Function Of Chromium Content Research Articles

Effect of chromium variation on evolution of magnetic properties in laser direct energy additively processed CoCrxFeNi alloys

The soft magnetic behavior of laser directed energy deposited CoCrxFeNi (x = 0 - 24 at.% Cr) alloys has been investigated as a function of chromium content. The saturation magnetization of these CoCrxFeNi alloys monotonically decreased with increasing concentration of Cr, and exhibited paramagnetic behavior at room temperature for equiatomic CoCrFeNi alloy composition. Similarly, the Curie temperature (Tc) of the ferromagnetic CoFeNi alloy linearly decreased with Cr content, while the paramagnetic equiatomic alloy indicated a ferromagnetic transition temperature of 94 K. Interestingly, all the as-deposited alloys exhibited coercivity values less than 2 Oe irrespective of the Cr content. The results indicate that the magnetic behavior of the ferromagnetic CoFeNi alloy can be systematically tuned with addition of antiferromagnetic Cr, and the additive manufacturing route was successful in rapid processing alloys of any desired composition, in a high throughput manner, with negligible chemical variation. These findings are promising for the fabrication of components for applications demanding gradient magnetic coatings and alloys.

Effect of Cr Content on Corrosion Resistance of Low-Cr Alloy Steels Studied by Surface and Electrochemical Techniques

The electrochemical behavior of low alloyed Fe-Cr steels with 3 and 5% wt. of Cr in neutral Na2SO4 electrolyte combined with a detailed chemical and morphological characterization of these alloys performed by Auger electron spectroscopy, X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry and scanning electron microscopy are presented here. The corrosion of low alloyed Fe-Cr steels proceeds in the prepassive range, with the formation of corrosion surface films having a duplex structure with outer iron oxide/hydroxide layer and inner Cr oxide-rich layer. The thickness, composition, and the morphology of the surface films vary as a function of chromium content in the alloy as well as conditions of electrochemical tests (temperature). Even a low chromium content shows a beneficial effect on the corrosion performances of the Fe-Cr steels. The chromium as a more active component than iron of ferrite increases the anodic activity of this phase, which results in a rapid saturation of the surface with the anodic reaction products forming a fine crystalline-like and compact layer of corrosion products. In this way, the chromium acts as a modifier of formation/crystallization of the iron-rich surface film (mainly magnetite) in the prepassive range.

The peculiarities in oxidation behavior of the ZrB2-SiC ceramics with chromium additive

ZrB2-SiC-Cr powder sintering at 1600 °C and its oxidation behavior at 1000–1500 °C in air were studied as a function of chromium content. It was shown that the relative density of the ZrB2-SiC ceramics increases with an increase in chromium content in the powdered mixture. This is related to the formation of the liquid Cr-Si-C-B phase during the high-temperature interaction of SiC with chromium and ZrB2.It was stated that the mechanism of ZrB2-SiC-Cr ceramics oxidation is changed from bulk to passive. The oxidation resistance is improved for the ceramics with 13% of chromium or less, which can be explained by a decrease in its porosity. The ceramics with higher chromium content demonstrates the opposite effect, namely, large-size Cr2O3 crystals are formed during oxidation, this promotes microcracking in the oxidizing layer and causes damage of surface integrity. As a result, the oxidation resistance of the ZrB2-SiC-Cr ceramics with high chromium content is decreased.

Влияние наносекундных однополярных электроимпульсных воздействий на свойства сплава Сu-1%Сr. Часть 2. Связь свойств сплава с содержанием Cr в решетке Сu

The effect of treatment of copper melt with chromium additives in the amount of 1% by weight is considered nanosecond unipolar electric pulses with a frequency of 1000 Hz, a single signal duration of one nanosecond and a power of 10 kW on the electrical resistivity and hardness of the resulting alloy. A study was made of the macro and microstructure of alloy samples created using electropulse effects and comparison samples obtained under the same thermal conditions, but without it. The samples were aged for 2 hours at 4500C. It has been found that electropulse treatment of the melt leads to an increase in hardness and decrease in the electrical resistance of the alloy as well as during aging, and the influence of this effect remains noticeable even after the aging process. Hardness and electrical resistance in all alloy samples are described mathematically as a function of chromium content in the copper lattice and in secondary precipitates. The role of nanosecond unipolar electroimpulsive effects on the Cu-1% Cr melt in improving the above characteristics of the resulting alloy compared with the thermo-time treatment without the electropulse effect is revealed. An explanation of the mechanism of the electropulse effect on the melt, leading to the separation of chromium atoms in the liquid state and the subsequent decrease in its solubility in the copper lattice, is proposed. The results of the study are presented in the form of drawings of macro- and microstructure of samples of the alloy Cu-1% Cr, tables, graphs and mathematical formulas. It was concluded that it is advisable to use a nanosecond unipolar electropulse effect with a frequency of 1000 Hz, a single signal duration of one nanosecond and a power of 10 kW per Cu-1% Cr melt to produce the corresponding alloy with improved hardness and electrical resistance.

Effect of chromium concentration on the structural, magnetic and electrical properties of praseodymium-calcium manganite

The influence of Cr doping on magnetic, magnetocaloric and electrical properties in a polycrystalline sample of Pr0.7Ca0.3MnO3 is investigated. Structural studies show that our samples are single phase. The magnetization shows that the Pr0.7Ca0.3Mn1−xCrxO3 ceramics exhibit a paramagnetic–ferromagnetic transition with a large magnetic entropy change. The relative cooling power (RCP) values are comparable to those of other manganite. DC conductance GDC measurements show that all samples are characterized by a semiconductor behavior. It is found that GDC decreases by two decades when increasing chromium concentrations. For the parent compound, dc-conductance is characterized by the appearance of a saturation region at a specific temperature (Tsat = 200 K). For the doped compound, Tsat go beyond room temperature. Conduction mechanism is found to be dominated by the small polaron hopping (SPH) process at high temperature and by variable range hopping one (VRH) at low temperature. AC conductance study confirms that the conductivity is governed by hopping process and obeys to the Jonscher universal power law. The exponent ‘n’ variation with temperature is in good agreement with Mott theory. Its variation as a function of chromium content indicates that the material turns from metallic to semi-insulating behavior when chromium composition increases. Impedance analysis proves the presence of electrical relaxation phenomenon in the material and confirms that grain boundaries played a main role in the conduction process.

Room temperature deposited p-channel amorphous Cu 1−x Cr x O 2−δ thin film transistors

Transparent p-type amorphous Cu1−xCrxO2−δ thin films were grown on the glass substrate by RF magnetron co-sputtering at room temperature. Structural, optical and electrical properties of these films were studied as a function of chromium content in the film. Composition of Cu1−xCrxO2−δ thin films could be varied by tuning the RF power to Cr sputtering target. Bandgap of as deposited Cu1−xCrxO2−δ thin films varies from 2.8 eV to 2.1 eV as chromium content increases in the film. The bottom gate structured TFTs fabricated using p-type Cu1−xCrxO2−δ operated in enhancement mode with an on–off ratio of 104 and field effect mobility 0.3 cm2 V−1 s−1.

Spectroscopic and dielectric response of zinc bismuth phosphate glasses as a function of chromium content

20ZnF2–(20−x)Bi2O3–60P2O5:xCr2O3 (0≤x≤2mol%) glasses are prepared by melt quenching technique. Amorphous nature of these samples is confirmed by X-ray diffraction (XRD) analysis. FTIR study reveals bands due to CrO6(od) and CrO42−(Td) units along with conventional phosphate groups. The optical absorption and ESR studies of present glasses are analyzed as a function of chromium content. The absorption bands are assigned to 4A2g(F)⟶4T1g(F), 4A2g(F)⟶4T2g(F), 4A2g(F)⟶2T1g(G) and 4A2g(F)⟶2Eg(G) transitions of Cr3+ ions. The highest concentration of Cr3+ ions (in octahedral sites, with network modifying positions) is found in the sample with 2.0mol% of Cr2O3. The analysis of dielectric properties indicates a gradual increase in semiconducting character with increase in the concentration of Cr2O3 from 0.2 to 2.0mol%. The studies on dielectric breakdown strength identify the highest insulating strength for lowest mol% of Cr2O3 in the present samples.

Surface tension of liquid Fe-Cr-O alloys at 1823 K

The surface tension of liquid Fe-Cr-O alloys has been determined by using the sessile drop method at 1823 K. It was found that the surface tension of liquid Fe-Cr-O alloy markedly decreases with oxygen content at constant chromium content, and the surface tension at a given oxygen content remains almost constant, regardless of the chromium content. When the surface tension of liquid Fe-Cr-O alloys is plotted as a function of oxygen activity, with an increase in the chromium content, the surface tension shows a much steeper decrease with respect to oxygen activity. The surface tension of liquid Fe-Cr-O alloys at 1823 K is given as follows: σ=1842-279 ln (1+K O a O). Here, assuming a Langmuir-type adsorption isotherm, the adsorption coefficient of oxygen, K O(Fe-Cr), as a function of chromium content, was shown to be K O=140+4.2 × [wt pct Cr]+1.14 × [wt pct Cr]2.

フェライト系高温用鋼溶接熱影響部のクリープ強度低下現象と組織変化−フェライト系高温用鋼のＨＡＺ軟化機構（第１報）−

The effect of chromium content on creep rupture strength and microstructural change at high temperature service was investigated to clarify the mechanism of deterioration of creep rupture strength in Heat Affected Zone (HAZ) of heat resistant ferritic steel. Simulated weld thermal cycles, a temperature range from 1103 to 1473 K, were applied to test specimens machined from 2% Cr-1.5% W-V, Nb ferritic steel plates. After heat treatment at 1013 K for 1.8 ks, simulating Post Weld Heat Treatment (PWHT), creep rupture strength were evaluated at 923 K with the applied stress of 98 MPa and various microstructural examinations were carried out. In 2% Cr steel as well as 10% Cr steel shown in previous report, creep rupture strength was deteriorated in HAZ heated in the peak temperature range of 1173-1273 K, and that HAZ after creep test had the lower density of fine particle mainly consisting of MX type carbo-nitride less than 0.1 μm in diameter effective for dispersion strengthening as compared in base metal. However, a degree of deterioration of creep rupture strength in HAZ was smaller in 2% Cr steel than in 10% Cr steel. The growth rate of fine particles such as M23C6 type carbide and MX type carbo-nitride was lower in HAZ of 2% Cr steel compared with in that of 10% Cr steel. The growth of fine MX in 2% Cr HAZ was confirmed in accordance with the Ostwald ripening dominated by chromium diffusion as well as 10% Cr HAZ. The growth rate in the Ostwald ripening was described as a function of chromium content which increased as the increase of chromium content. As results, the mechanism of deterioration of creep rupture strength suggested in HAZ of 10% Cr steel, which the partial dissolution of carbide during weld thermal cycle could accelerate Ostwald ripening, was confirmed to have the universal validity to that in HAZ of 2% Cr steel.

Structural evolution of co-deposited Zn–Cr coatings produced by vacuum evaporation

Zn and Cr were evaporated simultaneously using two e-beam guns to heat crucibles containing the pure metals. The metallic vapors generated are intermixed and pass through a specially designed aperture that assures homogeneous deposition at the surface of the steel substrate, which continuously advances. The source positions were adjusted to produce a coating with a chromium content which decreases from the substrate interface to the external surface. This article discusses the chemical and microstructural variations of these co-deposited layers as a function of chromium content. In order to improve the adhesion of these coatings on low carbon steel, the deposition chamber has been designed in such way as to produce a thin precoat (<200 nm) consisting of a ZnCr alloy with a high chromium concentration.

Structural and Mössbauer spectroscopic studies of Fe 0.7− xCr xAl 0.3 alloys

Fe 0.7− x Cr x Al 0.3 alloys with x=0, 0.1, 0.2, 0.3 and 0.35 have been synthesized by arc melting and studied by X-ray diffraction and Mössbauer spectroscopy. All the samples studied were found to have single phase with body center cubic structure. The lattice parameter a, and hence the volume, were obtained from the X-ray diffraction patern and found to increase with increasing the chromium concentration. At room temperature Mössbauer studies show magnetic ordering for small values of x and paramagnetic behavior for large values of x under investigation. The Mössbauer spectra were analyzed considering a distribution of magnetic hyperfine fields for small values of x and two singlets were added for large values of x. During the fitting procedure, the relation between the hyperfine field and the isomer shift in the hyperfine field distribution was linear relation. The average hyperfine field and isomer shift as a function of chromium content x were found to decrease with increasing x. The results are explained in terms of local environmental effects on the hyperfine interactions.

Effect of chromium on the corrosion behavior of iron aluminides in thiosulfate-chloride solution

Aqueous corrosion characteristics of iron aluminides in thiosulfate-chloride solution were studied as a function of chromium addition. Four kinds of iron aluminides, namely, FA-61, FA-77, FA-72 and FA-78, were prepared by arc melting followed by thermomechanical treatment. The corrosion behavior in thiosulfate-chloride solution for the prepared alloys were investigated by electrochemical tests (potentiodynamic test, potentiostatic test and electrochemical impedance spectroscopy (EIS) measurement) and surface analyses. The results of the potentiodynamic test indicated that the breakdown potential increased with increasing Cr content. Cr additions were found to prevent passive film from undergoing pitting corrosion. In EIS measurement, the depression angle was inversely related to pitting resistance, and decreased with increasing chromium content. The SEM observations of the sample surfaces reveal the different forms of pit as a function of chromium content. The AES results give evidence that the thiosulfate ions are reduced on the metallic surface, which inhibits the repassivation process.

Thermodynamics of Molten Fe-Cr-Csatd. Alloy.

The activity of chromium in molten Fe-Cr-Csatd. alloy has been measured at temperatures ranging from 1548 to 1773 K by a chemical equilibrium technique. There is little temperature dependence of the activiy of chronium in the region of low chromium contents by weight, and the activity coefficient of chromium decreases as the chromium content increases.The activity coefficient of chromium in silver, which was needed for the foregoing measurement, was predetermined.By thermodynamic discussion in combination with the carbon solubility in molten iron-chromium alloys, the expression for the activity coefficient of chromium in Fe-Cr-Csatd. alloy has been obtained as a function of chromium content and temperature as follows.lnγCr(s)= -2.52+T3880 +(8.31-T23300)XCr+(-4.21+T14900)XCr2 (1623 to 1773K)The standard Gibbs energy of mixing of Fe-Cr-Csatd. alloy was also estimated using the Gibbs-Duhem relationship, indicating that chromium and manganese behave similarly in terms of affinity for carbon and iron in molten carbon-saturated iron.

Control of the chromium-oxygen reaction in pure iron melts

en

Influence of chromium concentration on point defect properties in austenitic Fe-Cr-Ni alloys

Austenitic Fe-Cr-Ni alloys have been investigated as a function of chromium content (8 to 16 wt% Cr, 25 wt% Ni) during 21 K electron irradiation and subsequent isochronal anneals by electrical resistivity measurements. Frenkel-pair resistivities evaluated from the damage rates by a relative method are nearly independent of the chromium level: ρF = 12.7 ± 0.5 μΩ cm/at% (based on the value of 12.9 μΩ cm/at% of the reference 16 wt% Cr alloy). The mobility of point defects was deduced from the recovery behaviour. Self-interstitials become more mobile as the chromium concentration decreases whereas the mobility of vacancies is insensitive to composition. Activation enthalpies for the migration of self-interstitials and vacancies were estimated and compared to the values previously reported for alloys with varying nickel concentration.

Corrosion Properties of Cast Iron Ball Materials in Wet Grinding

Abstract The influence of chromium addition to grinding media on corrosion rates of various chromium containing cast iron ball materials was investigated using Tafel plot DC polarization resistance measurements under abrasion in a quartzite slurry. The high chromium cast iron ball materials exhibited low corrosion rates at low and non-abrasive conditions, and the corrosion rates were increased markedly with rotation speed. Whereas corrosion rates of low chromium cast iron ball materials were high, indicating little dependence on rotation speeds. To understand the properties of surface films of ball materials as a function of chromium content, AC impedance measurements were made at various cathodic and anodic potentials. The high chromium cast iron ball materials exhibited high polarization resistance values at an applied potential of −0.05 V (vs SCE). The polarization resistance values obtained by DC polarization resistance and AC impedance methods were correlated.

The distribution of Cr(V) and Cr(III) ions in ZSM-5 and chemisorption of oxygen on reduced [formula omitted

The distribution of Cr(V) and Cr(III) ions in ZSM-5 as a function of chromium content and redox treatment was studied by e.s.r.. It was assumed that O 2 chemisorption on reduced Cr ZSM-5 samples is determined by the number of isolated chromium cations capable of changing their valence state upon redox treatment. It has been shown that the quantity of such isolated cations located inside zeolitic channels does not exceed ∼ 20% from the number of Al 3+ lattice ions, and the excess of chromium is located on the outer surface of zeolite in the form of inactive Cr 2O 3 crystals.

The decomposition of isopropanol over spinel solid solutions MgAl 2 − xCr xO 4

Isopropanol decomposition has been studied over the spinel solid solutions MgAl 2 − x Cr x O 4 where x = 0 → 2. There are two zones of activity as a function of chromium content. There is an activity minimum at x = 0.4. The active sites on catalysts below x = 0.4 are thought to be electronically isolated, whereas above x = 0.4 they interact electronically. Dehydration activity is high over catalysts very dilute and very concentrated in chromium. Dehydrogenation activity seems to be favored by chromium pair sites.

Hydrogen-deuterium exchange catalysed by chromia-alumina solid solutions

α -Alumina, α-chromia and ten corundum-phase chromia-alumina solid solutions α-Cr χ .Al 2 _ χ .O 3 with χ ranging from 0.002 to 1.4 have been studied as catalysts for hydrogen-deuterium exchange over the temperature range from 100 to 700 K. The adsorption of hydrogen has also been investigated. α-Alumina is an active catalyst only above 500 K. When chromium ions are introduced, activity at 500 K and above is increased. In addition, a new zone of catalytic activity is generated at 110-350 K. This low temperature activity, specific to the presence of chromium, exhibits a maximum at 250-300 K. For both low- and high-temperature activity zones, the catalytic activity is not a monotonic function of chromium content. The activity per chromium ion exhibits a periodic variation as χ is increased, with a high value at χ ≈ 0.1 and a second peak as χ approaches 2.0. A general analysis of the coordinative unsaturation to be expected on the principal surface planes of the corundum structure is presented and local charge variations at multiplet sites are identified. The implications of introducing transition metal ions are then indicated. r

Effect of Palladium-Addition on the Oxidation Characteristics of W-Cr Sintered Alloys

W-Cr sintered alloys (up to 30%Cr) containing 0.2-1.0% of palladium were produced from W-Cr alloyed powders and subjected to the oxidation at the temperatures, 1200°C and 1300°C in air. The effect of palladium-addition on the oxidation characteristics of these alloys was examined as a function of chromium content, and the protection mechanism to the oxidation was also examined.The results were summarized as follows:1) The oxidation characteristics of W-Cr sintered alloys was markedly influenced by the small addition of palladium. The alloy of W-9.87%Cr-0.2%Pd, for example, failed catastrophically in 2 hrs, while the alloys of W-9.87%Cr-0.41.0%Pd resisted over 1000 hrs to the oxidation at 1300°C in air.2) The more chromium content increased, the more amount of palladium was required for improving the oxidation resistance of these alloys.3) The improvement of oxidation resistance in W-Cr-Pd alloys owes the a-Pd phase which precipitates pre-ferentially in the vicinity of grain boundaries. This phase shows not only good oxidation resistance, but also contributes to the formation of the protective Cr2O3 surface layers.