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Surface irregularities in titanium marine parts formed by the particulate injection moulding process.


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High-alloy steels with the addition of > 10 % chromium are known as stainless steels and due to their increased strength and oxidation resistance are used for food production equipment, in the chemical industry and in the marine environments. A problem within some marine environments is that corrosion still occurs. The corrosion still occurs despite the alloying content because of high mechanical stress a result of high loading. This is particularly seen in structural applications and load points. While this may be acceptable within industries such as commercial fishing and container transportation it is not desirable in luxury vessels or high-performance sports vessels. To eliminate the effects of stress on these components materials with greater oxidation resistance are recommended one of which is titanium metal. Not only does titanium metal have greater oxidation resistance than marine alloyed chromium steels it also has lower density and higher yield strength which enable lower weight and lower material utilisation. In this study a structural hold down component was designed and produced using the particulate injection moulding (PIM) process. The material of choice was titanium due not only to the material properties mentioned previously but also due to the desire to create custom made components for a state-of-the-art marine vessel, Earthrace 2. The component was produced using the particulate injection moulding (PIM) process. This fabrication technique was used due to several efficiencies offered by the process. It supports materials sustainability of the powder metallurgy approach by using only the volume of metal required to create the necessary part geometries (material utilisation). It has high reproducibility which is desirable for high volume of parts, it produces isotropic material properties and where necessary can be used to provide unique alloys not possible from wrought material. The original design was modified to better utilise the titanium properties and using a polymer mould tool green parts were produced with green machining used to mark the parts with logos and identifiers and apply final features. The tests were never completed as the break was always the lifting shackle used to connect mounts to the universal testing instrument. The load shackles had working capacity six times that required for the mounts. To this end, the mounts were redesigned and a material saving of some 40 % was realised. The new components, therefore, having a thinner wall section and a corresponding reduction in loading capability is expected. One unexpected result of reducing the wall thickness was seen on the upper surface of the mount known as surface bloom. It can be seen during plastic moulding of single-phase commodity polymers as a result of changes in the polymer density, due to shear stresses and irregularities of turbulent flow. The PIM process, however, uses a two-phase (polymer carrier and the titanium particles) metallic blend or feedstock that behaves in a different manner to a polymer. The literature suggests the surface bloom is a result of a separation between the two phases, but the preliminary findings show little evidence of this within the sectioned profile. It is this phenomenon that is being investigated and will be presented in relation to melt flow modelling, mechanical simulation and visual analysis. The sections are subjected to mechanical testing and it is these results combined with SEM imaging that shows in greater detail a more likely scenario.

Item Type: Paper presented at a conference, workshop or other event, and published in the proceedings
Uncontrolled Keywords: melt flow modelling, particulate injection moulding, polymer, separation, surface bloom, titanium metal
Subjects: T Technology > T Technology (General)
Divisions: Schools > Centre for Engineering and Industrial Design
Depositing User: Hong Zhou
Date Deposited: 08 Jul 2020 21:01
Last Modified: 21 Jul 2023 08:52

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