AN INVESTIGATION OF TOUGHENING IN NIAL COMPOSITES REINFORCED WITH YTTRIA-PARTIALLY STABILIZED ZIRCONIA PARTICLES

The results of an investigation of toughening mechanisms in NiAl compo sites reinforced with yttria-partially stabilized zirconia polycrystal s are presented. Different yttria stabilization levels in the zirconia , between 0 and 6 mole pct are employed. It is shown that substantial improvements in fracture toughness are obtained in all the composites reinforced with partially stabilized zirconia particles. The phase con tents and microstructures of the composite systems are characterized b y X-ray diffraction and transmission electron microscopy (TEM) techniq ues. Crack tip deformation was also studied using crack tip TEM analys is, and laser Raman spectroscopy was used to estimate the size of the transformation zone. The results show that transformation toughening i s significant only in the 2 mole pct yttria-stabilized zirconia compos ite. Toughening is also shown to occur via slip phenomena within the N iAl grains in the near-tip regions of the composites reinforced with 2 , 4, or 6 mole pct yttria-stabilized zirconia particles.