Diffusion Bonding Titanium Alloys to Stainless Steels

Lead Research Organisation: Open University
Department Name: Faculty of Sci, Tech, Eng & Maths (STEM)

Abstract

Background: Advanced engineering components for modern sustainable society require not only better materials but also new joining or welding processes. A critical topic for the advent of the next generation of nuclear reactors is the development of improved methods for joining dissimilar alloys. Due to the high temperatures inherent in fusion welding processes, the use of these methods for joining certain dissimilar alloys, e.g. Titanium and Stainless Steels, has proved unsuccessful. Gallium-assisted diffusion bonding is an award-winning new method, invented by the proposer (PI), for joining the advanced alloys and composites that cannot be welded using conventional processes.

Previous results: The outcome of research carried out under the EPSRC's Indo-UK Civil Nuclear Programme research project "JOINT" (Grant EP/I01215X/1) has proved very promising. High strength joints between Titanium and Stainless Steels were produced using gallium-assisted diffusion bonding as well as active brazing processes leading to publication of several joint papers by the UK and India partners.

Proposed research: The quality of Titanium to Stainless Steel joints made using Gallium-assisted diffusion bonding processes will be studied where the process conditions are systematically varied. This will allow the bonding conditions to be optimised for strength and integrity. The bonded samples will be subjected to careful microstructural characterisation in India and larger samples made for mechanical testing. Results from the research programme will be published in peer-reviewed journals.

Planned Impact

Much of the latest scientific and technological aspects of diffusion bonding are in hands of the certain aerospace and military industries, such as NASA and Lockheed Martin, who keep the relevant information and know-how highly confidential. The present EPSRC funded research will allow freedom of publication so that the new findings will be available to European manufacturers as well as academic institutions. This has the potential to open up new frontiers in research as well as allowing the development of novel and more efficient products. Hence, this type of research will allow the outcomes to be disseminated publicly, with potentially high benefits to certain UK companies and research institutions.

The research project will allow us to publish at least 4 new collaborative journal papers covering the work started in JOINT (and currently continuing on a voluntary basis). It will also allow future bi-lateral visits that will deepen OU-India relationships and provide UK access to extensive materials fabrication and characterisation facilities, and laboratory- based excellence in atomic, molecular and plasma physics at Indian partners' research centres. The research outcomes will expand the UK knowledge base of dissimilar metal joining techniques providing data needs for advanced nuclear plant (e.g. heat exchangers for small modular reactors) and fusion/plasma physics applications.

The Open University is a strategic research partner of major industrial players in the UK civil nuclear sector, including EDF Energy, Rolls-Royce and AREVA. It also interfaces with the NAMRC (Nuclear Advanced Manufacturing Research Centre) and the NNUMAN (New Nuclear Manufacturing) project being led by the Universities of Manchester and Sheffield. The industrial partners are aware of our strong collaboration with India in the civil nuclear field and value the feedback and opportunities we can offer both to share knowledge and integrate research advances to the mutual advantage of all parties.

Publications

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Description Titanium and Stainless Steel have vast applications in nuclear power plants. However, it is close to impossible to join these alloys together using conventional welding processes. The objective of this project is to join these alloys using a method called "Diffusion Bonding". A variant of diffusion bonding was used in this project, which is one of my own inventions and patented some years ago. However, the joining parameters needed to be optimised for each set of alloys. I have managed to make bonds with tensile strengths up to 90% of the original Titanium alloy (i.e. solid unbounded Titanium). This is a very impressive outcome in comparison with the results reported by other researcher to date. A joint publication (high quality and detailed) is prepared for submission to a top journal in the field. The Indian partner is reviewing the latest version. The Open University will cover the cost of Open Access to the joint paper.
Exploitation Route The outcome of the project has direct engineering application in nuclear waste management systems.
Sectors Aerospace, Defence and Marine,Chemicals,Energy,Manufacturing, including Industrial Biotechology,Pharmaceuticals and Medical Biotechnology