MICROSTRUCTURAL HOMOGENEITY IMPROVEMENT IN SI3N4 BY A POWDER COATING METHOD

摘要

The efficiency of a powder coating technique has been quantitatively evaluated through a comparison of the densification behaviour, green compact and dense material microstructural homogeneity in terms of a ''homogeneity dimension'', and mechanical properties, using coated powders and mixed powders in the case of Si3N4 powder densified by hot-pressing with the liquid-forming additive system Al2O3-TiO2-SiO2. For coated powder, a significantly smaller value of the homogeneity dimension was obtained. The oxide phases became re-distributed during densification, with the aluminium-containing phase distributed on a finer scale, and the titanium-containing phase on a coarser scale, compared with the green body. Materials prepared by hot-pressing of coated powders showed a more homogeneous microstructure, higher bend strength and higher Weibull modulus, compared with materials prepared from mixed powders. There were no differences in fracture toughness and hardness between the two types of material. [References: 47]