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Investigation of reheated weld metal micro-structure as a function of feedstock chemistry and extrapolation for additive manufacture - Funded by Lloyd’s Register Foundation (NSIRC238 PhD Studentship)


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Dr P Moore , Ms Hannah Stedman Applications accepted all year round

About the Project

Additive manufacturing (AM) is a suite of processes which “join materials to make parts from 3d model data, usually layer upon layer”. AM is causing disruptive changes in manufacturing applications across the world, the advantages and benefits of which are becoming well understood. As metallic applications increase in size, wire and arc additive manufacturing (WAAM) which uses arc welding equipment and industrial manipulators as the basis of an AM system is becoming of increasing interest. WAAM has theoretically unlimited build envelope, reasonable resolution, accuracy and deposition rates, as well as the ability to deposit a wide range of materials. However, research into this process is showing that although it may appear simple, the interconnectivity between inputs such as the part design, feedstock material, deposition process variables and thermal history can result in unusual microstructures and mechanical properties. Understanding and monitoring the effects of inputs and how they affect the final part is felt to be a significant step in acceptance of the design and manufacture of large scale parts by WAAM. This is one of three projects planned to work closely together to generate knowledge for respective areas, and the interconnectivity between them and their applicability to WAAM. The output of these projects will make a significant contribution to moving WAAM towards industrial acceptance.

Project Outline
TWI has been seen as an authority on weld metal microstructures, and this strategic PhD research project intends to establish that ongoing expertise into the 21st Century. While a large programme of research in the 1980s systematically investigated the influence of different alloying elements on as-deposited weld metal microstructures, it did not consider the microstructural modifications occurring through reheating by subsequent weld layers. The nature of WAAM means that the resulting microstructure is extensively reheated by subsequent passes. Hence, there is a need to extend the understanding of weld metal microstructural evolution towards the reheated weld microstructures that form in WAAM.
This work will adapt the understanding of carbon and low alloy steel weld metal microstructures in multi-pass butt welds to identify relationships between weld metal alloying additions and optimised reheated microstructure in order to help develop optimised weld consumable chemistries for WAAM applications. Three main tasks will be performed:
Activity 1 – Review of microstructure formation in multi-pass weld metals;
Activity 2 – Correlating element compositions and weld thermal parameters with reheated weld metal microstructures;
Activity 3 – Modelling and extrapolation of feedstock chemistry and thermal field from multi-pass welding to WAAM
An existing set of butt welds fabricated using a systemic series of different weld metal compositions will be provided for analysis. Further experimental trials from linked projects will be used to extend and validate results and new material families may be introduced if time and resource allow.

About Industrial Sponsor
The Lloyd’s Register Foundation funds the advancement of engineering-related education and research and supports work that enhances the safety of life at sea, on land and in the air, because life matters. Lloyd’s Register Foundation is partly funded by the profits of their trading arm Lloyd’s Register Group Limited, a global engineering, technical and business services organisation.

About Coventry University
Our research in Materials Engineering and Structural Integrity builds on our historical research strengths at Coventry and adds new research teams through investment and growth. We are part of the newly established University Research Institute for Future Transport and Cities. We bring value to our partners by adding value, effecting knowledge transfer, generating intellectual property and fostering new technologies. This is underpinned by our expertise in Metrology, Advanced Experimentation, Residual Stress Analysis, Structural Integrity, and proven models of effective collaboration with academic peers and industrial partners from all over the world.
We are delighted to have been awarded 15 PhD studentships from NSIRC, with funding support from the BP Ltd, LRF and TWI.

The National Structural Integrity Research Centre is a state-of-the-art postgraduate engineering facility established and managed by structural integrity specialist TWI. Working closely with top UK and International Universities and a number of leading industrial partners, NSIRC aims to deliver industry led and relevant cutting edge research and highly qualified personnel to its key industrial partners.

Candidate Requirements
Candidates should have a relevant degree at 2.1 minimum, or an equivalent overseas degree in Material Science, Metallurgy, Mechanical, Electrical/Electronics or Civil/Structural Engineering or Physics. Candidates with experience in experimental research, numerical modelling and / or applied industrial research are particularly encouraged to apply. Overseas applicants should also submit IELTS results (minimum 7.0) if applicable.

Funding Notes

This project is funded by Coventry University, Lloyds Register Foundation and TWI. The funding covers the cost of Home/EU tuition fees and a standard tax-free RCUK stipend for three years. Non-EU students are welcome to apply, but the funding will only cover the cost of overseas tuition fees and the applicant need to self-fund their living cost for three years.

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