The purpose of development programs for propulsion and transport technology is to continuously improve performance by increasing the efficiency of combustion engines. This can be ensured by increasing the working temperature and reducing the masses being moved. The materials used are, therefore, exposed to increasingly extreme conditions, which means that intermetallic γ-TiAl alloys are becoming more and more important due to their excellent high-temperature properties. In addition to the material, the manufacturing route of the components is also a crucial factor. Next to conventional processes, such as casting and forging, additive manufacturing is moving into the spotlight with the already established selective laser melting (SLM) process. With this manufacturing technology it is possible to produce near-net shaped components with complex geometries in a resource-efficient manner. In terms of high-temperature applications in aircraft engines it is essential to produce pore- and crack-free components. With the help of an adapted SLM machine of type EOS M290 from AM Metals GmbH equipped with a heatable base plate (up to 900 °C) as well as a powder bed heater (up to 1200 °C) and a gas cleaning system for low O2 contents, it was possible for this work to produce high-quality TNM- and TNM+-samples that meet these requirements. Thorough metallographic characterization using light optical microscopy and scanning electron microscopy as well as X-ray diffraction and hardness measurements of the SLM produced (as-built) samples allowed to study the microstructure development during the SLM process. Subsequently, two different heat treatment routes, which resulted in a NLβ-microstructure, were applied to the TNM- and TNM+-components to study the process related influence on the final microstructure after the heat treatment. In addition to a discontinuous grain coarsening, which occurred during both heat treatment routes, a thermally induced porosity could be detected in the TNM-alloy. Based on a heat treatment study and a thorough literature review, an optimized heat treatment route could be generated specifically for SLM produced TNM-components. To elicit the potential of the three different heat treatment routes in terms of creep resistance, comparisons were made with specimens fabricated via the casting and forging routes. In particular, the TNM creep specimen which was subjected to the optimized heat treatment route showed excellent results compared to the literature. However, the two NLβ-microstructures of TNM- and TNM+-alloy also achieved excellent values in this regard. The SLM route as process above the brittle-to-ductile transition temperature is therefore a promising alternative to conventional manufacturing methods for TiAl alloys.
|Translated title of the contribution||Development of a tailored heat treatment route for SLM manufactured γ-TiAl high-temperature components|
|Publication status||Published - 2021|
Bibliographical noteembargoed until 26-02-2026
- selective lasermelting
- creep properties