Influence of granule characteristics on microstructure quality of compacts made from spray-dried powders.

摘要

Powder compaction is a widely used technique for the manufacture of high volume of ceramic components that have simple shapes and sizes. However, this technique is inherently prone to strength-limiting defects like large intergranular pores and remnants of the initial granule structure. These defects are a major obstacle that hinder the use of powder compaction to fabricate parts for applications where strength is an important criterion. The objective of this work is to understand the important factors that control the elimination of strength-limiting defects in compacts made from spray dried powders.; The influence of granule density, internal lubricants, particle shape and external application of a plasticizer to already spray dried powders on compaction behavior was investigated. Emphasis was placed on role of these factors in the elimination of large intergranular pores and persistent granule interfaces. The powders were spray dried under varying conditions to tailor the granule characteristics, including granule density, granule size distribution, binder content and lubricant content. These powders were compacted at different pressures, and the microstructures of green and sintered compacts were then evaluated, and strength-limiting features were quantified. Comparisons were made on the basis of compaction curves, green strength, green density and microstructure quality at different pressures.; Lowering the granule density reduced the number of granule relics and large intergranular pores. The presence of an internal lubricant improved particle packing and yielded compacts with higher green density and fewer large intergranular pores at comparable pressures. Spray dried powders with the externally applied plasticizer deformed at lower compaction pressures. This allowed easier knitting of particles across granule interfaces and elimination of large intergranular pores and persistent granule interfaces. Spherical (equiaxed) particles rearranged better at granule interfaces and packed more uniformly than elongated and platelet-like particles. Uniform grain growth and uniform sintering was obtained with the equiaxed particles. Particle shape had a less significant influence on elimination of large intergranular pores than granule density or binder characteristics. However, when soft and deformable low-strength granules were obtained, equiaxed particles rearranged better into intergranular pores than elongated or platelet-like particles.