Investigation on the mechanical properties and formability of Ti3Al2.5V tubes deformed at elevated temperatures

Titanium and titanium alloys are largely used in aircrafts to manufacture piping and structural components, thanks to the high strength-to-weight ratio and the excellent corrosion resistance. However, despite the advantages in terms of mechanical and chemical performances, they present significant limits when shaped at room temperature due to the high strength and the low ductility. The use of temperature-assisted processes might represent an interesting option to overcome the above-mentioned limitations, although the effects on the microstructural and chemical properties should be accurately considered. The paper presents the results of investigations on the Ti3Al2.5V alloy, carried out to evaluate the influence that the thermal-cycle parameters have on the mechanical properties and microstructural characteristics of tubes draw bent at elevated temperatures. Tensile tests at elevated temperatures have been performed on specimens directly cut from tubes in order to get the flow-stress curves and elastic material properties. With reference to typical industrial process conditions, different heating rates and soaking times were tested to analyse the influence on the microstructure, namely the grain size, the precipitation of secondary phases and superficial oxidation. Scanning Electron Microscopy and micro-hardness measurement techniques were used to assess the the post-forming characteristics at different temperature and strain rate conditions.