Young-Sam Kwon

Investigation of powder size effects on sintering of powder injection moulded 17-4PH stainless steel

ABSTRACT Densification behaviours of 17-4PH stainless steel powders (SUS17-4PH) of three different particle sizes during the sintering were investigated. The samples with different mean particle sizes of 3.17, 4.22 and 8.30 µm were prepared through powder-binder mixing, injection moulding, and solvent and thermal debindings. The in situ shrinkage data measured by dilatometry tests were treated to analyse the densification behaviour of each sample. In order to characterise the densification behaviour with a minimum set of experiments, the master sintering curve (MSC), as well-known and straight-forward approach, was employed. After constructing the MSCs for powders of different particle sizes, the effects of particle size on the densification were analysed in many respects including shrinkage, strain rate, apparent activation energy, and work of sintering.

Femtosecond laser micromachining of zirconia green bodies

In this study, we developed micromachining processes using a femtosecond Ti: sapphire laser for zirconia green bodies, i.e., composites comprising zirconia particles and polymer binders. The laser ablation characteristics of the zirconia composites were analysed to optimise the process. In comparison with bulk zirconia, ablation of the zirconia green bodies occurred at lower fluences. In the high-fluence regime, laser irradiation directly ablated the zirconia particles, causing aggregation of resolidified particles. The ablated depth increased with fluence (F) and overlap number (N) initially, but saturated when F and N became larger. Microchannels with a minimum width of 4 µm were fabricated. The microchannel width decreased with decreasing fluence and overlap number. Microholes, microchannels and three-dimensional structures with a size of several tens of micrometres and aspect ratio of 5-15 were successfully fabricated using the zirconia composite.

Hybrid manufacturing of stainless steel and zirconia micro components using laser micromachining and powder injection molding

This work reports a hybrid manufacturing process for fabricating zirconia and SUS micro components using ns/fs laser micromachining and powder injection molding. Mechanisms of material removal and characteristics of the process were analyzed.