Development of gamma-TiAl forgings in a low-cost near conventional hot-die process and process evaluation

The strong need for higher efficiency, reduced CO2 emissions and weight reduction in aircraft engines leads to a demand of innovative light-weight high-temperature resistant materials which can partly substitute the materials currently employed. Presently, Ni-base alloys are used for turbine blades in aero-engines which satisfy the high mechanical and thermal requirements. A disadvantage of Ni-base alloys, however, is their high density of about 8 g/cm3. Intermetallic titanium aluminides, which exhibit a low density of about 4 g/cm3, are certainly among the most promising candidates to meet the required thermal and mechanical specifications. During the last decade several “wrought” gamma-TiAl alloys have been developed. These alloys exhibit excellent mechanical properties, but show a narrow processing window.

Böhler Schmiedetechnik GmbH & Co KG (BSTG) is specialised in forging processes of materials like Ni-base and Ti-alloys for aero engine applications with a high demand on structure mechanical requirements. In cooperation with the department of physical metallurgy and materials testing at the University of Leoben as well as other project partners a novel Nb and Mo containing gamma-TiAl based alloy (TNM™ alloy) was developed. Due to optimised microstructure, the alloy showed good malleability in first forging trials. An innovative approach of near conventional hot-die forging, which means that conventional forging equipment with minor and inexpensive modifications can be used, was made by BSTG.

The aim of this project was to develop a robust low-cost near conventional hot-die forging process for low pressure turbine blades which meets on the one hand the requirements of the OEM and gives the right direction for future serial production on other hand.