Processing, Microstructure and Hydrogen embrittlement of 3D printed Inconel718

Additive manufacturing (AM), also known as 3D printing, is expected to revolutionise the way of designing, supplying and making materials, holding great potential for automotive, energy, medical and aerospace applications. Amongst all AM, powder bed fusion is the most effective method to fabricate complex metallic components with high accuracy.
Inconel718 is one of the most widely used nickel-based alloys thanks to its good weldability, excellent resistance to fatigue, to hot corrosion and to wear and high strength, making it an excellent candidate for high-temperature applications including in gas and oil.
Although the microstructure and mechanical behaviour of Inconel 718 have been extensively studied, there is still significant lack of understanding regarding the relationship between AM process parameters, microstructure and performance - in particular the hydrogen embrittlement. Therefore, this project will use the laser powder bed fusion to fabricate Inconel718 with various print parameters. Subsequently, detailed studies will be carried to examine the microstructure evolution of the alloy from single to multiple tracks of deposition and in subsequent heat treatments. Mechanical tests will be done on both as-printed and heat-treated conditions with and without charged Hydrogen to study the susceptibility of the alloy to hydrogen embrittlement.
Tasks will be carried out in this project:
- Fabrication: Relating print parameters (i.e laser intensity, exposure time, laser spot distance, hatch spacing, layer thickness and scanning strategy) to consolidation and solidification microstructure.
- Uniaxial tension testing at room and elevated temperatures will be carried out on the printed alloy with and without the charging of Hydrogen to study the hydrogen embrittlement.
- Microstructure characterisation: Microstructure morphology, crystal phases, crystallographic orientations and chemical distribution of as-printed and deformed samples will be characterised by optical and scanning/transmission electron microscopy (including EDX) and X-ray diffraction.

The production and processing of materials accounts for 15% of UK GDP and generates exports valued at £50bn annually, with UK materials related industries having a turnover of £197bn/year. It is, therefore, clear that the success of the UK economy is linked to the success of high value materials manufacturing, spanning a broad range of industrial sectors. In order to remain competitive and innovate in these sectors it is necessary to understand fundamental properties and critical processes at a range of length scales and dynamically and link these to the materials' performance. It is in this underpinning space that the CDT-ACM fits.

The impact of the CDT will be wide reaching, encompassing all organisations who research, manufacture or use advanced materials in sectors ranging from energy and transport to healthcare and the environment. Industry will benefit from the supply of highly skilled research scientists and engineers with the training necessary to advance materials development in all of these crucial areas. UK and international research facilities (Diamond, ISIS, ILL etc.) will benefit greatly from the supply of trained researchers who have both in-depth knowledge of advanced characterisation techniques and a broad understanding of materials and their properties. UK academia will benefit from a pipeline of researchers trained in state-of the art techniques in world leading research groups, who will be in prime positions to win prestigious fellowships and lectureships. From a broader perspective, society in general will benefit from the range of planned outreach activities, such as the Mary Rose Trust, the Royal Society Summer Exhibition and visits to schools. These activities will both inform the general public and inspire the next generation of scientists.

The cohort based training offered by the CDT-ACM will provide the next generation of research scientists and engineers who will pioneer new research techniques, design new multi-instrument workflows and advance our knowledge in diverse fields. We will produce 70 highly qualified and skilled researchers who will support the development of new technologies, in for instance the field of electric vehicles, an area of direct relevance to the UK industrial impact strategy.
In summary, the CDT will address a skills gap that has arisen through the rapid development of new characterisation techniques; therefore, it will have a positive impact on industry, research facilities and academia and, consequently, wider society by consolidating and strengthening UK leadership in this field.