Joo Won Oh

Thermal decomposition behavior of nano/micro bimodal feedstock with different solids loading

Debinding is one of the most critical processes for powder injection molding. The parts in debinding process are vulnerable to defect formation, and long processing time of debinding decreases production rate of whole process. In order to determine the optimal condition for debinding process, decomposition behavior of feedstock should be understood. Since nano powder affects the decomposition behavior of feedstock, nano powder effect needs to be investigated for nano/micro bimodal feedstock. In this research, nano powder effect on decomposition behavior of nano/micro bimodal feedstock has been studied. Bimodal powders were fabricated with different ratios of nano powder, and the critical solids loading of each powder was measured by torque rheometer. Three different feedstocks were fabricated for each powder depending on solids loading condition. Thermogravimetric analysis (TGA) experiment was carried out to analyze the thermal decomposition behavior of the feedstocks, and decomposition activation energy was calculated. The result indicated nano powder showed limited effect on feedstocks in lower solids loading condition than optimal range. Whereas, it highly influenced the decomposition behavior in optimal solids loading condition by causing polymer chain scission with high viscosity.

Analysis of Nano/Micro Bimodal SUS316L Powder Behavior

The components fabricated with nanopowder tend to show better surface roughness and mechanical properties with low sintering temperature. However, at the same time, its high price and reactivity are critical problems of nanopowder. Thus, nano/micro bimodal powder has been introduced in powder process to minimize the problems of nanopowder. In this research, the effect of nanopowder content in nano/micro bimodal powder has been investigated. Bimodal powder was prepared with 100-nm and 4-μm-sized stainless steel 316L powder. They were mixed into 5 grades depend on nanopowder volume ratio from 0 to 100%. The apparent and tap density of the powders were measured, and their flowability was compared with Hausner ratio. Unlike theoretical calculation, the tap density of bimodal powders did not show the packing effect due to distribution of nanoparticles. The compaction behavior was also investigated to verify the bimodal packing effect. The result indicated that the bimodal powder with 25 vol. % nanopowder had the highest relative density.