- Review the current state-of-the-art of additively manufacturing functionally graded materials.
- Arrive at an alloy design concept, from a metallurgical point of view, in particular identifying the chemical composition necessary in each built layer and the materials, using conventional wire or powder consumables, to achieve this concept.
- Investigate and develop the processing parameters for each of the selected additive manufacturing processes.
- Develop and conduct destructive and non-destructive evaluation (NDE) in order to assess the subsequent quality of the different builds.
A range of industry sectors face applications where transitions between dissimilar metals are required. Significant plant outage and repair costs are often encountered due to failures or degradation associated with joining strategies, processes or manufacturing methodologies for such transitions. A relatively common example is a joint between ferritic steel and stainless steel. Such joints typically include multiple dissimilar metal welds, leading to abrupt discontinuities in physical properties. The proposed solution consists of designing and then additively manufacturing a single engineering transition piece, with a suitable gradual change in chemical composition along its axial direction (i.e. a “functionally-graded material”). The composition of the transition piece will be produced to match, approximately, the chemical compositions of the ferritic steel at one side and the stainless steel at the other.
Candidate processes include wire arc additive manufacture (WAAM) and laser beam additive manufacture, using either two powders or two wires. In order to transform the typical coarse and columnar as-deposited microstructure into a more homogenous and finer one, the transition piece will then require additional thermomechanical processing. The project will develop a process to include hot forging and appropriate heat-treatment. Finally, machining to the desired shape and dimensions will be carried out.
Relevant Industry Sectors
Benefits to Industry
Potential benefits to industry of developing this innovative technology include:
- Only one engineering transition piece would be required to link both structures, minimising the amount of on-site welding, thus reducing costs.
- Only two similar welds, i.e. ferritic steel to the ferritic end of the transition piece, and stainless steel to the stainless steel end of the transition piece, will be required.
- The final result would be a forged and heat treated component with a homogeneous, fine equiaxed grained microstructure, more likely to be acceptable in conservative end-use applications.
- A smooth material transition (free of abrupt discontinuities in composition and properties) from one end to the other will result in a more even distribution of thermal stresses, reducing the likelihood of thermal shock cracking occurring.
- Overall improved in-service performance, reducing repair costs.
- If required, internal cladding could potentially be built-up during manufacture of the transition piece.
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