Particle Impact Tests of Ceramic Gas Turbine Materials at Room Temperature

Abstract

In developing ceramic gas turbines (CGT), evaluation of impact strength of ceramic materials is one of the most important subjects. For the purpose of evaluating impact strength of ceramics, particle impact tests of ceramics are carried out at room temperature by using electrothermal (ET) gun and micro-sabot system. Power turbine nozzles and circular disk specimens made of three kinds of Si3N4 are impacted by samarium - cobalt (Sm - Co) magnet flyer particles in vacuum. Weight of particles is fixed to 4mg and particle velocities range from 300 to 900 m/sec. Thickness of specimens are 1.0, 1.5 and 2.0 mm. In this study critical impact velocity, Vc, is defined as threshold velocity which causes visible cracks on the rear surface of the impact side. The cracks seem to be brought by flexural fracture mode. It is found that Vc is related with bending strength, σ, and thickness, t, of the target material as : Vc = C · σ5/6 · t5/3. It is found that impact results with and without rear cracks are well categorized based on this empirical relationship.