The 2001 Pollock Memorial Lecture
Jointly presented by the Royal Society of New South Wales and the University of Sydney
Enhancing the Functionality of Materials:
Recent Advances in Surface Modification Technology
Professor Marcela Bilek,School of Physics, University of Sydney
Time: 5:30 for 6:00 pm
Date: May 17th 2001
Venue: University of Sydney
For any given materials application both bulk properties and surface properties are important, although requirements may sometimes conflict. For example, for an aircraft component, strength and light weight are important bulk properties while corrosion resistance and electrical conductivity are desirable surface properties. Finding a single material that satisfies all the requirements can be quite difficult and in some cases impossible. Recent developments in surface modification technologies allow us to "mix and match" properties by finding a material that meets the bulk requirements and adjusting its surface to suit. Plasma based ion implantation (PBII), also known as plasma immersion ion implantation (PIII), is a powerful new surface modification technique. This talk will examine the technique and some prospective new applications in the particularly demanding field of biomaterials, where crack resistance, adhesion and chemical inertness requirements are extreme. Recent breakthroughs in this field include modified surfaces for mechanical heart pumps and joint replacement prostheses. Benefits for mechanical tooling applications and commercialisation of the technology will also be discussed.
Professor Bilek is the new Professor of Applied Physics in the School of Physics, University of Sydney, and only the second female to hold a Chair in the Faculty of Science. She holds a B.Sc. (Hons) in Physics from U. Sydney, a PhD in Engineering from the University of Cambridge (UK), and an MBA from the Rochester Institute of Technology (USA). She holds a visiting professorship at the Technische Universität, Hamburg, a Fellowship at Emmanuel College, Cambridge, and research scientist positions at Lawrence Berkeley Laboratory (USA), the Comalco Research Centre (Melbourne), and IBM Asia Pacific Group Headquarters (Japan).
Reported by Edmund Potter
The Pollock Memorial Lecture marks the life and work of Professor T.A. Pollock, former Head of the School of Physics at Sydney University, and is given by a distinguished scientist under the joint patronage of the University and our Royal Society. At the University on May 17 the Pollock Lecture was delivered by Marcela Bilek, the new Professor of Applied Physics in the University of Sydney’s School of Physics. She selected the title “Enhancing the Functionality of Materials: Recent Advances in Surface Modification Technology”, and as is the custom spoke in a style admirable suited for the non-specialist to enjoy.
Almost every material in common use eventually suffers wear and tear, as is exemplified by the deterioration of metals, polymers, and ceramics, whether outdoors or indoors, suburban, rural, or coastal.
Modifying just the surface of an otherwise durable bulk material is an attractive prospect for countering wear and tear. Professor Bilek traced new advances by her team and several collaborating companies in (high voltage) plasma-based ion implantation (PBII), also known as plasma immersion ion implantation (PIII). This procedure generates sub-micrometre surface layers integrated without cracks or voids by ion penetration into the exposed atomic lattice of the bulk material or substrate. The lecturer explained how the damaging surface stress accompanying ordinary implantation techniques can be avoided only if adequate lattice mobility is created by the impact of highly energetic ions and then maintained for long enough to allow stress relaxation. This requirement was convincingly illustrated by an analogy to craters on our moon, the radii of which are proportional to the cube root of the energy of the impacting object. In PIII the requisite energy is imparted to the impacting ions by applying a high electric field.
Moving closer to everyday engineering practice, the lecturer showed how surface modification by PIII imparted a super-hard cutting surface to, for example, a titanium substrate, which is thereby “coated” with its own nitride. Professor Bilek and her associates have devised and refined new electrical “tricks” to make ion implantation of surfaces more controllable. Examples are raising the voltage to 20kV to produce plasma in sheath form, and using electrical pulses (5-150 s up to 2kHz, peaking to 50kV at 1-4kW) to prevent the plasma filling the containment vessel. In this way a silicon substrate has been surface modified with carbon to a depth of 4 microns in around 2 hours.
Considerable development is being centred on the PIII modification of an alloy of titanium, aluminium, and vanadium already in use for prostheses in the human body, which imposes a challenging saline and abrasive environment for replacement skeletal joints made from this alloy. A problem awaiting full solution here is the production of adequately uniform ion implantation over irregularly shaped prostheses. While the mathematics of ion trajectories in 3 dimensions is proving difficult to master, progress is being made with computer simulation of the implantation process, ion-by-ion, allowing optimization of the levels of the various relevant factors. A video was shown of computer-simulation of the 2-dimensional growth of a 500-ion implantation layer, leading to the promise that computer-based “experimentation” on these lines will eventually replace tedious replicate practical trials.
Many of the large audience engaged in an energetic discussion of this fascinating lecture, and afterwards a presentation was made to Professor Bilek by David Craddock, President of the Royal Society of New South Wales.