Plasma Immersion Ion Implantation ( PI3 ) - The Technology, Applications and Success to Date

The Australian Nuclear Science and Technology Organisation (ANSTO) has for some time been perfecting a process of hardening metals, mainly for the tooling and materials processing industries, known as Plasma Immersion Ion Implantation or PI³ TM. Apart from world-breaking scientific research, one of the other outcomes has been to sell the equipment developed by ANSTO for profit. ANSTO has recently announced that its sales of PI³ related equipment has just topped the $A1 million mark. While sales to date have been to organisations interested in researching the process, ANSTO is looking forward to its eventual industrial application. Expressions of interest in this technology continue to be received from companies all over the world as well as from various parts of Australia.

Origins of PI³ Technology

ANSTO’s research into PI³ originally grew out of a project in the 1980s that investigated the fundamental properties of plasmas relevant to their use in nuclear fusion. At the completion of that project, ANSTO looked for ways to utilise its plasma expertise in areas with possible industrial applications. ANSTO scientists realised that many of the problems associated with using ion beams to modify the surface of three dimensional objects such as tools, dies and mechanical parts could be overcome by immersing objects to be treated in a plasma. The positive ions from the plasma are accelerated towards all exposed surfaces by applying a high negative voltage to the object. This forms the basis of PI³. This was proved in experiments in late 1987, leading to a successful patent application by ANSTO in 1988. Further testing using nitrogen ions, has shown that PP is able to extend the use of nitriding (a well-known heat treatment technique) to alloys not amenable to normal nitriding treatments. According to ANSTO, the depth of the modified layer ranges from 1-200μm, depending on the treatment time, temperature and composition of the material.

Plasmas and Plasma Processing

Plasmas are ionised gases and are sometimes referred to as the ‘fourth state of matter’. Ion implantation causes ions to penetrate below the surface of a material, giving it unique electronic, mechanical or chemical properties. Plasma nitriding as this method is also called, allows the desired object to be immersed in a plasma of nitrogen gas. The ANSTO process is somewhat unique in that the plasma gas is independently generated by the use of radio frequency (RF) excitation. Although extensively used in the microelectronics industry, ion implantation has not been adopted by the broader manufacturing industry, despite its potential for surface hardening and for improving the corrosion properties of metals. Subsequently, PI³ has emerged as a viable alternative to the conventional methods of ion implantation, particularly in applications such as ion nitriding and ion-assisted deposition of hard coatings.

What Materials Can Benefit from PI³ Treatments?

While nitriding has been extensively used for treating steels to improve their surface hardness, there are many components and alloys that cannot be treated by conventional nitriding techniques. The PI³ process, which uses lower treatment temperatures, is particularly suited to stainless steel and high precision items that suffer distortion or lose their corrosion resistance during standard nitriding processes.

The PI³ Process

The process requires careful control of several parameters. Treatment is carried out in a vacuum and temperature is held at between 300 to 500°C. ANSTO for its part, has been using a PLC and SCADA system connected to a PC to run the whole system which it finds very suitable due to the need to connect many other monitoring devices such as a temperature controller, a mass spectrometer and an optical emission spectrometer.

PI³ Equipment and Applications

In developing the technology that allows high voltage pulses to be applied to components immersed in a plasma, ANSTO has produced equipment which is not only effective, but can be also scaled up or down to suit a particular purpose. In this respect, equipment has been sold to research laboratories in the UK, Germany, Hungary, Thailand and Singapore as well as to universities within Australia. According to Dr George Collins, team leader for the project, “There are a number of uses for this process ranging from metal hardening in the toolmaking field to improving the adhesion of coatings as well as more exotic applications such as changing the surface properties of polymers.”

Success and Acceptance of PI³ Technology

Dr Collins goes on to say that, “We have selected our market very carefully. Our current model is ideal for use in research labs but provides the basis for one that would be suitable for industrial settings. We have put a lot of effort into the control and instrumentation so that this equipment can be operated by non-plasma specialists.” In this respect, he says this process and the associated equipment will be of interest to many areas of the manufacturing sector, particularly those that deal with metals, alloys and the modification of their properties. Dr. Collins qualifies this by adding, "While we have concentrated on a particular application of the process - that of improving the wear resistance of steels our technology can also be used for a range of surface treatments." Following the success of the past 12 months, ANSTO is looking to increase sales and market penetration of its PI³ process and associated technology.

Source: Materials Australia, Vol. 34, no. 1, pg. 9, Jan/Feb 2002.

For more information on this source please visit The Institute of Materials Engineering Australasia.