X.F. Wang

Third-generation plasma immersion ion implanter for biomedical materials and research

A third generation plasma immersion ion implanter dedicated to biomedical materials and research has been designed and constructed. The distinct improvement over first and second generation multipurpose plasma immersion ion implantation equipment is that hybrid and combination techniques utilizing metal and gas plasmas, sputter deposition, and ion beam enhanced deposition can be effectively conducted in the same machine. The machine consists of four sets of high-efficiency metal arc plasma sources with magnetic filters, a custom designed high voltage modulator for operation up to 60 kV, a separate high-frequency, low-voltage power supply for hybrid treatment processes, special rotating sample stage for samples with an irregular shape, and other advanced features. The machine has been installed at Southwest Jiaotong University and operated reliably for 6 months. This article describes the design principles and performances of the machine as well as pertinent biomedical applications.

Radio-frequency plasma nitriding and nitrogen plasma immersion ion implantation of Ti-6A1-4V alloy

Abstract Nitrogen ion implantation improves the wear resistance of Ti-6A1-4V alloys by forming a hard TiN superficial passivation layer. However, the thickness of the layer formed by traditional ion implantation is typically 100–200 nm and may not be adequate for many industrial applications. We propose to use radio-frequency (RF) plasma nitriding and nitrogen plasma immersion ion implantation (PIII) to increase the layer thickness. By using a newly designed inductively coupled RF plasma source and applying a series of negative high voltage pulses to the Ti-6A1-4V samples, RF plasma nitriding and nitrogen PIII can be achieved. Our process yields a substantially thicker modified layer exhibiting more superior wear resistance characteristics, as demonstrated by data from micro-hardness testing, pin-on-disc wear testing, scanning electron microscopy (SEM), as well as Auger electron spectroscopy (AES). The performance of our newly developed inductively coupled RF plasma source which is responsible for the success of the experiments is also described.

Methane and nitrogen plasma immersion ion implantation of titanium metal

Abstract Plasma immersion ion implantation (PIII) is employed to enhance the tribological properties of titanium. The effectiveness of methane PIII and glow discharge nitrogen PIII, as well as radio-frequency (RF) nitrogen PIII, is compared by measuring the microhardness, mass loss due to wear and the coefficient of friction of samples treated by the three methods. Nitrogen PIII is a hybrid surface treatment technique combining nitrogen-ion implantation, which occurs during the high-voltage pulses, and plasma nitriding, which takes place in between pulses. Our experimental data show that the surface properties of titanium are enhanced by all three treatment processes, but nitrogen PIII yields better results than methane PIII, and RF nitrogen PIII is the best treatment process of the three. On the basis of our Auger depth profiling results, the discrepancy appears to be related to the larger penetration depth (implantation plus radiation-enhanced diffusion) of nitrogen by the RF PIII process. The slight difference between methane PIII and glow discharge nitrogen PIII samples appears to arise from the absolute implanted dose.

Process window and mechanism of surface property enhancement of 9Cr18 steel using plasma immersion ion implantation

9Cr18 martensite steel is commonly used as a bearing material in the aerospace industry in China. Because of its ability to treat large and irregular industrial components, plasma immersion ion implantation (PIII) is a good technique to enhance the wear resistance of 9Cr18 precision bearings to extend the working lifetime. We have recently conducted a systematic investigation to determine the process window of nitrogen PIII as well as to identify the enhancement mechanism. The surface properties of 9Cr18 steel after nitrogen PIII under different dosage and plasma conditions (filament hot electron discharge and radio frequency glow discharge) are evaluated by measuring the microhardness, wear property, coefficient of friction, corrosion resistance, as well as elemental depth profiles. Our data indicate that the degree of improvement does not differ substantially under the various PIII conditions thereby suggesting a fairly large process window as long as enough nitrogen is incorporated to form nitride phases.

Surface modification of 2Cr13 oil pump steel by plasma immersion ion implantation-ion beam enhanced deposition (PIII-IBED)

2Cr13 martensite steel is often used as a piston material in oil pumps. In the harsh environment of an oil field, the materials and components undergo extensive and accelerated wear and tear. In this study, we employ Ti and N plasma immersion ion implantation and ion beam enhanced deposition (PIII-IBED) to enhance the surface wear resistance of 2Cr13 steel in an effort to prolong its working lifetime. To assess the technique efficacy and surface properties of the 2Cr13 steel samples treated by PIII-IBED using different voltages, the coefficient of friction, wear tracks, microhardness, anode polarization curves, chemical composition and elemental depth profiles were determined. The experimental data show that the wear resistance of the treated 2Cr13 steel samples is improved significantly by the method, and the nitride phases formed in the modified layer play an important role in the enhancement mechanism.

Improve retained dose and impact energy of inner surface plasma immersion ion implantation using long pulse duration with deflecting electric field

Not restricted by the line-of-sight process, plasma immersion ion implantation (PIII) has shown great potential for inner surface modification, but the impact energy and retained dose turned to be very low. The process was investigated numerically and experimentally in this paper. The results show that a high percentage of low impact energy ions was the key factor that resulted in low impact energy on the inner surface. This was caused by sheath overlapping and appearance of the dead zone during inner surface PIII. Long pulse duration could alleviate this problem and increase ion impact energy on the inner surface, hence the implant depth, which was key factor for the modifying effect of PIII. Also, long pulse duration was helpful in improving the retained dose on the inner surface.

High duty, long lifetime, cathodic arc plasma source

We have developed a repetitively pulsed cathodic arc plasma source that can operate at high duty cycle and with long lifetime between downtimes for cathode maintenance. The arc discharge current can be up to 300 A, the arc pulse width can be varied from 0.1 to 4 ms, and the source can operate at a duty cycle of up to 30% for many hours. The cathode can be of a diameter from 20 to 40 mm, and can be easily and quickly changed. A 45° magnetic duct is used for macroparticle filtering, employing a pulsed magnetic field. We have operated the source over a wide parameter range, and we report here on the variation of plasma ion deposition current with arc current, duct magnetic field, and duct bias voltage. A momentary ion deposition current of 0.7 A was obtained with the source running stably for more than 8 h with an arc current of 100 A and duty cycle of 20%.

Simulation of dose uniformity for different pulse durations during inner surface plasma immersion ion implantation

Without the line-of-sight limitation, plasma immersion ion implantation (PIII) emulates conventional beam-line ion implantation in inner surface modification of industrial components. However, dose uniformity on the inner surface is critical. Inner surface PIII of a cylindrical bore is modeled using a two-dimensional fluid model. It is found that the retained dose is not uniformly distributed on the inner surface and the maximum dose is observed away from the edge. The exact location of the maximum dose, which varies with the implant pulse duration, is closer to the center when the pulse width is longer. The maximum relative difference of the retained dose along the interior also depends on the implant pulse duration. It is smaller for a longer pulse duration after a threshold value has been exceeded.

A reconstruction method based on evolution of partial differential equation for the Laser-driven Ion-beam Trace Probe (LITP)

The Laser-driven Ion-beam Trace Probe (LITP) is a new poloidal magnetic field (Bp) diagnostic method in tokamak devices. It measures the ion displacements which are linear integrations of Bp along the ion beam traces, and a proper tomography method is necessary for the Bp reconstruction. A tomography method based on the solution of partial differential equation is used. The diffusion term and perturbation term are used to avoid the divergence and smooth the reconstructed results. Numerical results show that both the diffusion term and the perturbation term obviously improved the reconstruction results of Bp for LITP.

Special 10kV solid state power modulator for plasma immersion ion implantation treatment of industrial bearings

Summary form only given. We have recently developed a 10kV solid state power modulator for the processing of industrial bearings by plasma immersion ion implantation. According to our research results, high energy implantation is not preferred in the treatment of industrial bearings because of the geometry of the races, and a dedicated and less expensive power supply will suffice. In our new design, optical communication modules are used to synchronize the control pulse of each IGBT and a new method is used to generate power for the IGBT gate drive in the solid state modulator In addition to a maximum voltage of 10kV, our inexpensive power modulator can output pulses 2 to 100 microseconds in duration with a rise time of 2 microseconds. The maximum pulsing frequency is 2kHz. We will present the details of the design and the experimental results in this paper.