Sintering behavior and mechanical properties of nano-sized Cr3C2/Al2O3 composites prepared by MOCVI process

Abstract

Abstract A process using metal-organic chemical vapor infiltration (MOCVI) conducted in fluidized bed was employed for the preparation of nano-sized ceramic composites. The Cr-species was infiltrated into Al 2 O 3 granules by the pyrolysis of chromium carbonyl (Cr(CO) 6 ) at 300–450 °C. The granulated powder was pressureless sintered or hot-pressed to achieve high density. The results showed that the dominant factors influencing the Cr-carbide phases formation, either Cr 3 C 2 or Cr 7 C 3 , in the composite powders during the sintering process were the temperature and oxygen partial pressure in the furnace. The coated Cr-phase either in agglomerated or dispersive condition was controlled by the use of colloidal dispersion. The microstructures showed that fine (20 –600 nm) Cr x C y grains (≤8 vol.%) located at Al 2 O 3 grain boundaries hardly retarded the densification of Al 2 O 3 matrix in sintering process. The tests on hardness, strength and toughness appeared that the composites with the inclusions (Cr 3 C 2 ) had gained the advantages over those by the rule of mixture. Even 8 vol.% ultrafine inclusions have greatly improved the mechanical properties. The strengthening and toughening mechanisms of the composites were due to grain-size reduction, homogenous dispersion of hard inclusions, and crack deflection.