Jesse N. Matossian

A comparative study of beam ion implantation, plasma ion implantation and nitriding of AISI 304 stainless steel

Abstract This paper presents the results of a comparative study using beam ion implantation (BII), plasma ion implantation (PII), ion nitriding and gas nitriding of AISI 304 stainless steel. We have demonstrated that under controlled conditions (the same treatment times of 30 and 60 min, and the same treatment temperature of 400 °C), the microstructures produced by all four techniques are similar, being mainly the formation of nitrogen in solid solution (γ N phase). However, the concentrations of nitrogen and the detectable depths of the nitrogen-enriched layers are significantly different, depending on the process. Both BII and PII produce thick nitrogen-enriched layers (greater than 1 μm) at high concentrations (20–30 at.%) compared with either ion nitriding or gas nitriding (layers less than 1 μm thick with low nitrogen concentrations). As a result, the load-bearing capacity after either BII or PII is much greater than after either ion or gas nitriding. It has also been found that high current density implantation is crucial for the formation of the thick N-enriched layers.

Plasma-enhanced magnetron-sputtered deposition of materials

Plasma-enhanced magnetron-sputtered deposition (PMD) of materials is employed for low-temperature deposition of hard, wear-resistant thin films, such as metal nitrides, metal carbides, and metal carbo-nitrides, onto large, three-dimensional, irregularly shaped objects (20) without the requirement for substrate manipulation. The deposition is done by using metal sputter targets (18) as the source of the metal and immersing the metal sputter targets in a plasma (16) that is random in direction and fills the deposition chamber (12) by diffusion. The plasma is generated from at least two gases, the first gas comprising an inert gas, such as argon, and the second gas comprising a nitrogen source, such a nitrogen, and/or a carbon source, such as methane. Simultaneous with the deposition, the substrate is bombarded with ions from the plasma by biasing the substrate negative with respect to the plasma to maintain the substrate temperature and control the film microstructure. The substrate, metal targets, and plasma are all electrically decoupled from each other and from walls (14) of the deposition chamber (12), so as to provide independent electrical control of each component. The PMD process is applicable not only to the deposition of hard coatings, but also can be applied to any thin film process such as for electrically and thermally conductive coatings and optical coatings, requiring simultaneous, high-flux, ion-bombardment to control film properties.

Relative roles of ion energy, ion flux, and sample temperature in low-energy nitrogen ion implantation of FeCrNi stainless steel

Abstract A matrix of nitrogen ion energies (0.4, 0.7 and 1.0 keV) and ion fluxes (1, 2, and 3 mA/cm2) has been selected to investigate the systematics of ion-beam processing of an austenitic FeCrNi stainless steel (AISI 304) at 400°C for 60 min. In addition, the role of temperature was examined over the range from 280°C to 475°C at fixed processing conditions of 0.7 keV, 2 mA/cm2, and 60 min. Characterization of the composition, structure, magnetic nature, thickness and strength of the nitrogen-containing layers was made by a combination of Auger electron spectroscopy, X-ray diffraction, backscatter Mossbauer spectroscopy, and microhardness measurements. A high N content layer, which is a magnetic, fcc phase, is predominant for all conditions and its thickness increases linearly with either ion energy at fixed ion flux or with ion flux at fixed ion energy. This behavior is consistent with layer growth that is controlled primarily by the N supply rate into the first few atomic layers rather than by thermal diffusion.

Microstructural features of wear-resistant titanium nitride coatings deposited by different methods☆

Titanium nitride, TiN, is used as wear protective and decorative coatings in various applications. These coatings are deposited by standard industrial methods such as chemical and physical vapor deposition (CVD and PVD, respectively), including magnetron sputtering or its modifications [e.g. the plasma-enhanced magnetron sputtered deposition (PMD) method]. The coatings have different microstructures (size and morphology of grains, orientation, dislocation structure, residual stress, etc.) depending on the method used and the deposition regime. The results of comparative transmission electron microscopy (TEM) investigations of the microstructure of thin TiN coatings deposited by classical CVD and PVD, including PMD, are presented. The microstructure was studied in sections perpendicular and parallel to the coating surface. The grain size was estimated from dark field images and the residual stress was determined using the bend extinction contours in the bright field images. It was found that the coatings deposited by PVD and CVD methods have different grain microstructures and residual stresses. The CVD coatings have an equiaxed microcrystalline structure with very low levels of the local residual stress. The mean grain size is 0.4–0.6 μm. The PVD coatings (Balzers and Metaplas) have a non-equilibrium submicron grain structure with a high level of the local residual stress equal to 0.06–0.08E, where E is Youngs modulus, and a mean grain size of 0.1–0.2 μm in the section parallel to the coating surface. The PMD coating structure is highly non-equilibrium nanocrystalline, with a very high level of residual stress equal to 0.13E and a much finer grain size of 0.06 μm.

Plasma ion implantation of nitrogen into silicon: Characterization of the depth profiles of implanted ions

The in‐depth concentration distribution or depth profile of nitrogen implanted into silicon wafer substrates using plasma ion implantation (PII) is studied using secondary‐ion‐mass spectrometry and Auger electron spectroscopy sputtered depth profiling. Plasma ion implants were performed using a low‐pressure (5×10−5 Torr) collisionless plasma at voltages of 50 and 100 kV to a fluence of 1.5×1017 cm−2 using voltage pulses 10 μs in duration, with 1 μs rise time, and at a repetition rate of 200 Hz. The measured depth profiles are compared with those from both conventional ion‐beam implantation and numerical simulations. The comparisons indicate an incident flux composed of ∼90% N+2 and ∼10% N+ ions. Compared with ion‐beam implants, which exhibit a nearly Gaussian‐shaped depth profile, the plasma ion implantation profiles are ‘‘filled in’’ with an approximately constant nitrogen concentration for depths less than the predicted ion range. The profiles are modeled assuming that incident ions have a distribution ...

Operating characteristics of a 100 kV, 100 kW plasma ion implantation facility

Abstract The design characteristics of the 100 kV, 100 kW plasma ion implantation (PII) facility at Hughes Research Laboratories are described. The facility is comprised of a vacuum chamber in which parts are implanted and a pulse modulator which provides voltage pulses to implant ions into parts. The vacuum chamber is a horizontally-mounted, 4 ft diameter × 8 ft long, stainless-steel vessel. Parts to be implanted are placed on a rectangular, 3 ft wide × 6 ft long stainless-steel table with a weight capacity of 7000 lb that is electrically isolated from the vacuum chamber walls. For small loads, a 3 ft wide × 3 ft long support table is used with the chamber masked in half using a transparent grid. Plasma production is achieved using remotely-located plasma sources installed in the front, sides or top of the vacuum chamber to tailor the plasma-uniformity profile for the type and size of the part being implanted. The pulse modulator provides high-power (100 kW), high-voltage (100 kV) near-square-wave pulses for ion implantation. Voltage modulation is provided by the Hughes CROSSATRON tm switch, which can achieve turn-ON and turn-OFF times of less than 1 μsec, and maximum pulse currents of 1 kA. Two modes of pulse-modulation are possible; single-polarity, negative-voltage operation for ion implantation and alternating-polarity, positive-and negative-voltage operation for thermally-enhanced ion implantation via electron bombardment of the part surface. To date, over 1000 h of operations have been accumulated for both the vacuum-chamber and the pulse-modulator PII facility. An upgrade of the facility for 250 kV operation is presently under way.

Plasma ion implantation (PII) to improve the wear life of tungsten carbide drill bits used in printed wiring board (PWB) fabrication

Abstract Plasma ion implantation (PII) is a process that allows for cost-effective implantation of large-scale (or large numbers of small-scale) three-dimensional objects. In PII an object to be implanted is immersed in a plasma comprised of the ions to be implanted (such as nitrogen). The object is then pulsed biased to a very high (50–100 kV) negative potential, using a repetitive train (100–1000 Hz) of short duration (10–30 μm) voltage pulses to achieve omnidirectional andsimultaneous implantation of ions over its entire surface. This paper describes the use of PII to extend the wear life of tungsten carbide drill bits used in multilayer printed wiring board (PWB) fabrication. A twofold to threefold wear life improvement was achieved withnitrogen ions implanted at 95 kV using the PII facility at Hughes Research Laboratories. The PII process was compared with three conventional processes known to improve PWB drill bit wear life: conventional nitrogen ion beam implantation, ion beam mixing of TiN and CrN, and physical vapor deposition of TiN. Comparable wear life results from all four techniques.

Challenges and progress toward a 250 kV, 100 kW plasma ion implantation facility

Abstract Plasma ion implantation (PII) is a large-scale cost-effective technique for modifying the surface properties of materials via omnidirectional ion implantation. The implantation voltage and ion species define the energy-to-ion ratio which, together with the ion dose, determines the effectiveness of an implant in achieving successful tribological improvements in materials. For most metal treatment applications of PII, modest energy-to-ion ratios and high ion doses are required to achieve respectable improvements in hardness and wear life. For example, implantation of N 2 + ions into metal tools and dies via PII at 100 kV (energy-to-ion ratio of 50 keV per N + ion) at a dose of 3×10 17 N + cm −2 can result in an increase of wear life by a factor of -8. In contrast with metals, polymers require high energy-to-ion ratios and low doses to achieve significant improvements in hardness and wear life. For example, ion beam implantation of N + ions into Kapton at 300 kV (energy-to-ion ratio of 300 keV per N + ion) and a dose of 3×10 15 N + cm −2 can increase hardness by a factor of 13. This energy-to-ion ratio is six times higher than that achievable using present PII technology. A provocative question to ask is how this can be achieved in a PII system. Work is under way at the Hughes Research Laboratories (HRL) to address this issue. The approach being used involves first scaling PII voltage technology from 100 to 250 kV, and then implanting doubly and triply charged atomic nitrogen ions at 250 kV to achieve an energy-to-ion ratio range of 500–750 keV per N + ion. To date single-pulse ion implants have been conducted at 250 kV in the HRL PII facility. A plasma source has been built for the production of multiply charged nitrogen ions. A technique for treating non-conducting objects in a PII facility has been developed, and a method of reducing X-ray production in a PII system operating at 250 kV has been investigated.

Quenching optical breakdown with an applied electric field

Application of an external electric field across the focal volume of a high-pressure gas cell can increase the threshold for optical breakdown by electrostatic purification of the gas and by removal of free electrons from the laser focal volume in times that are short relative to the interpulse separation and/or the laser pulse duration. Experiments with 1.06-μm pulse trains (200-psec duration with a 7.5-nsec interpulse separation) demonstrate that electrostatic purification effectively quenches all optical breakdown in 20 atm of SF6 for the highest available single-pulse fluences of 140 J cm−2 (~0.7 TW cm−2).

The smoothness, hardness and stress in titanium nitride following argon gas cluster ion beam treatment

The surface smoothing of TiN coatings, deposited by CVD or PVD methods, by argon ion clusters comprising a few hundred to a few hundred thousand atoms and carrying a single positive charge has been confirmed. In addition, the present work has shown that there was no change in the mechanical condition, nanohardness or residual stress, of the PVD coatings after treatment. In contrast, the nanohardness in the near-surface region of the CVD TiN coating was increased but, remarkably, there was no concomitant increase in residual stress. A comparison is made with the established effects of classical single ion implantation on the near-surface properties of TiN where a high compressive residual stress is developed if the ion energy lies beyond a threshold value. It was concluded that only a fraction of the atoms in the cluster impact the surface and the vast majority of argon atoms move sideways. It appears to be generic that the smaller clusters are responsible for the increase in hardness as well as the well-known lateral sputtering effects associated with the technology. Larger clusters do not carry enough energy per atom to cause such effects and their energy is dissipated in the substrate as heat.