Carbon and Silicon on Structure and Properties of an Fe-27Cr-15Ni-N Alloy at 1250 °C

In order to design a new kind of low-cost oxidation-resistant high-temperature alloy with good weldability which might be used as structure material of iron-ore sintering furnaces and magnesium-smelting tanks, the complex effects of carbon and silicon on the structure and properties of the Fe-27Cr-15Ni-N alloy are investigated simultaneously by the orthogonal experiment. It has been shown that as the carbon content increases, the alloy rupture at 1250 °C increases at first until carbon content reaches about 0.45 %, and then decreases notably. Meanwhile its oxidation resistance degrades apparently. As the silicon content increases, the alloy rupture strength at 1250 °C decreases acutely, while its oxidation resistance improves at first and then deteriorates remarkably. At 1250 °C, the grain-boundary (GB) is vital to the alloy rupture strength, the variation of carbon content in the alloy affects the GB structure obviously so as to influence the alloy strength. However, the solubility of carbon in solid and its activity are strongly dependent on the silicon addition to the alloy. The suitable carbon content to the alloy ranges from 0.30 to 0.40 %, and the silicon content from 2.00 to 3.00 %.

Effects of additives Si on casting structure of ceramic liner produced by a centrifugal-thermit process

In order to control the quality of ceramic layer produced by a centrifugal—thermit process, effects of the amount of additives Si on phase constituents and casting structure of the layer are studied. The results show that silicon is mainly distributed over the matrix phase of the inner part of the layer, and the matrix belongs to a spinel“solid solution” having many Si4+ ions replacing Al3+. Because of its low melting point, the fluidity of liquid ceramic and thus the surface quality are improved. However, the effect of silicon is not always positive, since the dissolution of Si4+ ions enlarges the temperature range of freezing, thus it increases the tendency of “constitutional supercooling” and facilitates the development of equiaxed zone. In addition, with increasing silicon content the viscosity of liquid ceramic will increase as well. All these factors make the liquid feeding more difficult and lead to poor surface quality and high porosity of the layer. The changes in casting structure with various Si contents are discussed from the above point of view.

Maximum-entropy reconstruction of the internal magnetization density distributions in Fe3(AlxSi1-x) alloys

Magnetization distributions in Fe3Al, Sendust, Fe3Si and Fe4Si have been reanalysed by applying the model-free maximum-entropy method. The results show that in the first three alloys the magnetic moments of iron at the B sites decrease while their eg-type asphericities increase with increasing silicon content. The asphericities at (A, C) sites are not very different from those at B sites. Compared with the situation in BCC iron, the formation of D03 ordering with the presence of silicon increases the number of eg states at the Fermi level, while the opposite is true for aluminium atoms. Iron substituting for aluminium or silicon exhibits a substantially different degree of asphericity than exhibited at B sites. In the case of substitution for silicon a decrease in the magnetic moments at D sites with respect to the B sites is seen. The spatial extent of the magnetization distribution at iron sites is generally more extended than observed in pure iron. From the purely maximum-entropy point of view, negative magnetization is not needed for the magnetic structure factor reconstruction. However, at least in the case of Sendust alloy, it is shown that such magnetization is necessary in order to obtain a sensible spatial distribution of the magnetization at the D site. It is shown that, once negative magnetization is allowed, its distribution throughout the unit cell has a localized character.

Oxidation of ?-Ni?Al?Si alloys at 1073 K

The formation and development of oxides in Ni−4Al and Ni−4Al−xSi (at.%, x=1, 3, 5) alloys at 5–9×10−6 and 1 atm oxygen pressure at 1073 K have been studied. The oxidation rate increased with an increase of silicon content in the alloy at the early stage of oxidation, but decreased after longer time exposure due to formation of an intermediate layer composed of NiO and spinel (NiAl2O4 and Ni2SiO4) between the top NiO layer and the internal-oxidation zone. This intermediate layer became a barrier for releasing stress, generated by the volume expansion associated with oxidation of solute atoms, resulting in high dislocation density and severe distortion in the internal-oxidation zone for the Ni−Al−Si alloys. In Ni−4Al alloy where no complete intermediate-layer formation occurred, stress was easily released by an enhanced vacancy gradient, and therefore an enhanced vacancy-injection rate into the alloy, resulting in a higher oxidation rate than the situation where a sample was oxidized at an oxygen pressure associated with the dissociation of NiO.

Effect of silicon on CGHAZ toughness and microstructure of microalloyed steels

The aim of this article is to present the beneficial effect of a reduction of silicon content on coarse-grained heat-affected zone (CGHAZ) toughness. This study was achieved with experi-mental and industrial E355 structural steels. These 0.09 wt pct C steels were Ti-microalloyed with silicon contents ranging from 0.05 to 0.5 wt pct. First, we demonstrate that the CGHAZ toughness is predominantly affected by the volume fraction of retained austenite (γr). Second, we show that the existence of retained austenite pertains only to its carbon enrichment. This enrichment is promoted essentially by an increase of the silicon level due to the retarding action of silicon on the formation of carbides in ferrite as well as in austenite. In the same way, the increase of silicon content slows down the decomposition of retained austenite into pearlite. The reduction of the silicon content of the steel greatly increases the ductility of the CGHAZ through the decrease of the volume fraction of retained austenite.

The contribution of grain boundary effects to low-alloy steel irradiation embrittlement

The contribution of irradiation-induced enrichment of grain boundaries by impurities to irradiation embrittlement of reactor pressure vessel materials is discussed. Possible mechanisms of impurities and the effect of alloying elements on irradiation embrittlement of reactor pressure vessel steels are considered. Nickel has been found to influence greatly the tendency to irradiation embrittlement of nickel-containing steels with Ni wt% > 0.9. Irradiation resistance of nickel-containing steels has been shown to decrease significantly with the increase of silicon concentration from 0.24–0.28 to 0.3–0.4 wt%. The model for irradiation-induced enrichment of grain boundaries by impurities is used in order to explain the effect of silicon and nickel on irradiation embrittlement. In terms of the model, Si and Ni themselves do not prove the embrittlement, but they only influence thermodynamic and kinetic parameters of the phosphorus gain boundary adsorption. The embrittlement process itself is a result of decreasing of grain boundary cohesion with formation of phosphorus irradiation-induced grain boundary segregation.

Study of Dendrite Coherency in Al-Si Alloys During Equiaxed Dendritic Solidification

Dendrite coherency (or impingement) is important for the formation of solidification structures. The effects of silicon concentration and modification of eutectic silicon crystals on dendrite coherency in Al-Si alloys have been studied by continuous torque measurement in solidifying samples. The fraction solid at the dendritic coherency point in the alloys decreases with increasing silicon concentration, and varies from 0.09 to 0.39 when the silicon concentration in the alloy is in the range 0.5 to 11 mass%. Modification of eutectic silicon crystals may increase the coherency fraction solid somewhat, but not much. When a grain refiner and a modifier are added together the coherency fraction solid will increase greatly. A theoretical approach is proposed to describe how these factors affect the dendrite coherency in the alloy. (orig.)

Codeposition of Free Silicon during CVD of Silicon Carbide

Factors influencing the concentration and distribution of elemental silicon codeposited during chemical vapor deposition (CVD) of SiC from MTS (CH3SiCl3) and hydrogen diluted by argon are reported. The experiments were carried out in both hot‐ and cold‐wall reactors at 1383–1473 K at atmospheric pressure. Codeposition of free silicon was detected even at very low excess hydrogen, contrary to the prediction of thermochemical calculations. In the hot‐wall reactor, under conditions of high exchange rate of the feed gases, deposits of uniform composition were obtained, containing 0%–90% free silicon, depending upon feed gas composition. The deposits of pure silicon carbide consisted of β‐SiC with a microhardness of 2400 kg/mm2 at a typical formation rate of 30 μm/h. Microhardness decreased to 800 kg/mm2 with increasing silicon concentration. In the cold‐wall reactor, under impinging gas flow conditions, nonuni‐form deposition occurred: a local gradient of Si/SiC was obtained with free silicon concentrations varying gradually between 0% and 35%. Si/SiC ratios in the deposits were determined by a combination of XRD, scanning AES, and SMP.

Thermodynamics of phosphorus in carbon-saturated manganese-based alloys

The interaction coefficient of phosphorus with silicon in a Mn-Si-Csat alloy has been measured at 1573 K, equilibrating CaC2, C, and Ca3P2 in a quartz capsule to keep the phosphorus partial pressure as high as 33.7 Pa. The activity coefficient of phosphorus in the melts increases with increasing silicon content, and the interaction parameter between silicon and phosphorus in the melts at carbon saturation εSiP, Csat was found to be 10.4. The activity of phosphorus in a carbon-saturated Fe-Mn alloy was also determined at temperatures of 1573 to 1673 K using a chemical equilibration technique between BaO-BaF2 fluxes and Fe-Mn-Csat with manganese mass contents ranging from 0 to 85.3 %. A slight decrease in the activity coefficient of phosphorus in Fe-Mn-Csat alloys was observed with increasing manganese content, as a reflection of a stronger interaction between manganese and phosphorus than that between iron and phosphorus. The value for eMnP,Csat was found to be -0.0029 between 1573 and 1673 K. Der Wechselwirkungskoeffizient von Phosphor und Silicium in einer Mn-Si-Csat-Legierung wurde bei 1573 K gemessen. CaC2, C und Ca3C2 wurden in einer Quartzkapsel im Gleichgewicht gehalten, um den Phosphorpartialdruck bei 33,7 Pa zu halten. Der Aktivitätskoeffizient von Phosphor in der Schmelze steigt mit zunehmendem Siliciumgehalt und der Wechselwirkungsparameter zwischen Silicium und Phosphor in der Schmelze bei Kohlenstoffsättigung wurde zu 10,4 bestimmt. Die Aktivität von Phosphor in einer kohlenstoffgesättigten Fe-Mn-Legierung wurde ebenfalls für den Temperaturbereich 1573 - 1673 K bestimmt. Das chemische Gleichgewicht zwischen BaO-BaF2-Flußmitteln und der Fe-Mn-Csat-Legierung mit Mn-Massengehalten zwischen 0 und 85,3 % wurde eingestellt. Mit steigendem Mn-Gehalt nahm der Aktivitätskoeffizient von Phosphor leicht ab. Dies bedeutet, daß die Wechselwirkung zwischen Mn und P stärker ist als zwischen Fe und P. Für kohlenstoffgesättigte Schmelzen beträgt der Wert für eMnP,Csat -0,0029 im Temperaturbereich von 1573-1673 K.

A neutron diffraction and Mössbauer spectral study of the structure and magnetic properties of the Y2Fe14−xSixB solid solutions

A neutron diffraction and Mössbauer spectral study of Y2Fe14−xSixB shows that silicon preferentially occupies the 4c, and to a lesser extent, the 8j1 sites in Y2Fe14−xSixB. The trend in the site occupancy is the same as in Nd2Fe14−xSixB. The Curie temperature of Y2Fe14−xSixB increases with increasing silicon content. Neutron diffraction data show that the increase in Curie temperature is accompanied by a contraction of the unit cell. Wigner–Seitz cell calculations, using the Y2Fe14−xSixB lattice and positional parameters obtained by neutron diffraction, show that the silicon site occupancy is correlated with the rare earth contact area of that site. The Mössbauer spectra of Y2Fe14−xSixB have been fit with a model which takes into account the distribution of near-neighbor environments of an iron atom due to the presence of silicon. The weighted average of Hmax, the average hyperfine field of the iron sites with no silicon near neighbors, decreases by 42 and 45 kOe per silicon substitution per formula unit at 85 and 295 K, respectively. The weighted average of ΔH, the average reduction in the hyperfine field caused by the addition of one silicon near neighbor to the near neighbor environment, is about 13.5 and 18 kOe at 85 and 295 K, respectively, and does not show an appreciable dependence on the silicon content. The isomer shifts obtained from these fits suggest an increase in covalency of bonding on silicon substitution, an increase which is consistent with the preference of silicon to bond with yttrium.

Wear characteristics of Al-Si alloys

The wear characteristics of Al-Si alloys containing 2–20 wt.% have been studied using a pin-on-disc type wear testing machine at room temperature. The effects of alloy composition, sliding distance, sliding speed and load on wear rate of Al-Si alloys have been investigated. It has been found that the wear rate is strongly dependent on alloy composition, applied load and sliding speed. The wear rate decreases and the load-bearing capacity of the alloy increases with increasing silicon content. The nature of the wear process changes with alloy composition and experimental conditions.

Combustion of Binary and Ternary Silicon/Oxidant Pyrotechnic Systems, Part I: Binary Systems with Fe203 and Sn02 as Oxidants

Abstract Abstract– The results of a detailed study of the combustion of several binary silicon/oxidant pyrotechnic systems are reported in this and three immediately following papers. The overall aim of the study was to investigate the role of different oxidants in binary combination with silicon as the common fuel. Temperature profiles of the burning pyrotechnic compositions have been recorded. simultaneously with measurements of linear burning rates. by using thermocouples embedded in pressed columns of the pyrotechnic material. In this paper, results for systems containing the more thermally stable oxidants, Fe2O3 and SnO2, are reported and compared. Burning of the Si/Fe2O3 system is a multi-stage process. Burning rates were in the range 2.3 to 5.7 mm s-1, generally increasing with increasing silicon content and burning fails below 20% and above 40% silicon. The burning rates of the Si/SnO2 compositions ranged from 5.3 mm s-1 (20% Si) to 17.0 (40% Si) and were sensitive to the loading and pressing of the pyrotechnic column. Below 20% silicon and beyond 55% burning fails. The maximum temperatures measured were of the order of 1230°C (30% Si/Fe2O3) and 1360°C (30% Si/SnO2) which are approaching. but still belnw the melting point of Si (1410°C) and the oxidants (Fe2O3. 1565°C;SnO2. 1630°C). which suggests that burning in both systems must occur either through solid-solid reactions, or that the products may form some lower melting eutectics. Evidence in support of a condensed-phase reaction is the increase in the burning rate with increasing density as a result of better contact between the fuel and oxidant particles. and negligible mass-loss during combustion.

Friction and wear behaviour of amorphous hydrogenated Si1−x Cx films

Amorphous hydrogenated Si1−x Cx films (a-Si1−x:H) (x=0.65-1) were deposited by r.f. plasma-assisted chemical vapour deposition. Their friction and wear properties were investigated with the help of a conventional ball-on-disk apparatus. These results are correlated with chemical (Si to C atomic ratio), structural (laser Raman Spectroscopy) and mechanical (internal stress, hardness and elastic modulus) properties. With increasing silicon content, the film material evolves from diamond-like carbon (DLC) to amorphous SiC-like material. Simultaneously, the values for hardness, elastic modulus and internal stress are reduced by 15%–30%. For a low normal load (1 N) in the ball-on-disk test, a-Si1−x:H films (0.7<x<0.9) show a very low wear rate of both the film and the counterbody, combined with a steady state low friction coefficient of 0.05 in a humid ambient atmosphere. For the higher loads (5 and 10 N), however, this low friction coefficient lasts for only a relatively short time. In this case, the harder DLC films perform tribologically better because of their higher wear resistance, low wear rate of the counterbody and generally low friction coefficient between 0.15 and 0.35 in a humid ambient atmosphere.

Structure/property relationships in HSLA steel with low carbon and manganese and increased silicon content

The influence of an increased Si and reduced C and Mn content on structure and mechanical properties of HSLA steel plate with low carbon equivalent is investigated. With a C content of 0.06... 0.08% Mn should be ≥0.8%, and Si concentrations up to 1.0%may be used. On air cooled 30 mm plate (CE (IIW)=0.30%, FRT-850 o C) R e ≤420 MPa and T tr <-70 o C has been obtained

Low friction composite coating of Cr xSi y/MoS 2 on steel

The manufacture of the system tool steel/intermediate layer of Cr x Si y /low friction MoS 2 film was achieved by r.f. magnetron sputtering. The substrate material was X100CrMoV51 with a surface roughness of R z <100 nm and average roughness of R a <10 nm. The intermediate layers of Cr 3Si, CrSi, and CrSi 2 varied in film thickness between 150 and 300 nm, and the MoS 2 film was 300 or 600 nm thick. The films, deposited without a substrate heating, were amorphous, as shown by X-ray diffraction, and homogeneous in chemical composition (determined by secondary ion mass spectrometry and Auger electron spectroscopy). The Cr x Si y films corresponded in chemical composition to that of the target material but the low friction MoS 1.86 film (examined by ESMA) was understoichiometric. The oxygen content was below the detection limit of less than 5 at.%, as is shown in the Auger electron spectroscopy measurements. The tribological pin-on-disk experiments were carried out with ceramic, cemented carbide, stainless steel and with coated steel as the pin material. These experiments showed a significant effect of the chemical composition of the intermediate layer on the tribological behaviour of the multilayer film. The pin-on-disk tests were carried out under the following standard conditions: load, 5 N; feed, 0.1 m s -1; temperature, 22°C; relative humidity 40%. The layer system Cr 3Si/MoS 2 showed the best values, with the disk undergoing 5000 rev and the pin covering a sliding distance of 9 m. These values decreased with increasing silicon content in the intermediate layer. Thinner films yielded the same relationships with smaller absolute values. The friction coefficients μ are independent of the film thickness: 0.05 for MoS 2, 0.07 for CrSi 2/MoS 2, 0.09 for CrSi/MoS 2 and 0.1 for Cr 3Si/MoS 2.