Piston-based material extrusion (PEX) is an additive manufacturing technology that enables the processing of metal injection moulding (MIM) feedstock to form green parts. The extrusion process does not require moulds and hence is a competitive alternative for the shaping of MIM process routes, offering short lead times and cost-efficiency for lower lot sizes, while integrating into the remaining process chain and equipment. This paper focuses on the microstructure and properties of Ti-6Al-4V fabricated by PEX and followed by a subsequent hot isostatic pressing (HIP) step for parts requiring superior density and mechanical properties. The HIP process is performed using standard as well as high-purity conditions (Quintus Purus ® ). After sintering, a globular, mostly α microstructure is observed. A subsequent HIP followed by rapid quenching transforms the microstructure to a bi-modal state. A similar effect on microstructure is observed for the Quintus Purus ® HIP; however, the formation of α-case on the part surface is avoided. While the mean density of the sintered parts is 97.2%, HIP leads to an increase to 98.9–99.3% with the remnant porosity mainly stemming from open, connected pores. Although the sintered specimens already fulfil the industrial requirements, the Quintus Purus ® HIP leads to a slight increase in yield and ultimate tensile strength at minimal reduction of elongation. The standard HIP shows the same but slightly more pronounced trend. The results show that by a careful design of the specific HIP conditions, the microstructure and properties can be tailored for a specific application.
Bartsch et al. (2026) studied this question.