Fabrication and Testing of Ceramic Turbine Wheels

Abstract

A silicon nitride (Si3 N4 ) radial inflow turbine wheel was fabricated by injection molding at Toyota Central R&D Labs. The wheel was 142 mm in outer diameter and had 14 blades. The radial wheel was too bulky to manufacture as a homogeneous and defect-free body in one piece. It was divided into two pieces for injection molding and put together into one body by a cold isostatic pressing step after binder removal. Spin testing was executed at room temperature and the resulting photographs, taken from three directions, provided useful information about the fraction mode of the wheels. The maximum burst speed of the wheels at room temperature was 98,900 rpm, which corresponded to 145 percent of the design speed. In a hot rig test, one of the wheels survived 75,000 rpm for ten minutes at a turbine inlet temperature of 1050°C.