Effect of powder shape and size on the properties of low- viscosity iron-based feedstock used in low-pressure powder injection molding

Abstract

Low-pressure powder injection molding (LPIM) is a cost-effective advanced manufacturing technology to produce low or high production volumes of complex-shaped metal parts with good mechanical properties. Although there has been some study conducted on sphericalshaped metal powders, there is a poor understanding of the application of irregularly-shaped metal powders on the physical and micro-structural such as density of the sintered components produced by LPIM. The current research work presents an experimental approach to investigate the effect of powder shape and size on the properties of metallic parts fabricated by LPIM. Four low-viscosity feedstocks were prepared using three irregularly-shaped iron powders, sieved in three mesh sizes, and labeled as -10, -20, -45 μm, and one spherical carbonyl iron powder (CIP) with an average particle size of 4 m. The binder system consisted of 1 vol. % of stearic acid, 2 vol. % of carnauba wax, 2 vol. % of ethylene-vinyl acetate for their surfactant, demolding, and thickening effects, respectively, and where the balance of the binder was constituted of paraffin wax. Rectangular specimens were injected at constant volumetric flow and thermally wick-debound and sintered at high temperatures under a hydrogen atmosphere. The feedstock viscosity profiles were obtained using a rotational rheometer. The density of powder, polymeric binders, and feedstock were measured using a gas pycnometer. The melting point of the feedstocks and the binders' burnout temperatures were obtained using differential scanning calorimetry tests (DSC) and thermogravimetric analysis (TGA), respectively. The density of sintered specimens was measured using the oilimpregnation method based on Archimedes’ principle. Finally, the debinding network and metallographic observations of the sintered parts were performed using a scanning electron microscope (SEM) and optical microscope, respectively. It has been shown that the -45 μm mesh irregular iron-based powder can be blended at higher solid loading as compared to -10 μm powder resulting in a slight increase in the relative density that was correlated with metallographic analysis showing a higher level of isolated pores in sintered part.

Date	13 Jun 2021
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Vincent Demers (Supervisor) & Vladimir Brailovski (Co-supervisor)