Mechanical and microstructural effects of new thermomechanical treatments to boost damping of Beta III titanium

Metastable beta (?) Titanium alloys are a class of metallic materials, which find application in the aerospace field due to their high yield strength and low density [1]. Some compositions in this class of materials also display a pseudoelastic behaviour [2]. The presence of a hysteresis area in the stress-strain response, and the associated energy loss, could, when combined with optimal strength, prove to be of interest in structural applications where intensely loaded elements are subjected to vibrations, impulsive or dynamic forces in general. The present work aims to provide a better understanding of the effects of microstructural modifications on the damping properties of Beta III titanium alloy (Ti-11.5Mo-6Zr-4.5Sn). We investigated the effects of annealing treatments followed by plastic deformation. Microstructural changes were observed through X-ray diffraction, optical (Fig.1 Right) and electron microscopy. The damping behaviour of the material in terms of hysteresis and internal friction response was evaluated by quasi-static tensile tests (Fig.1 Left) and dynamic mechanical analysis (DMA). Through heat treatment at 800°C for 3 hours followed by plastic deformation to 16%, we obtained up to 75.55% increase in hysteresis in quasi-static conditions with good cycle stability, as well as an improved damping capacity in dynamic conditions, especially for 1-2% strain amplitudes. Microstructural analysis results also suggest that, differently from the conclusions of previous works [3,4], the main phenomena underlying the observed increase in damping capacity are likely connected to the reversible motion of semi-constrained structures, namely twin boundaries interacting with dislocations, without the involvement of martensitic transformations.