Prof Michael Cortie from the University of Technology Sydney has been fascinated by gold-copper-aluminium based shape memory alloys for 15 years, but it wasn't until he came to the powder diffraction beamline at the Australian Synchrotron that he discovered the true nature of the alloy's structure and transformations.

"It is hard to describe the fascination I have had with gold-copper-aluminium based shape memory alloys over the last 15 years or so. Ever since the idea of such materials was formed during a brainstorm involving my former colleague Ira Wolff and myself in 1992, I have kept up an intermittent and personal research program directed at these alloys and their properties.

"My involvement has taken me around the world, to jewellery trade shows, to scientific conferences, to industry, and more. It has been a lot of fun. It has not been a solo journey, and along the way it has been the basis of a PhD project, honours projects, research grants and more. It has involved collaboration and favours from friends and colleagues from ANSTO, UTS and Mintek (my former employer in South Africa) and others.

"Of course, like many ideas developed in brainstorms, the alloy did not work well at first. Not at all in fact. At first, the sample of bright yellow metal refused to do 'its thing': to undergo the transformation between the martensite and parent phases that is necessary to obtain the shape memory effect.

"Fortunately, a 'recipe' to make this particular shape memory to work was found by then PhD student Fiona Levey, who developed a heat treatment that guaranteed that the shape memory effect would operate. Why was this? What was happening in this material that switched on its shape memory effect? Why was it immune to the undesirable phenomenon of 'martensite stabilisation' that has compromised the application of most copper-based shape memory alloys? What were its crystal structures, its phase boundaries, its kinetic features? What was it good for? And so many more questions.

"I hope my family have forgiven me for all the long evenings and weekend days spent poring over these mysteries. Over the years I have run plenty of x-ray and neutron diffraction on the material, and have learned much. So when the opportunity came to use the Australian Synchrotron to do more diffraction I was certainly keen, but perhaps not expecting all that much more.

"How wrong I was. In one nocturnal marathon session of 12 hours or so, the alloy gave up many of its secrets. Pattern after pattern of superb quality scrolled over the screen as we slowly took the alloy up from room temperature, passed its austenite transformation, through its ternary-disordering temperature and upwards into uncharted territory.

"What would happen as we approached the melting point? Would it disorder? Would it decompose by a peritectic reaction? These were answers I have sought for over a decade, and which have great practical relevance if the alloy ever reaches routine commercial production.

"Laptops and the beam station worked furiously as we compared, simulated and measured patterns and discovered the true nature of the alloy's structure and transformations. And yes, the results were surprising, and not what I had expected, although, with hindsight, entirely logical. 

"With this new knowledge on board we are able now to take our alloy into new and exciting directions (and, of course, produce some quality scientific publications).

"I'll be back."

Michael Cortie

Professor & Director, UTS Institute for Nanoscale Technology

University of Technology Sydney, Australia

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