Fe Ni Cr Research Articles

An Interpretation on Kinetics of Martensitic Transformation

We have investigated athermal and isothermal martensitic transformations (typical displacive transformations) in Fe–Ni, Fe–Ni–Cr, and Ni-Co-Mn-In alloys under magnetic fields and hydrostatic pressures in order to understand the time-dependent nature of martensitic transformation, that is, the kinetics of martensitic transformation. We have confirmed that the two transformation processes are closely related to each other, that is, the athermal process changes to the isothermal process and the isothermal process changes to the athermal one under a hydrostatic pressure or a magnetic field. These findings can be explained by the phenomenological theory, which gives a unified explanation for the two transformation processes previously proposed by our group.

Formation of nano-contacts on Fe–Ni–Cr alloy for bipolar plate of proton exchange membrane fuel cell

The strength and bulk electrical conductivity of Fe–Ni–Cr alloy are high; it is a potential material as the bipolar plate for proton exchange membrane fuel cell (PEMFC). However, its interfacial contact resistance is too high and the corrosion resistance is too low to survive in the hostile environment. A novel method by altering the surface morphology to improve directional conductivity is developed in the present study. Instead of preparing conductive coating on metal surface, a nano-oxidation layer with many nano-scaled pyramids is formed by solution treatment for Fe–Ni–Cr alloy. The formation of the dense oxide layer improves the corrosion resistance of the alloy. Furthermore, many nano-scale contacts on the surface of the treated specimen offer channels for directional electron conduction and decrease the interfacial contact resistance.

Nickel-plating for active metal dissolution resistance in molten fluoride salts

Ni electroplating of Incoloy-800H was investigated with the goal of mitigating Cr dissolution from this alloy into molten 46.5%LiF–11.5%NaF–42%KF eutectic salt, commonly referred to as FLiNaK. Tests were conducted in graphite crucibles at a molten salt temperature of 850 °C. The crucible material graphite accelerates the corrosion process due to the large activity difference between the graphite and the alloy. For the purposes of providing a baseline for this study, un-plated Incoloy-800H and a nearly pure Ni-alloy, Ni-201 were also tested. Results indicate that Ni-plating has the potential to significantly improve the corrosion resistance of Incoloy-800H in molten fluoride salts. Diffusion of Cr from the alloy through the Ni-plating does occur and if the Ni-plating is thin enough this Cr eventually dissolves into the molten salt. The post-corrosion test microstructure of the Ni-plating, particularly void formation was also observed to depend on the plating thickness. Diffusion anneals in a helium environment of Ni-plated Incoloy-800H and an Fe–Ni–Cr model alloy were also investigated to understand Cr diffusion through the Ni-plating. Further enhancements in the efficacy of the Ni-plating as a protective barrier against Cr dissolution from the alloy into molten fluoride salts can be achieved by thermally forming a Cr 2O 3 barrier film on the surface of the alloy prior to Ni electroplating.

Fabrication and characterization of ODS austenitic steels

Pure Fe, Cr, Ni, W, Ti elemental powders and nano-Y2O3 powders (the compositions of the mixed powders are Fe–18Cr–8Ni–2W–1Ti–0.35Y2O3) were processed by high energy mechanical milling. The as milled powders were consolidated by hot isostatic pressing for 3h at 1423K under a pressure of 200MPa. The microstructure of the fabricated ODS austenitic steels and chemical composition of the oxide particles were examined by field emission scanning electron microscopy with energy dispersive spectrometry. The dispersed fine oxides were determined to be Y–Ti–O oxides. The tensile properties were improved significantly by oxide dispersion strengthening but the ductility deteriorated.

The properties of scandium and cerium stabilized zirconium thin films formed by e-beam technique

Scandium and cerium stabilized zirconium (10Sc1CeSZ) thin ceramic films were formed evaporating (ZrO 2) 0.89(CeO 2) 0.01(Sc 2O 3) 0.10 micro powder using e-beam evaporation technique. The influence of deposition rate on formed thin films electrical properties and microstructure was studied. 10Sc1CeSZ thin films were deposited on two types of different substrates: optical quartz (SiO 2) and Alloy 600 (Fe–Ni–Cr). Deposition rate was changed from 2 to 16 Å/s to understand its influence on thin film formation and other properties. The formed 10Sc1CeSZ thin films keep the cubic crystal structure as the initial evaporated powder material but change the main crystallographic peak from (111) to (200) for both types of substrate and used deposition rates. It was determined that the crystallites size increases from 19.0 to 24.9 nm and from 15.6 to 19.9 nm on optical quartz and Alloy 600 respectively by increasing the deposition rate (in range from 2 to 16 Å/s). The thin film density decreases by increasing the deposition rate. The ionic conductivity of 10Sc1CeSZ thin films was determined by impedance spectroscopy in the frequency range from 0.1 Hz to 1.0 MHz in temperature range from 473 K to 873 K. The best ionic conductivity σ tot = 4.91 · 10 − 2 Sm − 1 at 873 K temperature and the lowest value of activation energy ΔE a = 0.88 eV were found for 10Sc1CeSZ thin films formed at 4 Å/s deposition rate.

Influence of initial powder particle size on yttrium stabilized zirconium thin films formed by e-beam technique

Yttrium stabilized zirconium (YSZ – (Y 2O 3) 0,08(ZrO 2) 0,92) thin films were formed by e-beam evaporation technique. The powders of different surface areas were used to prepare thin ceramic films. The influence of the initial powder material on formed thin films electrical and microstructure properties was studied. YSZ thin films were deposited on two types of substrates: optical quartz (SiO 2) and Alloy 600 (Fe–Ni–Cr) substrates. Deposition rate was changed from 2 to 16 Å/s to test its influence on thin film formation and properties. Electrical parameters of YSZ thin ceramics were investigated in the frequency range from 0.1 to 1.0 MHz in temperature range from 473 to 873 K. The conductivity of the electrolyte YSZ-8 thin films was determined by impedance spectroscopy. The formed YSZ films repeat the crystallographic orientation of the initial powder material and do not depend on the powder grain size. It was determined that the deposition rate has influence on the crystallite size. Initial powder grain size and deposition rate influence the relative density of formed YSZ thin films. The ionic conductivity of formed films depends on the grain size of initial powder, also.

Scandium stabilized zirconium thin films formation by e-beam technique

Scandium stabilized zirconium (10ScSZ) thin ceramic films were deposited by e-beam evaporation of (ZrO2)0.90(Sc2O3)0.10 micro powder (particle size 0.5÷0.7μm). The influence of deposition rate on formed thin films microstructure and electrical properties was studied. 10ScSZ thin films were deposited on two types of different substrates: optical quartz (SiO2) and Alloy-600 (Fe–Ni–Cr) substrates. Deposition rate was changed from 2 to 16Å/s to test its influence on thin film formation and its properties.The microstructure of formed 10ScSZ thin ceramic films was studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Electrical parameters of formed thin ceramics were investigated in the frequency range from 0.1Hz to 1.0MHz (in temperature range from 473 to 873K). The ionic conductivity of the deposited electrolyte 10ScSZ thin films was determined by impedance spectroscopy.It was determined that the deposition rate (in range from 2 to 16Å/s) has influence on crystallite size. It increases by increasing the deposition rate from 18.4 to 26.9nm. The XRD measurements show that the formed 10ScSZ thin films do not repeat the crystallographic phase of the initial evaporated powder material—it is changes from rhombohedra (initial powder) to cubic (the formed thin films).

O59 Low power visible and polychromatic (visible + near IR) light enhances sensitivity of tumor cells to cytolytic activity of natural killers

This chapter discusses the as-quenched microstructures in Fe–25Cr–20Ni-based melt-spun and sputtered alloys. The microstructure morphology and the phase type encountered in the as-quenched Fe–25Cr–20Ni steels are liable to contain high segregation coefficients elements such as sulfur, carbon, or boron. These steels are prepared by melt spinning or sputtering. The sputtering targets are massive or compacted powder mixtures; the sputtered films obtained have approximately the chemical composition of the targets. As opposed to ribbons, sputtered films crystalline structure is composed, at room temperature, of a great amount of b.c.c. metastable ferrite. The microstructure is characterized by very fine regular grains with a 10 nm average size, in agreement with the calculated value from Scherrer's law relative to the half-intensity width of X-ray lines. This chapter also discusses the effects of sulfur, carbon, and boron addition on microstructures.

Effects of Al on the microstructure and ductility of NiAl-strengthened ferritic steels at room temperature

One of the major problems for the development of ferritic steels strengthened by NiAl-type ( B2) precipitates is their poor ductility at room temperature. In conjunction with the computational alloy design, selected experiments are performed to investigate the effect of Al content on the ductility of prototype Fe–Ni–Cr–Al alloys. The microstructure and composition of the matrix ( α-Fe type) and precipitate phases are characterized by transmission electron microscopy (TEM) and analytical electron microscopy (AEM). Three-point-bending experiments show that alloys containing more than 5 mass% Al exhibit poor ductility (<2%) at room temperature, and their fracture mode is predominantly cleavage type. Two major factors governing the poor ductility are (i) the volume fraction of NiAl-type precipitates, and (ii) the Al content in the α-Fe matrix. A bend ductility of more than 5% can be achieved by lowering the Al concentration to 3 mass% in the alloy. The alloy containing about 6.5 mass% Al is found to have an optimal combination of hardness and ductility.

Microstructural studies on nanocrystalline oxide dispersion strengthened austenitic (Fe–18Cr–8Ni–2W–0.25Y2O3) alloy synthesized by high energy ball milling and vacuum hot pressing

In the present work, nanostructured (Fe–18Cr–8Ni–2W) austenitic base and oxide dispersion strengthened (ODS) alloy powders were produced through mechanical alloying and these nano powders were consolidated by vacuum hot pressing. The results showed that initially bcc solid solution formed in both the alloys and this transformed to fcc with continued milling. The bcc solid solution formation and the subsequent transformation to fcc were significantly faster in the ODS alloys when compared to the base alloy. In the ODS alloy, a grain size of ~25 nm is achieved within 5 h of milling. Study of variation of microhardness of mechanically alloyed powder particles with grain size showed linear Hall–Petch kind of behavior. Following vacuum hot pressing of mechanically alloyed powders, nearly fully dense (>99% of theoretical density) compacts were obtained with a grain size of ~80 nm. The bulk hardness of base and ODS alloys are ~530 and ~900 HV, respectively. These are significantly higher than the values reported in the literature so far. The enhanced strength the ODS alloy is due to increased dislocation density and presence of fine dispersoids along with the nanocrystalline grains.

Use of Fe–31Mn–7.5Al–1.3Si–0.9C Alloy for Fabrication of Resistive Elements

Abstract Austenitic Fe–Mn–Al–Si–C steel provides excellent cold formability and good oxidation resistance for possible fabrication of resistive elements. In this work, austenitic Fe–31Mn–7.5Al–1.3Si–0.9C steel wire was obtained by cold rolling and then tested with respect to oxidation resistance and electrical resistive behavior. After being subjected to an isothermal oxidation test at 700°C in air, this steel exhibited behavior similar to that the AISI 304 stainless steel. When the test was conducted at 800°C, the performance was inferior to that the AISI 304 steel. However, after 40 h of testing, the mass-gain curve stabilized. From these results and the results of the electric resistance tests, the Fe–Mn–Al–Si alloy proved to be a promising candidate for substitution of thermo-resistive alloys of Ni–Cr and Fe–Ni–Cr for use at temperatures of up to 800°C. Such alloys provide the potential for cost performance savings by using lower cost alloying elements.

Oxygen partial pressure dependence of surface tension and its temperature coefficient for metallic melts: a discussion from the viewpoint of solubility and adsorption of oxygen

Surface tension of molten Si, Ag, and Fe–18Cr–8Ni alloy (Type-304 stainless steel) were measured as a function of the temperature and oxygen partial pressure of an ambient atmosphere by an oscillating drop method using electromagnetic levitation, which assures measurement over a wide range of temperatures below and above the melting point and of oxygen partial pressure. For molten silicon, the lower limit of measured temperature was determined by equilibrium oxygen partial pressure for SiO2 formation; as oxygen partial pressure increases, undercooled conditions necessary for taking measurements become smaller. This is attributed to the low solubility of oxygen in molten silicon. For Ag, however, surface tension can be measured in a wide range of temperature and oxygen partial pressures due to the high solubility of oxygen. A boomerang-shaped behavior of surface tension was observed for Ag in an atmosphere with high oxygen partial pressure; surface tension has a maximum value when plotted against temperature. This boomerang-shaped behavior is attributed to desorption of oxygen at high temperature; surface tension increases with increasing temperature. The boomerang-shaped behavior was also observed for Fe–18Cr–8Ni alloy.

Samarium doped cerium oxide thin films deposited by e-beam technique

Samarium doped cerium oxide (SDC) thin films were grown evaporating cubic phase cerium oxide doped by 15% of samarium nanopowder (Sm 0.15Ce 0.85O 1.95). SDC thin films were formed on Alloy 600 (Fe–Ni–Cr) and optical quartz (SiO 2) substrates using e-beam deposition technique controlling (influencing thin film properties) deposition parameters: substrate temperature and electron gun power. SDC thin films (1.5–2 μm of thickness) were deposited when the electron gun power was 0.12 kW, 0.3 kW, 0.45 kW, 0.6 kW, and 0.78 kW during thin films deposition. The formed SDC thin films were studied by scanning electron microscopy (SEM), Energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). It was determined that electron gun power (in the range from 0.12 kW to 0.78 kW) has the influence on crystallite size (increased from 5 nm to 19.2 nm) which increases as the gun power increases. The crystallite size increases from 12 nm to 47 nm by increasing substrate temperature from 100 °C to 600 °C. The texture of formed SDC thin films is not influenced by e-beam gun power, but it is influenced by substrate temperature when it is above 300 °C. Deposited SDC thin films are stoichiometric and repeat the stoichiometry of elements of the chosen evaporated SDC material. The deposited SDC films were annealed in air to 800 °C temperature and were investigated by X-ray diffraction (XRD) in order to understand the stability and influence the temperature on the structure of formed thin films. The thermal treatment shows that deposited SDC thin films are stable and the crystallite size and texture are not changing during the heating and cooling.

The effects of microstructure on creep behaviour—A study through synchrotron X-ray tomography

A preliminary study has been carried out to investigate the influence of microstructure on creep behaviour using an Fe–Ni–Cr steel alloy as a model material. Creep rupture tests and synchrotron X-ray tomography were performed on as-cast (AC) and ex-service (ES) specimens. The results indicate that the combination of larger cavity volume and lower ductility in the AC specimen was attributed to initial microstructural differences in terms of carbide size and distribution. The location, orientation and shape of the voids were also considered to be important microstructural features as voids on grain boundaries were seen to have coalesced preferentially along the plane normal to the loading axis to form ‘wedge’ shaped voids.

The properties of samarium doped ceria oxide thin films grown by e-beam deposition technique

One of the main challenges in today's solid oxide fuel cell (SOFC) technology is the reduction of their operating temperature. New types of oxygen ion conducting materials are currently under investigation to overcome the problems which SOFC faces at high temperatures. Samarium doped ceria oxide (SDC) was the material of investigation in this work. Optical quartz (SiO 2) and Fe–Ni–Cr alloy (Alloy 600) were the two types of chosen substrates onto which SDC thin films were deposited by e-beam evaporation technique. The bias voltage was applied to the substrate during film growth. It had an influence on film formation, its microstructure and density because of the ionized particles presence in the SDC vapor stream. Changes in crystallite size and surface morphology were determined from X-ray diffraction data and scanning electron microscopy images. Influence of bias voltage on porosity of formed SDC thin films on optical quartz were calculated from transmittance spectra data by using Swanepoel method. The porosity decreases up to 12% by decreasing bias voltage from 0 to −150 V.

Oxidation of Minor Elements from an Iron–Nickel–Chromium–Cobalt–Phosphorus Alloy in 17.3% CO2–H2 Gas Mixtures at 700–1000 °C

Fe–Ni–Cr–Co–P alloys were exposed to 17.3% CO2–H2 gas mixtures to investigate the oxidation of minor elements in metallic alloys in the early solar system. Reaction temperatures varied between 700 and 1000 °C. Gas-phase equilibrium was attained at 800, 900, and 1000 °C, yielding H2–H2O–CO–CO2 gas mixtures. Experiments at 700 and 750 °C did not achieve gas-phase equilibrium and were performed in H2–CO2 gas mixtures. Reaction timescales varied from 1 to 742 h. The experimental samples were characterized using optical microscopy, electron microprobe analysis, wavelength-dispersive-spectroscopy X-ray elemental mapping, and X-ray diffraction. In all experiments Cr experiences internal oxidation to produce inclusions of chromite (FeCr2O4) and eskolaite (Cr2O3) and surface layers of Cr-bearing magnetite [(Fe,Cr)3O4]. At 900 and 1000 °C, P is lost from the alloy via diffusion and sublimation from the metal surface. Analysis of P zoning profiles in the remnant metal cores allows for the determination of the P diffusion coefficient in the bulk metal, which is constant, and the internally oxidized layer, which is shown to vary linearly with distance from the metal surface. At 800 and 900 °C, P oxidizes to form a surface layer of graftonite [Fe3(PO4)2] while at 700 and 750 °C P forms inclusions of the phosphide-mineral schreibersite [(Fe,Ni)3P].

Lengthening, Cracking and Weldability Problems of Fe–Ni–Cr Alloy Tube

Ethylene pyrolysis furnace tubes which are made of high Cr-Ni alloys often become difficult to weld after few years in service due to carburization and creep damage. The presence of carburization, often attempted to detect by magnetic permeability, can escape detection due to high Cr-Ni content of the alloy. Based on optical microstructural analysis and supported by scanning electron microscopy, this paper establishes that carburized material becomes difficult to weld due to carburized internal layers of the tube and cause hot shortness. To provide a practical way out for ethylene furnace operators, a solution annealing heat-treatment is recommended to have a successful weld.

Preparation and characterization of nanocrystalline Fe–Ni–Cr alloy electrodeposits on Fe substrate

Fe–Ni–Cr alloy layers were prepared by electrodeposition from trivalent chromium plating bath in chloride-sulfate based solution. The influences of bath composition and plating parameters on the alloy electrodeposition process and the properties of deposited alloy were studied. The effects of plating parameters and bath composition such as current density, bath pH, bath temperature, the concentrations of FeSO4 · 7H2O and CrCl3 · 6H2O on the contents of Fe and Cr in Fe–Ni–Cr alloy layer were investigated. Electrodeposited Fe–Ni–Cr alloy layers on Fe substrate were characterized by X-ray diffraction (XRD), Electronic Differential System (EDS) and a CHI600B electrochemistry workstation. The composition of the Fe–Ni–Cr coatings depends on bath composition and plating conditions including pH, current density, and temperature. The internal structure of the alloy is nanocrystalline, the average grain size is 87 nm, and the corrosion resistance of the alloy layers is better than that of pure nickel layers.

Properties of Fe–Ni–Cr alloy coatings by using direct and pulse current electrodeposition

This paper describes the effects of using direct and pulse current on composition and corrosion resistance of Fe–Ni–Cr alloy coatings. In both direct and pulse current electrodeposition, increasing the current density has a decreasing effect on Fe and Ni and an increasing influence on Cr. In pulse current electrodeposition, duty cycle has a greater effect than frequency on composition of the alloy coating, particularly in the range of 10–50%. In this range, by increasing the duty cycle, Ni decreases, Fe sharply increase and Cr shows an increasing trend. Following a study of the microhardness of coatings, it is determined that the microhardness increases about 1.5 times by pulse current electrodeposition. The corrosion resistance of the alloy coatings (electrodeposited by direct and pulse current) has been investigated in NaCl solution. The micro-cracks of alloy coating can be decreased by using pulse current, which demonstrates a better corrosion resistance than direct current coating.

Microstructure and interface interaction in laser induction hybrid cladding of Ni-based coating

Based on the powder feeding laser induction hybrid cladding experiments by means of three different laser and induction energy, the microstructure of Ni-based coating and interface characteristics between the Ni-based coating and steel substrate were investigated. The results show that the hybrid cladding energy including laser and induction energy has an important influence on the formation of the interface and the microstructure of the Ni-based coating characterized by the dendrite. In addition, the laser and induction energy can complement each other. For high hybrid cladding energy, the single phase Fe–Ni–Cr solid solution is formed at the interface between the coating and substrate, while the microhardness of the Ni-based coating decreases. For low hybrid cladding energy, the solid solution phases of Fe–Ni–Cr and Ni–Fe–Cr are respectively obtained on both sides of the interface and microhardness of the Ni-based coating is relatively high. During laser induction hybrid cladding, the metallurgical bond characterized by the white light layer is achieved between the coating and substrate, and the extent of metallurgical reaction can be controlled by adjusting the laser energy and induction energy appropriately.