Studies on Mechanical Properties of Ti-6Al-4V ELI at Liquid Hydrogen Temperature

Abstract:

Ti-6Al-4V alloy is widely used in Aerospace applications owing to its high specific strength, low coefficient of thermal expansion and good corrosion resistance. Presence of interstitial elements in the alloy has some significant effects on its properties. However the poor notch toughness and cryogenic ductility restricts the usage of Ti-6Al-4V for temperatures lower than 77 K (-196 °C). The Extra Lower Interstitial grade alloy was developed in order to improve the notch toughness and cryogenic ductility of the Ti-6Al-4V alloy. In this refined grade, the interstitials, Oxygen and Carbon are controlled to a maximum limit of 0.12% and 0.08% respectively as compared to a maximum of 0.2% and 0.1% of standard Ti-6Al-4V alloy. In this study, the ELI grade of Ti-6Al-4V rods from three different manufacturing sources were subjected to tensile test at liquid hydrogen temperature at 20 K (-253 oC). The tensile properties obtained are compared and analyzed. The obtained ductility at 20 K is observed to have close relation with the chemical composition and interstitial content and compared with the Ti5Al2.5Sn-ELI which is ideally suitable for low temperatures upto 20 K, owing to its single phase HCP structure. A correlation has been made between the ductile properties and microstructure. By close control of chemical composition and mechanical working, Ti6Al4V-ELI can be used for temperatures lower than 77 K (-196 oC), which is otherwise is forbidden. This paper details the test data obtained from three different compositions of Ti6Al4V-ELI at 20 K, which enables the usage of this material for temperatures lower than 77 K (-196 °C) upto 20 K.