Investigation on temperature control in the SPS process with titanium aluminides

Abstract

Spark Plasma Sintering (SPS) or Field-Assisted Sintering Technique (FAST) is a powder metallurgical (PM) heat-assisted process, where loose metal powder is pressed to a compact. Powders, which are difficult to consolidate, can be processed much more efficiently than within the conventional PM process route, i.e. die pressing followed by sintering. However, temperature measurement in the SPS process is challenging since it can only be done on the die surface or within the die wall without influencing the process. In case of γ-based Titanium aluminide (TiAl) powders, a suitable sintering temperature allows for a modification of the three grain morphologies lamellar, equiaxed and duplex, and thus for the mechanical properties to be selectively adjusted. In this study, temperature control during the SPS process is investigated using the commercially available pre-alloyed TiAl48-2Cr-2Nb (GE48) powder. For this purpose, temperature measurement with thermocouples and a pyrometer is considered. Furthermore, the influences of graphite and boron nitride lubricants or rather release agents and insulators on the temperature profile are investigated. The evaluation is carried out based on microstructure analysis and hardness measurements. The results show that a suitable temperature control of the process is possible. In addition, it seems that the choice of release agent has a significant influence on the temperature and thus on microstructure and mechanical properties.