Z. M. Zeng

Properties of titanium oxide biomaterials synthesized by titanium plasma immersion ion implantation and reactive ion oxidation

Abstract As an artificial heart valve material, titanium oxide is superior to low temperature isotropic pyrolytic carbon in terms of mechanical properties and biocompatibility. The irregular shape of a heart valve makes conventional fabrication techniques like beam-line ion implantation and ion beam enhanced deposition (IBED) difficult. Plasma immersion ion implantation (PIII) does not suffer from the line-of-sight limitation and is an excellent technique for this purpose. In this work, titanium oxide thin films are synthesized on Ti6Al4V by titanium metal PIII and oxygen PIII. By controlling the deposition/implantation rate of titanium and oxygen plasma density, TiO x films with different compositions and properties can be fabricated. The film properties are evaluated by techniques including atom force microscopy (AFM), X-ray diffraction (XRD), and various mechanical testing methods. AFM results reveal that the TiO x film surface is quite dense without gross voids. The microhardness is enhanced with increasing oxygen partial pressure between the range of 0–3×10 −2 Pa and reaches a maximum value of 17 GPa at an oxygen partial pressure of 3×10 −2 Pa. The wear resistance is also much better than that of Ti6Al4V. In spite of our encouraging results, the TiO x films synthesized in our experiments are still too thin. In order to exploit its full potential as an artificial heart valve material, the films must be thicker. It can be achieved by using a more efficient metal arc source or by increasing the PIII duty cycle.

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.

Intense blue-light emission from carbon-plasma-implanted porous silicon

We have investigated the room-temperature photoluminescence (PL) characteristics of porous-silicon plasma implanted with carbon. Before implantation, the porous silicon made by anodizing emits intense orange light. After carbon-plasma-immersion ion implantation, the orange light disappears and blue light appears. Furthermore, intense blue light is obtained after annealing at 400 °C for 30 min. Analytical results show that the quenching of orange light and appearance of blue light are due to the reduction of the size of nanocrystallites caused by implantation. The effects of different annealing temperature on the light-emission properties of the implanted porous silicon are also studied. The intensity decreases with increased temperature from 600 to 1000 °C, but the PL intensity increases drastically again after annealing at 1250 °C due to the formation of a substance.

Medium-temperature plasma immersion-ion implantation of austenitic stainless steel

Conventional elevated-temperature plasma immersion-ion implantation (PIII) is usually conducted at 350°C, or above, to achieve a thick modified layer for practical engineering applications. In this paper, we focus on medium-temperature PIII treatment of SS304 stainless steel. Two experimental protocols: high frequency, low voltage (LV); and high voltage (HV), low frequency are evaluated. The samples are characterized by Auger electron spectroscopy, glancing angle X-ray diffraction (XRD), corrosion test, pin-on-disk friction and wear test, and so on, to determine the composition, phase structure, as well as the tribological properties of the modified layer. Our results indicate that PIII at 300°C not only improves the mechanical properties, but also the corrosion resistance. Comparison of the wear tracks shows that 300°C-PIII results in an 11-fold improvement in the surface-wear resistance. A procedure involving high implantation flux at LV is more favorable to the formation of a thick modified layer with a higher nitrogen concentration.

VACUUM ARC PLASMA TRANSPORT THROUGH A MAGNETIC DUCT WITH A BIASED ELECTRODE AT THE OUTER WALL

Metal plasma formed by a vacuum arc plasma source can be passed through a toroidal-section magnetic duct for the filtering of macroparticles from the plasma stream. In order to maximize the plasma transport efficiency of the filter the duct wall should be biased, typically to a positive voltage of about 10–20 V. In some cases it is not convenient to bias the duct, for example if the duct wall is part of the grounded vacuum system. However, a positively biased electrode inserted into the duct along its outer major circumference can serve a similar purpose. In this article, we describe our results confirming and quantifying this effect. We also show the parametric dependence of the duct transport on the experimental variables.

DYNAMIC MIXING DEPOSITION/IMPLANTATION IN A PLASMA IMMERSION CONFIGURATION

A surface layer consisting of titanium, nitrogen, and oxygen is implanted/deposited onto SS304 stainless steel using dynamic mixing and plasma immersion ion implantation. Titanium is introduced into a nitrogen glow discharge plasma from a metal arc plasma source. Dynamic mixing is achieved via the co-implantation of Ti ions with high charge states as well as nitrogen and oxygen ions in the plasma. The resulting surface layer possesses superior tribological properties and corrosion resistance. The observed improvement in the wear resistance is more than a factor of 10. The enhancement in the surface properties is believed to be due to the synergistic effects of the coexistence and dynamic mixing of titanium, nitrogen, and oxygen at the interface.

In situ sample temperature measurement in plasma immersion ion implantation

Plasma immersion ion implantation (PIII) is an excellent surface modification technique because it is not restricted by the line-of-sight limitation that plagues conventional beamline ion implantation. However, the lack of in situ monitoring has hampered wider acceptance of the technique in industry. It is known that the implantation temperature has a large influence on the surface properties of the treated specimens in addition to the more obvious parameters such as implantation voltage, pulse duration, pulsing frequency, and so on. Direct measurement of the target temperature is complicated by the sample high voltage as well as by interference from the electromagnetic field and plasma. In this article, we present a novel interference-free, in situ temperature measurement technique employing a shielded thermocouple directly attached to the sample stage. Our experiments show that the setup can monitor the target temperature in real time, even under severe arcing conditions. Our results also indicate that ...

Hybrid simulation of sheath and ion dynamics of plasma implantation into ring-shaped targets

A collisionless hybrid simulation (particle ions and Boltzmann electrons) has been used to study sheath and ion dynamics following the application of a large negative voltage pulse to three different ring-shaped targets: a thin ring, a thick ring, and an outer bearing race. The influence of a coaxial auxiliary electrode has also been investigated. The normalized potential, ion density, incident dose and accumulated impact energy on the target surfaces are presented. Three classes of ion trajectories are identified: those that impact the target directly, those that pass through the ring and impact the target, and those that pass through the ring and back into the ambient plasma. Implantation of the top and outer surfaces of the thick ring/bearing are influenced by the use of the auxiliary electrode because it significantly reduces the number of ions passing through the ring. The implications of this work for the plasma immersion ion implantation process are discussed.

Mechanism of enhanced plasma transport of vacuum arc plasma through curved magnetic ducts

The mechanism of the enhanced transport efficiency in a vacuum arc plasma source equipped with a curved magnetic filter is investigated. The relationship between the transported ion current and the cathodic arc current is determined, and our results suggest that the outer and inner walls of the duct interact with the plasma independently. The plasma flux is composed of two components: a diffusion flux in the transverse direction due to particle collisions, and a drift flux due to the ion inertia. The inner wall of the magnetic duct sees only the diffusion flux while the outer wall receives both fluxes. Thus, applying a positive potential to the outer duct wall reflects the ions and increases the output current. Our experimental data also show that biasing both sides of the duct is more effective than biasing the outer wall alone.

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 .