R.A. Dodd

Plasma source ion‐implantation technique for surface modification of materials

Plasma source ion‐implantation (PSII) is a new ion‐implantation technique which has been optimized for surface modification of materials such as metals, plastics, and ceramics. PSII departs radically from conventional implantationtechnology by circumventing the line‐of‐sight restriction inherent in conventional ion implantation. In PSII, targets to be implanted are placed directly in a plasma source and then pulse biased to a high negative potential. A plasma sheath forms around the target and ions bombard the entire target simultaneously. Preliminary experiments have demonstrated that PSII: (1) efficiently implants ions to concentrations and depths required for surface modification, (2) produces material with improved microhardness and wear properties, and (3) dramatically improves the life of manufacturing tools in actual industrial applications. For example, the tool life of M‐2 pierce punches used to produce holes in mild steel plate has been increased by a factor of 80.

Plasma source ion implantation: A new, cost-effective, non-line-of-sight technique for ion implantation of materials☆

Abstract Surface modification by ion bombardment is a well-established technique for improving the hardness, friction, wear resistance and corrosion resistance of materials. Surface modification of materials by conventional ion implantation is a line-of-sight process in which a directed beam of energetic ions is rastered across a target. If the target is three dimensional, the process generally requires target manipulation to achieve uniform implantation over the entire surface of the object. This target manipulation requirement can seriously limit the cost effectiveness of ion implantation relative to more conventional surface treatments, especially for large and/or heavy targets. We are developing a new technique, plasma source ion implantation (PSII), which circumvents the line-of-sight restriction of conventional ion implantation. In PSII, targets to be implanted are placed directly in a plasma source chamber and are then pulse biased to high negative voltage (10 – 100 kV in our experiments). A thick, ion matrix sheath forms around the target, and ions accelerate through the sheath drop and bombard the target from all sides simultaneously without the necessity of target manipulation. Although the PSII process bears a superficial resemblance to existing techniques such as “ion plating”, “ion coating” or “plasma nitriding”, PSII produces a deposition profile characteristic of high energy ion implantation. Our experiments have demonstrated that PSII (1) efficiently implants ions to the concentrations and depths required for surface modification, (2) produces material with improved microhardness and wear properties and (3) dramatically improves the life of manufacturing tools in actual industrial applications. For example, in recent industrial field tests the tool life of M-2 pierce punches used to produce holes in mild steel plate has been increased by a factor of 70 – 80. In this paper we describe (1) the latest results from a series of ongoing field tests, (2) extensions of the PSII process to ion beam mixing and ion beam enhanced deposition modes of operation, and implantation of molecular ions, and (3) the comparative economics of surface modification by PSII relative to conventional ion implantation.

Ion beam assisted coating and surface modification with plasma source ion implantation

Plasma source ion implantation (PSII) is a non‐line‐of‐sight technique which is being developed as an alternative to beamline accelerator technology for ion implantation. The initial development phase of PSII concentrated on implantation of ion species which are gaseous at room temperature (primarily nitrogen ions) and employed a cylindrical vacuum chamber 16 in. high and 14 in. in diameter. A second generation PSII system is being constructed to extend the PSII process to ion beam mixing and ion beam assisted coating modes of operation. The new, larger system (with dimensions 36×36×36 in.) will feature multiple‐array sources for sputter deposition concurrent with ion bombardment.

Structure and wear properties of carbon implanted 304 stainless steel using plasma source ion implantation

Abstract Methane plasma source ion implantation was used to implant carbon ions into 304 stainless steel. This paper examines the effects of high voltage pulse repetition rate on the structure and wear properties of implanted samples. The implantations were carried out at a target bias of -30 keV to a dose of 3 × 10 17 atoms cm -2 . Three repetition rates (42 Hz, 87 Hz and 126 Hz) were used. At low repetition rate, a carbon coated-implanted surface forms, which only an implanted surface is produced at high repetition rates. Metastable phases were observed and identified, and the microstructure at the surface was observed to be dependent on the chosen implantation parameters. Fe 2 C formed in the implantation layer which is produced at 42 Hz. Smaller size Fe 2 C and other forms of carbides (possibly Fe 3 C and/or (Cr, Fe) 7 C 3 ) formed in samples implanted at 87 Hz. An increase in repetition rate to 126 Hz produced a shallower amorphous implantation layer. Possible explanations of phase formation mechanisms are given. Wear resistance of all the implanted samples was improved, with the coated-implanted sample produced at 42 Hz showing the greatest improvement. The mechanism of wear was observed to change from an adhesive mode to a mild abrasive mode after implantation.

Corrosion behavior of nitrogen implanted aluminum

Abstract Pure (99.999%) aluminum has been implanted with nitrogen using a plasma source ion implantation process. A glow discharge plasma and a 50 kV bias were used to achieve a retained dose of ∼ 10 18 N-at/cm 2 . Some samples were Ar sputter-cleaned prior to nitrogen implantation. Auger depth profiling and TEM analysis indicated a stoichiometric AlN layer about 150 nm thick formed on the surface as a result of the nitrogen implantation process. Potentiodynamic corrosion tests performed in 3.5 wt% NaCl solution (seawater) indicated that nitrogen implantation gave pure aluminum improved corrosion resistance. Without argon sputter-cleaning, nitrogen implanted samples exhibited insulating behavior to the extent of completely suppressing the corrosion current. Sputter-cleaned and nitrogen implanted samples did not exhibit the insulating behavior, but still provided a reduction in the corrosion current and a more noble corrosion potential. This work shows that a significant modification of the corrosion resistance of pure aluminum can be accomplished using a nitrogen plasma source ion implantation process.

Methane plasma source ion implantation (PSII) for improvement of tribological and corrosion properties

Abstract Although ion implantation of tools is now available on a regular basis, there are still many applications where the method is successful but is not being applied commercially, this generally being due to the cost of the process being significantly higher than the value of the tools to be treated. A new approach currently being tested is Plasma Source Ion Implantation (PSII), this process operating by filling the entire treatment chamber with implantation gas, creating a plasma and injecting the ions from the plasma directly into the workpiece. It eliminates line-of-sight restrictions and the need for sample manipulation, and the entire part to be treated is implanted simultaneously, making the process simpler and more efficient. An approach of this sort might well take ion implantation to the factory floor. In this study, methane Plasma Source Ion Implantation (PSII) was used to implant carbon into type 304 stainless-steel and Ti6A14V. Implantation was carried out at a target bias of − 30 keV. The effects of high voltage repetition rates on implantation structure, wear and corrosion properties were investigated. It was found that the carbon depth profile, the structure and the resultant properties of 304 stainless-steel after implantation are sensitive to the implantation repetition rate. No dependence of either the structure or the extent of improvement of the properties of the Ti6A14V alloy on the implantation repetition rate was observed.

Microstructural study of nitrogen-implanted Ti6Al4V alloy

A comprehensive study of the microstructural effects of nitrogen ion implantation on Ti6Al4V alloy has been carried out. The work was promoted by the fact that the corrosive wear resistance of Ti6Al4V alloy in an environment similar to that encountered in medical applications can be considerably improved by nitrogen ion implantation using the plasma source ion implantation technique. The alloy was implanted with 50 keV nitrogen ions to different doses ranging from 9 × 1020 to 1 × 1022atoms/m2. Composition distribution within the implanted region was characterized by Auger electron spectroscopy. Microstructural studies were based on transmission electron microscopy. Better understanding of the wear/corrosion behavior is obtained from the study of the microstructures resulting from implantation and provides guidelines for further improvement of the wear/corrosion properties of Ti6Al4V alloy.

Ion-induced spinodal-like decomposition of Fe-Ni-Cr invar alloys

Abstract It was recently discovered that Fe-Cr-Ni alloys with (35 ± 10)wt.% nickel decompose in a spinodal-like manner when irradiated with fast neutrons. This unexpected decomposition has many consequences. Not only do the anomalous properties characteristic of the Invar compositional regime disappear, but pronounced changes occur in both tensile properties and void swelling. Ion bombardment experiments have also been used to study void swelling and are now being used to study the decomposition. Microscopy and EDX examination of specimens employed in earlier void swelling studies confirm that ion irradiation induces spinodal-like decomposition in these alloys. The period and amplitude of the compositional fluctuations induced by radiation are sensitive to temperature, nickel content and perhaps crystallographic direction, but are not very sensitive to chromium content or displacement rate.

Plasma Source Nitrogen Ion Implantation of Ti-6AI-4V

A plasma source technique has been used to implant nitrogen into a Ti-6Al-4V alloy, initially of an (α+β) microstructure. Electron diffraction indicates that TiN is formed as a result of the implantation, but energy dispersive X-ray (EDX) data suggest that the phase may, in fact, be Ti(V)N. The properties of the implanted alloy, for example, as judged by pin-on-disc wear tests, appear to be comparable with those of conventionally implanted Ti-6Al-4V

Gas effects on void formation in 14 MeV nickel ion irradiated pure nickel

Abstract Nickel samples with various helium and oxygen concentrations have been irradiated with 14 MeV Ni ions at 500 °C to a fluence of 8 × 10 19 ions/m 2 (2 dpa at a 1-μm depth). Helium atoms with energy varying from 200 to 700 keV were pre-injected at room temperature. The samples with low oxygen content were obtained by a hydrogen reduction treatment and high vacuum outgassing. The density and the average diameter of voids were determined by TEM examination of cross-section specimens. In the as-received Ni which was cold-worked, a heterogeneous void distribution was observed that could be attributed to the heterogeneous oxygen distribution. In the specimen irradiated after vacuum annealing at 800°C for one hour, voids are uniformly distributed. Small amounts of helium (10 appm) enhanced the void nucleation remarkably in both high (180 appm) and low (75 appm) oxygen content samples, while larger amounts of helium (30 appm) reduced the observable void density in the high oxygen content sample. The void density is much lower and the void size is much larger in the low oxygen content samples compared to those observed in the high oxygen content samples.