Material and process design for additive manufacturing of hard metals

The design of materials resistant to wear is an area that could offer significant industrial benefits ranging from applications in the construction, machining and manufacturing sectors. Despite that, wear resistant material innovation, in particular related to metal-based materials, is limited by constraints encountered in processing and prototyping and hence, few novel materials have been able to compete with tungsten carbide (WC) based components. However, the rapid growth and development of additive manufacturing (AM) methods offers an avenue for the holistic design of both new wear resistant materials and their manufacturing process.

Using AM, processing can be modified to occur at non-equilibrium states and these methods can be used to tailor the formation of hardening phases to a later stage in the post-processing cycles, hence allowing for improved material processability. It is therefore the aim of this project to investigate avenues for materials design and processing for wear resistant applications using AM-based methods.

The project will focus on the evaluating the potential and processability of three classes of materials initially: high entropy alloys and high entropy carbides and the possibilities of high entropy cemented carbide design and high-hardness steels. Material design efforts will focus on high entropy alloys and hardenable steels. High entropy alloys have provided a domain of metallurgical research that has expanded exponentially over the last few years, yet few studies have evaluated high entropy alloys for wear resistance. In this work several compositions of refractory metal high entropy alloys (HEAs) will be initially evaluated for hardness and processability, before further AM processing and wear resistance tests can be carried out. In addition, the possibilities of inducing significant carbide formation using post-AM processing heat treatments will be explored. Several HEAs are known to result in the precipitation of carbide species following prolonged exposures at high temperatures. By experimenting with the C content as well as AM processing within promising systems, the kinetics of carbide formation can be significantly altered to induce carbide formation with industrially viable heat treatment durations. Furthermore, and if time permits, several species of high-hardness high entropy carbides (HEC) based on refractory metals are known to exist and HEC-HEA type cemented carbide systems may also be evaluated.

The EPSRC Centre for Doctoral Training in Advanced Metallic Systems was established to address the metallurgical skills
gap, highlighted in several reports [1-3] as a threat to the competitiveness of UK industry, by training non-materials
graduates from chemistry, physics and engineering in a multidisciplinary environment. Although we will have supplied ~140
highly capable metallurgical scientists and engineers into industry and academia by the end of our existing programme,
there remains a demonstrable need for doctoral-level training to continue and evolve to meet future industry needs. We
therefore propose to train a further 14 UK based PhD and EngD students per cohort as well as 5 Irish students per
cohort through I-Form.

Manufacturing contributes over 10% of UK GVA with the metals sector contributing 12% of this (£10.7BN [4,5]) and
employing ~230,000 people directly and 750,000 indirectly. It is estimated that ~2300 graduates are required annually to
meet present and future growth [5]. A sizeable portion of these graduates will require metallurgical expertise and current
numbers fall far short. From UK-wide HESA data, we estimate there are ~330 home UG/PGT qualifiers in materials and
~35 home doctoral graduates in metallurgy annually, including existing AMSCDT graduates, so it is unsurprising that
industry continues to report difficulties in recruiting staff with the required specialist metallurgical knowledge and
professional competencies.

As well as addressing this shortfall, the CDT will also impact directly on the companies with which it collaborates, on the
wider high value manufacturing sector and on the UK economy as a whole, as follows:

1. Collaborating companies, across a wide range of businesses in the supply chain including SMEs and research
organisations will benefit directly from the CDT through:

- Targeted projects in direct support of their business and its future development and competitiveness.
- Access to the expertise and facilities of the host institutions.
- Involvement in the training of the next generation of potential employees with advanced technical and leadership skills
who can add value to their organisations.

2. The UK High-Value Manufacturing Community will benefit as the CDT will:

- Develop the underpinning science and advanced-level knowledge base required by future high technology areas, where
there is high expectation of gross added value.
- Provide an enhanced route to exploitation, by covering the full spectrum of technology readiness levels.
- Ensure dissemination of knowledge to the sector, through student-led SME consultancy projects, the National Student
Conference in Metallic Materials and industry events.

3. The wider UK economy will benefit as the CDT will:

- Promote materials science and engineering and encourage future generations to enter the field, through outreach
activities developed by the students that will increase public awareness of the discipline and its contribution to modern
life, and highlight its importance to future innovation and technologies.
- Develop and exploit new technologies and products which will help to maintain a competitive UK advanced
manufacturing sector, ensure an internationally competitive and balanced UK economy for future generations and
contribute to technical challenges in key societal issues such as energy and sustainability.

References:
1. Materials UK Structural Materials Report 2009
2. EPSRC Materials International Review 2008
3. EPSRC Materially Better Call 2013
4. The state of engineering, Engineering UK 2017
5. Vision 2030: The UK Metals Industry's New Strategic Approach, Metals Forum