© 2018 Universidade Federal de Sao Carlos. All rights reserved.The Friction Stir Welding Process (FSW/P) is an innovative technique to join metals using the plasticity, not occurring the melting. It was initially applied in aluminum alloys, but recently it has been extended to other materials, for example, copper, steel alloys, polimers and others. In this work it is analyzed the thermo mechanical modelling of the energies involved in the FSW process, performed using AA2024-T3 Alclad aluminum alloy. The temperature of the process surface was also calculated in the interval where it was not measured by type k thermocouples, visual inspection, forging force and energy per weld length analysis were also performed. The equations developed in this work were able to describe the behavior found in the experimental data of temperature and energy per weld length, which allows concludes that can be used to define any temperature point in a region of interest.

© Springer Science+Business Media Singapore 2017.The search for alloys with improved high-temperature specific strength and creep-resistance properties for aerospace applications has led in the last decades to sustained research activities to develop new alloys and/or improve existing ones. Titanium and its alloys are excellent for applications in structural components submitted to high temperatures owing to their high strength to weight ratio, good corrosion resistance and metallurgical stability. However, the high affinity to oxygen is one of the main factors that limit their application as a structural material at high temperatures. Materials with adequate behavior at high temperatures and in aggressive environments have become a scientific requirement for technological and economic reasons. The goal of this work is the roughness and creep studies of the Ti–6Al–4V alloy after treatment by the nitrogen Plasma Immersion Ion Implantation (PIII-N) process. The aim of this process is the improvement of the superficial mechanical properties of the Ti–6Al–4V alloy. The selected alloy after ionic implantation process by plasma immersion was submitted to creep tests in 600 °C at 250 and 319 MPa. The techniques used in this work were Auger spectroscopy, Atomic Force microscopy (AFM), X ray, Raman spectroscopy and creep testing. The results show the significant increase of material resistance, it can be used as protection of oxidation in high temperatures applications.

Copyright © 2016 The Authors.NiTi SMA wire with Ni-free surface is desirable as construction materials for a range of biomaterials to actuators associated to shape memory and superelastic properties. In biomaterials a potential problem with NiTi implant devices is the release of Ni in the human body. This work analyzes the effects of nitrogen plasma based ion implantation (PBII) technique in a wire of NiTi with shape memory effect associated to a Ni-free surface. The samples were treated for 60 min at 741 °C, with 16 kV high voltage pulses. Results of the thermo-mechanical properties of the PBII treated samples showed that there is no effect of the PBII treatment on the shape memory effect when compared to NiTi samples with no PBII treatment, which is desirable for applications addressing Ni-free surface and shape memory effect. Although it was noted that the stress-strain test causes cracks perpendicular to the stress direction on the treated surface.

Transition metal nitrides present high hardness, good wear resistance and chemical stability. The formation of a surface layer of these materials on different types of substrates can improve surface properties without changing bulk characteristics. Molybdenum is used in many technological applications and the search for ways to effectively improve its properties is justified. In this work nitrogen ions were implanted into molybdenum by means of high temperature plasma based ion implantation (HTPBII), in order to produce a layer of molybdenum nitride on the surface of the material. The treatment was performed in the temperature range of 800-1200°C, for 1 h. X-ray diffraction spectra showed the presence of the cubic-Mo 2 N phase in most of the samples. The tetragonal-Mo 2 N phase was also observed, depending on treatment conditions. Glow discharge optical emission spectroscopy was used to study the composition and thickness of the nitride layer. A 12 μm thick Mo 2 N layer was observed for samples treated at 1100°C, although beyond this temperature threshold, a significant amount of nitride can no longer be produced. In relation to the surface mechanical properties, a ninefold increase in surface hardness was obtained, as well as a decrease in the friction coefficient. Wear against an alumina ball was not observed. © 2014 Elsevier B.V.

© Springer International Publishing Switzerland 2014.The advancement of technology leads to the development of new materials improving their tribology properties. It can be noticed in different areas like aerospace industry, chemical and oil that need resistant material in high temperatures and aggressive environments. In this case, it is important to think in its tribological properties, like wear, oxidation, toughness, and hardness. An effective mean, economic and with easy application is the plasma immersion ion implantation (PIII) technique. In the case of difficult shapes, the material can be equally treated. In this work, the Ti-Al-4V alloy was submitted to PIII during 2 and 3 h. The comparative analysis to determine which of which time was more efficient related to the tribological improvement measured by Auger, X-ray diffraction and wear. It will be observed images by MEV of the alloy submitted to PIII treatment.

© (2014) Trans Tech Publications, Switzerland.Titanium and its alloys are largely used for many industrial applications due to their high mechanical and corrosion resistance and low specific mass. Ti-6Al-4V alloy is the most used in aerospace industry and it is applied for the manufacturing of aircraft blades and steam turbines. This alloy has high affinity with oxygen which constrains its application at high temperatures due to creep resistance reduction. Methods to increase creep resistance of Ti-6Al-4V alloys includes the use of metallic coatings and its combination with ceramic thermal barrier coating deposition on the material surface. The aim of this work is to compare the creep behavior of Ti-6Al-4V alloy in three different conditions: uncoated, metallic coated, metallic + ceramic coated specimens. The metallic coating layer (CoNiCrAlY) and the ceramic coating (ZrO2 + 8wt%Y2O3) are both applied by plasma spray deposition technique. The specimens were submitted to constant load creep tests at 600ºC and stress conditions of 125, 250 and 319MPa. Specimens of metallic + ceramic coating have presented higher creep resistance, longer lifetime and lower stationary creep rate when compared to uncoated and metallic coated specimens.

© (2014) Trans Tech Publications, Switzerland.Titanium alloys are widely used in machine building, aircraft manufacturing, medicine, motors, chemistry, and biomedicine due to their high strength-to-weight ratio, elasticity, corrosion resistance, and biocompatibility. In particular, Ti-6Al-4V containing (α + β) structure plays a very important role in aerospace industry in the manufacturing of components such as disks and blades for aircrafts turbines and structural forgings. However, one of the major factors limiting the life of titanium alloys in service is their degradation due to gaseous environments, in particular, to environments containing oxygen at elevated temperatures during long-term use. The sensitivity of titanium alloys to high-temperature exposure is a well-known phenomenon. When titanium alloys are heated to temperatures above approximately 800ºC, oxygen, hydrogen and nitrogen can penetrate into them. The penetration of these elements increases hardness and brittleness while decreasing the toughness of the alloy. Laser surface nitriding is a technique used to modify the nearsurface microstructure and/or composition by melting the surface using a high-power laser beam with reactive gas as a shrouding environment, forming a nitride layer on the surface of Ti–6Al–4V to improve the alloy’s tribological and mechanical properties. The results of laser gas nitriding of Ti–6Al–4V showed a significant increase of microhardness and enhanced erosion resistance significantly compared with untreated Ti–6Al–4V, since the nitride layer acts as a diffusion barrier for inward oxygen diffusion into the alloy, reducing the contribution of oxygen dissolution in the substrate to the total mass gain. Other important technique that was developed for the beneficial modification of surface sensitive properties is Nitrogen Plasma Immersion Ion Implantation N-PIII. A sample is immersed in plasma and subjected to negative high-voltage pulses. In the electrical field, the ions are accelerated to high energies and incorporated into the sample. Enhancing of the hardness and wear process of the materials due to the N-enriched layer caused by diffusion of N in the sample at PIII process can be expected. Both techniques provide an improvement in the creep resistance. The objective of this work was evaluating the creep resistance of the Ti-6Al-4V alloy with superficial treatments of laser nitriding and Nitrogen Plasma Immersion Ion Implantation NPIII in creep test of Ti-6Al-4V alloy. It was used Ti-6Al-4V alloy as cylindrical bars under forged and annealing of 190 ºC by 6 hours condition and cooled by air. The Ti-6Al-4V alloy after the superficial treatment of laser nitriding and N-PIII was submitted to creep tests at 600 ºC in the stress of 250 MPa and 319 MPa, under constant load mode. The creep parameters are determined and a comparative analysis is established with the results gotten from the alloy with both treatments. The laser nitrided has showed an improved creep behavior compared with the same alloy with N-PIII coating, with a reduction in the creep rate and increasing the creep lifetime.

The substitution of conventional components for NiTi in distinct devices such as actuators, valves, connectors, stents, orthodontic arc-wires, e.g., usually demands some kind of treatment to be performed on the surface of the alloy. A typical case is of biomaterials made of NiTi, in which the main drawback is the Ni out-diffusion, an issue that has been satisfactorily addressed by plasma based ion implantation (PBII). Even though PBII can tailor selective surface properties of diverse materials, usually, only thin modified layers are attained. When NiTi alloys are to be used in the harsh space environment, as is the case of devices designed to remotely release the solar panels and antenna arrays of satellites, e.g., superior mechanical and tribological properties are demanded. For this case the thickness of the modified layer must be larger than the one commonly achieved by conventional PBII. In this paper, new nitrogen PBII set up was used to treat samples of NiTi in moderate temperature of 450 °C, with negative voltage pulses of 7 kV/250 Hz/20 μs, in a process lasting 1 h. A rich nitrogen atomic concentration of 85 at.% was achieved on the near surface and nitrogen diffused at least for 11 μm depth. Tribological properties as well as corrosion resistance were evaluated. © 2012 Elsevier B.V.

The NiTi shape memory alloys (SMA) are employed in various applications, thanks to its specific mechanical properties. However, for many applications, it is interesting to improve its surface mechanical resistance to tribological or chemical attacks. This work aims to analyze the effects of nitrogen plasma based ion implantation (PBII) technique on the surface of NiTi produced by electron beam melting (EBM). The samples were treated for 120min (550°C and 770°C) and 360min (550°C), with 16kV high voltage pulses. The surfaces were analysed by X-ray diffraction (XRD), white light interferometry (WLI) and glow discharge optical emission spectrometry (GDOES). In addition to martensitic and austenitic NiTi, the XRD analysis shows the appearance of titanium nitride TiN and Ni 3Ti phase in the PBII treated samples. Whereas the untreated specimen presents a RMS roughness R RMS around 16nm, the PBII treatments were shown to increase it, from 44nm, at 550°C, to 82nm at 770°C. The nitrogen incorporation ranges from 150nm (at 550°C, whatever the duration), up to more than 500nm (770°C) thanks to temperature activated diffusion. The increase of R RMS may be explained by the sputtering effect but it may be linked to the presence of a buried oxi-nitride phase grown by diffusion at higher temperature. © 2011 Elsevier B.V.

The search for alloys with improved high-temperature specific strength and creep-resistance properties for aerospace applications has led in the last decades to sustained research activities to develop new alloys and/or improve existing ones. Titanium and its alloys are excellent for applications in structural components submitted to high temperatures owing to their high strength to weight ratio, good corrosion resistance and metallurgical stability. Its high creep resistance is of great importance in enhancing engine performance. However, the affinity by oxygen is one of main factors that limit its application as structural material at high temperatures. Materials with adequate behavior at high temperatures and aggressive environmental became a scientific requirement, technological and economically nowadays. The objective of this work is the mechanical and microstructural characterization of the Ti-6Al-4V alloy after treatment by nitrogen Plasma Immersion Ion Implantation (PIII) process. The aim of this process is the improvement of superficial mechanical properties of the Ti-6Al-4V alloy. The selected alloy after ionic implantation process by plasma immersion was submitted to creep tests at 600°C, in constant load mode at 250 and 319 MPa. The techniques used in this work were optical microscopy and scanning electronic microscopy. The fractograph analysis of the samples tested in creep shows narrowing phenomena and microcavities. The creep results show the significant increase of material resistance, it can be used as protection of oxidation in high temperatures applications. © (2012) Trans Tech Publications, Switzerland.

NiTi SMA is a promising material in the biomedical area due to its mechanical properties and biocompatibility. However, the nickel in the alloy may cause allergic and toxic reactions and thus limiting its applications. It was evaluated the influence of surface modification in NiTi SMA by nitrogen plasma immersion ion implantation (varying temperatures, and exposure time as follows: <250 °C/2 h, 290°C/ 2 h, and 560°C/1 h) in the amount of nickel released using immersion test in simulated body fluid. The depth of the nitrogen implanted layer increased as the implantation temperature increased resulting in the decrease of nickel release. The sample implanted in high implantation temperature presented 35% of nickel release reduction compared to reference sample. © ASM International.

This study aims to investigate the creep resistance of the Ti-6Al-4V alloy after surface modification by plasma immersion ion implantation (PIII). For the PIII treatment it was used nitrogen gas (ion implantation) to the formation of plasma, the material was treated for 100 minutes. After PIII treatment the samples were analyzed using the techniques of X-ray diffraction, spectrometry energy dispersive X-ray and atomic force microscopy. The creep tests were realized at 600°C, at constant load of 250 and 319 MPa. After the creep tests the samples were analyzed by optical microscopy and scanning electron microscopy. By chemical analysis by X-ray and EDS it is possible to determinate the Ti2N on the surface. Through the study of the creep curves it is observed an increasing in creep resistance of the alloy after PIII treatment. Copyright © (2010) by Associação Brasileira de Metalurgia Materiais e Mineração (ABM).

Superalloy are alloys developed for elevated temperatures applications, where relatively severe mechanical stressing is found, and a high surface stability is frequently required. Improvements in the surface properties of a wide range of alloys have been obtained by the implantation of nitrogen while field test results for industrial tools and components from a diverse range of applications have been positive. The objective of this work is to improve the mechanical surface properties of Inconel 718 by PIII (Plasma Immersion Ion Implantation - PIII). In these experiments, samples of Inconel 718 without heat treatment are used. Nitrogen ions in Inconel samples were implanted: a) for a period of one hour, and b) for a period of 3 hours. Tribological properties of PIII treated samples were compared with the ones for untreated samples are compared. The best result is obtained for the samples treated for 3 hours after 5000 cycles of an unlubricated pin-on-disk test, with very little wear.

The objective of this work was evaluating the creep resistance of the Ti-6Al-4V alloy with superficial treatment of PIII superficial treatment and ceramic coating in creep test of Ti-6Al-4V alloy. It was used Ti-6Al-4V alloy as cylindrical bars under forged and annealing of 190°C by 6 hours condition and cooled by air. The Ti-6Al-4V alloy after the superficial treatment of PIII and ceramic coating was submitted to creep tests at 600°C and 250 and 319 MPa under constant load mode. In the PIII treatment the samples was put in a vacuum reactor (76×10-3 Pa) and implanted by nitrogen ions in time intervals between 15 and 120 minutes. Yttria (8 wt.%) stabilized zirconia (YSZ) with a CoNiCrAlY bond coat was atmospherically plasma sprayed on Ti-6Al-4V substrates by Sulzer Metco Type 9 MB. The obtained results suggest the ceramic coating on Ti-6Al-4V alloy improved its creep resistance © (2010) Trans Tech Publications.

In order to achieve improved surface in components with high reliability required by the tool or metallurgical industries by means of plasma immersion ion implantation (PIII), it is necessary to obtain quite thick treated layers with reasonable thickness uniformity. One effective way to achieve such a thick nitrogen-rich layer in Ti-6Al-4V alloy is to run PIII process in high temperatures of about 800 °C. In these experiments, we heated the sample-holder and subjected the Ti-6Al-4V samples to nitrogen glow discharge PIII with relatively low peak voltages (5 kV). We also treated the Ti-6Al-4V samples by the traditional PIII method, increasing slowly the high voltage pulse intensities, and at the end of processing, reaching temperatures of up to 350 °C. These modes of treatments were compared with respect to nitrogen implantation profiles, tribological and mechanical properties. Nitrogen profiles measured by AES showed that auxiliary heating leads to richer and deeper layers. The best results were obtained for the samples treated for 4 h that, after 25,000 cycles in unlubricated pin-on-disk test, presented very small wear (reduction of 89%). In spite of friction coefficient being higher in the beginning of the test, probably due to the increase of the average roughness (Rms) in the surface of the treated material, it decreases when the rough surface wears away, due to the reduction of frictional force necessary to slide the pin on the sample. The material treated at 800 °C presents high wear resistance, which is desired in this alloy, that normally possesses excellent mechanical properties, however, poor tribological properties. © 2009 Elsevier B.V. All rights reserved.

Ti-6Al-4V alloy is one of the most frequently used Ti alloys with diverse applications in aerospace and biomedical areas due to its favorable mechanical properties, corrosion resistance and biocompatibility. Meanwhile, its surface can suffer intense corrosion caused by wear processes due to its poor tribological properties. Thus in the present study, PIII processing of Ti-6Al-4V alloy was carried out to evaluate its corrosion resistance in 3.5% NaCl solution. Two different sets of Ti-6Al-4V samples were PIII treated, varying the plasma gases and the treatment time. The corrosion behavior is correlated with the surface morphology, and the nitrogen content. SEM micrographs of the untreated sample reveal a typical two-phase structure. PIII processing promotes surface sputtering and the surface morphology is completely different for samples treated with N2/H2 mixture and N2 only. The highest penetration of nitrogen (∼ 88 nm), corresponding to 33% of N, was obtained for the sample treated with N2/H2 mixture for 1:30 h. The corrosion behavior of the samples was investigated by a potentiodynamic polarization method. A large passive region of the polarization curves (∼ 1.5 V), associated with the formation of a protective film, was observed for all samples. The passive current density (∼ 3 × 10- 6 A cm- 2) of the PIII-treated Ti-6Al-4V samples is about 10 times higher than for the untreated sample. This current value is still rather low and maintains good corrosion resistance. The anodic branches of the polarization curves for all treated Ti-6Al-4V samples demonstrate also that the oxide films break down at approximately 1.6 V, forming an active region. Although the sample treated by N2/H2 mixture for 1.30 h has thicker nitrogen enriched layer, better corrosion resistance is obtained for the PIII process performed with N2 gas only. © 2007 Elsevier B.V. All rights reserved.

The present work is aimed to analyzing the influence of the plasma potential in the efficiency of plasma immersion ion implantation (PIII) process with nitrogen, at high temperatures (550 °C and 800 °C), applied to the Ti6Al4V alloy to increase its wear resistance. Treatments with plasma potentials (PP) at 420 V and 90 V were carried out. In the first case, in accordance with AES (Auger Electron Spectroscopy) analysis, nitrogen rich layers of 100 nm and 150 nm of thickness had been obtained, for total treatment times of 60 min and 120 min, respectively. For the treatments with lower PP of 90 V, the treated layers thicknesses have been measured by GDOS (Glow Discharge Optical Spectroscopy) and their values are 1 μm and 1.5 μm for treatments of 120 min and 240 min, respectively. The hardness values were determined for the samples treated with high PP by nanoindentation technique and a significant increase was observed for this treatment, reaching 11 GPa (60 min) and 19 GPa (120 min), which can be compared to 3.5-4.0 GPa obtained for the untreated samples. Pin-on-disk wear tests show that wear resistance increases after all these treatments. The friction coefficient as well as the wear rates are measured with a tribometer. © 2007 Elsevier B.V. All rights reserved.

We have performed high temperature nitrogen plasma immersion ion implantation (PIII) of Ti6Al4V by heating the samples for up to 800 °C, using tungsten filaments inside the sample holder. Ion implantation was done with the high voltage pulser at 5 kV, 40 μs duration and 400 Hz frequency, and a nitrogen glow discharge as the plasma source. Nanoindentation analysis of the treated surface indicated an improvement of 5 times in hardness for PIII treatment of 120 min. X-ray diffraction indicated the formation of Ti2N. Auger Electron Spectroscopy (AES) showed that the peak concentration is greater than 30% in the implanted nitrogen with the maximum penetration of 150 nm for the sample treated during 120 min. © 2006 Elsevier B.V. All rights reserved.

Nitrogen implantation into Ti alloys at higher temperatures improves their mechanical and corrosion resistance properties by forming a thicker nitride layer. In this paper, two different sets of Ti-6Al-4V samples were plasma immersion ion implantation (PIII)-treated using nitrogen plasma, varying the treatment time from 30 to 150 min (800 °C) and the process temperature from 400 °C 800 °C (t = 60 min). Nanoindentation measurements of the PIII-treated samples at 800 °C during 150 min showed the highest hardness value, 24 GPa, which is about four times bigger than untreated sample hardness. The N penetration at these conditions reached approximately 150 nm as analyzed by Auger spectroscopy. On the other hand, the lowest passive current density (3 × 10-7 A · cm-2) was obtained for a PIII-treated sample during 30 min at higher temperature (800 °C). The corrosion resistance of this sample is almost the same as for the untreated specimen. Corrosion behavior evidenced that in strong oxidizing media, all PIII-treated samples are more corrosion resistant than the untreated one. PIII processing at higher temperatures promotes smoothing of the sample surface as observed by scanning electron microscopy (SEM). Grazing incidence X-ray diffraction analyses of the untreated samples identified the two typical Ti phases, Ti α and Ti β. After the implantation, Ti2N and TiO2 phases were also detected. © 2006 IEEE.

Ti-6Al-4V samples have been treated by PHI processing at different temperatures (400-800°C), treatment time (30-150 min) and plasma potential (100 and 420 V). Hardness measurements results showed an enhancement of the hardness for all implanted samples. XRD results detected the Ti2N phase and the best corrosion resistance was found for the samples processed at higher temperature and lower PIII time.

Based on the fact that the Ti-6A1-4V alloy has good mechanical properties, excellent resistance to corrosion and also excellent biocompatibility, however with low wear resistance, this work aims to test plasma processes or combination of plasma and ion implantation processes to improve these characteristics. Two types of processing were used: two steps PIII (Plasma Immersion Ion Implantation) combined with PN (Plasma Nitriding) and single step PIII treatment. According to Auger Electron Spectroscopy (AES) results, the best solution was obtained by PM for 150 minutes resulting in ∼ 65 nm of nitrogen implanted layer, while the sample treated with PIII (75 minutes) and PN (75 minutes) reached ∼ 35 nm implanted layer. The improvement of surface properties could also be confirmed by the nanoindentation technique, with values of hardness increasing for both processes. AFM (Atomic Force Microscopy) characterization showed that the single step PIII process presented greater efficiency than the duplex process (PIII + PN), probably due to the sputtering occurring during the second step (PN) removing partially the implanted layer of first step (PIII).

Thermal or radiation enhanced diffusion of nitrogen are extensively utilized for the surface hardening of metallic components. Plasma-immersionion implantation (PIII) is a newly developed technology, which rovides ion implantation at moderate energy (10-50 keV), and thereby allowing penetration depths deeper than the surface oxide barrier. The damage caused by ion implantation together with the surface sputtering may create favorable boundary conditions for an efficient subsequent diffusive treatment such as nitriding. Surface modification of aluminum alloy 5052, Ti6Al4V alloy and steels (AISI 304 and H13) by a combination of PIII and plasma nitriding (PN) has been investigated. Nitrogen ions were implanted into specimens at 15 kV and then ion nitrided at low pressure with bias of -800 V. Compared to the untreated samples the hardness of Ti6Al4V alloy and AISI 304 steel could be improved significantly. The hardness of H13 steel can be increased by 20% using a duplex process with 4-h nitriding time. X-ray diffraction (XRD) results have shown some structural modification of the metallic samples and formation of a double-layer structure in AISI 304, treated by PIII and PN. Nitrogen depth profile of the same stainless steel sample, obtained by Auger electron spectroscopy (AES), shows two rather well-defined nitrogen enriched regions with different N contents: high (25-30 at.%) in a surface layer and medium (∼10%) in a subsurface layer. © 2004 Elsevier B.V. All rights reserved.

The 6XXX series aluminum alloys (Al-Mg-Si) are widely used in many different engineering and architectural applications. These alloys usually undergo a thermal treatment, which consists of a heat treatment solution and artificial aging, since the desirable mechanical properties depend on the microstructural state of the material. The recycling of materials has been increasing recently for economic and ecologic reasons. By using scrap as raw material, important reductions in energy and total costs can be achieved, and, at the same time, negative environmental impacts can be greatly reduced. In the present work, the possibility of using a larger amount of scrap as raw material in the production of an AA 6060 alloy is evaluated by analyzing the difference in microstructure and mechanical properties between a commercial 6060 alloy and a variation with higher Fe and lower Si contents that was specially produced for this study. Both materials were placed into a heat treatment solution at 560°C for 1 h, and then underwent water quenching followed by artificial aging at 180°C for different periods of time. Hardness and tension tests were used to evaluate the mechanical properties. Light and transmission electron microscopy have been used to determine important features such as grain size before and after being placed into the heat treatment solution, and the characteristics of the second-phase particles in the two materials. This study leads to the conclusion that a higher amount of scrap material can be used in the production of 6060 Al alloy without significant changes in mechanical properties compared with the more usual compositions.

The present work was aimed to study the improvement of mechanical characteristics of the Ti6Al4V alloy surface, induced by ion nitriding process. The increase of hardness and other improvements of the Ti6Al4V alloy surface allow wider applicability of this material in several industrial areas, in particular, biocompatibility applications. One of the used processes was Plasma Immersion Ion Implantation (PIII), where the three-dimensional samples can be homogeneously treated. In such technique, the target is surrounded by the plasma and then pulse biased to high negative voltage. Another technique studied in this article was the process of nitrogen plasma jet. In this case, a reactor of low plasma density is the source of an expansion gas through a constriction hole that separates the source chamber from the vacuum chamber, where the nitriding is processed. Physical and chemical characterizations of nitrided samples were carried out to formulate the correlations between superficial characteristics of the material and of the parameters of the ion nitriding process.

To improve the performance of critical part components, new methods for surface strengthening are being developed with success, like plasma immersion ion implantation (PHI) and hybrid surface treatments mixing PIII and ion nitriding processes. A combination of high pressure (4 × 10 1Pa), moderate temperature (up to 450°C) glow discharge nitriding with low pressure (8 × 10-2Pa) and low DC bias voltage ion nitriding (or DC PHI) was implemented. Depending on the particular conditions of the treatment and the depth probed, mixed phases of γ N and ε were measured in the treated SS304 steel sample. This near surface modification resulted in an improved hardness (up to a factor of 2.7 ×) of the sample which could also enhance its wear properties. Surface modification of Ti6Al4V alloy and SS304 steel by a combination of PHI and subsequent ion nitriding was investigated as well. Nitrogen ions were implanted into the specimens at 15 keV and then ion nitrided at low pressure (7 × 10-2Pa) with a bias of -800 V. Compared to the untreated samples, the hardness of Ti6Al4V alloy and the steels could be improved significantly. AES results indicated high retained doses in both samples, confirming the high efficiency of this hybrid process.

Samples of AISI 304 austenitic stainless steel were treated by a modified ion nitriding process. The process consists of a nitriding cycle at high pressure and temperature, followed by a cycle at low pressure under the high temperature attained in the first cycle. These treatments were performed using two gas mixture of (N 2/H 2):(50/50) and (80/20). Results of glancing and normal X-ray diffraction showed clearly the standard austenite ã-phase, the expanded austenite ã N-phase, induced by the presence of nitrogen atoms in solid solution and also the martensite á-phase. Microhardness Vickers tests, with 25gf load, showed surface hardness 1.8 to 2.7 times higher than the standard AISI 304 value. These results were attained within treatment times ranging from 70 to 150 min. These times are very short, compared with more classical nitriding processes.

The aim of this work is to modify Ti-6Al-4V alloy surface properties, to improve its tribological behavior and biocompatibility. The process used is Plasma Immersion Ion Implantation (Pill), where the tridimensional samples are homogeneously treated. The titanium alloy specimens are treated for time intervals between 15 and 120 minutes and subsequently characterized by techniques: AES, ball-on-disc and nanoindentation. AES can confirm titanium nitride presence on surface, however this modified layer is very thin, around 40 nm of thickness for specimens treated around 90 minutes of implantation. The tribological properties improvement is confirmed through ball-on-disc test, where coefficient of friction decreases from 0.7 for the untreated sample and to 0.15-0.2 for the sample treated during 45 minutes. Nanoindentation test permits to verify that mechanical properties are improved with hardness increasing around 50% more than original values.

Plasma immersion nitrogen implantation of Ti6Al4V (TAV) alloy was carried out to improve the surface tribological properties of test samples for artificial heart valves. Our results show that a good implantation with nitrogen peak concentration of 40% was achieved but with only approximately 50 nm implanted layer, after 60 min of treatment. Longer treatments showed no improvement in the retained dose, probably due to sputtering effects. However, both significant reduction of friction coefficient and increase in hardness was seen even for such a shallow implantation. Furthermore, the hardness improvement extended to regions much deeper than the implanted layer. Improvements of the wear resistance of such nitrogen implanted Ti alloy is expected, increasing considerably the useful lifetime of components made of TAV which is finding widespread use in biomedical and aerospace applications. © 2003 Elsevier Science B.V. All rights reserved.