Silicon nitride has long been seen as a potential ceramic material for manufacturing high-efficiency engine components for transportation and in portable power generators due to its high temperature stability, good wear resistance, excellent corrosion resistance, thermal shock resistance and low density (weight). However, the use of silicon nitride in engine components greatly depends on the ability to produce the near net-shape components required economically.
A research project at Oregon State University in Corvallis, USA, led by Juergen Lenz has been investigating the use of powder injection moulded silicon nitride for components used in engines for Unmanned Aerial Vehicles (UAVs) such as drones (Fig.1) where the target was to develop an energy efficient powertrain capable of operating in remote mission locations and with very low maintenance requirements.
The project for the UAV engine used a new material system consisting of a mixture of nanoscale and microscale particles of silicon nitride. Magnesia and yttria were used as sintering additives. The powders were mixed with a multi-component polymer binder system based on paraffin wax. The binder-powder (60% vol% solids loading) was analysed for its properties and moulding attributes. The study involved several steps of development and processing. These steps include torque rheometery analysis, mixing scale-up, property measurements of binder-powder, injection moulding with an Arburg 221M moulder, binder removal, sintering, scanning electron microscopy analysis and mechanical property measurements.
Simulations of the injection moulding process were conducted to assess the feasibility of manufacturing a ceramic engine and to determine its optimal process parameters. The study resulted in the successful development of design parameters that will enable fabrication of silicon nitride engine components by powder injection moulding.
Results from the research were recently published in the Journal of Minerals, Metals and Materials Society (JOM), Vol 64, issue 3, 2012, 388-392.