Novel 3D printing strategies to produce high performance, nanostructured steels

Improving the mechanical performance of metal alloys is a longstanding effort in engineering. Stronger and tougher metals are conducive to more efficient transportation, more secure infrastructure, and reduced overhauling in several industrial sectors. One common approach to improve the mechanical behaviour of metals is to impart them with a complex, nanoscale structure. A myriad of different manufacturing processes may be employed to produce nanostructured metals. However, they all suffer from limited scalability, which hampers their use in structural applications. In this thesis, I will explore the possibility of using laser powder bed fusion (LPBF) technology to produce bulk high-performance nanostructured alloys. LPBF is a class of additive manufacturing processes which relies on small scale melting and solidification of a metal feedstock into a 3-D part. By fine-tuning the laser parameters it is possible to manipulate the thermal history of the material and engineer the material's solidification structure at nanoscale. To showcase the opportunities offered by this technology, I will focus on 17-4 PH martensitic stainless steel. The LPBF strategies which I will employ will aim at controlling the parent phase that the material will retain upon cooling, as well as the occurrence of the strengthening copper-rich nanoprecipitates and submicron solidification cells which dictate the alloy's mechanical performance. Notably, these structures can be formed in conventional and LPBF produced 17-4 PH through long specialised heat treatments. However, the time and cost of this additional post processing step is prohibitive to the scalability of LPBF. Part of my work will thus also focus on achieving this structural control without post-processing, leading to a more cost-effective and sustainable manufacturing approach.

Our main impacts will be:
- a new generation of interdisciplinary nano researchers with expertise across science and innovation, fluent in the combination of approaches and technologies
- strategic developments in the study and control of nano-interfaces connecting complex architectures, for advances in emerging scientific grand challenges across vital areas of energy, health and ICT
- integration of new functional nanotechnologies together by harnessing nano-interfaces within larger application systems, and their translation into innovative products and services through our industry partners and student-led spin-outs
- a paradigm change of collaborative outlook in this science and technology
- a strong interaction with stakeholders including outreach and public engagement with cutting edge nano research
- improved use of interdisciplinary working tools including management, discipline bridging and IT

Economic impact of the new CDT is focused through our industrial engagement programme, as well as our innovation training. Our partner companies include - NPL, Hitachi, Oxford Nanopore, TWI, ARM, Eight19, Mursla, Britvic, Nokia Bell Labs, IBM, Merck, Oxford Instruments, Aixtron, Cambridge Display Technologies, Fluidic Analytics, Emberion, Schlumberger, Applied Materials and others. Such partnerships are crucial for the UK to revive high value manufacturing as the key pillar to lead for future technologies. We evidence this via the large number of CDT projects resulting in patents, with their exploitation supported by Cambridge Enterprise and our Industry Partners, and direct economic impact has also resulted from the large proportion of our students/alumni joining industry (a key outcome), or founding startups including: Echion Technologies (battery materials), Inkling Cambridge (Graphene inks and composites), HexagonFab (2D materials), Simprints (low-cost biometrics), Cortirio (rapid diagnosis of brain injury).

Training impact emerges through not just the vast array of Nano techniques and ideas that our cohorts and associated students are exposed to, but also the interdisciplinary experience that accrues to all the academics. In particular the younger researchers coming into the University are plugged into a thriving programme that connects their work to many other sciences, applications, and societal challenges. Interactions with external partners, including companies, are also strong and our intern programme will greatly strengthen training outcomes.

Academic impact is fostered by ensuring strong coherent plans for research in the early years, and also the strong focus of the whole CDT on study and control of nano-interfaces connecting complex architectures. Our track record for CDT student-led publications is already strong, including 4 Nature/Science, 6 Nature Chem/Nano/Mat, 13 Nat. Comm., with student publications receiving >6000 citations in total, including 16 papers with >100 citations each and high altmetric scores. Students have also given talks and posters at international conferences and won numerous awards/fellowships for research excellence.

Societal impacts arise from both the progression of our cohorts into their careers as well as their interaction with the media, public, and sponsors. We directly encourage a wide variety of engagement, including interaction with >5000 members of the public each year (mostly pre-university) through Nano exhibits during public events such as the Cambridge Science Festival and Royal Society Summer Science Exhibition, and also art-science collaborations to reach new audiences. We also run public policy and global challenges workshops, and will further develop this aspect with external partners. Our efforts to bring societal challenges to students' awareness frames their view of what a successful career looks like. Longer term societal impact comes directly from our engagement with partner companies creating jobs and know-how in the UK.