Processing Methods for Reaching Full Density Powder Metallurgical Materials

Powder metallurgy (PM) is one of the most cost effective methods for manufacturing structural components with complex shapes. Utilisation of the metal powder to shape the components allows to minimise material waste and increase energy efficiency. However, with the increased usage of PM parts in high performance applications, there is a demand for components with properties that can withstand extreme loading conditions and are equivalent or better than the properties of their wrought counterparts. The PM steels fabricated with press and sinter, even with all its advantages have limitations due to the presence of residual porosity. Hence, reaching full density is necessary to meet the high performance demands. The scope of this study covers different approaches of powder consolidation with the aim of reaching near full density. Liquid phase sintering and double pressing-double sintering approach for water atomised powders, high velocity compaction approach for agglomerated gas atomised powders, and finally additive manufacturing approach to produce samples with almost full density were utilised. These approaches were complimented by capsule free hot isostatic pressing (HIP) to reach full density and improve component performance.The liquid phase sintering approach utilised is based on addition of Ni-Mn-B master alloy for enhanced sintering and densification. The results obtained clearly indicated that the master alloy addition effectively enhances the densification process through the liquid phase generation. The mechanical properties were improved when boron content was optimised from 0.2 to 0.12 wt. %. Density levels up to 98% were realised after sintering with addition of this master alloy. In the double pressing-double sintering process, cylindrical and gear samples, fabricated from water atomised powder, prealloyed with Mo were studied. The studies included the comparison of using both standard and fine