Nitriding in cathodic cage of stainless steel AISI 316: influence of sample position

R.R.M. de Sousa et al. Nitriding in cathodic cage of stainless steel AISI 316: Influence of sample position. Vacuum, [s.l.], n.83, 2009. Disponivel em: . Acesso em: 04 out.2010.

Nitriding in cathodic cage of stainless steel AISI 316: influence of sample position

R.R.M. de Sousa et al. Nitriding in cathodic cage of stainless steel AISI 316: Influence of sample position. Vacuum, [s.l.], n.83, 2009. Disponivel em: . Acesso em: 04 out.2010.

A Comparati ve Study of Mechanical and Tribological Properties of AISI-304 and AISI-316 Submitted to Glow Discharge Nitriding

Mechanical and tribological properties of AISI 304 and AISI 316 stainless steels submitted to glow discharge ion nitriding are reported. The atmosphere was 20:80 - N2:H2 with substrate temperatures ranging from 300 to 500 °C. Treatment at 300 °C produced expanded austenite (γN) in both steels. Increasing the temperature, the phases γ′-Fe4N and ε- Fe2+xN were present and the latter is the major phase for AISI 304. At 500 °C, the CrN phase was also identified in both steels. Hardnesses of about 13-14 GPa at near surface regions were obtained in both steels. Moreover, AISI 316 nitrided at 500 °C has the deepest hard layer. Tribological tests showed that wear can be reduced by up to a factor of six after the nitriding processes, even for a working temperature of 300 °C. The profiles during and after nanoscratch tests did not reveal significant differences after nitriding processes in both steels.

A Comparative Study of Mechanical and Tribological Properties of AISI-304 and AISI-316 Submitted to Glow Discharge Nitriding

Mechanical and tribological properties of AISI 304 and AISI 316 stainless steels submitted to glow discharge ion nitriding are reported. The atmosphere was 20:80 - N2:H2 with substrate temperatures ranging from 300 to 500 °C. Treatment at 300 °C produced expanded austenite (γN) in both steels. Increasing the temperature, the phases γ′-Fe4N and ε- Fe2+xN were present and the latter is the major phase for AISI 304. At 500 °C, the CrN phase was also identified in both steels. Hardnesses of about 13-14 GPa at near surface regions were obtained in both steels. Moreover, AISI 316 nitrided at 500 °C has the deepest hard layer. Tribological tests showed that wear can be reduced by up to a factor of six after the nitriding processes, even for a working temperature of 300 °C. The profiles during and after nanoscratch tests did not reveal significant differences after nitriding processes in both steels.

Estudo da sinterização do aço inox 316L reforçado com 3% Carbeto de Tântalo - TaC

The present work shows a contribution to the studies of development and solid sinterization of a metallic matrix composite MMC that has as starter materials 316L stainless steel atomized with water, and two different Tantalum Carbide TaC powders, with averages crystallite sizes of 13.78 nm and 40.66 nm. Aiming the metallic matrix s density and hardness increase was added different nanometric sizes of TaC by dispersion. The 316L stainless steel is an alloy largely used because it s high resistance to corrosion property. Although, its application is limited by the low wear resistance, consequence of its low hardness. Besides this, it shows low sinterability and it cannot be hardened by thermal treatments traditional methods because of the austenitic structure, face centered cubic, stabilized mainly in nickel presence. Steel samples added with TaC 3% wt (each sample with different type of carbide), following a mechanical milling route using conventional mill for 24 hours. Each one of the resulted samples, as well as the pure steel sample, were compacted at 700 MPa, room temperature, without any addictive, uniaxial tension, using a 5 mm diameter cylindrical mold, and quantity calculated to obtain compacted final average height of 5 mm. Subsequently, were sintered in vacuum atmosphere, temperature of 1290ºC, heating rate of 20ºC/min, using different soaking times of 30 and 60 min and cooled at room temperature. The sintered samples were submitted to density and micro-hardness analysis. The TaC reforced samples showed higher density values and an expressive hardness increase. The complementary analysis in optical microscope, scanning electronic microscope and X ray diffractometer, showed that the TaC, processed form, contributed with the hardness increase, by densification, itself hardness and grains growth control at the metallic matrix, segregating itself to the grain boarders

Sinterização de aço inoxidável reforçado com partículas nanométricas dispersas de carbeto de nióbio - NbC

Metal powder sintering appears to be promising option to achieve new physical and mechanical properties combining raw material with new processing improvements. It interest over many years and continue to gain wide industrial application. Stainless steel is a widely accepted material because high corrosion resistance. However stainless steels have poor sinterability and poor wear resistance due to their low hardness. Metal matrix composite (MMC) combining soft metallic matrix reinforced with carbides or oxides has attracted considerable attention for researchers to improve density and hardness in the bulk material. This thesis focuses on processing 316L stainless steel by addition of 3% wt niobium carbide to control grain growth and improve densification and hardness. The starting powder were water atomized stainless steel manufactured for Höganäs (D 50 = 95.0 μm) and NbC produced in the UFRN and supplied by Aesar Alpha Johnson Matthey Company with medium crystallite size 16.39 nm and 80.35 nm respectively. Samples with addition up to 3% of each NbC were mixed and mechanically milled by 3 routes. The route1 (R1) milled in planetary by 2 hours. The routes 2 (R2) and 3 (R3) milled in a conventional mill by 24 and 48 hours. Each milled samples and pure sample were cold compacted uniaxially in a cylindrical steel die (Ø 5 .0 mm) at 700 MPa, carried out in a vacuum furnace, heated at 1290°C, heating rate 20°C stand by 30 and 60 minutes. The samples containing NbC present higher densities and hardness than those without reinforcement. The results show that nanosized NbC particles precipitate on grain boundary. Thus, promote densification eliminating pores, control grain growth and increase the hardness values

Nitretação em plasma com gaiola catódica: investigação do mecanismo e estudo comparativo com a nitretação em plasma de tensão contínua

The ionic plasma nitriding is one of the most important plasma assisted treatment technique for surface modification, but it presents some inherent problems mainly in nitriding pieces with complex geometries. In the last four years has appeared a plasma nitriding technique, named ASPN (Active Screen Plasma Nitriding) in which the samples and the workload are surrounded by a metal screen on which the cathodic potential is applied. This new technique makes possible to obtain a perfect uniform nitrided layer apart from the shape of the samples. The present work is based on the development of a new nitriding plasma technique named CCPN (Cathodic Cage Plasma Nitriding) Patent PI 0603213-3 derived from ASPN, but utilizes the hollow cathode effect to increase the nitriding process efficiency. That technique has shown great improvement on the treatment of several types of steels under different process conditions, producing thicker and harder layers when compared with both, ASPN and ionic plasma nitriding, besides eliminating problems associated with the later technique. The best obtained results are due to the hollow cathode effect on the cage holes. Moreover, characteristic problems of ionic plasma nitriding are eliminated due to the fact that the luminescent discharge acts on the cage wall instead of on the samples surface, which remains under a floating potential. In this work the enhancement of the cathodic cage nitriding layers proprieties, under several conditions for some types of steels was investigated, besides the mechanism for nitrides deposition on glass substrate, concluding that the CCPN is both a diffusion and a deposition process at the same time

Efeito da moagem de alta energia na microestrutura e nas propriedades magnéticas do compósito wc-10%p.Co

This work a studied the high energy milling effect in microstructure and magnetic properties of the WC-10wt.%Co composite. The composite powders were prepared by mechanical mixed and milled at 2 hours, 100 hours, 200 hours and 300 hours in planetary milling. After this process the composite were compacted in stainless steel die with cylindrical county of 10 mm of diameter, at pressure 200 Mpa and sintered in a resistive furnace in argon atmosphere at 1400 oC for 5 min. The sintered composite were cutted, inlaid, sandpapered, and polished. The microestrutural parameters of the composite was analyzed by X-ray diffraction, scanning electronic microscopy, optical microscopy, hardness, magnetic propriety and Rietveld method analyze. The results shows, with milling time increase the particle size decrease, it possibility minor temperature of sintering. The increase of milling time caused allotropic transformation in cobalt phase and cold welding between particles. The cold welding caused the formation of the particle composite. The X-ray diffraction pattern of composite powders shows the WC peaks intensity decrease with the milling time increase. The X-ray diffraction pattern of the composite sintered samples shows the other phases. The magnetic measurements detected a significant increase in the coercitive field and a decrease in the saturation magnetization with milling time increase. The increase coercitive field it was also verified with decrease grain size with milling time increase. For the composite powders the increase coercitive field it was verified with particle size reduction and saturation magnetization variation is relate with the variation of free cobalt. The Rietveld method analyze shows at milling time increase the mean crystalline size of WC, and Co-cfc phases in composite sintered sample are higher than in composite powders. The mean crystallite size of Co-hc phase in composite powders is higher than in composite sintered sample. The mean lattice strains of WC, Co-hc and Co-cfc phases in composite powders are higher than in composite sintered samples. The cells parameters of the composite powder decrease at milling time increase this effect came from the particle size reduction at milling time increase. In sintered composite the cells parameters is constant with milling time increase

Estudo sobre o efeito dos parâmetros de processamento dos pós e sinterização do aço inox 316l reforçado com NbC

This masther dissertation presents a contribution to the study of 316L stainless steel sintering aiming to study their behavior in the milling process and the effect of isotherm temperature on the microstructure and mechanical properties. The 316L stainless steel is a widely used alloy for their high corrosion resistance property. However its application is limited by the low wear resistance consequence of its low hardness. In previous work we analyzed the effect of sintering additives as NbC and TaC. This study aims at deepening the understanding of sintering, analyzing the effect of grinding on particle size and microstructure and the effect of heating rate and soaking time on the sintered microstructure and on their microhardness. Were milled 316L powders with NbC at 1, 5 and 24 hours respectively. Particulates were characterized by SEM and . Cylindrical samples height and diameter of 5.0 mm were compacted at 700 MPa. The sintering conditions were: heating rate 5, 10 and 15◦C/min, temperature 1000, 1100, 1200, 1290 and 1300◦C, and soaking times of 30 and 60min. The cooling rate was maintained at 25◦C/min. All samples were sintered in a vacuum furnace. The sintered microstructure were characterized by optical and electron microscopy as well as density and microhardness. It was observed that the milling process has an influence on sintering, as well as temperature. The major effect was caused by firing temperature, followed by the grinding and heating rate. In this case, the highest rates correspond to higher sintering.

Construção, caracterização e aplicação de eletrodos para descarga por arco de cátodo oco

The system built to characterize electrodes and, consequently, deposited fine films are constituted by a hollow cathode that works to discharges and low pressures (approximately 10-3 to 5 mbar), a source DC (0 to 1200 V), a cylindrical camera of closed borossilicato for flanges of stainless steel with an association of vacuum bombs mechanical and spread. In the upper flange it is connected the system of hollow cathode, which possesses an entrance of gas and two entrances for its refrigeration, the same is electrically isolated of the rest of the equipment and it is polarized negatively. In front of the system of hollow cathode there is a movable sample in stainless steel with possibility of moving in the horizontal and vertical. In the vertical, the sample can vary its distance between 0 and 70 mm and, in the horizontal, can leave completely from the front of the hollow cathode. The sample and also the cathode hollow are equipped with cromel-alumel termopares with simultaneous reading of the temperatures during the time of treatment. In this work copper electrodes, bronze, titanium, iron, stainless steel, powder of titanium, powder of titanium and silício, glass and ceramic were used. The electrodes were investigated relating their geometry change and behavior of the plasma of the cavity of hollow cathode and channel of the gas. As the cavity of hollow cathode, the analyzed aspects were the diameter and depth. With the channel of the gas, we verified the diameter. In the two situations, we investigated parameters as flow of the gas, pressure, current and applied tension in the electrode, temperature, loss of mass of the electrode with relationship at the time of use. The flow of gas investigated in the electrodes it was fastened in a work strip from 15 to 6 sccm, the constant pressure of work was among 2.7 to 8 x 10-2 mbar. The applied current was among a strip of work from 0,8 to 0,4 A, and their respective tensions were in a strip from 400 to 220 V. Fixing the value of the current, it was possible to lift the curve of the behavior of the tension with the time of use. That curves esteem in that time of use of the electrode to its efficiency is maximum. The temperatures of the electrodes were in the dependence of that curves showing a maximum temperature when the tension was maximum, yet the measured temperatures in the samples showed to be sensitive the variation of the temperature in the electrodes. An accompaniment of the loss of mass of the electrode relating to its time of use showed that the electrodes that appeared the spherical cavities lost more mass in comparison with the electrodes in that didn't appear. That phenomenon is only seen for pressures of 10-2 mbar, in these conditions a plasma column is formed inside of the channel of the gas and in certain points it is concentrated in form of spheres. Those spherical cavities develop inside of the channel of the gas spreading during the whole extension of the channel of the gas. The used electrodes were cut after they could not be more used, however among those electrodes, films that were deposited in alternate times and the electrodes that were used to deposit films in same times, those films were deposited in the glass substrata, alumina, stainless steel 420, stainless steel 316, silício and steel M2. As the eletros used to deposit films in alternate time as the ones that they were used to deposit in same times, the behavior of the thickness of the film obeyed the curve of the tension with relationship the time of use of the electrode, that is, when the tension was maximum, the thickness of the film was also maximum and when the tension was minimum, the thickness was minimum and in the case where the value of the tension was constant, the thickness of the film tends to be constant. The fine films that were produced they had applications with nano stick, bio-compatibility, cellular growth, inhibition of bacterias, cut tool, metallic leagues, brasagem, pineapple fiber and ornamental. In those films it was investigated the thickness, the adherence and the uniformity characterized by sweeping electronic microscopy. Another technique developed to assist the production and characterization of the films produced in that work was the caloteste. It uses a sphere and abrasive to mark the sample with a cap impression, with that cap form it is possible to calculate the thickness of the film. Through the time of life of the cathode, it was possible to evaluate the rate of waste of its material for the different work conditions. Values of waste rate up to 3,2 x 10-6 g/s were verified. For a distance of the substratum of 11 mm, the deposited film was limited to a circular area of 22 mm diameter mm for high pressures and a circular area of 75 mm for pressure strip. The obtained films presented thickness around 2,1 µm, showing that the discharge of arch of hollow cathode in argon obeys a curve characteristic of the tension with the time of life of the eletrodo. The deposition rate obtained in this system it is of approximately 0,18 µm/min

Estudo da sinterização de cavacos de aço ferritico

This research studies the sintering of ferritic steel chips from the machining process. Were sintered metal powder obtained from machining process chips for face milling of a ferritic steel. The chip was produced by machining and characterized by SEM and EDS, and underwent a process of high energy mill powder characterized also by SEM and EDS. Were constructed three types of matrixes for uniaxial compression (relation l / d greater than 2.5). The differences in the design of the matrixes were essentially in the direction of load application, which for cylindrical case axial direction, while for the rectangular arrays, the longer side. Two samples were compressed with different geometries, a cylindrical and rectangular with the same compaction pressure of 700 MPa. The samples were sintered in a vacuum resistive furnace, heating rate 20 °C / min., isotherm 1300 °C for 60 minutes, and cooling rate of 25 °C / min to room temperature. The starting material of the rectangular sample was further annealed up to temperature of 800 ° C for 30 min. Sintered samples were characterized by scanning electron microscopy, optical microscopy and EDS. The sample compressed in the cylindrical matrix did not show a regular density reflecting in the sintered microstructure revealed by the irregular geometry of the pores, characterizing that the sintering was not complete, reaching only the second phase. As for the specimen compacted in the rectangular array, the analysis performed by scanning electron microscopy, optical microscopy and EDS indicate a good densification, and homogeneous microstructure in their full extent. Additionally, the EDS analyzes indicate no significant changes in chemical composition in the process steps. Therefore, it is concluded that recycling of chips, from the processed ferritic steel is feasible by the powder metallurgy. It makes possible rationalize raw material and energy by manufacture of known properties components from chips generated by the machining process, being benefits to the environment

Obtenção de polímeros de LCC para aplicação como antioxidante de biodiesel de soja

Biodiesel is a fuel obtained from vegetable oils, such as soy, castorbean, among others. The monoester of fatty acid of these oils have chains with mono, di and tri double connections. The presence of these insaturations are susceptible to oxidization. Antioxidants are substances able to prevent oxidization from oils, fats, fat foods, as well as esters of Alquila( biodiesel). The objective of this work is to summarize a new antioxidant from the Cashew Nut Shell Liquid (CNSL) using the electrolysis technique. A current of 2 amperes was used in a single cell of only one group and two eletrodos of stainless steel 304 in a solution of methanol, together with the eletrolits: acetic acid, sodium chloride and sodium hydroxide, for two hours of agitation. The electrolysis products are characterized by the techniques of cromatography in a thin layer, spectroscopy of infrared and gravimetric analysis. The material was submitted to tests of oxidative stability made by the techniques of spectropy of impendancy and Rancimat (EN 14112). The analyses of characterization suggest that the polimerization of the electrolytic material ocurred. The application results of these materials as antioxidants of soy biodiesel showed that the order of the oxidative stability was obtained by both techniques used

Estudo da viabilidade técnica para obtenção de superfície duplex em aço inoxidável martensítico AISI 410 através do processo de deposição a plasma por gaiola catódica

The technique of plasma nitriding by the cathode cage mainly stands out for its ability to produce uniform layers, even on parts with complex geometries. In this study, it was investigated the efficiency of this technique for obtaining duplex surface, when used, simultaneously, to nitriding treatment and thin film deposition at temperatures below 500°C. For this, were used samples of AISI 41 0 Martensitic Stainless Steel and performed plasma treatment, combining nitriding and deposition of thin films of Ti and/or TiN in a plasma atmosphere containing N2-H2. It was used a cathodic cage of titanium pure grade II, cylindrical with 70 mm diameter and 34 mm height. Samples were treated at temperature 420ºC for 2 and 12 hours in different working pressures. Optical Microscopy (OM), Scanning Electron Microscopy (SEM) with micro-analysis by Energy Dispersive Spectroscopy (EDS), X-Ray Diffraction (XRD), Atomic Force Microscopy (AFM) and analysis of Vickers Microhardness were used to investigate coating properties such as homogeneity and surface topography, chemical composition, layer thickness, crystalline phase, roughness and surface microhardness. The results showed there is a direct proportionality between the presence of H2 in plasma atmosphere and the quantity of titanium in surface chemical composition. It was also observed that the plasma treatment at lowpressure is more effective in formation of TiN thin film

Comportamento da adição do carbeto de nióbio (nBC) na matriz metálica do aço ferrítico 15kH2mfa

The 15Kh2MFA steel is a kind of Cr-Mo-V family steels and can be used in turbines for energy generation, pressure vessels, nuclear reactors or applications where the range of temperature that the material works is between 250 to 450°C. To improve the properties of these steels increasing the service temperature and the thermal stability is add a second particle phase. These particles can be oxides, carbides, nitrites or even solid solution of some chemical elements. On this way, this work aim to study the effect of addition of 3wt% of niobium carbide in the metallic matrix of 15Kh2MFA steel. Powder metallurgy was the route employed to produce this metallic matrix composite. Two different milling conditions were performed. Condition 1: milling of pure 15Kh2MFA steel and condition 2: milling of 15Kh2MFA steel with addition of niobium carbide. A high energy milling was carried out during 5 hours. Then, these two powders were sintered in a vacuum furnace (10-4torr) at 1150 and 1250°C during 60 minutes. After sintering the samples were normalized at 950°C per 3 minutes followed by air cooling to obtain a desired microstructure. Results show that the addition of niobium carbide helps to mill faster the particles during the milling when compared with that steel without carbide. At the sintering, the niobium carbide helps to sinter increasing the density of the samples reaching a maximum density of 7.86g/cm³, better than the melted steel as received that was 7,81g/cm³. In spite this good densification, after normalizing, the niobium carbide don t contributed to increase the microhardness. The best microhardness obtained to the steel with niobium carbide was 156HV and to pure 15Kh2MFA steel was 212HV. It happened due when the niobium carbide is added to the steel a pearlitic structure was formed, and the steel without niobium carbide submitted to the same conditions reached a bainitic structure

Desenvolvimento e caracterização de um compósito matriz metálica (CMM): aço EUROFER97 reforçado com Carbeto de Tântalo - TaC

Steel is an alloy EUROFER promising for use in nuclear reactors, or in applications where the material is subjected to temperatures up to 550 ° C due to their lower creep resistance under. One way to increase this property, so that the steel work at higher temperatures it is necessary to prevent sliding of its grain boundaries. Factors that influence this slip contours are the morphology of the grains, the angle and speed of the grain boundaries. This speed can be decreased in the presence of a dispersed phase in the material, provided it is fine and homogeneously distributed. In this context, this paper presents the development of a new material metal matrix composite (MMC) which has as starting materials as stainless steel EUROFER 97, and two different kinds of tantalum carbide - TaC, one with average crystallite sizes 13.78 nm synthesized in UFRN and another with 40.66 nm supplied by Aldrich. In order to improve the mechanical properties of metal matrix was added by powder metallurgy, nano-sized particles of the two types of TaC. This paper discusses the effect of dispersion of carbides in the microstructure of sintered parts. Pure steel powders with the addition of 3% TaC UFRN and 3% TaC commercial respectively, were ground in grinding times following: a) 5 hours in the planetary mill for all post b) 8 hours of grinding in the mill Planetary only for steel TaC powders of commercial and c) 24 hours in the conventional ball mill mixing the pure steel milled for 5 hours in the planetary mill with 3% TaC commercial. Each of the resulting particulate samples were cold compacted under a uniaxial pressure of 600MPa, on a cylindrical matrix of 5 mm diameter. Subsequently, the compressed were sintered in a vacuum furnace at temperatures of 1150 to 1250 ° C with an increment of 20 ° C and 10 ° C per minute and maintained at these isotherms for 30, 60 and 120 minutes and cooled to room temperature. The distribution, size and dispersion of steel and composite particles were determined by x-ray diffraction, scanning electron microscopy followed by chemical analysis (EDS). The structures of the sintered bodies were observed by optical microscopy and scanning electron accompanied by EDS beyond the x-ray diffraction. Initial studies sintering the obtained steel EUROFER 97 a positive reply in relation to improvement of the mechanical properties independent of the processing, because it is obtained with sintered microhardness values close to and even greater than 100% of the value obtained for the HV 333.2 pure steel as received in the form of a bar