Effects of Thermal Parameters on the Mechanical Characteristics of Ti6Al4V Sheets Deformed at Elevated Temperatures

摘要

Over these last decades, titanium and its alloys have been largely used for many applications in different sectors such as aerospace, military and biomedical ones. Many studies have investigated the behaviour of the most broadly used alloy, the Ti6AI4V, under hot forging and superplastic forming conditions, whereas almost no records can be found about the Ti6AI4V sheet behaviour at elevated temperature and moderate strain rate (i.e. above 0.1 s~(-1)). The research starts analysing the influence of the thermal-cycle parameters on the Ti6AI4V mechanical properties and microstructural characteristics by means of micro-hardness measurements and Optical Microscopy (OM) analysis. Different soaking times, cooling rates and heating technologies, namely furnace and induction, were considered and their effects investigated. Based on these results, uniaxial tensile tests were carried out at different temperatures, ranging from room temperature up to 900°C, and strain rates of 0.1 and Is~(-1), adopting the thermal parameters and heating means previously investigated. The Ti6AI4V sensitivity to the rolling direction was highlighted, calculating the average normal anisotropy as a function of the testing parameters. The samples fracture areas were then measured in order to calculate the strain at fracture as a function of the temperature and strain rate, while the fracture morphology was investigated through Scanning Electron Microscopy (SEM). OM and SEM analyses were also used to investigate the deformed samples microstructure. Finally, the samples micro-hardness, as a measure of the post-forming characteristics, was measured in order to evaluate its sensitivity to the temperature and strain rate.