Effects of Radiation Damage on ALM produced components

Additive Layer Manufactured (ALM) components are currently being developed for use in a range of industries, and variants of ALM have been investigated since the 1980s. The development of next generation nuclear reactor technologies combined with the increasing use of novel manufacturing methods is therefore a key area for exploration. An essential criterion for materials/components used within nuclear reactors is the requirement of withstanding radiation induced damage within the core. Therefore, for ALM to be used more frequently in nuclear engineering, the effect of radiation on material properties is key to both the long-term stability of the component, as well as the acceptance of ALM within the nuclear industry

Hypothesis
The PhD student would seek to characterise and understand the impact of radiation damage on the structure and properties of materials manufactured using ALM, with a view to answering two key questions:

I) Is the microstructure produced by ALM capable of tolerating radiation induced damage, or will the microstructure extenuate damage, whilst potentially inhibiting recovery?
II) Could such a microstructure be capable of ameliorating radiation induced changes, by providing enhanced recovery pathways?

Aim:

There are several challenges in using ALM fabricated components that continue to be addressed.
• Process - must provide stability, repeatability, and consistency in results.
• Materials - suitable materials, materials availability and traceability.
• Structural - mechanical properties (e.g. surface finish, effect on fatigue)
• Design - can we design for ALM?
• Validation - can it be tested/characterised?

Given the challenges above, the PhD would be comprised of three main parts; fabrication, irradiation and analysis, with micro-structural/mechanical properties changes induced by radiation damage being key to the proposal.

Objectives
The criteria for the project are:
• To identify the potential uses for ALM materials within a reactor core, and suitable components that could be manufactured. This would lead to a further detailed study of potentially susceptible regions (voids, interfaces etc) of the ALM components.

• To identify a set of “standard” nuclear alloys which are accepted within the nuclear industry and can be used in ALM processes in order to test component manufacturing. This could include standard materials such as SS316 but also move into non-metallic componentry based on carbides such as SiC.
• Appropriate testing/characterisation methodology for components, e.g conditions for irradiation and how they can be used for testing/examination of radiation damage in materials.

Methodology and Approach
Initially, a standard nuclear alloy would be fabricated into a pre-determined shape, which would then be characterised pre- and post-irradiation, with the irradiation being undertaken at DCF through the Mid-Range Facility funding. The initial experiments would characterise simple geometries in order to enhance fundamental understanding of the effects of irradiation on ALM sample geometry, with more complex components being fabricated at a later point.

As such, the systems will be then be carefully chosen to identify those factors in ALM formed materials that may impact on the radiation damage. For example, are an ALM component’s microstructure advantageous in hindering defect migration, or does it act as a source for cracking to initiate along the layered planes.

In order to answer these questions the pre-/post-irradiation analysis will be based on micro- and macro-structural techniques. These characterization techniques will include microscopic examination of materials (optical and electron microscopy), coupled with hardness/tensile testing with DIC/DVC to understand any induced strains resulting in stresses within the material.

The proposed samples and components would be fabricated using the ALM facilities in Liverpool, with materials chosen in the early stages around manufacturable systems i.e. those alloys that can be manufactured via ALM. As the PhD progresses more realistic systems would be chosen, specifically those that have been identified for use within a next generation core, such as novel alloys, or carbide hybrids.

Training
The specific training required for the student will be broken down into two parts, the initial stage will focus on training on ALM fabrication, and initial analysis, followed by an interim report on the fabrication of the initial materials. This will be followed by the second training package focusing on the impacts arising from radiation damage, and how they can be determined, coupled with training in the examination of radiation damage, e.g. TEM, SEM, TKD etc.

CDT name: GREENCDT