Reduction Effect on Microstructure and Mechanical Properties of Alumina-Cobalt Composite

The purpose of this research was to compare different reduction methods of alumina-cobalt composite from cobalt aluminate spinel. For this approach, the reduction of spinel with three methods of coke bed, reaction reduction with aluminum powder and reaction reduction with aluminum powder during sintering were investigated. The comparison of the results showed that the coke bed method was too time consuming which finally lead to excessive growth of the metal grains. The density of the sample which prepared from reaction reduction after sintering was 87% of theoretical density, while the density of the sample prepared from reaction reduction during sintering was 95%. The bending strengths of the reduced sample after sintering and during sintering were 227 and 354 Mpa respectively and The hardness of those samples were 7.2 and 9.1 Mpa.m1/2 respectively. With comparison of these results, it is clear that the reaction reduction during sintering method was a better way with no extra heat treatment and fines microstructure. Although this method can solve the wetting problem between metal and ceramic and leads to higher density which helps better mechanical properties.