Fracture Toughness and Slow Crack Growth Behavior of Ni-YSZ and YSZ as a Function of Porosity and Temperature.

Abstract

In this paper we report on the fracture toughness of YSZ and Ni-YSZ and slow-crack growth behavior of Ni-YSZ at 20C and 800C. Results are presented for tests carried out in air for YSZ and in a gas mixture of 4%H2 and 96%Ar for Ni-YSZ containing various levels of porosity. The double-torsion test method was utilized to determine the fracture toughness from the peak load obtained during fast loading test specimens that had been precracked, while crack velocity versus stress intensity curves were obtained in the double torsion using hte load relaxation method. It was found that fracture toughness of these materials decreases with temperature and int he case of Ni-YSZ it also decreases with increasing porosity. The effect of temperature and microstructure, which was characterized by Scanning Electron Microscopy, on the fracture behavior of these materials, is discussed.