T.K. Kwok

Investigation of dose uniformity on the inner races of bearings treated by plasma immersion ion implantation

Plasma immersion ion implantation (PIII) is an effective technique for the surface modification of industrial components possessing an irregular shape. We have recently used PIII to treat a real industrial ball bearing to enhance the surface properties of the race surface on which the balls roll. The implantation dose uniformity along the groove is assessed using theoretical simulation and experiments. The two sets of results agree very well, showing larger doses near the center. However, the highest dose is not observed at the bottom or center of the groove, but rather offset toward the side close to the sample platen when the bearing is placed horizontally. The minimum dose is observed near the edge or corner of the groove and our model indicates that it is due to the more glancing ion incidence as a result of the evolution of the ion sheath near the corner. The dose nonuniformity along the groove surface is about 40% based on our experimental data.

Kinetic model for plasma-based ion implantation of a short, cylindrical tube with auxiliary electrode

Plasma-based ion implantation of the inner surface of a short, cylindrical tube is modeled using a two-dimensional particle-in-cell simulation. An auxiliary electrode, here a coaxial anode, is used to increase the ion impact energy. Initially, ions inside the tube impact the inner surface at approximately normal angles. At later times, ions enter the tube from the exterior plasma and impact predominantly near its center at glancing angles. Ions are found to cross the midplane of the tube and in some cases to pass completely through the tube, in contrast to the predictions of the “collisionless” fluid model. The total incident dose is greatest around the center of the tube, and least at its ends.

PLASMA IMMERSION ION IMPLANTATION OF THE INTERIOR SURFACE OF A LARGE CYLINDRICAL BORE USING AN AUXILIARY ELECTRODE

A model utilizing cold, unmagnetized, and collisionless fluid ions as well as Boltzmann electrons is used to comprehensively investigate the sheath expansion into a translationally invariant large bore in the presence of an auxiliary electrode during plasma immersion ion implantation (PIII) of a cylindrical bore sample. The governing equation of ion continuity, ion motion, and Poisson’s equation are solved by using a numerical finite difference method for different cylindrical bore radii, auxiliary electrode radii, and voltage rise times. The ion density and ion impact energy at the cylindrical inner surface, as well as the ion energy distribution, maximum ion impact energy, and average ion impact energy for the various cases are obtained. Our results show a dramatic improvement in the impact energy when an auxiliary electrode is used and the recommended normalized auxiliary electrode radius is in the range of 0.1–0.3.

Effects of the auxiliary electrode radius during plasma immersion ion implantation of a small cylindrical bore

The temporal evolution of the plasma sheath in a small cylindrical bore in the presence of an auxiliary electrode is determined for different electrode radii. The ion density, velocity, flux, dose, ion energy distribution, and average impact energy are calculated by solving Poisson’s Equation and the equations of ion motion and continuity using finite difference methods. The particle-in-cell method is also used to confirm the validity of the data. Our results indicate that more ions will attain high impact energy when the auxiliary electrode radius is increased, but the dose will decrease. Our results suggest that the normalized auxiliary electrode radius should range from 0.10 to 0.30 in order to maximize the dose and produce a larger number of ions with higher impact energy.

Surface modification of 9Cr18 bearing steels by a metal and carbon co-plasma immersion ion implantation

In the aerospace industry, 9Cr18 martensitic stainless steel AISI 440 is commonly used as a bearing material. Because of its . ability to rapidly treat irregular industrial components, plasma immersion ion implantation PIII is an effective method to improve the wear resistance of 9Cr18 precision bearings and prolong their working lifetime. Vacuum arc plasma sources provide a good means of introducing metal ions into the bearing steel to create a special surface to enhance its surface properties. In this work, tungsten and titanium PIII was performed on 9Cr18 bearing steel using a vacuum arc plasma source, followed by carbon . PIII using acetylene C H plasma, without breaking the vacuum. The surface properties were evaluated by measuring the 22 microhardness, wear properties and friction coefficient, as well as the elemental depth profiles and chemical composition of the modified layer. It was found that the microhardness of the treated samples was much higher. The tribological characteristics were also significantly improved, as demonstrated by the reduced friction coefficient and wear track width. This improvement can be . attributed to the diamond-like-carbon DLC surface layer, as well as favorable ion mixing caused by the implanted metal ions. Q 2000 Elsevier Science S.A. All rights reserved.

Hybrid elevated-temperature, low/high-voltage plasma immersion ion implantation of AISI304 stainless steel

Elevated-temperature plasma immersion ion implantation (PIII) is an effective non-line-of-sight technique to harden austenitic stainless steel by producing expanded austenitic phases in the near surface region. We report here a hybrid elevated-temperature, low/high voltage approach, which improves the efficiency while retaining the non-line-of-sight advantages of PIII. A low-voltage (4 kV), elevated-temperature (355°C) PIII process is first used to produce the modified layer, but the nitrogen concentration in this layer is typically relatively low and the thickness may not be adequate. This is followed by high-voltage (25 kV) PIII at a lower temperature to increase the nitrogen concentration and to achieve the desirable surface enhancement effects. To assess the efficacy of the technique, the samples are characterized using X-ray diffraction (XRD), nanohardness measurements, and secondary ion mass spectrometry (SIMS) depth profiling. The experimental results show that the nitrogen concentration increases by nearly 75% and the nitrogen penetration depth nearly doubles that of the low-voltage sample. The surface microhardness also improves by 150% and our data suggest that it is due to the formation of expanded austenites.

Plasma-immersion ion implantation of the interior surface of a small cylindrical bore using an auxiliary electrode for finite rise-time voltage pulses

Plasma-immersion ion implantation (PIII) can be used to process the interior surfaces of odd-shape specimens such as a cylindrical bore. The temporal evolution of the plasma sheath in a small cylindrical bore in the presence of a grounded coaxial auxiliary electrode is derived for voltage pulses of different rise times by solving Poissons equation and the equations of ion continuity, and motion numerically using the appropriate boundary conditions. It is found that the maximum ion impact energy and the average impact energy are improved for finite rise-time voltage pulses, and shorter rise times yield better results. Our results allow the selection of a suitable auxiliary electrode radius to improve the average impact energy for a given rise time.

Plasma immersion ion implantation into inner and outer races of industrial bearings

Plasma immersion ion implantation (PIII) is a proven surface treatment technique and can be used to prolong the working lifetime of industrial components. However, the lateral implantation dose uniformity may not be very good, particularly for samples with an irregular shape. In this work, we focus on the PIII treatment of the inner and outer races of industrial bearings. The sheath expansion around the inner and outer races is simulated using a time-dependent, two-dimensional fluid model. The angular and spatial distributions of the incident ions along both the exterior and interior groove surfaces are derived. It is found that the ion dose is the highest on the bottom or center of the groove for both the inner and outer races. The minimum ion dose is near the corner of the groove as the ions impinge at a more glancing incident angle as a result of the ion-matrix sheath evolution. Compared with the exterior groove, the interior groove receives a smaller ion dose in the same implantation time. Our results also indicate that the spatial ion dose uniformity can be improved by reducing the implantation pulse width.

Macro-particle free metal plasma immersion ion implantation and/or deposition in a multifunctional configuration

For high-dose metal ion implantation, the use of plasma immersion offers the high-rate advantage, but the simultaneous formation of a surface film along with the sub-surface implanted layer is sometimes a detriment. In this work, we describe a metal . plasma immersion approach in which pure and macro-particle free implantation metal andror gas ions , pure deposition without ion implantation, or dynamic metal ion beam assisted deposition and gaseous plasma immersion ion implantation DIBAD metal . and gas plasma immersion can be obtained. We have demonstrated the technique by carrying out Ti and Ta implantation at .

Pulsed sheath dynamics in a small cylindrical bore with an auxiliary electrode for plasma immersion ion implantation

The temporal evolution of the plasma sheath in a small cylindrical bore with an auxiliary electrode is calculated for zero-rise-time voltage pulses. The ion density, flux, dose, ion energy distribu-tion, and electric field are determined by solving Poisson’s equation and the equations of ion motion and continuity using finite difference methods. Our results indicate that the implantation time is about halved and slightly more than 50% of the ions possess impact energy higher than the maximum achieved when an auxiliary electrode is absent. The resulting ion flux, ion current, as well as ion energy distribution, are also determined.