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Transition metal nitrides, as is the case of NbN, exhibit an attractive mixture of physical, chemical and mechanical properties and can be used to overcome a severe constraint of pure niobium, that is the high oxidation rate for temperature above 400 °C. In this work nitrogen ions were implanted into niobium by means of plasma based ion implantation (PBII) and high temperature PBII (HTPBII) in order to produce NbN on the surface of the material. In the case of HTPBII the treatment was performed in the temperature of 1000 °C and 1250 °C. In the process, negative pulses of 10 kV/20 μs/500 Hz were applied to Nb samples for 1 h. The depth of the modified layer reached up to 4.5 μm due to the diffusion of nitrogen atoms implanted into the material. X-ray diffraction spectra showed the presence of ɛ-NbN, β-Nb2N and γ-Nb4N3 phases. Wear rate was reduced from 1.5 × 10−2 mm3/Nm up to 2.6 × 10−6 mm3/Nm for treated samples at high temperature in comparison with pristine samples, while friction coefficient was reduced from 0.8 to 0.25. Hardness was significantly increased. Surface topography was measured by optical profilometry. Surface roughness increases with the sample temperature but it remains lower than the one obtained by conventional PBII, very probably due to the heating method, which was performed by electron bombardment.

Ion nitriding is an important surface modification technique used routinely in the advanced technology industries aiming at producing high added value components with increased hardness and wear resistance. To further improve the performance of critical-part components, new methods for surface strengthening are being developed with success, like plasma immersion ion implantation (PIII) and hybrid surface treatments combining PIII and ion nitriding. In particular, a combination of high-pressure (40 Pa), high-temperature (up to 450 degreesC) glow discharge nitriding with low-pressure (8 x 10(-2) Pa) ion nitriding was implemented. Analysis of the SS304 samples treated by this hybrid method was carried out using the technique of grazing incidence X-ray diffraction (GIXRD) and the results were supported by both normal XRD and AES (Auger electron spectroscopy) measurements. Depending on the particular conditions of the treatment and the depth probed, mixed phases Of gamma(N), and gamma were measured. The improvement in hardness of the obtained surfaces (up to a factor of 2.7) was also in accordance with the results of other analysis.

Thermal or radiation enhanced diffusion of nitrogen are extensively utilized for the surface hardening of metallic components. Plasma-immersion ion implantation (PIII) is a newly developed technology, which provides 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.

Surface modification of ultra-high molecular weight polyethylene (UHMWPE) has been explored by using the non-line-of-sight plasma immersion ion implantation (PIII) technique. The polymer specimens, immersed in nitrogen plasma, were pulsed through a metallic grid at repetition rate of 100 Hz with negative high-voltage pulse of 15 kV magnitude and 10 μs duration. The UHMWPE's structural changes induced by the PIII were analyzed by laser Raman spectroscopy (LRS) at 514.5 nm, X-ray photoelectron spectroscopy (XPS) and optical microscopy. From the Raman spectra it is observed that the chain structure of UHMWPE has been damaged due to ion bombardment and a layer of hydrogenated amorphous carbon is formed. The ratio of sp3/sp2 bonded carbon in the modified layer was obtained by suitable fitting of the XPS C 1s energy peak, using a four-curve fitting procedure, which recognizes a portion of C–O and CO surface bonding. The XPS results for N 1s peak show that the implanted nitrogen ions form chemical bonds with the polymer instead of forming precipitates by self-clustering.

Historical perspective of the development of PIII devices at the Instituto Nacional de Pesquisas Espaciais (INPE) is given, together with the description of the present system under operation and our overall results on this three-dimensional implantation research. Starting with an ignitron switched pulser (1 pulse per 3 min) and an intermittent microwave plasma, we improved our PIII system developing a pulse forming network (PFN) based pulser (20 Hz), 2 years later. We also improved our plasma source towards a DC, highly stable, medium density glow discharge system. A much faster hard tube pulser was recently incorporated to our PIII system (670 Hz) allowing us to achieve good implantation results in different materials. Presently, we are testing a recently purchased RUP-4 commercial pulser to obtain arc prevented, 1.1 kHz, square pulses for new experiments in this active field of PIII research.

A simple dc glow discharge with controlled plasma floating potential was applied as a novel source for plasma immersion ion implantation with excellent results. The glow discharge source is normally used for the conditioning of fusion device chambers, taking advantage of the available high accelerating potential which is necessary for the ion bombardment of the walls. Combining an electron-emitting hot filament with this source, it was possible to get a stable discharge at pressures as low as 8?10-4 mbar and, operating it with potentials lower then 70?V, it was possible to reduce the Si sample etching down to zero from 2500???seen at potentials of native 350?V, when exposure times of 750?min were used in the sample's surface subjected to plasma ion implantation of nitrogen. As a result, retained ion doses of 1.5?1017?cm-2 were obtained in etching-free Si surfaces.

Submitted by Guilherme Lemeszenski (guilherme@nead.unesp.br) on 2013-08-22T19:05:36Z No. of bitstreams: 1 S1516-14392005000400005.pdf: 417271 bytes, checksum: 28e0f9540157285bec292ac9bd4b9fde (MD5) Made available in DSpace on 2013-08-22T19:05:36Z (GMT). No. of bitstreams: 1 S1516-14392005000400005.pdf: 417271 bytes, checksum: 28e0f9540157285bec292ac9bd4b9fde (MD5) Previous issue date: 2005-12-01 Made available in DSpace on 2013-09-30T18:11:07Z (GMT). No. of bitstreams: 2 S1516-14392005000400005.pdf: 417271 bytes, checksum: 28e0f9540157285bec292ac9bd4b9fde (MD5) S1516-14392005000400005.pdf.txt: 10126 bytes, checksum: 546c8befe19179c7a2903352a6b90bd4 (MD5) Previous issue date: 2005-12-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T13:27:55Z No. of bitstreams: 2 S1516-14392005000400005.pdf: 417271 bytes, checksum: 28e0f9540157285bec292ac9bd4b9fde (MD5) S1516-14392005000400005.pdf.txt: 10126 bytes, checksum: 546c8befe19179c7a2903352a6b90bd4 (MD5) Made available in DSpace on 2014-05-20T13:27:55Z (GMT). No. of bitstreams: 2 S1516-14392005000400005.pdf: 417271 bytes, checksum: 28e0f9540157285bec292ac9bd4b9fde (MD5) S1516-14392005000400005.pdf.txt: 10126 bytes, checksum: 546c8befe19179c7a2903352a6b90bd4 (MD5) Previous issue date: 2005-12-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) SAE 1020 construction steel is widely used as mortar reinforcement and small machine parts, but aside good surface properties as high ductility, hardness and wear resistance, its surface is prone to severe corrosion. As it is known, Chromium in amount over 12%-13% in the Fe alloys renders them resistance to several corrosive attacks. SAE 1020 samples were recovered with Chromium film and then bombarded either by nitrogen Ion Beam (IB) or Plasma Immersion Ion Implantation (PIII) to recoil implant Cr atoms in the Fe matrix. Samples treated by 100 keV N+ IB showed irregular, thin Cr profile, remaining a part of the film on the surface, to about 10 nm. Samples treated by 40 kV N PIII presented Cr layer of about 18% at., ranging to around 90 nm. Cr of the film was implanted in the Fe matrix in an almost flat profile. Results of corrosion test showed good performance of the PIII treated sample. The IB treated sample showed some enhancement over the non-treated reference and the only Cr film deposited sample showed no modification on the corrosion behavior as compared to the non-treated reference sample. Instituto Nacional de Pesquisas Espaciais Laboratório de Combustão e Propulsão Science and Technology Analyst INPE LAP Laboratório Associado de Plasma INPE LAP Laboratório Associado de Sensores e Materiais UNESP FEG Depto. de Física e Química Forschungszentrum Rossendorf UNESP FEG Depto. de Física e Química

As an effort to improve the corrosion behavior of the mild steel under work conditions, we attempted to produce a high chromium content layer on its surface by applying the recoil implantation process. After polishing, SAE 1020 construction steel samples were covered with chromium and then bombarded with ions. As recoil bombarding atom, we used nitrogen, a light mass specimen. Recoil atoms were applied either by ion beam (IB) accelerator or by plasma immersion ion implantation (PIII) method. Samples treated by the PIII process showed better results, presenting a thicker layer of high Cr content, as measured by Auger electron spectroscopy (AES). The presence of nitrogen, from hitting process, caused little effect on the surface hardness, as SAE 1020 steel is not suitable for nitriding hardening. Corrosion tests of the PIII-treated samples showed significant enhancement in the steel behaviour under chloride medium attack.

Implantation of nitrogen ions into stainless steel in combination with oxidation often results in a decrease or even complete removal of the chromium in the nitrogen containing outermost surface layer. While iron nitrides can be formed easily by this method, due to the absence of chromium, the formation of chromium nitrides is impossible and the beneficial influence of chromium in the steel for corrosion resistance cannot be used. To overcome this problem we use the following hybrid technique. A thin chromium layer is deposited on steel and subsequently implanted with nitrogen ions. Chromium can be implanted by recoil into the steel surface and thus the formation of iron/chromium nitrides should be possible. Both beam line ion implantation and plasma immersion ion implantation are used. Due to the variation of the process parameters, different implantation profiles and different compounds are produced. The produced layers are characterized by Auger electron spectroscopy, conversion electron Mossbauer spectroscopy and X-ray diffraction. The obtained results show that due to the variation of the implantation parameters, the formation of iron/chromium nitrides can be achieved and that plasma immersion ion implantation is the most suitable technique for the enrichment of chromium in the outermost surface layer of the steel when compared to the beam line implantation.