Implementation of FAST-forge for Ti-5Al-5Mo-5V-3Cr and Ti-Ti composites

Titanium alloys are desired by aerospace manufacturers such as Safran Landing Systems due to their higher strength-to-weight ratio and improved corrosion resistance over steels. However, the expense of producing titanium has limited its use for applications such as landing gear. The aim of this project was to investigate an alternative process which would significantly reduce the number of processing steps for a metastable β titanium alloy, Ti-5Al-5Mo-5V-3Cr (Ti-5553), used in landing gear. The alternative process consists of: using field-assisted sintering technology (FAST) to heat and consolidate powder into a solid billet, by the application of direct current; forging the billet in one-step; and heat treating to produce an optimal microstructure. This process is known as the FAST-forge process. Initial small-scale FAST testing found that the β grain size could be controlled by adjusting the dwell temperature and time, which is not possible with conventional processing. Subsequent large-scale FAST testing was used to produce FAST billets, some of which were compressed to generate flow data, and one was industrially forged and heat treated: the flow curves and microstructures produced were found to be similar to those of conventionally produced Ti-5553. A microstructural prediction model was subsequently generated to predict the microstructure from the stress, and tested on a FAST-produced complex-shaped forging, which demonstrated the capability of FAST-forge to produce aerospace components. Composites of hard Ti-15.8Fe-36.6Mo alloy particles within a Ti-5553 matrix were produced with full diffusion bonding and an increase in compressive strength of >200 MPa compared to un-reinforced Ti-5553. Overall, FAST-forge has been found to be a viable process for a metastable β alloy such as Ti-5553, and gives greater versatility in producing composites to improve the strength. If an inexpensive powder can be produced, this process should make titanium alloys more affordable for a wide variety of applications and industries.