Stainless Steel Matrix Research Articles

Retention of Iron Oxide Particles by Stainless Steel and Magnetite Magnetic Matrix Elements in High-Gradient Magnetic Separation

ABSTRACTThe retention performances of a novel 80 wt% magnetite-silica composite HGMS matrix element and a traditional stainless steel wool HGMS matrix element were compared. Breakthrough and ultimate (strictly magnetic) retention experiments were carried out at different feed concentrations, flow velocities, and magnetic field intensities with an aqueous slurry containing iron oxide (Fe2O3) particles. Results from the ultimate retention experiments were also compared to those obtained from a potential flow model. Overall, when supported by silica in the form of the 80 wt% magnetite-silica composite, magnetite was about 30 to 40% as effective as stainless steel in retaining iron oxide, which was quite encouraging when considering that the magnetic saturation of magnetite is about five times smaller than that of stainless steel. Magnetite is also less expensive than stainless steel wool, even when encased in silica gel, which makes its use as an HGMS matrix element even more attractive for certain applications. The ultimate retentions predicted from the model for both matrix elements were of the same order of magnitude as the experimental results, an encouraging result: under predictions no greater than a factor of 7 for the stainless steel cylinder, and over predictions no greater than a factor of 3 for the magnetite spheres were obtained. The reasons for these discrepancies centered on the relatively wide size distributions of the Fe2O3 particles and both the magnetic matrix elements, which were not accounted for by the models. The potential flow model also could not account for the effects of laminar layers and separation zones on retention; nor could it account for the effects of the changing flow patterns caused by particle build-up on retention. Also, the models could not predict the dependence of the ultimate retention on the feed concentration observed experimentally, which suggested the existence of dynamic equilibrium at the external boundaries of the collection zones where the magnetic force was weaker.

Thermally Sprayed Wear Resistant Coatings With Nanostructured Hard Phases

The aim of this investigation was the development of a new quality of thermally sprayed coatings with high resistance against wear and corrosion and to evaluate the application potential of nano-sized hard phases in thermally sprayed layers. The newly developed material consists of a highly corrosion-resistant matrix of stainless steel (even without nickel) combined with nano-structured hard phases of vanadium nitrides (VN). On the other hand, matrices consisting of cobalt-chromium (CoCr) with submicron hard phases of tungstencarbides (WC) were investigated with respect to microstructure and wear resistance compared with conventional ones.

Thermally sprayed wear resistant coatings with nanostructured hard phases

The aim of this investigation was the development of a new quality of thermally sprayed coatings with high resistance against wear and corrosion and to evaluate the application potential of nano-sized hard phases in thermally sprayed layers. The newly developed material consists of a highly corrosion-resistant matrix of stainless steel (even without nickel) combined with nano-structured hard phases of vanadium nitrides (VN). On the other hand, matrices consisting of cobalt-chromium (CoCr) with submicron hard phases of tungstencarbides (WC) were investigated with respect to microstructure and wear resistance compared with conventional ones.

Diffusion bonded transition joints of titanium to stainless steel with improved properties

Diffusion bonding was carried out to produce transition joints between commercially pure titanium (cp Ti) and 304 stainless steel (304 ss) in the temperature range of 800–950 °C, under uniaxial pressure of 3 MPa for 5.4 Ks. The transition joints were evaluated by tensile testing, light microscopy, electron probe micro-analysis and X-ray diffraction. The study indicates that transition joints achieve 76% strength of pure Ti along with ∼5% ductility when processed at 850 °C. Electron probe microanalysis reveals substantial diffusion of Fe, Cr and Ni in the Ti side and Ti travels less distance in stainless steel matrix. A number of intermetallics σ phase, FeTi, Fe 2Ti 4O, NiTi and NiTi 2 have been identified by X-ray diffraction near the interface. Increases in the joining temperature cause the volume fraction of intermetallics to increase. These intermetallics lower the strength of diffusion bonds when processed at higher temperature.

Design and fabrication of specific ceramic–metallic fuels and targets

The fabrication of ceramic–metallic (cermet) composite fuel, containing (Y,An,Zr)O 2− x spheres, by dust free processes has been studied. The influence of several process parameters, such as, ceramic volume fraction, compaction pressure and sintering temperature, on the microstructure of the final composite have been investigated and optimised using cerium as a stand for americium and two metal matrices namely molybdenum and stainless steel. In addition, a cermet fuel with (near) spherical (Y,Pu,Zr)O 2− x particles, dispersed in stainless steel matrix, has been successfully fabricated and characterized.

Effect of intermetallic particles on wear behaviour of stainless steel matrix composites

Metal matrix composites were manufactured using 316L austenitic stainless steel as matrix and TiAl intermetallic as reinforcement. Three levels of reinforcement were used: 3, 6 and 9 % (vol.). Composites were made by P/M: mixing, uniaxial pressing and sintering. The sintering was carried out in vacuum, at three temperatures (1120, 1200 and 1250 °C). The influence of the addition of the intermetallic on the microstructure of the stainless steel was assessed by a complete metallographic study using optical and scanning electron microscopy, coupled with a semi-quantitative microanalysis. Wear behaviour was evaluated by a ‘pin on disk’ test. Materials were tested against tool steel, and the main test conditions were as follows: 5 N load, <30% moisture, 0.1 m/s speed, and 377 m sliding distance. X-ray diffraction of powder debris was also studied and wear tracks were observed by SEM.

Atmosphere Influence on Sintered 316L Austenitic Stainless Steel Matrix Composites Reinforced with Intermetallic and Carbide Particles

Atmosphere Influence on Sintered 316L Austenitic Stainless Steel Matrix Composites Reinforced with Intermetallic and Carbide Particles

Influence of path length and slurry velocity on the removal of iron from kaolin using a high gradient magnetic separator

The influence of path length and slurry velocity on the performance of a reciprocating canister type super-conducting magnetic separator has been investigated. The canister train of a Carpco 5 T separator was removed and replaced with seven test cells each with a different length of stainless steel matrix, varying from 25 to 500 mm. A kaolin sample from the St. Austell area in Cornwall was dispersed and pumped through each matrix. The resultant product was analysed for iron. The longer the path length, at a fixed flowrate, the greater was the removal of iron from the kaolin. Shorter path lengths, however, offer the potential advantage of multiple paths within a canister of fixed length. The optimum path length for the kaolin was found to be within the range 25–100 mm, depending on percentage iron removal. The optimum path length increased as the required iron removal rate was increased. Increasing the slurry velocity through the matrix reduced particle capture, with the effect being more significant at 2 T than at 5 T. The higher throughput achieved at the increased velocity however more than compensates for the reduction in performance.

Enhanced passivity of austenitic AISI 304 stainless steel by low-temperature ion nitriding

Low-temperature ion nitriding introduces interstitial nitrogen into the austenitic stainless steel matrix. An enhanced passivity of the nitrided stainless steel was detected by anodic potentiodynamic polarization in a 0.1 M H2SO4+0.05 M HCl electrolyte. Capacitance measurements by electrochemical impedance spectroscopy revealed a 3–4 nm thick oxide film on the surface of nitrided specimens that is two to three times thicker than on blank specimens. X-ray photoelectron spectroscopy analyses and Auger depth profiles indicate increased chromium uptake into the oxide film on the nitrided surface, supposedly through the kinetically stable oxide–metal interface enriched with nitrogen and nickel. Several possible mechanisms that influence passivation of the nitrided stainless steel may operate simultaneously. Among these mechanisms, austenite strengthening by interstitial nitrogen near the oxide/alloy interface associated with structural defects like dislocation branches and vacancies are most likely the explanation for the enhanced passivity of the nitrided stainless steel.

PARTICULATE CAPTURE OF PLUTONIUM BY HIGH GRADIENT MAGNETIC SEPARATION WITH ADVANCED MATRICES

A high performance superconducting magnetic separator is being developed for near single particle retrieval from low concentration field collected samples. Results show that maximum separation is obtained when the effective matrix element diameter approaches the diameter of the particles to be captured. Experimentally, we were able to capture very dilute levels of 0.2 to 0.8 μm PuO2 particles with dodecane as a carrier fluid. The development of new matrix materials is being pursued through the deposition of nickel dendrites on an existing stainless steel matrix material. The new materials are promising for the submicron collection of paramagnetic particles. Results indicate that these new matrices contain a high number of capture sites for the paramagnetic particles. We have also derived a force-balance model that uses empirically determined capture cross section values. The model can be used to optimize the capture cross section and thus increase the capture efficiency. This enables the prediction of high gradient magnetic separator performance for a variety of materials and applications.

Pit Initiation on Stainless Steels in 1 M NaCl With and Without Mechanical Stress

The onset of pitting corrosion at MnS inclusions on 304 stainless steel in 1 M NaCl was studied with and without applied mechanical stress with use of microelectrochemical cells. Polarization curves of areas (100 μm diam) without inclusion showed no pitting at potentials below that of oxidation evolution; stress had no effect on the corrosion behavior. Areas containing five round inclusions of about 4 μm in size showed stable pitting at about 400 mV; the effect of stress shifted the pitting potential to values that were 150 mV more negative. Polarization curves measured on large deep MnS inclusions showed active pitting. Curves of areas with single large, shallow MnS inclusions showed multiple current transients during dissolution of the inclusion without stress, but the metastable events did not initiate stable pitting. The dissolution of shallow MnS inclusion did not form a deep microcrevice between the MnS and stainless steel matrix. However, under applied stress, cracks were formed within the shallow MnS inclusion and active pitting occurred. To explore whether such cracks might serve to generate locally high concentrations of aggressive species, the pH and chloride concentration inside a crack were simulated using a finite difference model. For experimental conditions where stable pitting was observed, the simulations predicted that the solution composition at the base of a typical 13 μm deep crack correspond to a pH of around 2, and a chloride concentration of about 6 M led to stable pitting. © 2001 The Electrochemical Society. All rights reserved.

Laser cladding of stainless steel on magnesium ZK60/SiC composite

Laser cladding of stainless steel on ZK60/SiC composite was achieved by using a two-step method, i.e. thermal spray and laser re-melting. This was made possible by using interlayers of brass and copper, as a result, good metallurgical bond interfaces were obtained. However, the rapid solidification condition caused liquid phase separation. As a consequence, small spheroids of copper-rich phase were formed in the stainless steel matrix, which are found to be detrimental to the corrosion resistance of the material. Nonetheless, the corrosion potential ( E corr) of the laser-cladded sample was 1090 and 820 mV higher than that of the as-received and as-sprayed samples, respectively, while the corrosion current ( i corr) was some two and four orders of magnitude lower. The laser-cladded sample, like the untreated composite, did not show a passive region in the polarization plot. This is believed to be due to the segregation of copper-rich phase at interdendritic regions, and the presence of copper-rich spheroids in the stainless steel matrix.

Microstructure, corrosion and mechanical properties of 304 stainless steel containing copper, silicon and nitrogen

The effects of 0.086–0.336% nitrogen additions on the microstructure, corrosion and mechanical properties of type 304 austenitic stainless steel (SS) containing 2% copper and 2–3% silicon were studied. This study was carried out using scanning electron microscope (SEM), potentiodynamic, weight loss, hardness number and ball-punch bulge measurements. Mutual effects between Si and N were observed in the matrix of SS. Nitrogen offset the ferrite-forming tendencies of Si and was more efficient than Ni as austenitizer, but Si decreased the solubility of N in solid solution. N additions improved the pitting resistance of SS in acidic and neutral chloride solutions. This was more evident in more aggressive solutions than in solutions with low chloride concentrations. Segregation of second N-rich phases, like Cr2N, in SS containing 2% Cu, 3% Si and 0.237% N was occurred. This steel exhibited less pitting corrosion resistance than the plain 304 SS in most chloride solutions under study. Addition of 2% Si to 304 SS containing Cu has negative effect on the mechanical behavior. But presence of N improved the mechanical strength of steel irrespective of the drop solubility of N affected by Si.

Simultaneous and consistent analysis of NRA, RBS and ERDA data with the IBA DataFurnace

We present in this paper, for the first time, the extension of the ion beam analysis DataFurnace to the analysis of non-resonant nuclear reaction analysis (NRA) data. The NRA routine is general and can be used to analyse data from any reaction with known Q and cross section. The shape of the cross section is taken into account and hence depth profiling using reactions with non-flat cross sections is easily done. We show different applications of the program, including profiling of deuterium with a 3He beam and profiling of N in a stainless steel matrix using a deuterium beam. In the latter case, we also performed 35 MeV Cl-ERDA and D-RBS experiments of the same sample. The Ion Beam Analysis DataFurnace allows to analyse all the data simultaneously, taking into account all the information present in the different data sets in a fully consistent manner.

Sliding wear of stainless steel matrix composite reinforced with TiB 2 particles

AISI 304 stainless steel reinforced with 20 vol.% TiB 2 particles were prepared by hot isostatic pressing (HIP). The dry sliding wear behaviour of this ferrous composite was investigated by means of the pin-on-disc technique. The results showed that the TiB 2 particle addition was very effective to improve the wear resistance of soft and ductile austenitic stainless steel. The volumetric wear of the composite tended to decrease with increasing applied normal loads or with sliding velocity. This was due to the formation of a deformed surface layer whose microhardness values also increased with increasing applied load. Scanning electron microscopic observation revealed that the TiB 2 particles from the metal matrix composite (MMC) matrix were fractured into smaller particulates during sliding. These fragmented particles tended to orient themselves along the sliding direction, and redistributed near the subsurface region of MMC. Consequently, the hardness of the subsurface region of MMC after sliding was higher than that of the unreinforced stainless steel.

Microstructural evolution and oxidation behavior of nanocrystalline 316-stainless steel coatings produced by high-velocity oxygen fuel spraying

Abstract The microstructural evolution and oxidation behavior of nanocrystalline 316-stainless steel coatings produced by high-velocity oxygen fuel spraying is described. Stainless steel powders with a particle size in the range of 45–11 μm were mechanically milled for 10 h in liquid nitrogen to produce powders with a nanocrystalline grain size of 21±8 nm and an aspect ratio of 1.68. The cryomilled powders were subsequently sprayed onto a stainless steel substrate by high-velocity oxygen fuel spraying. The resultant coating exhibited a superior microhardness, despite an increased porosity, over that of the conventional coating sprayed with the same parameters. Transmission electron microscopy performed on the cross-sections of the nanocrystalline coating revealed the splat formation with a thickness ranging from 40 to 400 nm. Various oxide phases (Cr 2 O 3 , FeO, Fe 2 O 3 and γ-Fe 2 O 3 ) in the stainless steel matrix were identified using selected area diffraction. This observation suggests that in-flight oxidation may have occurred during spraying and/or during splat formation.

Comparative study of the partial oxidation of methane to synthesis gas in fixed-bed and fluidized-bed membrane reactors.: Part II – Development of membranes and catalytic measurements

The catalytic partial oxidation of methane (CPOM) to synthesis gas was carried out in fixed-bed and fluidized-bed membrane reactors over a Ni/α–Al 2O 3 catalyst. For gas separation silicalite membranes inside an alumina and a porous stainless-steel matrix were synthesized and applied in the catalytic measurements. Moreover, a membrane obtained by deposition of palladium on the stainless-steel silicalite membrane was tested. The zeolite membranes were stable in the whole investigated temperature range (700< T<750°C). The Pd-membrane was not stable; palladium layer did not withstand temperatures above 650°C. In the catalytic measurements in the fixed-bed reactor and in the fluidized bed ( P CH 4 =66.6 kPa, P O 2 =33.3 kPa, m cat/ V=14 gs/ml) nearly thermodynamic equilibrium was achieved. However, neither in the fixed-bed reactor nor in the fluidized-bed membrane reactor an improvement in the syngas yield by means of the integrated product separation could be achieved. In the fixed-bed membrane the unselective separation of methane was detrimental for methane conversion. In the fluidized-bed membrane reactor the amount of permeated hydrogen was not sufficient to shift significantly the equilibrium towards higher syngas yield. However, in the fluidized-bed membrane reactor significant better selectivities of separation were achieved.

Mechanical and corrosion behaviour of powder metallurgy stainless steel based metal matrix composites

Stainless steel matrix composites were manufactured using powder metallurgy techniques. Matrixes of AISI 316L stainless steel were reinforced with yttria or alumina particles. Chromium diboride was added in some cases and boron nitride in others to obtain steels with densities close to theoretical, using reactive (liquid phase) sintering techniques. The composites showed very good densification and better hardness than the 316L stainless steel without additions. The 316L steel reinforced with 4 wt-% yttria chromium diboride showed the highest density and strength, with an acceptable corrosion resistance.

Mechanical and corrosion behaviour of powder metallurgy stainless steel based metal matrix composites

Stainless steel matrix composites were manufactured using powder metallurgy techniques. Matrixes of AISI 316L stainless steel were reinforced with yttria or alumina particles. Chromium diboride was added in some cases and boron nitride in others to obtain steels with densities close to theoretical, using reactive (liquid phase) sintering techniques. The composites showed very good densification and better hardness than the 316L stainless steel without additions. The 316L steel reinforced with 4 wt-% yttria chromium diboride showed the highest density and strength, with an acceptable corrosion resistance.

ESTUDO IN VITRO DA RUGOSIDADE SUPERFICIAL E DO PERFIL PROXIMAL DE AMÁLGAMAS CONDENSADOS CONTRA MATRIZES DE AÇO INOXIDÁVEL REUTILIZADAS

O objetivo deste trabalho in vitro foi avaliar a rugosidade e o perfil de restaurações de amálgama obtidas com a reutilização de uma mesma matriz de aço inoxidável. A rugosidade superficial e o perfil proximal de amálgamas, obtidos com três tipos de limalhas com variação da pressão de condensação, foram avaliados e submetidos à análise estatística. É importante notar que uma mesma matriz foi reutilizada 15 vezes para cada grupo testado. O aumento constante da rugosidade da primeira até a última utilização, assim como a alteração do perfil evidenciam a deformação progressiva da matriz, alterando significantemente a lisura e o perfil desejados na face proximal. Os resultados obtidos mostram, portanto, que as matrizes de aço devem ser consideradas materiais descartáveis.