Abstract
Spark plasma sintering (SPS) or the field-assisted sintering technique (FAST) is commonly used to process powders that are difficult to consolidate, more efficiently than in the conventional powder metallurgy process route. During the process, holding time and applied holding pressure influence the product’s microstructure and subsequently its properties. In this study, in addition to the temperature impact, the influence of pressure and dwell time on the consolidation behaviour of titanium aluminide (TiAl) powders during the SPS process is investigated. Commercially available pre-alloyed TiAl48-2Cr-2Nb (GE48) and TiAl44-4Nb-0.7Mo-0.1B (TNM) powders were used, which have a high application potential in, for example, the aerospace industry. The results were evaluated based on microstructural analyses, hardness measurements and relative density calculations. It was shown that the investigated parameters significantly influence the sintering results, especially in the low temperature range. Depending on the temperature field in the sample, complete sintering is not achieved if the dwell time is too short in combination with too low a pressure. Above a certain temperature, the impact of holding pressure and holding time is significantly lower.
Highlights
Titanium aluminides (TiAl), especially intermetallic γ-based alloys, have a high application potential in the automotive industry, as well as in aerospace engineering, e.g., for the blades of low-pressure turbines
After an initial start-up phase in which the temperature remains at room temperature level, the temperature in the powder rises much faster than in the die
GE48 is sintered at a maximum of Tthermocouple = 1210 ◦ C, which, after applying the correction factor determined at 65 MPa, corresponds to a temperature of Tpyrometer = 1040 ◦ C
Summary
Titanium aluminides (TiAl), especially intermetallic γ-based alloys, have a high application potential in the automotive industry, as well as in aerospace engineering, e.g., for the blades of low-pressure turbines. For the SPS process, the influence of dwell time and pressure on the microstructure and relative densities has only been carried out for a few other powder alloys, so far. Cheng et al [12] demonstrated an increasing hardness and grain size for TiC with increasing temperature and holding time They were able to show that the relative density increases to varying degrees with increasing temperature and dwell time. From the studies with different alloys, it can be deduced that temperature, dwell time and pressure have different effects on the microstructure and the relative density. The aim is to investigate the influence of dwell time, holding pressure and temperature on relative density, resulting microstructure and resulting hardness, as well as to prove the proposed hypothesis
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