High strength titanium alloys

Metastable beta-alloys such as Ti-10V-2Fe-3Al (Ti-10-2-3) and Ti-5Al-5Mo-5V-3Cr (Ti-5-5-5-3) have been identified as key weight-saving materials for the aerospace industry. Using current empirical techniques it can take up to ten years of development before an alloy is considered safe enough to use for aircraft manufacture.

The DARE project designed new metastable beta alloys with superior properties to those already in use, with an aim to optimise all three stages of alloy development:

1. Optimising phase composition: A key determinant of alloy properties is the phase constitution and the properties of the interfaces between phases. One way of quantifying these properties is to calculate the Free Energy of each of the bulk phases and the interfaces. DARE proposes to calculate these for beta titanium alloys using a combination of density functional theory, the tight binding approximation, and calculated bond order potentials.
2. Thermomechanical processing: A key issue in these alloys is the heterogeneity of the beta structure, including segregation and the formation of metastable phases which will determine the nature of the secondary alpha phase precipitates that are key to the high strength levels. Therefore, control of homogeneity, combined with strength maximisation and formability will be achieved by a harmonious combination of alloy design and processing using the new approach where multiscale plasticity is based on irreversible thermodynamics.
3. Ageing treatments: One of the reasons for the high strength of beta-alloys is the formation of very fine precipitates.