Thu, 21 January, 2021
European funded H2020 project titled ‘Sustainable and flexible powder metallurgy processes optimization by a holistic reduction of raw material resources and energy consumption (SUPREME)’ focuses the attention on the use of advanced manufacturing processes to improve the manufacturing process efficiency and thus reduce material wastage.
The SUPREME project consortium includes CEA, Outotec, MBN, ASL, GKN, Prodintec, IPC, RHP, Tecnalia, Renishaw, IRIS, MBA, Weare Additive, Dellas, CRF, EPMA and TWI Ltd.
TWI Ltd, holding experience in powder metallurgy (PM) manufacturing processes has successfully developed a manufacturing strategy to produce Inconel®625 (IN625) Y-shaped submarine pipe using near net shape powder metallurgy hot isostatic pressing (NNS PM HIP) technology. NNS PM HIP is an advanced manufacturing process, capable of manufacturing complex-shaped parts with excellent material properties and microstructure. The process has the potential to vastly improve the “buy-to-fly” ratio of large industrial (marine, aerospace, power, aeronautical, nuclear, etc.) components (going from ~10:1 to ~2:1) when compared to a conventional manufacturing route such as casting-forging and machining. Figure 1 shows a CAD model of the submarine pipe which is currently produced using the conventional casting-forging and machining manufacturing route with a buy-to-fly ratio of 7.4:1, meaning that the current manufacturing process results in a high level of material waste with a relatively long lead time.
Figure 1. 3D CAD representation of Y-shaped pipe
The development of an efficient manufacturing process was led by Dr Raja Khan (TWI) along with Dr Nick Ludford (TWI), with the support of NSIRC PhD student Alessandro Sergi, and with the collaboration of the Advanced Material Processing Laboratory (AMPLab) at the University of Birmingham. The study focused on a deep understanding of the influence of the IN625 powder atomisation route and powder characteristics on the microstructure and mechanical properties of the material among four different powders including argon gas atomised (AGA), nitrogen gas atomised (NGA), plasma atomised (PA) and water atomised (WA) powders.
The first step of the manufacturing process consisted of the powder characterisation. A detailed powder characterisation was performed on the four powders, including chemical analysis, physical properties (apparent and tap density and flowability), powder morphology and particle size distribution (PSD). The powder morphology of Figure 2 shows that PA has a regular shape followed by NGA and AGA with some irregular shaped particles, while WA has a typical irregular shape. PSDs of the four powders highlights that NGA, PA and WA have similar distributions, while AGA has a more narrow distribution with a smaller particle size.
Figure 2. Powder morphology of (a) AGA; (b) NGA; (c) PA; (d) WA (left); PSD of the four powders (right)
The microstructure of the four HIPed powders is reported in Figure 3. HIPed PA microstructure shows the least amount of prior particle boundaries (PPBs), while WA is characterised by the strongest presence of PPBs. The results of as-HIPed tensile properties confirm that PA powder possesses the best balance between strength and elongation, with superior properties if compared to the minimum specification of wrought IN625 (Figure 4).
Figure 3. SEM backscattered micrographs of as-HIPed AGA (a); NGA (b); PA (c); WA(d); (PPBs highlighted in blue)
Figure 4. As-HIP Room temperature tensile properties of IN625 powders vs wrought minimum specifications
Thanks to its best response in terms of microstructure and mechanical properties, PA was selected for the manufacture of Y-shape pipe through NNS PM HIP.
The NNS PM HIP manufacturing process involved the design of a capsule (Figure 5), powder fill, degas, crimp, HIP and machining off the sacrificial canister to attain a netshape part geometry (Figure 6).
Figure 5. 3D CAD drawing of the designed capsule
Figure 6. Submarine Y-shaped IN625 pipes produced using NNS PM HIP technique
The prototype pipes produced during this work showed good geometrical accuracy with a reduced buy-to-fly ratio of 2.1:1, which is more than 3.5 times lower if compared to the conventional manufacturing process. To conclude, NNS PM HIP technique has been successfully adopted to manufacture IN625 Y-shaped submarine pipe with a low buy-to-fly ratio and superior mechanical properties.
SUPREME project partners
The SUPREME project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 768612