Development of niobium powder injection molding. Part II: Debinding and sintering

This article is a continuation of feedstock preparation and powder injection molding (PIM) of pure niobium. Part II discusses debinding and sintering of injection molded niobium. PIM of pure niobium powder was analyzed for efficiency of the process. After solvent and thermal debinding, sintering of injection molded material was conducted up to 2000 °C in vacuum as well as inert-gas low-oxygen partial pressure atmosphere. This paper investigates the effect of sintering time, temperature and atmosphere on the processing of pure niobium. Under all sintering conditions the oxygen content is reduced from ∼19,000 in the as-received powder to as low as 300 ppm, at e.g. 2000 °C for 2 h in a low-vacuum atmosphere. The carbon content increased from the as-received 70 to 200–300 ppm, depending on the sintering conditions. However, this amount of carbon is not considered detrimental for structural application. Master decomposition and sintering curves are introduced for pure niobium to study the optimum debinding and sintering conditions. Further, sintering parameters (atmosphere, peak temperature and hold time) are optimized for achieving maximum densities with minimal impurities.