“In order to remain competitive in the aerospace engine market, investment into both cutting-edge research and new engineering talent is needed. The Innovative metals processing CDT provides Rolls Royce with the opportunity to streamline investment for maximum return. This research is a promising project with the potential for a large increase in gas turbine engine efficiency. The Centre also provides training for its students with taught modules and practical work, creating knowledgeable and innovative engineers that Rolls Royce and other high added value manufacturing industries in the UK need.”
Prof Paul Withey, PhD, CEng, FIMMM, FICME, Rolls-Royce Engineering Associate Fellow in Casting Technology
Nickel-based superalloys, currently used in turbine blades of gas turbine engines, have reached a plateau in temperature capability. Increasing the operating temperature of jet engines increases their efficiency. A new material is needed that can withstand the increased temperatures required. Rolls Royce PLC is sponsoring research students at IMPaCT to investigate one such material that shows promise in being able to replace nickel-based superalloys – niobium silicides. They possess a high liquidus temperature of (1880°C) and a low density of (7g cm-3compared to 9g cm-3 for nickel-based superalloys). There are however material properties that need improvement if these materials are to succeed. Room temperature ductility is low, medium to high temperature oxidation resistance is poor and the material is difficult to cast due to high temperature reactions with mould materials such as alumina and silica. Improvement in these areas will be the focus of this collaborative project between IMPaCT and Rolls Royce PLC, which involves seven PhD students in total.
MPaCT student Adam Allen has travelled to a project collaborator, Northwestern Polytechnical University in China, to fabricate niobium silicide-based alloys using laser additive manufacture (pictured left). This relatively new technique eliminates the requirement for a mould, hence eliminating this processing issue. EPSRC equipment funding with matched funding from Leicester has invested in an induction furnace capable of directional solidification at the very high temperatures required. This technique is similar to the current technique for casting nickel-based superalloys. A variety of experimental techniques are being used to characterise these alloys, from x-ray diffraction (XRD) to transmission electron microscopy (TEM). IMPaCT student Ruiyao Zhang has conducted neutron diffraction experiments at the Diamond Light Source facility in Harwell as part of his first year summer project.
Wear-Resistant Anti-Bacterial Titanium Surfaces
External fracture fixation is a common orthopaedic procedure that is used increasingly in a variety of trauma settings. Titanium self-drilling/self-tapping Schanz pins offer a one-step insertion where pre-drilling is not required because the self-drilling tip acts like a new, sharp drill bit. However, pin track infection is a common complication in external fixation systems with infection rates as high as 30 %. The critical consequences of infected pin sites are pin loosening, fracture destabilisation and osteomyelitis, thus leading to additional surgical interventions and delayed or non-union. In addition, Ti alloys are characterised by low hardness and low wear resistance. Therefore, the wear of Ti self-drilling tip or cutting edge necessitates an increased insertion force. This will in turn result in increased temperature at bone-pin surface during insertion, which would cause damage to the bone and retard its healing after operation.
IMPaCT student Tatiana Mukinay has teamed up with researchers at University of Birmingham and orthopaedic surgeons from Royal Darby Hospital to address this technical and medical challenge via a surface engineering approach – one of the six themes of IMPaCT. The research team has applied, for the first time, an advanced ceramic conversion surface engineering technology to self-drilling external fixation pins to improve their performance in terms of biomechanical, bio-tribological and antibacterial properties. The properties of the surface engineered pins were evaluated by insertion into high density bone simulation material; and with Staphylococcus aureus bacteria.
The results have demonstrated that the surfaces of the pins were successfully converted into a thin TiO2 rutile layer supported by an oxygen hardened case with very good bonding due to the in-situ conversion nature. The hardness has increased significantly (more than 3 times) providing enhanced wear resistance of the cutting edge of the self-drilling Ti pins following the ceramic conversion treatment (picture above, a-untreated; b-surface treated). The antibacterial tests also revealed that there was a significantly reduced number of bacteria isolated from the ceramic conversion treated pins compared to the untreated pins of around 50 %. These encouraging results could pave the way towards high-performance anti-bacterial titanium external fixation pins with reduced pin-track infection and pin loosing. A technical paper based on the results has been accepted for publication in Journal of Materials Science – Materials in Medicine (DOI: 10.1007/s10856-016-5816-0).
Tat-Hean Gan (TWI)
“The IMPaCT CDT has enabled the university to cooperate with TWI’s industrial members on a number of research programmes and to build mutual understanding of future research challenges and opportunities. By coordinating the research capabilities with the Universities of Leicester, Birmingham and Nottingham through the IMPaCT CDT, we are developing the next generation of technologies and training scientists to become experts in the field of performance and mechanical behaviour of materials. The University of Leicester is also an academic partner of NSIRC, the postgraduate structural integrity research centre co-funded by TWI, and TWI is proud to be working with the university in a long-term strategic partnership for research in materials. This latest development will provide a platform for the consolidation and growth of this relationship between two organisations at the forefront of fundamental research in the materials field.”
Professor Tat-Hean Gan, TWI Associate Director and Director of Technology of the National Structural Integrity Research Centre (NSIRC)
MEMs are a new design for alloys where the material is composed of many elements in equal proportions. These materials can have a wide range of useful microstructural and mechanical properties. Cold spray additive manufacturing is a potential method for producing MEMs in near net shape structures and coatings. Cold spray additive manufacturing is a process in which powder materials are deposited without melting onto a solid surface, producing thick, wrought coatings up to 50mm. This aims to understand the effects of process and material parameters on the behaviour of cold sprayed MEMs. Future applications include wear and corrosion resistant coatings and repair of damaged components.
Fundamentals of Hydrogen Induced Stress Cracking in Duplex Stainless Steels (DSS)
The superior strength and corrosion resistance of DSSs makes them ideal alloys for subsea application, and they have been widely used in the oil and gas industry since the 1970s. However, important failures have shown they are susceptible to hydrogen induced stress cracking (HISC). The aim of this PhD project is to enable a step change in our understanding of the HISC mechanism using the state-of-the-art experimental methods to optimise manufacturing processes to prevent catastrophic failures in future.
I graduated in 2011 with a 2.1 BSc in Physics from Loughborough University. I had always had an interest in materials science and wanted to move into an academic career. I joined the CDT in 2014 and was particularly drawn to the taught component of the first year. Having been very interested in materials science, but with limited academic experience of the subject, the modules provided me with a valuable foundation that has been extremely useful in the first years of my project, giving me a running start on my research.
My time at IMPaCT has given me many skills and experiences that have been a distinct advantage in my PhD so far. As part of the CDT I have many opportunities to work with and alongside a community of like-minded individuals that have become close friends. Symposia and summer school activities have deepened my knowledge base and given me an insight into other students projects, giving my own work both a context and a group that can offer support or guidance, pooling our collective knowledge to help one another.
My PhD research is based at Leicester and is concerned with stress relaxation in nickel-based superalloy springs for high temperature use in the next generation of reduced emissions power plants. I am industrially sponsored by Alstom (now owned by General Electric (GE) since 2015), who are a major steam turbine manufacturer based in Rugby, about 30 miles away. My project has been varied, creating theoretical models, developing and conducting complex experiments (pictured left), investigating metal processing methods, and learning material characterisation techniques such as Transmission Electron Microscopy. The work has been challenging and exciting, requiring knowledge of engineering, physics and chemistry, and the CDT has been responsible for preparing and supporting me through this. I have spent time visiting Alstom/GE on placements and have had multiple useful discussions and talks at the site with technicians and specialists in the field, to guide the project over the next two years. I would recommend the CDT to anyone with an interest in the field, it has been an exciting, rewarding journey with my cohort, and is an excellent way to begin a career as a research scientist.
“Marc presented his first year research results at GE in October. This was to an audience of 15 turbine specialists from different development groups in the company. The talk was very well received and prompted some interesting discussion. He has developed a convincing physical model which corresponds well with his experimental results. The result of this is that we are now investigating a new processing route for these components and also a possible design change.”
Dr Gordon McColvin, Industrial supervisor at GE
IMPaCT student organise and run three symposia each year. On Monday 31st October, the University of Birmingham hosted the first IMPaCT symposium for the 2016/2017 academic year. The symposium topic was Materials Science in Chocolate. The aim of holding this symposium was to introduce the new CDT students to applications of materials science outside of our own specialised fields while strengthening basic materials theory through lectures and fun practicals. To promote team building and competition, the students were divided into teams for the day, and were scored in each practical.
The day started with a lecture from the Birmingham second year IMPaCT students on the chemistry and production of chocolate and its corresponding microstructure and resulting properties. This was followed by chocolate tasting, in which students were given four different unidentified milk chocolates with four different recipes; students had to match the recipes with the chocolate based on the taste and texture. Running parallel to this was a chocolate joining practical. Student teams were asked to join chocolate bars that had been previously cut into two; they had to make choices on what materials to use to join the chocolate back together and methods of heating and cooling the chocolate. Joints were later tested using a cantilever bend test. Following lunch, Birmingham third year students presented on the materials science in chocolate packaging, covering techniques such as Aluminium foil and Polypropylene film production, physical vapour deposition and adhesion. The day ended with three point bend testing of various chocolate bars, each of which represented different material strengthening mechanisms; for example, a KitKat was representative of a laminate composite structure and a whole nut chocolate bar representative of precipitation hardening. Students had to predict which chocolate bar would fail first and which would fail last based on its macrostructure.
Overall the symposium was very well received; it was a great opportunity for the new CDT students to meet and get to know the existing students, and provided us all with some light hearted relief while still being topical.
Rachel Jennings, Third year IMPaCT student, University of Birmingham
Jean-Christophe Gebelin (Doncasters Group Ltd)
Doncasters decided to support the IMPaCT CDT because the proposed research area is in line with Doncasters portfolio of manufacturing processes and there was a gap on the work market for skilled technical leaders in the area of high temperature material manufacturing and processing. Moreover it was seen as an opportunity to take up young talents and train them in the areas which are our core businesses and provide the opportunity to create an input stream of technically qualified leaders/managers with a research training that will provide them with a good toolset for the challenge they will face in the future in our manufacturing plants.
The technical opportunities for improvement or step changes are numerous within Doncasters, examples will mainly, but not only, be around casting technologies, as they represent more than 50% of our activities. For the project with IMPaCT student Stefano Cademartori (pictured left) based at the University of Birmingham, the opportunity was centred on ceramic core manufacturing for the investment casting industry. Cores that are used in manufacturing of parts for the power generation sectors are becoming more and more complex in terms of geometry and contain more and more small features making their manufacturing more challenging. The objective of Stefano’s PhD project is to model the core manufacturing processes and build up understanding of the different failure mechanisms that are present in the current processes.
So far, the project has allowed us to better understand the characteristics of the ceramic pastes being used in our different plants to manufacture cores. This understanding is now being built up in process models which will enable us to improve tooling design and optimise process parameters for the core injection process. In parallel, analysis of manufacturing data is being carried out in order to understand, for existing products, the type of defects being generated and their influence on production rate. This will allow us to better use the characterisation techniques and modelling tools we have to improve plant performance.
The long term impacts to Doncasters are expected to be firstly and more immediately better core manufacturing processes that will improve overall business performance and reduce New Product Development and Introduction lead time. Secondly, by improving the technical culture within the company, where process leaders understand the processes they are running and they have the ability to bring into the business well trained technical leaders able to question current practices and improve them.