Search

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.

When performing nitriding of stainless steels, there is a decrease or even complete depletion of chromium in the nitrogen rich region just beneath the surface, inhibiting the formation of passivated Cr oxide layer, beneficial to withstand corrosive attacks and Cr/Fe nitrides, responsible for hardness enhancement. To overcome this problem, a hybrid technique was used, consisting of depositing a thin chromium film on steel surface and then bombarding it with nitrogen ions. By a complex recoil process, chromium atoms are implanted into the steel matrix. Plasma immersion ion implantation (PIII) was used in this bombardment. The new Cr-rich layer allows the formation of Cr oxides and nitrides. Treated surfaces were characterized by Auger electron spectroscopy (AES) and conversion electron Mossbauer spectroscopy (CEMS), showing formation of a new Cr-rich layer. (c) 2005 Elsevier B.V. All rights reserved.

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.

A DC glow discharge plasma source was used in a plasma immersion ion implantation (PIII) experiment providing nitrogen plasmas with densities of 1–3 ×10 10 cm −3 and temperatures of 5–10 eV. Nitrogen ions were extracted from these plasmas and implanted in a variety of immersed samples (Al 5040, SS 304, Si) using repetitive high voltage pulses from two types of sources: PFN pulser and a hard tube pulser. Due to the high potential present in our plasma (350 V), a significant sputter etching of the samples surface occurred at long irradiation times. An electron shower source was used to lower this potential allowing its control from 0 to 350 V. Operating the plasma source at potentials below 70 V reduced the sputtering to negligible levels and a retained dose of 1.5×10 17 cm −2 was achieved in a silicon surface, after irradiation of 1500 min. For plasma with potential of 350 V (no electron shower), the retained doses in Al 5040 and SS 304 samples were smaller than 5×10 16 cm −2 , for same plasma and pulser conditions (but 2500 min irradiation), confirming the deleterious effects of sputtering measured in Si samples. Upon using the higher repetition rate pulser, the treatment time was reduced by a factor of 700, thus easing considerably the sputtering problem.

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.

To 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 mixing PIII and ion nitriding processes. A combination of high pressure (4 x 10(1)Pa), moderate temperature (up to 450degreesC) glow discharge nitriding with low pressure (8 x 10(-2)Pa) and low DC bias voltage ion nitriding (or DC PIII) was implemented. Depending on the particular conditions of the treatment and the depth probed, mixed phases of gamma(N) and epsilon were measured in the treated SS304 steel sample. This near surface modification resulted in an improved hardness (up to a factor of 2.7 x) of the sample which could also enhance its wear properties. Surface modification of T16Al4V alloy and SS304 steel by a combination of PIII 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 x 10(-2)Pa) 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.

SAE 1020 is a widely used plain carbon steel, as mortar reinforcement in buildings and small machine parts. But aside from good mechanical properties, its surface suffer from severe corrosion and high wear rate, due to modest hardness. Chromium (Cr) in excess of 12% in Fe alloys renders them resistant to several corrosive attacks. So we tried to introduce Cr in such amounts into the surface of that steel. Cr films were deposited by electron beam on SAE 1020 steel. Bombarding the Cr film either by nitrogen Plasma Immersion Ion Implantation (PIII) or nitrogen ion beam (IB), Cr atoms were recoil introduced into the Fe matrix. Normally, in the recoil process, heavy atoms are used, but in this set of experiments we used a relatively lighter atom, viz. nitrogen. SRIM simulation was used to show Cr atoms range in the steel matrix after being hit by nitrogen atoms. AES analysis showed ranges far beyond the calculated figures and in percentages above 13at. %, enough to the purposes of these works. Preliminary corrosion results showed remarkable enhancement under corrosive 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.

High-resolution X-ray diffraction methods have been used to characterize nitrogen-doped silicon obtained by plasma immersion ion implantation (PIII). The Si wafers were implanted with the plasma potential controlled at 70 V, and a plasma density of 1.5×10 10 cm −3 . The high voltage pulser was operated with peak voltage of 10 kV, 6 μs pulse duration and repetition frequency of 20 Hz. Auger electron spectroscopy (AES) measurements were carried out revealing successful implantation of ions with accumulated nitrogen dose of 1.5×10 17 cm −2 . The (0 0 4) Si rocking curve (ω-scan) was measured in a high resolution X-ray diffractometer equipped with a Ge(2 2 0) four crystal monochromator before and after implantation. A small distortion of the Si(0 0 4)-rocking curve was clearly observed for the as-implanted sample. This rocking curve was simulated by dynamical theory of X-ray diffraction, assuming a Gaussian strain distribution through the implanted region and using the data from the nitrogen profile obtained from the Auger measurements. With these assumptions, a good agreement between the measured and simulated rocking curves was obtained.

In the present study we use x-ray diffraction methods to characterize the surface of Si wafers irradiated with nitrogen by Plasma Immersion Ion Implantation. This is a non-line-of-sight ion implantation method, which allows three-dimensional treatment of materials including semiconductors, metals and dielectrics. The atomic concentration profiles in the implanted Si wafers were measured by Auger electron spectroscopy. The (004) Si rocking curve ( omega-scan) was measured in a high resolution x-ray diffractometer equipped with a Ge (220) four-crystal monochromator before and after implantation. A distortion of the Si (004)-rocking curve was clearly observed for the as-implanted sample. This rocking curve was successfully simulated by dynamical theory of x-ray diffraction, assuming a Gaussian strain profile through the implanted region. The analysis made by x-ray difraction and Auger electron spectroscopy revealed successful implantation of ions with ac- cumulated nitrogen dose of 1.5 x 10(17) cm-3 .The Si wafers can be used as high sensitivity monitors in the Plasma Immersion Ion Implantation process, especially at the low dose range.