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Cutting tools, such as machining inserts, which in addition to having a complex geometry need to handle different demands on more than one face during their application, stimulate investigation for new coating techniques. Even though many hard film deposition techniques are well accepted or even established among researchers and industries, these processes still need to meet a limitation that requires the repositioning of the sample for new treatments in order to cover all of its surfaces. This paper proposes a new methodology for coating deposition on complex geometry pieces, through a structure for three-dimensional plasma treatment, using a Rotary Cathodic Cage Plasma Nitriding (RCCPN). TiN films were deposited on cemented carbide inserts applied in machining processes using the RCCPN technique. The plasma parameters were kept constant and deposition time was the only variable input. The deposited films were characterized by SEM, EDS, XRD, and Vickers microhardness. It was observed that the RCCPN technique was useful in producing a uniform TiN layer in all insert surfaces, with a thickness proportional to deposition time.

A titanium surface nitrided by plasma contains nitrogen ions that guarantee resistance to corrosion and biocompatibility. Despite this, no descriptions concerning the influence of the expression of cell adhesion proteins and their influence on osteogenic cell differentiation are available. Thus, the present study aimed to assess the response of murine pre‐osteoblastic cells (MC3T3‐E1) cultured on nitrided titanium surfaces. Pre‐osteoblastic cells were grown on polished titanium discs, used as controls, and on previously characterized plasma‐nitrided titanium discs. Cells from both groups were submitted to the MTT cell viability test. The expressions of α5, α2, and β1 integrin were assessed by flow cytometry and immunofluorescence, while osteocalcin expression was assessed by flow cytometry. The nitrided surface presented higher α2 and β1 integrin expressions, as well as osteocalcin expression, when compared to the polished surface, with no alterations in cell viability. These findings seem to suggest that the plasma nitriding treatment produces a titanium surface with the potential for effective in vitro osseointegration.

We evaluated the effects of titanium plasma nitriding and oxidation on live endothelial cell viscoelasticity. For this, mechanically polished titanium surfaces and two surfaces treated by planar cathode discharge in nitriding (36N2 and 24H2) and oxidant (36O2 and 24H2). Surfaces were characterized regarding wettability, roughness and chemical composition. Rabbit aortic endothelial cells (RAECs) were cultured on the titanium surfaces. Cell morphology, viability and viscoelasticity were evaluated by scanning electron microscopy (SEM), methyl thiazolyl tetrazolium (MTT) assay and atomic force microscopy (AFM), respectively. Grazing Incidence X-ray Diffraction confirmed the presence of TiN0,26 on the surface (grazing angle theta 1°) of the nitrided samples, decreasing with depth. On the oxidized surface had the formation of TiO3 on the material surface (Theta 1°) and in the deeper layers was noted, with a marked presence of Ti (Theta 3°). Both plasma treatments increased surface roughness and they are hydrophilic (angle < 90°). However, oxidation led to a more hydrophilic titanium surface (66.59° ± 3.65 vs. 76.88° ± 2.68; p = 0.001) due to titanium oxide films in their stoichiometric varieties (Ti3O, TiO2, Ti6O), especially Ti3O. Despite focal adhesion on the surfaces, viability was different after 24 h, as cell viability on the oxidized surface was higher than on the nitrided surface (9.1 × 103 vs. 4.5 × 103cells; p < 0.05). This can be explained by analyzing the viscoelastic property of the cellular cytoskeleton (nuclear and peripheral) by AFM. Surface oxidation significantly increased RAECs viscoelasticity at cell periphery, in comparison to the nucleus (2.36 ± 0.3 vs. 1.5 ± 0.4; p < 0.05), and to the RAECs periphery in contact with nitrided surfaces (1.36 ± 0.7; p < 0.05) and polished surfaces (1.55 ± 0.6; p < 0.05). Taken together, our results have shown that titanium plasma treatment directly increased cell viscoelasticity via surface oxidation, and this mechanobiological property subsequently increased biocompatibility.

Bacterial adhesion on three different surfaces: untreated Ti, plasma nitriding, and plasma carbonitriding Ti substrates were investigated. The samples were placed in bacterial cultures of Pseudomonas aeruginosa to assess biofilm formation. The correlation between the amount of bacteria attached to the surface after a lapse of time with nanotopography and physicochemical properties was performed. TiN showed the highest capacity to avoid bacterial adhesion, while presenting intermediate roughness and wettability. Although the surface of TiCN had the highest surface roughness and low contact angle (high wettability), bacterial adhesion was intermediate on this sample. Untreated Ti, even though presenting a smooth surface and low wettability, had the highest tendency to form biofilms.

Direct current (DC) plasma nitriding offers some disadvantages, especially in parts with complex geometries, where the presence of edges is significant, such as gears, molds, and needle punched parts are strongly affected by this effect, leading to irregular formation of nitrided layers and high variation in surface hardness. To solve these problems two techniques were developed as alternatives, namely: pulsed plasma nitriding and cathodic cage nitriding. In this work, these three nitriding techniques were compared using AISI 1045 steel as substrate. Steel discs were nitrided with the purpose of evaluating the influence of these different plasma configurations on the characteristics of the nitrided layer. The treatments in the three techniques were carried out at the same pressure, temperature, time and gas atmosphere. The samples were characterized for the microstructure, microhardness and crystalline phases present. X-ray diffraction with grazing incidence was used to verify the order of the nitrites formed and to estimate the thickness of the single-phase layers. Differences between the configurations with respect to the occurrence of restriction rings, total thickness (xe + xγ') and relative (xe/xγ') compound layers were observed. Keywords: Plasma DC; cathodic cage; pulsed plasma; nitriding; GIXRD.

Objectives To evaluate the effects of the surface modification of 316L stainless steel (SS) by lowtemperature plasma nitriding on endothelial cells for stent applications. Results X-ray diffraction (XRD) confirmed the incorporation of nitrogen into the treated steel. The surface treatment significantly increased SS roughness and hydrophilic characteristics. After 4 h the cells adhered to the nitride surfaces and formed clusters. During the 24 h incubation period, cell viability on the nitrided surface was higher compared to the polished surface. Nitriding reduced late apoptosis of rabbit aorta endothelial cell (RAEC) on the SS surface. Conclusion Low temperature plasma nitriding improved the biocompatible of stainless steel for use in stents.

Biomedical devices introduced in the human body interact initially with blood cells, their success being dependent on the result of this interaction. This work aimed to obtain optimum biocompatibility and hemocompatibility of the titanium by plasma treatment. For this, discs of commercially pure titanium (CP) were subjected to plasma nitriding using different mixture of nitrogen and hydrogen; the effect of addition of hydrogen to the nitriding plasma was investigated. Before and after treatment, samples were evaluated in terms of topography and wettability using atomic force microscopy and sessile drop tests, respectively. The titanium biological response was evaluated in vitro through the application of platelet-rich plasma (PRP) on the surfaces modified and analysis of their behaviour from the point of view of surface tension and cell adhesion. Surface properties, such as roughness and wettability, were sensitive to the hydrogen/nitrogen ratio in the nitriding plasma, suggesting a strategy for producing different surfaces of biomedical devices. Results showed to be possible to obtain surfaces with different response to the adhesion of platelets, covering different applications.

We evaluated the effects of titanium plasma nitriding and oxidation on live endothelial cell viscoelasticity. For this, mechanically polished titanium surfaces and two surfaces treated by planar cathode discharge in nitriding (36N2 and 24H2) and oxidant (36O2 and 24H2). Surfaces were characterized regarding wettability, roughness and chemical composition. Rabbit aortic endothelial cells (RAECs) were cultured on the titanium surfaces. Cell morphology, viability and viscoelasticity were evaluated by scanning electron microscopy (SEM), methyl thiazolyl tetrazolium (MTT) assay and atomic force microscopy (AFM), respectively. Grazing Incidence X-ray Diffraction confirmed the presence of TiN0,26 on the surface (grazing angle theta 1°) of the nitrided samples, decreasing with depth. On the oxidized surface had the formation of TiO3 on the material surface (Theta 1°) and in the deeper layers was noted, with a marked presence of Ti (Theta 3°). Both plasma treatments increased surface roughness and they are hydrophilic (angle < 90°). However, oxidation led to a more hydrophilic titanium surface (66.59° ± 3.65 vs. 76.88° ± 2.68; p = 0.001) due to titanium oxide films in their stoichiometric varieties (Ti3O, TiO2, Ti6O), especially Ti3O. Despite focal adhesion on the surfaces, viability was different after 24 h, as cell viability on the oxidized surface was higher than on the nitrided surface (9.1 × 103 vs. 4.5 × 103cells; p < 0.05). This can be explained by analyzing the viscoelastic property of the cellular cytoskeleton (nuclear and peripheral) by AFM. Surface oxidation significantly increased RAECs viscoelasticity at cell periphery, in comparison to the nucleus (2.36 ± 0.3 vs. 1.5 ± 0.4; p < 0.05), and to the RAECs periphery in contact with nitrided surfaces (1.36 ± 0.7; p < 0.05) and polished surfaces (1.55 ± 0.6; p < 0.05). Taken together, our results have shown that titanium plasma treatment directly increased cell viscoelasticity via surface oxidation, and this mechanobiological property subsequently increased biocompatibility.

The research of the interaction between bacteria-surface has great importance for titanium biomedical applications once microorganisms offer risks because promoting implant loss. Therefore, study bacterial adhesion and colonization on titanium is interesting because are principal factors infections pathogeny on biomaterials. In this study, commercial grade II titanium was submitted to nitriding treatment to plasma at 2.2 mbar, using gas mixtures of 80% hydrogen (H2) and 20% nitrogen (N2) during 1 hour and 3 hour. The surfaces were physically and chemically characterized. In order to evaluate bacterial response, the surfaces were exposed to Pseudomonas aeruginosa. The titanium surface modified in nitriding plasma, although exposes a higher roughness as compared with untreated samples, exhibited lower bacterial growth. The nitrided sample for 3 hour exhibited the higher amount of TiN phase and the higher concentration of atomic nitrogen on surface and lower bacterial adhered count. These results were confirmed by scanning electron microscopy. Based on these results can be said to the thermochemical treatment of plasma nitriding on titanium samples results a significant reduction of adherence of Pseudomonas aeruginosa. It was found that the Ti surface nitrided offers significant reduction of bacterial adherence which prevent biofilm formation and offersing lower risk of infection and implant remotion.

Supermartensitic stainless steels (SMSS) are commonly employed in the oil exploitation industry and present a good balance between the necessary physical and chemical properties and financial costs. Certain applications, such as in extreme corrosive and abrasive environments, demand improvements in the surface properties of these steels. In the present work, HP13Cr SMSS with a fully martensitic microstructure were plasma nitrided in the 350–450 °C range. The high diffusivity and low solubility of nitrogen in the martensitic structure allowed the production of thick layers (16–61 μm) containing ɛ-Fe2–3N, γ′-Fe4N and expanded phase (αN) in all the temperatures. In addition, anisotropic sputtering rate and N-diffusion were observed for different grain orientations. Mechanical properties were measured by instrumented indentation, appropriately corrected from roughness effects on the results. Hardness profiles increased from 3.8 GPa (bulk) to ∼14 GPa (near surface region) in all the working temperatures, whereas the elastic modulus was 230 GPa, presenting no statistically significant differences with respect to the bulk value. Nanoscratch tests revealed a hardened-ductile like behavior of these nitride layers. The surface tribo-mechanical behavior was correlated with elastic–plastic responses of the precipitate-containing texturized layers. Results are interpreted in light of the effectiveness of plasma nitriding to modify the surface properties of SMSS.

The mechanical and tribological properties of martensitic AISI 420 (MSS) and supermartensitic HP13Cr (SMSS) stainless steels plasma nitrided using the cathodic cage design were investigated. Nitride compounds were produced in the plasma from the cage´s sputtered ions, which eventually deposited on the electrically isolated sample. Prior to nitriding, samples were austenitized and oil quenched in order to attain a fully martensitc microstructure. Nitriding was carried out at different temperatures (350-450 °C) for 6 h. Mechanical properties and scratch resistance were characterized by instrumented indentation and nanoscratch, and were correlated with morphological and microstructural changes by using atomic force microscopy, scanning electron microscopy, X-ray diffraction and profilometry. Both nitrided MSS and SMSS comprised two distinct regions: (i) an outermost nitride layer (300-800 nm thick) containing deposited e-Fe 2 -3 N and γ´-Fe 4 N nitrides and (ii) a diffusion zone composed of N-expanded martensite phase α N . At 450 °C, diffusion zones thicknesses were 4 μm (MSS) and 6 μm (SMSS). Nitride layers presented intense brittleness under normal and tangential loadings. Critical loads for nitride layer detachment were 49 mN and 127 mN for MSS and SMSS, respectively. However, after removal of the thin nitride layers, the toughened diffusion zones were revealed, being uniformly distributed through the entire sample area. Its hardness was 11 GPa. Such value corresponds to a twofold and threefold increase from the hardness of MSS and SMSS substrates, respectively, which are comparable with other plasma nitrided steels at similar temperature conditions.

A current goal of dental implant research is the development of titanium (Ti) surfaces to improve osseointegration. Plasma nitriding treatments generate surfaces that favor osteoblast differentiation, a key event to the process of osteogenesis. Based on this, it is possible to hypothesize that plasma-nitrided Ti implants may positively impact osseointegration. Objective The aim of this study was to evaluate the in vivo bone response to Ti surfaces modified by plasma-nitriding treatments. Material and Methods Surface treatments consisted of 20% N2 and 80% H2, 450°C and 1.5 mbar during 1 h for planar and 3 h for hollow cathode. Untreated surface was used as control. Ten implants of each surface were placed into rabbit tibiae and 6 weeks post-implantation they were harvested for histological and histomorphometric analyses. Results Bone formation was observed in contact with all implants without statistically significant differences among the evaluated surfaces in terms of bone-to-implant contact, bone area between threads, and bone area within the mirror area. Conclusion Our results indicate that plasma nitriding treatments generate Ti implants that induce similar bone response to the untreated ones. Thus, as these treatments improve the physico-chemical properties of Ti without affecting its biocompatibility, they could be combined with modifications that favor bone formation in order to develop new implant surfaces.

In this work, the influence of working pressure on the characteristics of the layers produced by the nitriding treatment on the AISI 316 austenitic stainless steel surface using the Cathodic Cage Plasma Nitriding technique (CCPN) is assessed. The treatments were carried out at a temperature of 723 K for 5 hours under working pressures of 120, 250 and 500 Pa. The morphology, microstructure and corrosion resistance were studied through optical microscopy, x-ray diffraction, and electrochemical potential curves. We analyzed the effects of working pressure on the layer thickness, microhardness and corrosion resistance. The E×i curves and the electrochemical impedance of polarized samples were measured in order to investigate the effect of the ion transfer inside the produced film placed into the anodic solution. The electrochemical impedance of the films were measured, and showed an apparent capacitive behavior. For treatment under a pressure of 120 Pa we found the nitrides Fe3N, Fe4N and CrN. For treatment at a pressure of 250 Pa, the CrN disappears and the observed phases are the nitrides Fe3N, Fe4N and the S-phase. For a treatment pressure of 500 Pa there is an increase in the corrosion resistance of nitrided layers, confirmed by the predominance of S-Phase in the x-ray diffraction pattern. On the other hand, the sample nitrided under the pressure of 250 Pa showed very unstable impedance behavior when immersed in NaCl solution, indicating that the treatment at this specific working pressure has a negative effect on the corrosion resistance of plasma nitrided AISI 316 stainless steel surfaces.

In this study, we assess how the ratio (N2/H2) – working atmosphere gas mixture – influences the properties of the layers produced on austenitic stainless steel surface by Cathodic Cage Plasma Nitriding (CCPN). The nitriding atmospheres contained nitrogen and hydrogen in three proportions: 20% N2 + 80% H2, 50% N2 + 50% H2, and 80% N2 + 20% H2 delivered at a flow rate of 20 sccm. The effect of 100% N2 was also examined. The morphology, microstructure and electrochemical properties of the layer produced were studied. The samples characteristics were determined by optical microscopy, x-ray diffraction, microhardness test and electrochemical potential curves.

Cylindrical samples of AISI 1020, AISI 316, and AISI 420 steels, with different heights, were simultaneously treated by a new technique of ionic nitriding, entitled cathodic cage plasma nitriding (CCPN), in order to evaluate the efficiency of this technique to produce nitrided layers with better properties compared with those obtained using conventional ionic nitriding technique. This method is able to eliminate the edge effect in the samples, promoting a better uniformity of temperature, and consequently, a smaller variation of the thickness/height relation can be obtained. The compound layers were characterized by X-ray diffraction, optical microscopy, and microhardness test profile. The results were compared with the properties of samples obtained with the conventional nitriding, for the three steel types. It was verified that samples treated by CCPN process presented, at the same temperature, a better uniformity in the thickness and absence of the edge effect.

Nesse trabalho, apresentamos a caracterização estrutural de regiões soldadas em aço austenítico AISI-304, que foram submetidas a processo de nitretação a plasma (20%N2 + 80%H2). Posteriormente as amostras foram hidrogenadas catodicamente. As temperaturas de nitretação foram de 400, 500 e 550°C. As regiões da solda e fora da solda hidrogenadas após a nitretação foram comparadas por DRX, microscopia ótica e microscopia eletrônica de varredura (MEV). As fases austenita-γ, martensita-α', martensita-ε, ferrita-α e os nitretos CrN, γ'-Fe4N e e-Fe2+xN foram identificados. As microestruturas de ambas as regiões e da zona termicamente ativada (ZTA) foram similares. Para 400°C, a estequiometria das fases formadas foi diferente das observadas em 500°C e 550°C. Os efeitos provocados pela hidrogenação foram mais acentuados em 550°C, com o arrancamento da camada nitretada. Structural characterization of weld and outside weld regions of AISI-304 nitrided (20%N + 80%H) and cathodically hydrogenated is presented. Nitriding temperatures were 400, 500 e 550°C. The weld and outside weld regions were compared by XRD, optical microscopy and SEM. The phases γ-austenite, α'-martensite, ε-martensita and α-ferrite and the nitrides: CrN, γ'-Fe4N e e-Fe2+xN were identified. Microstructures of both regions and the thermal active zone were similar. For 400°C the stoichiometry of the formed phases was different from that formed at 500°C and 550°C. Hydrogen effects were more intense for 550°C, due to chipping occurrence.

There is a need for new techniques that modify metallic implant surfaces, resulting in good bone response for low density areas. Among the different techniques, plasma nitriding is being applied in biomedicine with excellent results. However, its use in titanium dental implants is very limited owing to high process temperatures (between 700 and 800°C) that result in distortions. In order to solve this problem, the authors used a new plasma method with a hollow cathode discharge configuration. Ti grade II dental implants were nitrided in a 20% N2–H2 atmosphere at a temperature of 450°C, 150 Pa (1·5 mbar), for 1 h and inserted into rabbit tibias to assess osseointegration. The results showed that plasma nitriding caused a significant change in the surface texture of the nitrided implants and greater removal torque than that of the control implants.

Amostras cilíndricas do aço AISI D2 foram submetidas aos tratamentos térmicos de recozimento, têmpera e revenido e tratadas termicamente em baixas temperaturas para alívio de tensões. Em seguida foram nitretadas em gaiola catódica nas temperaturas de 400 e 480 ºC durante 3 e 4 horas com objetivo de avaliar as melhores condições de tratamento para este material. Nessa técnica as amostras são colocadas num potencial flutuante, dentro de uma gaiola que blinda o potencial catódico. Um estudo sistemático foi realizado para avaliar a eficiência desta técnica na melhoria da dureza deste aço e sem o surgimento dos problemas comuns da nitretação iônica convencional como o efeito de borda. As amostras nitretadas por essa nova técnica apresentaram, para uma duração de tratamento bem inferior, espessuras de camadas, fases cristalinas e durezas, semelhantes àquelas apresentadas na literatura para a nitretação iônica convencional. Observa-se que nas três condições de tratamento térmico, a condição de nitretação que apresentou maior espessura de camada de compostos foi para a duração de 3 horas na temperatura de 480 ºC.

Cathodic cage plasma nitriding is a new growth technique based on multiple hollow cathode effects. The samples are kept at a floating potential inside a cage that acts as a cathode and shields the samples from the cathodic potential. The aim of this work is to perform a systematic study of the properties of nitrided layers as a function of the distance from the nitriding sample surface to the cage wall using this technique. Cylindrical austenitic stainless steel AISI 316 samples were placed in different positions on an alumina plate inside the cathodic cage. The nitrided samples were characterized by optical microscopy, X-ray diffraction and microhardness measurements. The results show that the temperature inside the cage is nearly uniform and that the nitrided layers possess good physical properties and uniformity. Therefore, the differences in the nitrided layer thicknesses obtained at different positions must be due to particle flow reaching the sample surface, depending on how far the sample is from the cage walls.

In recent years, several technologies that modify implant surfaces have been emerged. Among these techniques, the plasma nitriding process has been successfully applied in biomedical field. Nevertheless, its use in dental implants is quite limited owing to the high temperatures of the process (between 700 and 800°C), which causes distortion. In order to solve this problem, a new approach is proposed in the present paper, by which nitriding under a hollow cathode discharge is used to modify surfaces. Grade II Ti plates were submitted to nitriding under hollow cathode discharge conditions and treated at a temperature 450°C and pressure of 150 Pa for 1 h. These showed that plasma nitriding helped bring about a significant change in the surface texture of the treated plates. Furthermore, cell proliferation was 2⋅5 times as high as that of the untreated plates.

Structural, mechanical and tribological properties of AISI 304 steel submitted to nitrogen glow discharge at different atmospheres (N 2 :H 2 , 60:40) and (N 2 :H 2 , 20:80) and substrate temperatures are reported. Expanded austenite γ N and Fe–Cr nitrides were identified as a function of the working conditions. Rietveld refinements indicate that ɛ-Fe 2+ x N is the predominant phase for the poorest nitrogen atmosphere while γ′-Fe 4 N phase is major for the richest one. The nitriding produces a surface hardening that can reach hardness values up to 14 GPa. Thicker nitrided regions are obtained in high nitriding temperatures. Reciprocating sliding tests in samples with rich or poor nitrogen atmosphere indicated long running-in regimes for high nitriding temperature. Both nitrogen atmospheres reduced the wear up to a factor of six even at the lowest temperature process. The nanoscratch tests do not show difference in the surface elastic recovering in all used nitriding conditions.

A series of austenitic stainless steel AISI 316 cylindrical samples with different heights and samples with the same height placed at different positions were simultaneously nitrided using the cathodic cage technique. In this technique the samples are placed on an insulate plate inside a metallic cage which shield the cathodic potential, therefore it stays under a floating potential. A systematic study of the nitriding temperature variation effects was carried out to evaluate the temperature uniformity inside the cage. The samples were characterised through optical microscopy, X-ray diffraction and microhardness measurement. The results were compared with those obtained through conventional ionic nitriding, and it was verified that the samples nitrided by conventional technique present similar surface hardness, less uniformity and lower nitrided layer thickness than the samples treated under similar conditions through this new technique.

Samples of austenitic stainless steel AISI 316 were nitrided using the cathodic cage technique with the addition of methane in the nitriding atmosphere. The aim was to study the influence of this technique in reducing the precipitation of chromium nitrite and in improving the wear resistance. The results show that there was a significant improvement in such properties when compared to the results of ionic plasma nitriding. Formation of a double layer, one more internal composed of carbon and another with high nitrogen content, was confirmed by Scanning Electron Microscopy (SEM). The microhardness profile of the layer showed an increase in hardness values and a larger uniformity, while X-ray analysis showed less chromium nitriding precipitation when compared with results obtained for samples treated using ionic plasma nitriding.

Nowadays, in plastic industry, mills are used to recycle residues generated from the manufacture of plastic components. These mills contain cut blades that suffer accelerated wear, since they are continually submitted to tribological efforts. This fact reduces its useful life. In this work, a new technique of plasma nitriding, called “cathodic cage”, was investigated. This technique eliminates some problems, like restriction rings, inherent of the conventional plasma nitriding. It was used AISI 4340 steel in substitution to AISI 01 steel, normally used in the cut blades manufacture. The AISI 4340 steel was, then, nitrided by conventional and cathodic cage techniques. After this stage, commercial and nitrided cut blades were submitted to analysis of acting. The AISI 4340 steel nitrided by cathodic cage presented uniforms thickness and hardness in the nitrided layer, promoting the average increase of 58% in its useful life, when compared with commercial blades.

A series of AISI 1020 steel cylindrical samples with different heights were simultaneously nitrided in cathodic cage plasma nitriding. In this technique, the samples are placed under a floating potential inside a cage in which the cathodic potential is applied. A systematic study of the nitriding temperature variation effects was carried out in order to evaluate the efficiency of such a technique over the uniformity of the formed layers. The samples were characterized by optical microscopy, X-ray diffraction and microhardness measurement. The results were compared with those ones obtained in the ionic nitriding, and was verified that the samples nitrided by this conventional technique presents less uniformity than the ones treated through this new technique.

In this work, AISI 1010 steel samples were plasma nitrided into 20% N2 plus 80% H2 atmosphere at a pressure of 500 Pa (partial pressure of 100 Pa and 400 Pa for N2 and H2, respectively), temperatures of 500 and 580 °C, during 2 h. Three different procedures for cooling were accomplished after nitriding. In the first procedure the cooling occurred naturally, that is, the sample was kept on substrate holder. In the second one the sample was pulled off and cooling in a cold surface. Finally, in the third cooling process the sample was pulled off the substrate holder down into special reservoir filled with oil held at ambient temperature. The properties of the AISI 1010 steel samples were characterized by optical and electron microscopy, X-ray diffraction, Mossbauer spectroscopy and microhardness tests. Thermal gradient inside the sample kept on substrate holder during cooling process was measured by three inserted thermocouples at different depths. When samples were cooled rapidly the transformation of ϵ-Fe2�3 Nt oγ′-Fe4N was inhibited. Such effect is indicated by the high concentration of ϵ-Fe2�3N phase observed in the compound zone. To get solid state solution of nitrogen in the diffusion zone, instead of precipitates of nitride phases, the cooling rate should be higher than a critical value of about 0.95 °C/s. When this value is reached at any depth of the diffusion zone, two distinct diffusion zones will appear. Temperature gradients were measured inside the samples as a consequence of the plasma treatment. It's suggested the need for standardization of the term “treatment temperature” for plasma treatment because different nitrided layer properties could be reported for the same “treatment temperature”. © 2007 Elsevier B.V. All rights reserved.

Cylindrical samples of 1020 steel and 316 stainless steel were nitrided under the conditions by conventional dc plasma nitriding (DCPN) and by a new technique denominate cathodic cage plasma nitriding (CCPN). The 1020 and 316 stainless steel samples were treated during 3 h and 5 h, respectively, in 773 K and 360 Pa. The samples were characterized by optical microscopy, X-ray diffraction and microhardness testing. All the samples nitrided by DCPN process presented erosion rings on the surface exposed to the plasma. In comparison, in samples nitrided by CCPN, the erosion rings were completely eliminated, without loss of the mechanical properties in the different phases of existence in the nitrided layer.

Standard plasma nitriding of commercially pure Ti or various Ti alloys for human body implants (e.g., hip, knee, shoulder and ankle implants) has already proven useful. However, its use in dental implantology is rather limited due to high nitriding temperatures. The small dental implants of complex geometries are frequently distorted. To solve this problem and benefit from the ability of the plasma treatment to modify the implant surface properties (needed for faster osseointegration process), such as creating different surface topographies, increasing surface roughness, changing local chemical properties by formation of different phases, cleaning/sterilizing contaminated surface and increasing the surface wettability, the titanium disk samples and industrial dental implants were nitrided using a hollow cathode discharge (HCD) configuration of a plasma nitriding system in a 20% N2–H2 atmosphere at pressures of 150 or 250 Pa and temperatures ranging from 400 to 500 °C for 1 or 2 h. The topography of the samples was characterized by optical and electron microscopy. Phases were determined by X-ray diffraction. The surface roughness and wettability were also quantified. Nitrided layer formation having better stability, increased surface roughness and higher wettability has been observed for samples treated at 450 and 500 °C and at a pressure of 150 Pa. Industrially fabricated dental implants were then nitrided at 500 °C/150 Pa for 2 h. The results show capability of HCD in treating dental implants. A significant change in the surface texture and superior wettability of the plasma-treated dental implants, with no geometric distortions, have been observed.

Plasma nitriding of shaped materials and materials of different sizes may yield non-uniform nitrided layers and/or reproducibility problems limiting its industrial-scale use to specific cases. The energy balance at the substrate surface and several non-uniformity effects related to geometry, size and sample position in the chamber during plasma nitriding are discussed. To investigate several of these effects, rods of SAE 1020 steel, of 8 mm in diameter, with different heights (1, 3, 5, 8 and 10 mm) were plasma nitrided in a mixture of N2–H2 (20%) at different temperatures (673, 773 and 843 K) and pressures (200 and 500 Pa). The samples were characterized by optical and electron microscopy, X-ray diffraction and microhardness testing. Hardness increases from the center to the edge of the samples. In the case of samples nitrided at 500 Pa, a macroscopically visible ring is obtained with low hardness inside the ring. The diameter of the ring increases for taller samples. The various formed phases, the thickness of nitrided layer and the microhardness of the samples are directly related to the height of the rod. This is associated with surface energy balance. The results show that the top surface temperature increases with height.

Cylindrical samples of AISI 1020 steel were nitrided, using the techniques of conventional plasma nitriding and cathodic cage. In the latter, the samples are kept at floating potential, inside of a cage that works as a cathode and to shield the samples from the cathodic potential. A systematic study was conducted in order to evaluate the efficiency of this technique in the elimination of edge effect, in comparison with conventional plasma nitriding. In addition, another comparative study of the phases obtained using the conventional plasma nitriding and nitriding with cathodic cage was performed. Two metallic cages were used, one made of austenitic stainless AISI 316 and other one made of AISI 1020 steel, to prove the effect of deposition in nitriding with cathodic cage. The samples which were nitrided by this new technique had shown nitriding rates, crystalline phases, and microhardness, similar to those samples which were nitrided conventionally. However, it was possible to confirm the elimination of edge effect through the characterization by optical microscopy and by microhardness test along the samples surfaces. The samples were characterized by optical microscopy, microhardness tests and X-ray diffraction.

Chromium is an important alloying element present in numerous commercial steels. A systematic study on the nitriding behavior of Fe–Cr alloys is helpful in predicting the properties of nitrided Cr-alloyed steels. Aspects such as microstructural evolution, growth kinetics, and mechanical properties should be particularly emphasized. Fe–Cr alloys containing 5, 10, and 20 wt.% Cr have been arc melted and subsequently plasma nitrided under a N 2 –80% H 2 atmosphere. The microstructure of the resulting nitrided layers was characterized and the microhardness profiles evaluated. Thicker layers developed on low chromium alloys. Differences in hardness profiles were also observed as a function of chromium contents. Nitriding Fe–5% Cr alloys resulted in two discrete fronts, refereed to as the diffusion front and the transformation front. Transformed regions sustained a decrease in hardness from 1000 down to 600 HV, associated with the conversion of homogeneously dispersed fine precipitates into coarser needle like particles immersed in the ferritic matrix. Similar behavior was not observed for the other alloys, where both fronts developed simultaneously.

Modern ion nitriding equipment are powered by pulsed sources in order to prevent arcing and overheating. In industrial applications, the pulse frequency is usually adjusted to set the working temperature. However, frequency variations may drastically affect the plasma species population, and consequently, the microstructure of the final nitrided layer. In this study, AISI-409 steel was nitrided in a mixture of 20% N2–80% H2 using a d.c power source. The depth and microstructure of the nitrided layer were assessed as a function of the time that the voltage was off, toff, in the range of 1–4 ms during a 10 ms pulse cycle. The results suggested that both the microstructure and mechanical behavior of the nitrided layer were affected by toff. Long toff values imply a deleterious effect on the mechanical properties of the nitrided layers.

Aim: To evaluate the proliferative capacity of mesenchymal cells derived from human periodontal ligament on polished and plasma-treated titanium surfaces. Methods: Eighteen titanium disks were polished and half of them (n=9) were submitted to plasma nitriding using the cathodic cage technique. Mesenchymal cells were isolated from periodontal ligament of impacted third molars (n=2) and cultured on titanium disks (polished and nitrided) and on a plastic surface as a positive control of cell proliferation. Cell proliferation was analyzed and growth curves were constructed for the different groups by determining the number of cells adhered to the different surfaces at 24, 48 and 72 h after plating. Results: Higher cell number was observed for the nitrided surface at 24 and 48 h. However, no statistically significant difference in cell proliferation was observed between the two different surface treatments (p>0.05). Conclusions: We concluded that plasma nitriding produced surfaces that permitted the proliferation of human periodontal ligament mesenchymal cells. Associated to other physical and chemical properties, it is possible to assume the feasibility of plasma nitriding method and its positive effect on the early cellular events of osseointegration.

AISI 409 ferritic stainless steel samples were nitrided using the cathodic cage plasma nitriding technique (CCPN), with the addition of methane to reduce chromium precipitation, increase hardness and wear resistance and reduce the presence of nitrides when compared to plasma carbonitriding. Microhardness profiles and X-Ray analysis confirm the formation of a very hard layer containing mainly ε-Fe3N and expanded ferrite phases.

Titanium samples have been used as the substrate that was submitted to a plasma discharge nitriding for the surface treatment of dental implants. Two different arrangements regarding the electrode shapes were tested: planar and hollow cathode. The treated samples were evaluated regarding surface phases, texture, roughness, layer thickness, wettability and visual appearance. The roughness of the surface of all samples submitted to the plasma nitriding process was lower compared to those treated by commercially available technology plasma spray, on the other hand, better wettability was achieved. Some commercially available implants were also treated under the best conditions found with the experiment at titanium samples. After plasma nitriding these implants, tests were carried out to evaluate both wettability and surface texture. As a result the treated implants had both their surface texture and wettability improved.

The growth behavior of plasma-nitrided layers on workpieces with complex geometry was systematically investigated. AISI 316 stainless steel pellets with different heights were nitrided under a mixture of N2–80% H2 at different temperatures (673, 773 and 843 K) and pressures (100 and 500 Pa). Significant differences in thickness and hardness of the resulting nitrided layers were observed as a function of nitriding parameters. The thickness of nitrided layers increased with sample height, excepted those nitrided at 843 K. The diameter of eroded rings, commonly observed on nitrided samples, varied with coupon height. Changes in both layer thickness and eroded ring diameter are presently addressed based on the thermal balance and charge density that take place near the edges of the samples.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior The pulsed plasma nitriding is a solution currently used in the metallurgical industry to resolve problems earlier in the processing of parts by using plasma DC voltage. These problems consisted mainly of edge effect and opening arches caused due to non-uniformity of electric fields on uneven surfaces. By varying the pulse width can reduce these effects. However, variations in pulse width can drastically affect the population of the plasma species and hence the final microstructure of the nitrided layer. In literature, little is known about the effect of process parameters on the properties of the plasma species and, consequently, the surface properties. We have developed a system of nitriding with pulsed source with fixed period of 800  pulse width is variable. Examined the variation of these parameters on the properties of nitrided surface when keeping constant temperature, gas composition, flow, pressure and power. It was found that the values of width and pulse repetition time of considerable influence in the intensities of the species present in plasma. Moreover, we observed the existence of the edge effect for some values of pulse widths, as well as changes in surface roughness and hardness A nitretação por plasma pulsado é uma solução utilizada atualmente na indústria metalúrgica para resolver problemas existentes anteriormente durante tratamento de peças usando plasma de tensão contínua. Esses problemas consistiam, principalmente, em efeito de bordas e abertura de arcos causados devido a não uniformidade de campos elétricos em superfície irregular. Através da variação da largura do pulso é possível reduzir estes efeitos. Entretanto, as variações de largura de pulso podem afetar drasticamente a população de espécies do plasma e, conseqüentemente, a microestrutura da camada nitretada final. Na literatura, pouco se sabe sobre o efeito dos parâmetros do processo nas propriedades das espécies do plasma e, conseqüentemente, nas propriedades superficiais. Neste trabalho foi desenvolvido um sistema de nitretação com fonte pulsada com período fixo de 800 s e largura de pulso variável. Analisou a variação desses parâmetros sobre as propriedades da superfície nitretada quando se mantêm constantes a temperatura, composição do gás, fluxo, pressão e potência. Verificou-se que os valores da largura e tempo de repetição do pulso influem fortemente nas intensidades das espécies presentes no plasma. Além disto, foi observada a existência do efeito de borda para alguns valores de larguras de pulso, bem como variação na rugosidade e dureza superficiais

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior Plasma process like ionic nitriding and cathodic cage plasma nitriding are utilized in order to become hard surface of steels. The ionic nitriding is already accepted in the industry while cathodic cage plasma nitriding process is in industrial implementation stage. Those process depend of plasma parameters like electronic and ionic temperature (Te, Ti), species density (ne, ni) and of distribution function of these species. In the present work, the plasma used to those two processes has been observed through Optical Emission Spectroscopy OES technique in order to identify presents species in the treatment ambient and relatively quantify them. So plasma of typical mixtures like N2 H2 has been monitored through in order to study evolution of those species during the process. Moreover, it has been realized a systematic study about leaks, also thought OES, that accomplish the evolution of contaminant species arising because there is flux of atmosphere to inside nitriding chamber and in what conditions the species are sufficiently reduced. Finally, to describe the physic mechanism that acts on both coating techniques ionic nitriding and cathodic cage plasma nitriding Processos a plasma como nitretação iônica e nitrtetação por gaiola catódica são utilizados para endurecimento de superfícies de aços. A nitretação iônica sendo já consolidada em aplicações industriais enquanto que o processo por gaiola catódica ainda se encontra em estágio de pesquisa. Esses processos dependem dos parâmetros de plasma como temperatura eletrônica e de íons (Te, Ti), densidade de espécies (ne, ni,) e da função de distribuição das mesmas. No presente trabalho, o plasma utilizado para esses dois processos foi diagnosticado utilizando a técnica de Espectroscopia de Emissão Óptica EEO para identificar as espécies presentes no ambiente de tratamento e quantifica-las relativamente. Assim, plasma de mistura gasosa típica como N2 H2 foi monitorado, com o intuito de estudar a evolução dessas espécies durante o processo. Além disso, foi realizado um estudo sistemático, também através de EEO, que acompanha a evolução das espécies contaminantes surgidas em vazamentos de modo a buscar condições onde as mesmas são suficientemente reduzidas. Finalmente busca-se, através do diagnóstico de plasma por EEO, descrever o mecanismo físico de atuação das duas técnicas de tratamento: nitretação iônica e gaiola catódica