Large, complex engineering components in many industries are made from forgings or castings, followed by joining. Limited capability and expertise means that consumers may be beholden to sole suppliers and have to pay high prices. The limited geometrical capabilities for forging processes means that extensive machining is also required, resulting in as much as 90% wastage of material, a loss that is undesirable and expensive.
There is an increasing interest in using powder manufacturing methods eg laser additive manufacturing (AM) and near net shape powder metallurgy hot isostatic pressing (NNS PM HIP) for making high value, complex structural parts. Such processes increase design freedom, reduce materials wastage (>50%) and lead-time and may reduce cost. Whilst significant research is currently focussed on AM technology, a limited amount of work has been done on NNS PM HIP technology, related to lack of knowledge and available facilities compared to AM technology. One of the key requirements for NNS PM HIP parts is to achieve fracture toughness similar to wrought material. No comprehensive prior work has been conducted on the effect of powder quality and processing parameters on the final mechanical properties of hot isostatically pressed (HIPed) materials for high value, safety critical parts.
The proposed work will enhance TWI knowledge and understanding about the role of powder quality for a broad range of applications.
This research project seeks to determine the effect of powder quality and manufacturing method on the microstructure and mechanical properties of HIPed material.
One chosen alloy, in the form of powder manufactured by three different atomisation processes, will be investigated to check powder characteristics and quantify how the powder manufacturing method influences the microstructure and mechanical properties of the resultant HIPed material.
The studentship will investigate the effect of powder manufacturing methods and the HIPing process parameters on microstructure and material properties, in particular the fracture toughness. A key part of the work will be to perform detailed powder characterisation (chemical composition, flowability, particle size distribution, apparent tap & packing densities and morphology) of the down-selected alloy powders using recently developed state-of-the-art TWI powder characterisation facilities.
In addition, a finite element (FE) model will be developed which can predict the geometrical and microstructural changes (including the canister wall thickness effect on the final part geometry) that occur during the HIP consolidation process. A detailed experimental plan to investigate the HIPing process parameters (temperature, pressure and dwell time) will enable validation of an FE model to predict the final dimensions of a part produced by HIPing. Assessment of HIPed material will be through chemical analysis, preparation and investigation of specimens using XRD, SEM and mechanical testing. Moreover, various post-HIP heat treatments will be performed in order to achieve the improved microstructure and mechanical properties of the HIPed material.
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