Project Details
Projekt
Thermomechanical Fatigue of Ti-Ta-X-Y High-Temperature Shape Memory Alloys: Cyclic Stress-Strain Response and Damage Evolution
Subject Area
Mechanical Properties of Metallic Materials and their Microstructural Origins
Term
from 2012 to 2020
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 200999873
Ti-Ta-X shape memory alloys are very attractive for elevated temperature applications, as they are based on substantially cheaper constituents than the competing materials. In addition, most high-temperature shape memory alloys are brittle even at high temperatures, and thus, are difficult to form. In contrast, the Ti-Ta-based alloys are fairly ductile, which makes processing easier.Subproject 4 focuses on the functional and structural fatigue behaviour of modified Ti-Ta-X alloys. Based on the results from the first funding period, alloying with Al and Sn is a promising approach to suppress the formation of the detrimental omega-phase. However, at the same time, the Ta-content needs to be reduced in order to obtain sufficiently high transformation temperatures (e.g. Ti-20Ta-5Al). The major objective of this subproject is to develop a fundamental understanding of the mechanisms that control degradation during thermomechanical fatigue. Eventually, this should allow for accurately predicting the limits of safe service conditions for these alloys based on the dominant microstructural processes.In the experiments, functional properties and their evolution will be studied under thermomechanical loading conditions. In addition, endurance tests and crack growth experiments will be conducted under conditions relevant for service. Another key aspect is in-situ studies to characterize the local deformation and transformation behaviour of the alloys. These high lateral resolution studies should allow for understanding the microstructure-transformation-property-relationship. In addition, these studies will also shed light on structural degradation, which we currently attribute to formation of the omega- and alpha-phase.Finally, the recovery heat-treatment successfully develop during the first funding period shall be developed further to allow for application to the new alloys under relevant operating conditions. The vision here is o fully suppress degradation during thermomechanical fatigue by rejuvenating the microstructure, and thus, fully recover transformation temperature and strains.
DFG Programme
Research Units
