Steady Progress on Superalloys (AMSEN)
[This is an update on Bernard Odera's work profiled in May 2009 here.]
When we last visited with Bernard Odera in 2009, he had recently joined AMSEN and arrived at the University of the Witwatersrand, in Johannesburg, from his home in Kenya. He was thrilled to find an opportunity at last, after many years of teaching at the University of Nairobi, to grapple with cutting-edge research in his chosen field of metallurgical engineering and have the chance to complete his PhD.
He is well on his way. Since then, he has become a mainstay at Wits, doing research on superalloys both at the university’s Faculty of Engineering and at the DST/NRF Centre of Excellence in Strong Materials, also located on the Wits campus. His work ethic has been exemplary, as has his collegial attitude toward collaboration at both institutions. “Bernard is just the rock on our team,” said Prof. Lesley Cornish, Director of the Center of Excellence, Assistant Dean for Research in the Faculty of Engineering, and Academic Director of AMSEN. “Whenever I feel overwhelmed, I know I can count on Bernard to calm things down and remind me that they will turn out right.”
It might be understandable for Bernard to feel overwhelmed as well, given the critical functions of the materials he is studying. Engineers have worked for half a century to design alloys that can hold their strength and resist corrosion at ever-higher temperatures – in applications where failure can be catastrophic. Some of the places superalloys are put to use include valves for internal combustion engines, bomb casings, nuclear reactors, space vehicles, and turbine blades for hot sections of jet engines. With continual demands for increasing power and performance from the airlines in particular, superalloys are expected to perform reliably under ever-greater stresses, including especially longer endurance under higher operating temperatures.
Current alloys are fast approaching the application limit because of the melting temperature of nickel. Most of them are based on nickel, which has been used since the 1940s with great success. Over the decades, the addition of more than a dozen complementary metals have helped to optimize the behavior of nickel-based alloys in terms of hardness, strength, and resistance to corrosion and melting. Today’s nickel alloys allow engines and other mechanisms to function safely at temperatures of around 1100 C. But such temperatures are now in the range of 85 to 90 percent of the melting point of these superalloys.
“Now we’ve just about reached the limit for nickel,” says Bernard. “The only way out is to develop a different alloy.” Following up on the work of others, he is working on a somewhat challenging new combination of platinum (Pt) and aluminum (Al). They are challenging because Pt is somewhat heavier than nickel, at a time when airlines in particular are seeking to lighten their materials, and it is more expensive. In addition, the same hard work that has gone into improving nickel superalloys must now be replicated for platinum-based alloys in order to increase its hardness, corrosion resistance, and melting point.
“We are trying to increase the operating temperature for platinum-based alloys to 1300 C,” he said. “That would bring a lot of benefits. Airlines can use fuel more efficiently if they can operate at higher temperatures. They can also have greater thrust with less pollution and less noise.”
At the recent annual meeting of AMSEN, Bernard brought his fellow AMSEN scientists up to date on his work, reporting that platinum alloys containing various amounts of aluminum, chromium, and ruthenium have proven to be the most promising so far. He is now adding vanadium, as a possible fifth element to one of the target alloys, which is expected to act as a solid solution strengthener, with high solubility in platinum. Vanadium is both cheaper and lighter than platinum, and his studies have already suggested that enough vanadium can be added to the alloy to more than compensate for the cost and weight disadvantages of platinum. It is also expected to increase the melting temperature of the alloy and reduce both cost and density as it replaces some of the platinum.
At the AMSEN meeting, Bernard reported on many of the details of his studies, including phase diagrams and scanning electron microscope images of the alloys, revealing fine details of structure that are associated with alloy strength and other qualities. He reported on his studies of other alloys as well, including a six-element alloy system of platinum-aluminum-chromium-ruthenium-vanadium-niobium. Much of this work has been published in peer-reviewed journals and at conferences.
Bernard is fortunate to be working with both industrial and international partners, which add to his perspective on superalloys. At the international level, he is a member of a Materials Science International Team (MSIT) based in Ringberg, Germany. On his last trip to Ringberg in February 2012, he attended an International Seminar on Heterogeneous Multi-component Equilibria and also took the opportunity to visit with their research collaborators at the University of Beyreuth. The industrial partner is Mintek, a minerals research and processing firm in South Africa that furnishes the arc-melting furnace he needs to melt the metals, as well as microscopy equipment and some of the precious metals themselves. His contact with industrial engineers also gives Bernard an understanding of the kinds of research outcomes that will interest the private sector and may be commercializable at some point.
He still cannot predict whether his platinum alloys will become useful in industrial applications, given the cost and weight challenges of platinum. One reason for choosing platinum for his work at Wits, he pointed out, is that more than 70 percent of the world’s known platinum deposits are located in South Africa. Platinum is not easy to extract from its ore and the cost of extraction makes it one of the most expensive metals, but should a company decided to commercialize a platinum-aluminum based superalloy, it could at least assume the availability of a reliable supply of platinum should the technology itself – through the work of Bernard and his colleagues – perform as well as expected.